History
The development of the solar cell started from the work of the French physicist Mr.Antoine-César Becquerel in 1839. Becquerel discovered the photovoltaic effect when experimenting with a solid electrode in an electrolyte solution; he could observe that voltage developed when light falls on the electrode. After about 50 years later, Charles Fritts could construct his first solar cells using junctions that was formed by coating the semiconductor selenium with an Ultrathin - transparent layer of gold. Fritts's devices were not that much efficient, only transforming less than 1 percent of the absorbed light into electrical energy.
In 1927 one of another metal-semiconductors:- junction solar cell, in this case it is made of copper and semiconductor copper oxide, which had been demonstrated. By 1930s both the selenium cell and copper oxide cell were used in light-sensitive devices, such as photometers which if for using in photography. However, these early solar cells, still had energy-conversion efficiency not more than 1 percent. Luckily this confusion was finally could be overcome with the development of silicon-solar-cell by Mr. Russell Ohl which is in 1941. In 1954, three other great U.S researchers, G.L. Pearson, Daryl Chapin, and Calvin Fuller, convinced a silicon solar cell which was capable of a 6 percent energy-conversion efficiency after using in direct sunlight. By the late 1980's - silicon made cells, and those made of gallium arsenide, with efficiencies of more than 20 percent had been produced. In 1989 a concentrator solar cell- type of device in which sunlight is concentrated onto the cell surface by using lenses, could achieve a great efficiency of 37 percent due to the increasing intensity of the collected energy. Nowadays different solar cells of higher efficiencies and cost are now available.
Thursday, January 7, 2010
How many solar cells would be need in order to provide all of the electricity that my house requires?
If you have been read the HSW article on "How Solar Yard Lights Work", then you can feel how an unbelievable can be produced by a solar cell. The solar panel shown below contains 4 cells, and believe it, each of them can produce 0.45 volts and 100 milliamps, or up to 45 milliwatts. Each cell is measured 2 inches by 0.5 inches. In other words, with these solar cells it can be generated about 45 milliwatts in one square inch (6.45 square cm),how amazing. As the sake of discussion, let's assume that a panel can generate 70 milliwatts per square inch.
What you need to know for calculating how many square inches of solar panel you need for a house.
* How much power the house consumes as an average.
* Where the house is located ( can calculate the mean solar days, average rainfall for a period of time and etc.). This question may be impossible to answer unless you have a specific location selected in mind. So we can assume that on an average day the solar panels can generate their maximum power possible for 5 hours.
A "typical home" in America can be using either electricity or a specific gas to provide heat needed amount heat for the house, the hot water, the clothes dryer and the stove/oven. If you want to power a house with solar electricity, you would use gas appliances instead, because using solar electricity is so expensive. This means that what you would be with solar electricity are the things like the refrigerator, the lights, the TV, the computer, stereo equipment, motors in things like furnace fans, washer and etc. Let's say that all of previously mentioned things is out to 600 watts on average. For the course of 24 hours, you will need about 600 watts * 24 hours = 14,400 watt hours will be definetely needed per day.
From the relevant calculations mentioned above, we should be known that a solar panel can generate up to 70 milliwatts per square inch * 5 hours which is equal to 350 milliwatt hours per day. Therefore you will be actually needed about 41,000 square inches solar cell for the house. That is a solar panel that is measured about 285 square feet (it is about 26 square meters). That is costed around $16,000. Then, because we know that the sun only shines part of the time, not the whole day, you would need to purchase a battery, an inverter and etc., and that definitely often doubles the cost of the installation.
If you want to have a small room air conditioner in your bedroom,what you have to do is double everything.
Because for the reason - solar electricity is so expensive, you would normally prefer at great lengths to reduce your electricity consumption. You may use a portable laptop instead of a desktop computer with a big monitor. You would use fluorescent lights[FLV bulbs] instead of incandescent. You would use a small LCD TV instead of a large color set. You would prefer to a small, extremely efficient refrigerator. By doing above things you might be able to reduce your average power consumption to at-least 100 watts. This would reduce the size of your solar panel and its cost, and this might bring it into the range of possibility.
The most important thing to remember, however is that about 100 watts per an hour purchased from the power grid may only cost about 24 cents a day normally, or in other words $91 a year. That's why you are not able to see more solar houses unless they are in a remote locations. When it costs about $100 a year to purchase power from the grid, it is really hard to justify the matter of spending thousands of dollars on a solar system.
What you need to know for calculating how many square inches of solar panel you need for a house.
* How much power the house consumes as an average.
* Where the house is located ( can calculate the mean solar days, average rainfall for a period of time and etc.). This question may be impossible to answer unless you have a specific location selected in mind. So we can assume that on an average day the solar panels can generate their maximum power possible for 5 hours.
A "typical home" in America can be using either electricity or a specific gas to provide heat needed amount heat for the house, the hot water, the clothes dryer and the stove/oven. If you want to power a house with solar electricity, you would use gas appliances instead, because using solar electricity is so expensive. This means that what you would be with solar electricity are the things like the refrigerator, the lights, the TV, the computer, stereo equipment, motors in things like furnace fans, washer and etc. Let's say that all of previously mentioned things is out to 600 watts on average. For the course of 24 hours, you will need about 600 watts * 24 hours = 14,400 watt hours will be definetely needed per day.
From the relevant calculations mentioned above, we should be known that a solar panel can generate up to 70 milliwatts per square inch * 5 hours which is equal to 350 milliwatt hours per day. Therefore you will be actually needed about 41,000 square inches solar cell for the house. That is a solar panel that is measured about 285 square feet (it is about 26 square meters). That is costed around $16,000. Then, because we know that the sun only shines part of the time, not the whole day, you would need to purchase a battery, an inverter and etc., and that definitely often doubles the cost of the installation.
If you want to have a small room air conditioner in your bedroom,what you have to do is double everything.
Because for the reason - solar electricity is so expensive, you would normally prefer at great lengths to reduce your electricity consumption. You may use a portable laptop instead of a desktop computer with a big monitor. You would use fluorescent lights[FLV bulbs] instead of incandescent. You would use a small LCD TV instead of a large color set. You would prefer to a small, extremely efficient refrigerator. By doing above things you might be able to reduce your average power consumption to at-least 100 watts. This would reduce the size of your solar panel and its cost, and this might bring it into the range of possibility.
The most important thing to remember, however is that about 100 watts per an hour purchased from the power grid may only cost about 24 cents a day normally, or in other words $91 a year. That's why you are not able to see more solar houses unless they are in a remote locations. When it costs about $100 a year to purchase power from the grid, it is really hard to justify the matter of spending thousands of dollars on a solar system.
If photovoltaics are such a wonderful source of free energy, then why doesn't the whole world run on solar power?
Solar-power Costs
Some people have a flawed concept of solar energy. While it's true that sunlight is free, the electricity generated by PV systems is not. As you can see from our discussion of a household PV system, quite a bit of hardware is needed. Currently, an installed PV system will cost somewhere around $9 per peak Watt. To give you an idea of how much a house system would cost, let's consider the Solar House -- a model residential home in Raleigh, North Carolina, with a PV system set up by the North Carolina Solar Center to demonstrate the technology. It's a fairly small home, and it is estimated that its 3.6-kW PV system covers about half of the total electricity needs (this system doesn't use batteries -- it's connected to the grid). Even so, at $9 per Watt, this installed system would cost you around $32,000.
That's why PV is usually used in remote areas, far from a conventional source of electricity. Right now, it simply can't compete with the utilities. Costs are coming down as research is being done, however. Researchers are confident that PV will one day be cost effective in urban areas as well as remote ones. Part of the problem is that manufacturing needs to be done on a large scale to reduce costs as much as possible. That kind of demand for PV, however, won't exist until prices fall to competitive levels. It's a Catch-22 situation. Even so, demand and module efficiencies are constantly rising, prices are falling, and the world is becoming increasingly aware of environmental concerns associated with conventional power sources, making photovoltaics a technology with a bright future.
Some people have a flawed concept of solar energy. While it's true that sunlight is free, the electricity generated by PV systems is not. As you can see from our discussion of a household PV system, quite a bit of hardware is needed. Currently, an installed PV system will cost somewhere around $9 per peak Watt. To give you an idea of how much a house system would cost, let's consider the Solar House -- a model residential home in Raleigh, North Carolina, with a PV system set up by the North Carolina Solar Center to demonstrate the technology. It's a fairly small home, and it is estimated that its 3.6-kW PV system covers about half of the total electricity needs (this system doesn't use batteries -- it's connected to the grid). Even so, at $9 per Watt, this installed system would cost you around $32,000.
That's why PV is usually used in remote areas, far from a conventional source of electricity. Right now, it simply can't compete with the utilities. Costs are coming down as research is being done, however. Researchers are confident that PV will one day be cost effective in urban areas as well as remote ones. Part of the problem is that manufacturing needs to be done on a large scale to reduce costs as much as possible. That kind of demand for PV, however, won't exist until prices fall to competitive levels. It's a Catch-22 situation. Even so, demand and module efficiencies are constantly rising, prices are falling, and the world is becoming increasingly aware of environmental concerns associated with conventional power sources, making photovoltaics a technology with a bright future.
Solving Solar-power Issues
Certainly, no one would accept only having electricity during the day, and then only on clear days, if they have a choice. We need energy storage -- batteries. Unfortunately, batteries add a lot of cost and maintenance to the PV system. Currently, however, it's a necessity if you want to be completely independent. One way around the problem is to connect your house to the utility grid, buying power when you need it and selling to them when you produce more than you need. This way, the utility acts as a practically infinite storage system. The utility has to agree, of course, and in most cases will buy power from you at a much lower price than their own selling price. You will also need special equipment to make sure that the power you sell to your utility is synchronous with theirs -- that it shares the same sinusoidal waveform and frequency. Safety is an issue as well. The utility has to make sure that if there's a power outage in your neighborhood, your PV system won't try to feed electricity into lines that a lineman may think is dead. This is called islanding.
If you decide to use batteries, keep in mind that they will have to be maintained, and then replaced after a certain number of years. The PV modules should last 20 years or more, but batteries just don't have that kind of useful life. Batteries in PV systems can also be very dangerous because of the energy they store and the acidic electrolytes they contain, so you'll need a well-ventilated, non-metallic enclosure for them.
Although several different kinds of batteries are commonly used, the one characteristic they should all have in common is that they are deep-cycle batteries. Unlike your car battery, which is a shallow-cycle battery, deep-cycle batteries can discharge more of their stored energy while still maintaining long life. Car batteries discharge a large current for a very short time -- to start your car -- and are then immediately recharged as you drive. PV batteries generally have to discharge a smaller current for a longer period (such as all night), while being charged during the day.
The most commonly used deep-cycle batteries are lead-acid batteries (both sealed and vented) and nickel-cadmium batteries. Nickel-cadmium batteries are more expensive, but last longer and can be discharged more completely without harm. Even deep-cycle lead-acid batteries can't be discharged 100 percent without seriously shortening battery life, and generally, PV systems are designed to discharge lead-acid batteries no more than 40 percent or 50 percent.
Also, the use of batteries requires the installation of another component called a charge controller. Batteries last a lot longer if care is taken so that they aren't overcharged or drained too much. That's what a charge controller does. Once the batteries are fully charged, the charge controller doesn't let current from the PV modules continue to flow into them. Similarly, once the batteries have been drained to a certain predetermined level, controlled by measuring battery voltage, many charge controllers will not allow more current to be drained from the batteries until they have been recharged. The use of a charge controller is essential for long battery life.
The other problem besides energy storage is that the electricity generated by your PV modules, and extracted from your batteries if you choose to use them, is not in the form that's used by the electrical appliances in your house. The electricity generated by a solar system is direct current, while the electricity supplied by your utility (and the kind that every appliance in your house uses) is alternating current. You will need an inverter, a device that converts DC to AC. Most large inverters will also allow you to automatically control how your system works. Some PV modules, called AC modules, actually have an inverter already built into each module, eliminating the need for a large, central inverter, and simplifying wiring issues.
Throw in the mounting hardware, wiring, junction boxes, grounding equipment, overcurrent protection, DC and AC disconnects and other accessories and you have yourself a system. Electrical codes must be followed (there's a section in the National Electrical Code just for PV), and it's highly recommended that the installation be done by a licensed electrician who has experience with PV systems. Once installed, a PV system requires very little maintenance (especially if no batteries are used), and will provide electricity cleanly and quietly for 20 years or more.
If you decide to use batteries, keep in mind that they will have to be maintained, and then replaced after a certain number of years. The PV modules should last 20 years or more, but batteries just don't have that kind of useful life. Batteries in PV systems can also be very dangerous because of the energy they store and the acidic electrolytes they contain, so you'll need a well-ventilated, non-metallic enclosure for them.
Although several different kinds of batteries are commonly used, the one characteristic they should all have in common is that they are deep-cycle batteries. Unlike your car battery, which is a shallow-cycle battery, deep-cycle batteries can discharge more of their stored energy while still maintaining long life. Car batteries discharge a large current for a very short time -- to start your car -- and are then immediately recharged as you drive. PV batteries generally have to discharge a smaller current for a longer period (such as all night), while being charged during the day.
The most commonly used deep-cycle batteries are lead-acid batteries (both sealed and vented) and nickel-cadmium batteries. Nickel-cadmium batteries are more expensive, but last longer and can be discharged more completely without harm. Even deep-cycle lead-acid batteries can't be discharged 100 percent without seriously shortening battery life, and generally, PV systems are designed to discharge lead-acid batteries no more than 40 percent or 50 percent.
Also, the use of batteries requires the installation of another component called a charge controller. Batteries last a lot longer if care is taken so that they aren't overcharged or drained too much. That's what a charge controller does. Once the batteries are fully charged, the charge controller doesn't let current from the PV modules continue to flow into them. Similarly, once the batteries have been drained to a certain predetermined level, controlled by measuring battery voltage, many charge controllers will not allow more current to be drained from the batteries until they have been recharged. The use of a charge controller is essential for long battery life.
The other problem besides energy storage is that the electricity generated by your PV modules, and extracted from your batteries if you choose to use them, is not in the form that's used by the electrical appliances in your house. The electricity generated by a solar system is direct current, while the electricity supplied by your utility (and the kind that every appliance in your house uses) is alternating current. You will need an inverter, a device that converts DC to AC. Most large inverters will also allow you to automatically control how your system works. Some PV modules, called AC modules, actually have an inverter already built into each module, eliminating the need for a large, central inverter, and simplifying wiring issues.
Throw in the mounting hardware, wiring, junction boxes, grounding equipment, overcurrent protection, DC and AC disconnects and other accessories and you have yourself a system. Electrical codes must be followed (there's a section in the National Electrical Code just for PV), and it's highly recommended that the installation be done by a licensed electrician who has experience with PV systems. Once installed, a PV system requires very little maintenance (especially if no batteries are used), and will provide electricity cleanly and quietly for 20 years or more.
Solar-powering a House - Easy
What would you have to do to power your house with solar energy? Although it's not as simple as just slapping some modules on your roof, it's not extremely difficult to do, either.
First of all, not every roof has the correct orientation or angle of inclination to take advantage of the sun's energy. Non-tracking PV systems in the Northern Hemisphere should point toward true south (this is the orientation). They should be inclined at an angle equal to the area's latitude to absorb the maximum amount of energy year-round. A different orientation and/or inclination could be used if you want to maximize energy production for the morning or afternoon, and/or the summer or winter. Of course, the modules should never be shaded by nearby trees or buildings, no matter the time of day or the time of year. In a PV module, even if just one of its 36 cells is shaded, power production will be reduced by more than half.
If you have a house with an unshaded, south-facing roof, you need to decide what size system you need. This is complicated by the facts that your electricity production depends on the weather, which is never completely predictable, and that your electricity demand will also vary. These hurdles are fairly easy to clear. Meteorological data gives average monthly sunlight levels for different geographical areas. This takes into account rainfall and cloudy days, as well as altitude, humidity, and other more subtle factors. You should design for the worst month, so that you'll have enough electricity all year. With that data, and knowing your average household demand (your utility bill conveniently lets you know how much energy you use every month),there are simple methods you can use to determine just how many PV modules you'll need. You'll also need to decide on a system voltage, which you can control by deciding how many modules to wire in series.
First of all, not every roof has the correct orientation or angle of inclination to take advantage of the sun's energy. Non-tracking PV systems in the Northern Hemisphere should point toward true south (this is the orientation). They should be inclined at an angle equal to the area's latitude to absorb the maximum amount of energy year-round. A different orientation and/or inclination could be used if you want to maximize energy production for the morning or afternoon, and/or the summer or winter. Of course, the modules should never be shaded by nearby trees or buildings, no matter the time of day or the time of year. In a PV module, even if just one of its 36 cells is shaded, power production will be reduced by more than half.
If you have a house with an unshaded, south-facing roof, you need to decide what size system you need. This is complicated by the facts that your electricity production depends on the weather, which is never completely predictable, and that your electricity demand will also vary. These hurdles are fairly easy to clear. Meteorological data gives average monthly sunlight levels for different geographical areas. This takes into account rainfall and cloudy days, as well as altitude, humidity, and other more subtle factors. You should design for the worst month, so that you'll have enough electricity all year. With that data, and knowing your average household demand (your utility bill conveniently lets you know how much energy you use every month),there are simple methods you can use to determine just how many PV modules you'll need. You'll also need to decide on a system voltage, which you can control by deciding how many modules to wire in series.
Energy Loss in a Solar Cell
Visible light is only part of the electromagnetic spectrum. Electromagnetic radiation is not monochromatic - it is made up of a range of different wavelengths, and therefore energy levels. (See How Special Relativity Works for a good discussion of the electromagnetic spectrum.)
Light can be separated into different wavelengths, and we can see them in the form of a rainbow. Since the light that hits our cell has photons of a wide range of energies, it turns out that some of them won't have enough energy to form an electron-hole pair. They'll simply pass through the cell as if it were transparent. Still other photons have too much energy. Only a certain amount of energy, measured in electron volts (eV) and defined by our cell material (about 1.1 eV for crystalline silicon), is required to knock an electron loose. We call this the band gap energy of a material. If a photon has more energy than the required amount, then the extra energy is lost (unless a photon has twice the required energy, and can create more than one electron-hole pair, but this effect is not significant). These two effects alone account for the loss of around 70 percent of the radiation energy incident on our cell.
Why can't we choose a material with a really low band gap, so we can use more of the photons? Unfortunately, our band gap also determines the strength (voltage) of our electric field, and if it's too low, then what we make up in extra current (by absorbing more photons), we lose by having a small voltage. Remember that power is voltage times current. The optimal band gap, balancing these two effects, is around 1.4 eV for a cell made from a single material.
We have other losses as well. Our electrons have to flow from one side of the cell to the other through an external circuit. We can cover the bottom with a metal, allowing for good conduction, but if we completely cover the top, then photons can't get through the opaque conductor and we lose all of our current (in some cells, transparent conductors are used on the top surface, but not in all). If we put our contacts only at the sides of our cell, then the electrons have to travel an extremely long distance (for an electron) to reach the contacts. Remember, silicon is a semiconductor -- it's not nearly as good as a metal for transporting current. Its internal resistance (called series resistance) is fairly high, and high resistance means high losses. To minimize these losses, our cell is covered by a metallic contact grid that shortens the distance that electrons have to travel while covering only a small part of the cell surface. Even so, some photons are blocked by the grid, which can't be too small or else its own resistance will be too high.
Light can be separated into different wavelengths, and we can see them in the form of a rainbow. Since the light that hits our cell has photons of a wide range of energies, it turns out that some of them won't have enough energy to form an electron-hole pair. They'll simply pass through the cell as if it were transparent. Still other photons have too much energy. Only a certain amount of energy, measured in electron volts (eV) and defined by our cell material (about 1.1 eV for crystalline silicon), is required to knock an electron loose. We call this the band gap energy of a material. If a photon has more energy than the required amount, then the extra energy is lost (unless a photon has twice the required energy, and can create more than one electron-hole pair, but this effect is not significant). These two effects alone account for the loss of around 70 percent of the radiation energy incident on our cell.
Why can't we choose a material with a really low band gap, so we can use more of the photons? Unfortunately, our band gap also determines the strength (voltage) of our electric field, and if it's too low, then what we make up in extra current (by absorbing more photons), we lose by having a small voltage. Remember that power is voltage times current. The optimal band gap, balancing these two effects, is around 1.4 eV for a cell made from a single material.
We have other losses as well. Our electrons have to flow from one side of the cell to the other through an external circuit. We can cover the bottom with a metal, allowing for good conduction, but if we completely cover the top, then photons can't get through the opaque conductor and we lose all of our current (in some cells, transparent conductors are used on the top surface, but not in all). If we put our contacts only at the sides of our cell, then the electrons have to travel an extremely long distance (for an electron) to reach the contacts. Remember, silicon is a semiconductor -- it's not nearly as good as a metal for transporting current. Its internal resistance (called series resistance) is fairly high, and high resistance means high losses. To minimize these losses, our cell is covered by a metallic contact grid that shortens the distance that electrons have to travel while covering only a small part of the cell surface. Even so, some photons are blocked by the grid, which can't be too small or else its own resistance will be too high.
Anatomy of a Solar Cell
Before now, our silicon was all electrically neutral. Our extra electrons were balanced out by the extra protons in the phosphorous. Our missing electrons (holes) were balanced out by the missing protons in the boron. When the holes and electrons mix at the junction between N-type and P-type silicon, however, that neutrality is disrupted. Do all the free electrons fill all the free holes? No. If they did, then the whole arrangement wouldn't be very useful. Right at the junction, however, they do mix and form a barrier, making it harder and harder for electrons on the N side to cross to the P side. Eventually, equilibrium is reached, and we have an electric field separating the two sides.
A = n type silicon
B = p type silicon
This electric field acts as a diode, allowing (and even pushing) electrons to flow from the P side to the N side, but not the other way around. It's like a hill -- electrons can easily go down the hill (to the N side), but can't climb it (to the P side).
So we've got an electric field acting as a diode in which electrons can only move in one direction.
When light, in the form of photons, hits our solar cell, its energy frees electron-hole pairs.
Each photon with enough energy will normally free exactly one electron, and result in a free hole as well. If this happens close enough to the electric field, or if free electron and free hole happen to wander into its range of influence, the field will send the electron to the N side and the hole to the P side. This causes further disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the path to their original side (the P side) to unite with holes that the electric field sent there, doing work for us along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is the product of the two.
There are a few more steps left before we can really use our cell. Silicon happens to be a very shiny material, which means that it is very reflective. Photons that are reflected can't be used by the cell. For that reason, an anti-reflective coating is applied to the top of the cell to reduce reflection losses to less than 5 percent.
A = n type siliconB = p type silicon
This electric field acts as a diode, allowing (and even pushing) electrons to flow from the P side to the N side, but not the other way around. It's like a hill -- electrons can easily go down the hill (to the N side), but can't climb it (to the P side).
So we've got an electric field acting as a diode in which electrons can only move in one direction.
When light, in the form of photons, hits our solar cell, its energy frees electron-hole pairs.
Each photon with enough energy will normally free exactly one electron, and result in a free hole as well. If this happens close enough to the electric field, or if free electron and free hole happen to wander into its range of influence, the field will send the electron to the N side and the hole to the P side. This causes further disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the path to their original side (the P side) to unite with holes that the electric field sent there, doing work for us along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is the product of the two.
There are a few more steps left before we can really use our cell. Silicon happens to be a very shiny material, which means that it is very reflective. Photons that are reflected can't be used by the cell. For that reason, an anti-reflective coating is applied to the top of the cell to reduce reflection losses to less than 5 percent. The final step is the glass cover plate that protects the cell from the elements. PV modules are made by connecting several cells (usually 36) in series and parallel to achieve useful levels of voltage and current, and putting them in a sturdy frame complete with a glass cover and positive and negative terminals on the back.
How Silicon Makes a Solar Cell
Silicon has some special chemical properties, especially in its crystalline form. An atom of silicon has 14 electrons, arranged in three different shells. The first two shells, those closest to the center, are completely full. The outer shell, however, is only half full, having only four electrons. A silicon atom will always look for ways to fill up its last shell (which would like to have eight electrons). To do this, it will share electrons with four of its neighbor silicon atoms. It's like every atom holds hands with its neighbors, except that in this case, each atom has four hands joined to four neighbors. That's what forms the crystalline structure, and that structure turns out to be important to this type of PV cell.
We've now described pure, crystalline silicon. Pure silicon is a poor conductor of electricity because none of its electrons are free to move about, as electrons are in good conductors such as copper. Instead, the electrons are all locked in the crystalline structure. The silicon in a solar cell is modified slightly so that it will work as a solar cell.
A solar cell has silicon with impurities -- other atoms mixed in with the silicon atoms, changing the way things work a bit. We usually think of impurities as something undesirable, but in our case, our cell wouldn't work without them. These impurities are actually put there on purpose. Consider silicon with an atom of phosphorous here and there, maybe one for every million silicon atoms. Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbor atoms, but in a sense, the phosphorous has one electron that doesn't have anyone to hold hands with. It doesn't form part of a bond, but there is a positive proton in the phosphorous nucleus holding it in place.
When energy is added to pure silicon, for example in the form of heat, it can cause a few electrons to break free of their bonds and leave their atoms. A hole is left behind in each case. These electrons then wander randomly around the crystalline lattice looking for another hole to fall into. These electrons are called free carriers, and can carry electrical current. There are so few of them in pure silicon, however, that they aren't very useful. Our impure silicon with phosphorous atoms mixed in is a different story. It turns out that it takes a lot less energy to knock loose one of our "extra" phosphorous electrons because they aren't tied up in a bond -- their neighbors aren't holding them back. As a result, most of these electrons do break free, and we have a lot more free carriers than we would have in pure silicon. The process of adding impurities on purpose is called doping, and when doped with phosphorous, the resulting silicon is called N-type ("n" for negative) because of the prevalence of free electrons. N-type doped silicon is a much better conductor than pure silicon is.
Actually, only part of our solar cell is N-type. The other part is doped with boron, which has only three electrons in its outer shell instead of four, to become P-type silicon. Instead of having free electrons, P-type silicon ("p" for positive) has free holes. Holes really are just the absence of electrons, so they carry the opposite (positive) charge. They move around just like electrons do.
The interesting part starts when you put N-type silicon together with P-type silicon. Remember that every PV cell has at least one electric field. Without an electric field, the cell wouldn't work, and this field forms when the N-type and P-type silicon are in contact. Suddenly, the free electrons in the N side, which have been looking all over for holes to fall into, see all the free holes on the P side, and there's a mad rush to fill them in.
Photovoltaic Cells: Converting Photons to Electrons
The solar cells that you see on calculators and satellites are photovoltaic cells or modules (modules are simply a group of cells electrically connected and packaged in one frame). Photovoltaics, as the word implies (photo = light, voltaic = electricity), convert sunlight directly into electricity. Once used almost exclusively in space, photovoltaics are used more and more in less exotic ways. They could even power your house. How do these devices work?
Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. PV cells also all have one or more electric fields that act to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off to use externally. For example, the current can power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.
Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. PV cells also all have one or more electric fields that act to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off to use externally. For example, the current can power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.
How It Works
You've probably seen calculators that have solar cells - calculators that never need batteries, and in some cases don't even have an off button. As long as you have enough light, they seem to work forever. You may have seen larger solar panels - on emergency road signs or call boxes, on buoys, even in parking lots to power lights.
Although these larger panels aren't as common as solar powered calculators, they're out there, and not that hard to spot if you know where to look. There are solar cell arrays on satellites, where they are used to power the electrical systems.
You have probably also been hearing about the "solar revolution" for the last 20 years - the idea that one day we will all use free electricity from the sun. This is a seductive promise: On a bright, sunny day, the sun shines approximately 1,000 watts of energy per square meter of the planet's surface, and if we could collect all of that energy we could easily power our homes and offices for free.
In this article, we will examine solar cells to learn how they convert the sun's energy directly into electricity. In the process, you will learn why we are getting closer to using the sun's energy on a daily basis, and why we still have more research to do before the process becomes cost effective.
ATS's fully-automated solar cell lines
The company's parent, ATS, has a strong background in the automation of
manufacturing processes. This has enabled Photowatt to install two new fullyautomated
high volume PV cell and module manufacturing lines which are shown in the
photo on the right. These lines started operating in 2000 and can undertake the screen
printing of the rear and front metallisation pastes, drying and firing of the pastes,
deposition of the anti-reflective coating (ARC), sorting, ribbon soldering, lamination of
the protective insulation layer and module assembly.
Today, the standard size of a multi-crystalline Si cell is 125 x 125 mm (5 inches square)
with a thickness of 300 Mm. Using a titanium dioxide anti-reflective coating, Photowatt's
solar cell efficiency was about 13 per cent. More recently, using new silicon nitride antireflective
coating technology, this efficiency has been improved to over 15 per cent on
the company's own multi-crystalline silicon.
manufacturing processes. This has enabled Photowatt to install two new fullyautomated
high volume PV cell and module manufacturing lines which are shown in the
photo on the right. These lines started operating in 2000 and can undertake the screen
printing of the rear and front metallisation pastes, drying and firing of the pastes,
deposition of the anti-reflective coating (ARC), sorting, ribbon soldering, lamination of
the protective insulation layer and module assembly.
Today, the standard size of a multi-crystalline Si cell is 125 x 125 mm (5 inches square)
with a thickness of 300 Mm. Using a titanium dioxide anti-reflective coating, Photowatt's
solar cell efficiency was about 13 per cent. More recently, using new silicon nitride antireflective
coating technology, this efficiency has been improved to over 15 per cent on
the company's own multi-crystalline silicon.
Photowatt chooses Dupont's Solamet materials for its PV solar cells
For many years, Photowatt has been a European leader in the manufacture of
photovoltaic (PV) solar cells. Since 1997, the company, based at Bourgoin-Jallieu, near
Lyon, France, has been a part of ATS (Automation Tooling Systems), a large
multinational concern with its headquarters in Toronto, Canada. ATS specializes in the
fabrication of automated production lines for the automotive and electronics industries.
In 2001, the PV market grew by 39 per cent,
based on power in megawatts (MWp), and Photowatt is well positioned to take advantage of this buoyant market. Like most large PV manufacturers, the company has increased capacity every year to cope with demand and, between 1995 and 2002, its production capacity has increased 10-fold, from 2 to 20 MW.
Photowatt has an advantage in the industry by being a vertically-integrated PV cell manufacturer with the capability to produce solar panels from silicon feedstock. It can therefore control all of the intermediate processing and manufacturing steps, including ingot casting, silicon wire sawing, solar cell metallisation, lamination and assembly.
photovoltaic (PV) solar cells. Since 1997, the company, based at Bourgoin-Jallieu, near
Lyon, France, has been a part of ATS (Automation Tooling Systems), a large
multinational concern with its headquarters in Toronto, Canada. ATS specializes in the
fabrication of automated production lines for the automotive and electronics industries.
In 2001, the PV market grew by 39 per cent,
based on power in megawatts (MWp), and Photowatt is well positioned to take advantage of this buoyant market. Like most large PV manufacturers, the company has increased capacity every year to cope with demand and, between 1995 and 2002, its production capacity has increased 10-fold, from 2 to 20 MW.
Photowatt has an advantage in the industry by being a vertically-integrated PV cell manufacturer with the capability to produce solar panels from silicon feedstock. It can therefore control all of the intermediate processing and manufacturing steps, including ingot casting, silicon wire sawing, solar cell metallisation, lamination and assembly.
Sunday, January 3, 2010
Building your solar Cell
Step 1.
Cut a piece sheet copper into the size and
shape you wish for your cell. Although .025 inch thick copper
was used for the cells described here, just about any thickness
will do.
Copper is a soft metal and can be cut with tin snips or even
with an old pair of scissors.
Cut your cell with a diameter of 1 1/2 inches, we strart with a
smaller cell because it is much easier to work with. The larger
the heat source the bigger the size copper you can use to create
your solar cell. After you get the hang of it you can then build
larger cells..
As you cut the copper, be sure to leave a "handle" so that you
may grip the cell with pliers without marring the cell's active
surface.
step 2
The surface of the cell
must be made extremely
clean. Prepare
a solution of nitric acid
by carefully mixing 20
parts nitric acid and 80
parts distilled water.
Remember towear protective
goggles or other
suitable eye protection
and to work in a well
ventilated area whenever
you work with
chemicals.
IMPORTANT! ALWAYS ADD ACID TO WATER!
NEVER ADD WATER TO ACID!
Begin by carefully polishing the face of the cell with a fine
grade of steel wool until it shines brightly. Then place the cell
with the shiny side up, in the solution of nitric acid.
Soon, tiny bubbles will form on the copper disk. Stir the
solution occasionally. When the disk seems shiny and well
cleaned, remove and rinse it under cool running water.
WARNING! Never to allow your skin to touch the acid, and
that no acid remains on the cell.
The cell will sometimes work without the acid cleaning if it is
simply well polished by the steel wool. However, we strongly
recommend the acid cleaning.
Nitric acid and the other chemicals mentioned in the text can
be easily ordered from a number of mail-order chemical houses
such as found in the classified section of magazines such as
Popular Science.
Step 3.
Cuprous oxide is now formed on the disk by heating
it over a Bunsen burner, or propane torch. A gas stove can be
used, but results may be unpredictable.
The time me disk must be heated varies greatly depending on
the heat of the torch, and the thickness and size of the copper
piece. Using a standard propane torch from the hardware store
and a disk of the described size, I found 2 minutes and 40 seconds
to be ideal. If you heat it too long, you run the risk of burning off
the oxides. Heating for too short a time may prevent the oxides
from forming fully.
Photo sensitive oxides are formed by heating the disk for several minutes.
The Copper is heated on one side only, until it is glowing and red hot!
copper must be kept at an even red hot,all over it's surface for about
2 minutes and 45 seconds by moving the copper over the tourch in a
round motion. counter clock wise. The side of the cell that is not exposed
to the flame will become coated with the black cupric oxide.
Now just beneath this black oxide is the photo sensitive red cuprouse oxide.
This red cuprouse oxide can be purchsed in powder form and mixed with a
special solvent, which is clear, and is described in the Japan Patent. The
Oxide can then be screen printed onto the copper surface. This oxide
material is different than the chemicals used in the Patent.
After heating your cell for the prescribed time, it must be carefully cooled.
There are two ways to go about this. You can cool the copper quickly by
either placing it face down on a flat metal surface, or by waiting a few moments
and then quenching it in cool water. The advantage to cooling the cell
quickly is that the unwanted black cupric oxide will often flake off the cell
due to the difference in contraction rates of the oxides. Unfortunately, I have
had bad luck with this method despite extensive experimentation with different
temperatures and procedures.
What has worked very well for me is to bring the cell's temperature down
as slowly as possible making sure the black oxide does not crack at all. Once
completely cool, the cell is immersed in the nitric acid bath. You must wait
while the acid begins to dissolve the black oxide. Then you remove and rinse
the cell.
A very weak solution of sodium cyanide can also be used with good results.
However, you should be extremely careful when using it. Cyanide is an extremely
poisonous chemical, and if accidentally mixed with an acid can create
deadly fumes. At this point the black oxide covering the cell can be rubbed
away with steel wool and a little elbow grease. After all of the Black oxide has
been removed, your cell should have a uniform caoting of deep red on one side.
black oxide has been removed, your cell should have a uniform coating of deep red on one side. Don't worry if the very outside
edges of your cell don't have the coating, this is due to uneven cooling and is normal. Keep in mind that the red coating must not
be scratched or scraped away to reveal the bare copper plate beneath. If this happens the cell might short in the final step and not
work at all.
Testing:
There are now several ways that you can test you solar cell even though it is not finished, it can generate power.
If you are building the cell for a science fair or other demonstration, you may want to stop and use the cell at this point while the
cuprous oxide is still visible. If you hold the cell near a source of bright light, a current will be generated between the cuprous oxide
coating and the copper plate. The copper will form the positive terminal and the cuprous oxide the negative.
Making contact with the copper portion of the disk is very easy. Simply sand a small bare spot on the back of the solar cell and attach
a wire. Attaching the wire and making a good contact with the cuprous oxide is more difficult, it is hard to solder and attach anything.
but it can be done by pressure gluing or other.
method of making a good contact with this large of a surface area, is by attaching a wire grid to it. A better way is to apply a very thin
layer of silver or gold called a transparent An easily fabricated but temporary transparent electrode can be made from salt water. Or as seen
in our Chlorine cells and a container glued to the cell and the liquid applied. A soloution of salt or acid will conduct electricity and also pass
light to the cell. Drip a small amount of salt water or your spit, on to the center of the cell. Make sure that the water rests only on the
cuprous oxide and does not touch any of the solar cell's copper surface or it will short out and will not produce any free electrical energy at
all.
Now, attach one wire from a galvanometer, digital voltmeter using the milliamp or low voltage setting to some exposed portion of the
cell's copper surface. Usually the back or the edges have some exposed copper. Touch the other meter lead to the surface of the water. The
meter will spring to life. Next, bring a bright source of light such as a 100 watt bulb near the cell. The meter should show a slightly smaller
voltage as the light approaches. Your cell will produce best in sunlight! The cell is changing some of the light into electricity but is having to
counteract the current generated by the saltwater, hence the drop in voltage. The salt water actually acts as an electrolyte and with the oxide
generates its own current just as a small battery would. Another way that you can test your cell is by making a wire electrode for the surface.
This is done simply by coiling some 30 gauge silver-plated wire or aluminum wire and by holding it against the ( cells ) cuprous oxide
surface with a sheet of glass. A good way is to coil the wire around is to use a cone shaped dowel or other
object first in order to make good even spirals. Make sure that the wire touches the cuprous oxide only, and none of the bare
copper. You will always have some bare copper around the edges of the cell, so it is best to paint with enamel paint, let dry and then work
with the cell.
By simply attaching one wire of your meter to the silver wire, and one to the cell's exposed copper, you will be able to register a small
current when a light is brought near. In this form, the cell can be operated indefinitely and makes an excellent Science Fair Display.
Final Step:
Making The Silvering Solution: The final step in making your own solar cell will be to make a permanent transparent electrode. When
properly applied, this will give your cell a beautiful semi-mirrored finish and allow you to make electrical contact with the whole cuprous
oxide face of the cell. This step is probably the trickiest in the production of the cell.
But, just as with the last steps, it becomes somewhat easier with practice. Using distilled water, make ten percent solutions each of ammonia
water, potassium hydroxide and potassium sodium tartrate in seperate test tubes. A ten percent solution can be created by mixing 10 parts by
weight of solute in 90 parts of water. Please remember that the test tubes can become warm or even hot when the water is first added, so be sure to use Pyrex
glass test tubes. Also, make certain you have ample ventilation when mixing the ammonia solution. Dissolve in 1 oz. water a single crystal of silver nitrate. The
crystal should be somewhat larger than the head of a match. Begin adding drops of the ammonia solution to the dissolved silver nitrate until the water first
becomes brown, and then just begins to clear. Add a drop of potassium hydroxide to this solution. Then again begin adding drops of ammonia water until the
solution just begins to clear. The solution will remain somewhat cloudy. Too much ammonia in the solution can dissolve the cuprous oxide coating and can
damage or ruin the cell. Stir the mixture while adding a single drop of the potassium sodium tartrate solution. The mixture is now ready and should be used
immediately.
Applying The Solution :
Temperature and variations in the chemical mixture can
dramatically change the time required to complete the silvering
process. The best way to complete this step is by simple visual
examination of the process as it proceeds.
With the cell on a flat surface, begin by carefully pouring the
silvering mixture on to the center of the cell. Remember to avoid
letting this mixture contact any exposed copper. A good trick is to cover with paint or lacquer any exposed copper surfaces on the face of the cell. Continue pouring until the liquid has covered as much of the
surface as you can . If all the exposed copper on the surface has
been properly protected with the lacquer, you can actually pour the solution until it comes right to the edge. Since water has an affinity for itself
called "cohesion", it won't spill over the edge. Very soon, a thin film of silver will begin to form over the cell's surface. The liquid should be
poured off when the red oxide is still slightly visible beneath the silver. allow the silvering process to go a little too long rather than not
long enough since some of the silver coating can be polished away.You should now have a smooth silver coating through which
the red oxide is barely visible.
Completing the Cell contact can now be made to the cuprous oxide face of the ell by means of a ring of lead or silver-coated wire which is
slightly smaller in diameter than the disk itself. With the ring held firmly against the disk, a protective coating of thin lacquer
can be applied. Make certain the lacquer does not come between the wire and the disk. With wires attached to the disk's copper back and the
lead or silver ring, the cell is complete. The disk can now be housed behind glass, mounted to a sheet of plastic, cast in a clear resin or
housed in any other enclosure you desire!
must be made extremely
clean. Prepare
a solution of nitric acid
by carefully mixing 20
parts nitric acid and 80
parts distilled water.
Remember towear protective
goggles or other
suitable eye protection
and to work in a well
ventilated area whenever
you work with
chemicals.
IMPORTANT! ALWAYS ADD ACID TO WATER!
NEVER ADD WATER TO ACID!
Begin by carefully polishing the face of the cell with a fine
grade of steel wool until it shines brightly. Then place the cell
with the shiny side up, in the solution of nitric acid.
Soon, tiny bubbles will form on the copper disk. Stir the
solution occasionally. When the disk seems shiny and well
cleaned, remove and rinse it under cool running water.
WARNING! Never to allow your skin to touch the acid, and
that no acid remains on the cell.
The cell will sometimes work without the acid cleaning if it is
simply well polished by the steel wool. However, we strongly
recommend the acid cleaning.
Nitric acid and the other chemicals mentioned in the text can
be easily ordered from a number of mail-order chemical houses
such as found in the classified section of magazines such as
Popular Science.
Step 3.
Cuprous oxide is now formed on the disk by heating
it over a Bunsen burner, or propane torch. A gas stove can be
used, but results may be unpredictable.
The time me disk must be heated varies greatly depending on
the heat of the torch, and the thickness and size of the copper
piece. Using a standard propane torch from the hardware store
and a disk of the described size, I found 2 minutes and 40 seconds
to be ideal. If you heat it too long, you run the risk of burning off
the oxides. Heating for too short a time may prevent the oxides
from forming fully.
Photo sensitive oxides are formed by heating the disk for several minutes.
The Copper is heated on one side only, until it is glowing and red hot!
copper must be kept at an even red hot,all over it's surface for about
2 minutes and 45 seconds by moving the copper over the tourch in a
round motion. counter clock wise. The side of the cell that is not exposed
to the flame will become coated with the black cupric oxide.
Now just beneath this black oxide is the photo sensitive red cuprouse oxide.
This red cuprouse oxide can be purchsed in powder form and mixed with a
special solvent, which is clear, and is described in the Japan Patent. The
Oxide can then be screen printed onto the copper surface. This oxide
material is different than the chemicals used in the Patent.
After heating your cell for the prescribed time, it must be carefully cooled.
There are two ways to go about this. You can cool the copper quickly by
either placing it face down on a flat metal surface, or by waiting a few moments
and then quenching it in cool water. The advantage to cooling the cell
quickly is that the unwanted black cupric oxide will often flake off the cell
due to the difference in contraction rates of the oxides. Unfortunately, I have
had bad luck with this method despite extensive experimentation with different
temperatures and procedures.
What has worked very well for me is to bring the cell's temperature down
as slowly as possible making sure the black oxide does not crack at all. Once
completely cool, the cell is immersed in the nitric acid bath. You must wait
while the acid begins to dissolve the black oxide. Then you remove and rinse
the cell.
A very weak solution of sodium cyanide can also be used with good results.
However, you should be extremely careful when using it. Cyanide is an extremely
poisonous chemical, and if accidentally mixed with an acid can create
deadly fumes. At this point the black oxide covering the cell can be rubbed
away with steel wool and a little elbow grease. After all of the Black oxide has
been removed, your cell should have a uniform caoting of deep red on one side.
black oxide has been removed, your cell should have a uniform coating of deep red on one side. Don't worry if the very outside
edges of your cell don't have the coating, this is due to uneven cooling and is normal. Keep in mind that the red coating must not
be scratched or scraped away to reveal the bare copper plate beneath. If this happens the cell might short in the final step and not
work at all.
Testing:
There are now several ways that you can test you solar cell even though it is not finished, it can generate power.
If you are building the cell for a science fair or other demonstration, you may want to stop and use the cell at this point while the
cuprous oxide is still visible. If you hold the cell near a source of bright light, a current will be generated between the cuprous oxide
coating and the copper plate. The copper will form the positive terminal and the cuprous oxide the negative.
Making contact with the copper portion of the disk is very easy. Simply sand a small bare spot on the back of the solar cell and attach
a wire. Attaching the wire and making a good contact with the cuprous oxide is more difficult, it is hard to solder and attach anything.
but it can be done by pressure gluing or other.
method of making a good contact with this large of a surface area, is by attaching a wire grid to it. A better way is to apply a very thin
layer of silver or gold called a transparent An easily fabricated but temporary transparent electrode can be made from salt water. Or as seen
in our Chlorine cells and a container glued to the cell and the liquid applied. A soloution of salt or acid will conduct electricity and also pass
light to the cell. Drip a small amount of salt water or your spit, on to the center of the cell. Make sure that the water rests only on the
cuprous oxide and does not touch any of the solar cell's copper surface or it will short out and will not produce any free electrical energy at
all.
Now, attach one wire from a galvanometer, digital voltmeter using the milliamp or low voltage setting to some exposed portion of the
cell's copper surface. Usually the back or the edges have some exposed copper. Touch the other meter lead to the surface of the water. The
meter will spring to life. Next, bring a bright source of light such as a 100 watt bulb near the cell. The meter should show a slightly smaller
voltage as the light approaches. Your cell will produce best in sunlight! The cell is changing some of the light into electricity but is having to
counteract the current generated by the saltwater, hence the drop in voltage. The salt water actually acts as an electrolyte and with the oxide
generates its own current just as a small battery would. Another way that you can test your cell is by making a wire electrode for the surface.
This is done simply by coiling some 30 gauge silver-plated wire or aluminum wire and by holding it against the ( cells ) cuprous oxide
surface with a sheet of glass. A good way is to coil the wire around is to use a cone shaped dowel or other
object first in order to make good even spirals. Make sure that the wire touches the cuprous oxide only, and none of the bare
copper. You will always have some bare copper around the edges of the cell, so it is best to paint with enamel paint, let dry and then work
with the cell.
By simply attaching one wire of your meter to the silver wire, and one to the cell's exposed copper, you will be able to register a small
current when a light is brought near. In this form, the cell can be operated indefinitely and makes an excellent Science Fair Display.
Final Step:
Making The Silvering Solution: The final step in making your own solar cell will be to make a permanent transparent electrode. When
properly applied, this will give your cell a beautiful semi-mirrored finish and allow you to make electrical contact with the whole cuprous
oxide face of the cell. This step is probably the trickiest in the production of the cell.
But, just as with the last steps, it becomes somewhat easier with practice. Using distilled water, make ten percent solutions each of ammonia
water, potassium hydroxide and potassium sodium tartrate in seperate test tubes. A ten percent solution can be created by mixing 10 parts by
weight of solute in 90 parts of water. Please remember that the test tubes can become warm or even hot when the water is first added, so be sure to use Pyrex
glass test tubes. Also, make certain you have ample ventilation when mixing the ammonia solution. Dissolve in 1 oz. water a single crystal of silver nitrate. The
crystal should be somewhat larger than the head of a match. Begin adding drops of the ammonia solution to the dissolved silver nitrate until the water first
becomes brown, and then just begins to clear. Add a drop of potassium hydroxide to this solution. Then again begin adding drops of ammonia water until the
solution just begins to clear. The solution will remain somewhat cloudy. Too much ammonia in the solution can dissolve the cuprous oxide coating and can
damage or ruin the cell. Stir the mixture while adding a single drop of the potassium sodium tartrate solution. The mixture is now ready and should be used
immediately.
Applying The Solution :
Temperature and variations in the chemical mixture can
dramatically change the time required to complete the silvering
process. The best way to complete this step is by simple visual
examination of the process as it proceeds.
With the cell on a flat surface, begin by carefully pouring the
silvering mixture on to the center of the cell. Remember to avoid
letting this mixture contact any exposed copper. A good trick is to cover with paint or lacquer any exposed copper surfaces on the face of the cell. Continue pouring until the liquid has covered as much of the
surface as you can . If all the exposed copper on the surface has
been properly protected with the lacquer, you can actually pour the solution until it comes right to the edge. Since water has an affinity for itself
called "cohesion", it won't spill over the edge. Very soon, a thin film of silver will begin to form over the cell's surface. The liquid should be
poured off when the red oxide is still slightly visible beneath the silver. allow the silvering process to go a little too long rather than not
long enough since some of the silver coating can be polished away.You should now have a smooth silver coating through which
the red oxide is barely visible.
Completing the Cell contact can now be made to the cuprous oxide face of the ell by means of a ring of lead or silver-coated wire which is
slightly smaller in diameter than the disk itself. With the ring held firmly against the disk, a protective coating of thin lacquer
can be applied. Make certain the lacquer does not come between the wire and the disk. With wires attached to the disk's copper back and the
lead or silver ring, the cell is complete. The disk can now be housed behind glass, mounted to a sheet of plastic, cast in a clear resin or
housed in any other enclosure you desire!
Homemade Copper Solar Cells
Selenium was extensively used in the production of commercial
solar cells before silicon. Although it can be a somewhat
difficult to find a supplier and it is a toxic heavy metal, it is
relatively inexpensive and can often be found in old model radio
sets, where it was used in the rectifier of the power supply.
A selenium photocell is made from a metal plate (usually iron)
with one side being covered with a layer of selenium. A very thin
layer of silver or gold is spattered over the selenium layer forming
a layer of current-carrying material that allows light to pass through
it. This layer is called a transparent electrode. A metal electrode
called a collector, rests on the gold or silver near the edge of it.
Wires are attached to the collector and the iron plate to deliver
the electric current to the load. Although not as great an output
as more modern cells, a selenium photocell can produce as much
as eight milliamperes for each square inch of surface area exposed
to bright sunlight.
Cadmium sulfide is probably the most promising low-cost
solar cell second only to silicon.
If you have an interest in electronics, you will undoubtedly
recognize cadmium sulfide (the common "CDS" cell) as the
material used in light detecting circuits. Although inventors
have realized for some time that a number of materials such as
cadmium sulfide change their electrical resistance in the presence
of light, it has only been in fairly recent times that it was
realized they could also be used to generate power also.
The most important attribute of cadmium sulfide is that it
could be mass-produced efficiently using a thin-film procedure
wherein very thin layers of its photosensitive components are
evaporated onto a base metal or screen printed.
Cadmium cells are fairly efficient (3-5 typical) making
them a good rival for amorphous silicon cells.
An Experimental Cell With Cuprous Oxide
The best cell by far for the you to start with, is a cell made
with cuprous oxide (Cu^O). Copper actually has two oxides, a red oxide called cuprous oxide, and a black oxide called cupric oxide
(CuO).
The dark red cuprous oxide has photoelectric properties but
black cupric oxide does not. The black oxide that forms on the
outside of your cell must be removed because it is opaque and
will not allow light to reach the cell's active surface.
solar cells before silicon. Although it can be a somewhat
difficult to find a supplier and it is a toxic heavy metal, it is
relatively inexpensive and can often be found in old model radio
sets, where it was used in the rectifier of the power supply.
A selenium photocell is made from a metal plate (usually iron)
with one side being covered with a layer of selenium. A very thin
layer of silver or gold is spattered over the selenium layer forming
a layer of current-carrying material that allows light to pass through
it. This layer is called a transparent electrode. A metal electrode
called a collector, rests on the gold or silver near the edge of it.
Wires are attached to the collector and the iron plate to deliver
the electric current to the load. Although not as great an output
as more modern cells, a selenium photocell can produce as much
as eight milliamperes for each square inch of surface area exposed
to bright sunlight.
Cadmium sulfide is probably the most promising low-cost
solar cell second only to silicon.
If you have an interest in electronics, you will undoubtedly
recognize cadmium sulfide (the common "CDS" cell) as the
material used in light detecting circuits. Although inventors
have realized for some time that a number of materials such as
cadmium sulfide change their electrical resistance in the presence
of light, it has only been in fairly recent times that it was
realized they could also be used to generate power also.
The most important attribute of cadmium sulfide is that it
could be mass-produced efficiently using a thin-film procedure
wherein very thin layers of its photosensitive components are
evaporated onto a base metal or screen printed.
Cadmium cells are fairly efficient (3-5 typical) making
them a good rival for amorphous silicon cells.
An Experimental Cell With Cuprous Oxide
The best cell by far for the you to start with, is a cell made
with cuprous oxide (Cu^O). Copper actually has two oxides, a red oxide called cuprous oxide, and a black oxide called cupric oxide
(CuO).
The dark red cuprous oxide has photoelectric properties but
black cupric oxide does not. The black oxide that forms on the
outside of your cell must be removed because it is opaque and
will not allow light to reach the cell's active surface.
Free Energy System
An example of a complete Free Energy System, Using Solar cells in series and parallel to charge 12
volt deep cycle batteries, which in turn runs our 5,000 watt inverter to run your home on 120 vac x 60
Hz. We recommend replacing the solar panels with our Fuel less Engine connected to a 12 volt car
alternator to keep up batteries. The lawn mower motor we use as a back up.
COPPER SOLAR CELLS
A small, carefully made solar cell of approximately 2 1/2"
diameter will produce around 5 milliamperes of current in direct
sunlight. This is enough to drive a sensitive light meter or
extremely sensitive relay. Banks of these cells have even been
used to run small electric motors.
Experiment with the procedures described. You may stumble
onto a method of producing even more efficient cells than we have.
Just be sure to be very careful. The chemicals described can be
dangerous if abused or mishandled. You build at your own risk!
There are an estimated 80 trillion kilowatts of solar electrical
energy available in the northern hemisphere.
Many Different types of Chemicals Have Photoelectric Properties!
There are a number of elements and chemical compounds
that can be used to produce photoelectric power. They include
titanium, selenium, thorium, cuprous oxide, and metals of the
alkali group including sodium, potassium, rubidium, lithium,
cesium and francium.
The two best substances for a homemade cells are, selenium
and cuprous oxide.
diameter will produce around 5 milliamperes of current in direct
sunlight. This is enough to drive a sensitive light meter or
extremely sensitive relay. Banks of these cells have even been
used to run small electric motors.
Experiment with the procedures described. You may stumble
onto a method of producing even more efficient cells than we have.
Just be sure to be very careful. The chemicals described can be
dangerous if abused or mishandled. You build at your own risk!
There are an estimated 80 trillion kilowatts of solar electrical
energy available in the northern hemisphere.
Many Different types of Chemicals Have Photoelectric Properties!
There are a number of elements and chemical compounds
that can be used to produce photoelectric power. They include
titanium, selenium, thorium, cuprous oxide, and metals of the
alkali group including sodium, potassium, rubidium, lithium,
cesium and francium.
The two best substances for a homemade cells are, selenium
and cuprous oxide.
A MORE SIMPLIFIED SOLAR CELL
The fabrication of a modem solar cell is very complicated and
a delicate process. In most cases, a large silicon ingot is grown
from a small crystal in an extremely clean and sterile environment.
Any dust or particle contamination even down to the
atomic level during the growing process can completely ruin the
ingot. Impurities must typically be kept to one part per billion.
The growing process itself is slow, and the very pure materials
required are extremely costly. Because of this, a single ingot
which is later sliced into thin cells approximately 0.05 centimeters
thick often costs thousands of dollars to produce.
This fact coupled with the general inefficiency (7-14 typically)
of even these modem cells has kept the price of photoelectric
cells too high to be competitive with other sources of power.
Someday, lower cost production techniques together with
higher efficiency will make widespread use of clean, renewable
solar energy possible. Someday solar cells will be a very common
Source of energy, the idea of deriving electricity directly from
sunlight will continue to excite the inventor and experimenter.
It is well known that if even 1 of the Sahara desert were
covered with the solar cells just described, it would more than
supply our worlds current energy needs. We will briefly outline
some of the processes and materials that are now being researched
for converting the use of solar energy into electricity.
You should have no trouble building the cells that will be
described in the following pages. Be cautious. Use good judgement
and common sense in handling the chemicals and heating
processes described. You'll find that a simple solar cell can be
constructed by a persistent student, Solar cells that can make
outstanding science fair projects.
The electrical output from the homemade copper cells in
this article will be well below that of modern commercial cells,
but the materials cost is also very low. Often a cell can be literally
produced for pennies! The loss in efficiency is probably more
than made up in the reduction of their price.
But again the Screen printed solar cells are far more powerfull
than the copper type solar cells.
How to prepare THE COPPER CHLORINE SOLAR CELL:
Buy a roll of Thin Copper sheeting, cut
a 1.5" diameter piece out with a pair of cutters, then sand polish the copper on both sides
with some fine grade steel wool. then by using a propane torch heat the copper while
griping it with rubber handled pliers, and let the copper get red hot, until it glows, move
the copper over the flame evenly for about 3 minutes then allow to cool slowly. Then
once it is cooled dip it down in an acid solution of 1/2 water and 1/2 acid, WARNING!
Never pour water into acid always pour acid into water. The acid that you can use is
MURIATIC ACID ( Hydrochloric Acid ) you can buy it at any hardware store, or you
can use a solution of nitric acid. REMEMBER TO WEAR PROTECTIVE
GOGGLES OR OTHER SUITABLE EYE PROTECTION, AND WORK IN A
WELL VENTILATED AREA. DO NOT SMELL THE FUMES OR MAKE
CONTACT WITH YOUR SKIN, WEAR RUBBER GLOVES. THESE ACIDS
CAUSE SEVERE BURNS. KEEP OUT OF THE REACH OF CHILDREN.
NOTICE: WE ARE NOT RESPONSIBLE FOR ANYTHING IN THESE PLANS ,
YOU BUILD AND EXPERIMENT AT YOUR OWN RISK.
Keep it in the acid for only a half a minute or longer, the idea is to keep it dipped in the
acid long enough for the black oxide to come off of the top layer, under that is the photo
sensitive red cuprous oxide. Remember you should only have a dark bright red layer left.
Note: do not leave it in to long it will eat away the red. once you have done that then it's
O.K. to wash off the acid with water, do all of this outside or in your garage, make sure
all of the acid is off. wash no less than 3 minutes, now look at the copper disk on one
side you will have bright copper, this is the positive side, and on the other side you will
have red this the negative side the side you face toward the sun. now mix a small
solution of 95 water and 5 Clorox bleach, now take the red side and look for
scratches if there are any you must paint them with enamel oil base paint, apply paint to
any where on that side where copper is showing through, now glue a plastic lid on to red
side, let it dry them drill a small hole in the top pour in Clorox bleach and water solution
and then place a copper or steel wire through the hole and onto the bottom, wire must be
submerged in the solution, now tape or glue the hole up with the wire in it. now tape
Solar cell out into the sun and using a DC volt meter attach + to the copper back, and - to
the steel wire coming out of hole. you will see the meter move showing a voltage, now
block the sun with your hand and watch the voltage drop.
make many of these for just pennies and put them in series or parallel to increase your
voltage or amperage. These type of cells are only 5 of the japan cells.
I have heard that the Japanese cells are about 95 of the American made silicon cell that
is a very expensive process. Screen printing them is the cheapest way to go and is easy,
once you get the hang of it.
Chemicals: needed: 1. Cadmium Sulphide = cds 2. Cadmium Chloride == cdcl 2
( These can be in powder form ) 3. Propylene Glycol = pg this is used to mix the
powders into a pasty but screen printable liquid ink type. 4. Carbon powder, if you can
not find it make some yourself out of burnt wood etc... 5. Cadmium = cd
6. Tellurium = Te
The Japan Solar Cell Patent
Note: You can Use an outside Grill to bake the Screen Printed layers. It is a good
idea to make small cells, 8" x 10" or what ever. It is easier to fit into the Grill,
We suggest Baking in side a large roasting pan and then put the roasting pan inside
the preheated grill and shut the lid. It is suggested that you try and make 3 prototype
cells first, Work out all the details, Test them, and then start on a large production of
Solar Cells. It will all get much easier once you have done it. It is also suggested that
you bake them out side. You don't want any fumes in the house, an outside grill is the
best and most readily available oven there is and propane is cheap. I hear you may be
able to make them without a Nitrogen atmosphere if not try special gas companies or
make some yourself, it is supposed to be nonflammable.
Screen Printing: You start with a small 14" x 14" wood frame 2x2". Then a plastic
or clothe screen is stretched over the frame tightly one side at a time, and then stapled
down on all 4 sides, we suggest buying a yellow 200 mesh screen from a screen
printing supplier, Then you put an image of what ever you want to print into the
screen by photo emulsion or by cutting a lacquer or water film with an exacto knife.
( see our Screen Printing Video ) Once you have your image you place the finished
screen onto a flat smooth table top, attach it to a 14" long 2" x 4" with 2 door hinges.
using wood screws, then you attach the 2" x 4" on to the table so it and the screen will
not move. the screen should only go up or down.
you then put your 8" x 10" glass under the screen, register it, then lay the screen
down over the glass and apply your ink and then with a small 12" rubber Squeegee,
You pull the ink over the image and it is pushed thru the screen mesh and thru the
image that you cut and smoothly is printed onto the glass.
SUPPLIERS;
Screen Printing Books and supplies; NDS 1-800-783-3883 Indianapolis, IN.
( See also Art Store's, Hobby Shop's, Arts and Crafts, Screen printing company's.)
They also sell copper sheeting.
Solar Cell Screen Print Chemicals: Search the web, simply type in the chemical
you are looking for and many suppliers will pop up. Example: Cadmium Sulphide
Supplier..... We have checked and you can find all the chemicals and info on them
free on the web.
Also see: www.stanfordmaterials.com/semi.html
The Stanford Materials Company
1. Cadmium Sulphide in powder form = Cds (or if already thick liquid or ink OK.)
2. Cadmium Chloride + Cdcl 2 ( Powder or liquid form )
3. Propylene glycol + pg in liquid form
4. Carbon Powder, if you can not find none make your own wood carbon powder?
5. Cadmium = Cd
6. Tellurium = Te
idea to make small cells, 8" x 10" or what ever. It is easier to fit into the Grill,
We suggest Baking in side a large roasting pan and then put the roasting pan inside
the preheated grill and shut the lid. It is suggested that you try and make 3 prototype
cells first, Work out all the details, Test them, and then start on a large production of
Solar Cells. It will all get much easier once you have done it. It is also suggested that
you bake them out side. You don't want any fumes in the house, an outside grill is the
best and most readily available oven there is and propane is cheap. I hear you may be
able to make them without a Nitrogen atmosphere if not try special gas companies or
make some yourself, it is supposed to be nonflammable.
Screen Printing: You start with a small 14" x 14" wood frame 2x2". Then a plastic
or clothe screen is stretched over the frame tightly one side at a time, and then stapled
down on all 4 sides, we suggest buying a yellow 200 mesh screen from a screen
printing supplier, Then you put an image of what ever you want to print into the
screen by photo emulsion or by cutting a lacquer or water film with an exacto knife.
( see our Screen Printing Video ) Once you have your image you place the finished
screen onto a flat smooth table top, attach it to a 14" long 2" x 4" with 2 door hinges.
using wood screws, then you attach the 2" x 4" on to the table so it and the screen will
not move. the screen should only go up or down.
you then put your 8" x 10" glass under the screen, register it, then lay the screen
down over the glass and apply your ink and then with a small 12" rubber Squeegee,
You pull the ink over the image and it is pushed thru the screen mesh and thru the
image that you cut and smoothly is printed onto the glass.
SUPPLIERS;
Screen Printing Books and supplies; NDS 1-800-783-3883 Indianapolis, IN.
( See also Art Store's, Hobby Shop's, Arts and Crafts, Screen printing company's.)
They also sell copper sheeting.
Solar Cell Screen Print Chemicals: Search the web, simply type in the chemical
you are looking for and many suppliers will pop up. Example: Cadmium Sulphide
Supplier..... We have checked and you can find all the chemicals and info on them
free on the web.
Also see: www.stanfordmaterials.com/semi.html
The Stanford Materials Company
1. Cadmium Sulphide in powder form = Cds (or if already thick liquid or ink OK.)
2. Cadmium Chloride + Cdcl 2 ( Powder or liquid form )
3. Propylene glycol + pg in liquid form
4. Carbon Powder, if you can not find none make your own wood carbon powder?
5. Cadmium = Cd
6. Tellurium = Te
The Research group
Jabbour's group, print very flat,
thin cells, onto glass in a similar way. First they coat the glass with a
transparent electrically conducting material (metal ink) that acts as one of the
solar cell's electrodes. On top of this, they lay down a thin film of a polymer,
which helps to gather current from the photovoltaic material.
Finally they deposit a blend of two organic compounds that convert light into
electricity. One is a carbon-based molecule called a fullerene, it produces
charged particles that carry an electrical current when light shines onto the
molecules. The other is a polymer, it ferries the current to the electrodes on
the top and the bottom of the solar cell.
Under blue light, these screen-printed solar cells have an efficiency of 4.3 per
cent. And the Japanese cells are much greater than that! Many of the flexible
solar cell panels that you see today are screen printed.
Now lets take a look at what The Dupont Company is doing with there solar
cells. Dupont is involved in the development of solar cell metallisation since
the 1970's. Although all PV cell manufacturers use different processes to
make there solar cells, the metallisation of the rear and front sides is in many
cases DONE BY SCREEN PRINTING! Which has shown itself to be one
of the most economic way to produce solar cells.
Recently, Dupont achieved a real breakthrough in the formulation of front-side
contacts for silicon solar cells that has resulted in customers, such as
photowatt, to realize the screen printing efficiency by changing their antireflection
technology from titanium dioxide to silicon nitride. This came at
just the right time for the Photowatt solar cell company, Because they have
been using there own past material for the front side metallisation since it first
started manufacturing solar cells. The development of the metallisation from
Dupont for the back side, (p-side). These pasty inks are either silver pastes
containing Al, or pure Al pastes to secure a good ohmic contact with the pside
of the solar cell. We have told you all this to help you better understand
and leam the screen printing solar cell process and what others are doing.
thin cells, onto glass in a similar way. First they coat the glass with a
transparent electrically conducting material (metal ink) that acts as one of the
solar cell's electrodes. On top of this, they lay down a thin film of a polymer,
which helps to gather current from the photovoltaic material.
Finally they deposit a blend of two organic compounds that convert light into
electricity. One is a carbon-based molecule called a fullerene, it produces
charged particles that carry an electrical current when light shines onto the
molecules. The other is a polymer, it ferries the current to the electrodes on
the top and the bottom of the solar cell.
Under blue light, these screen-printed solar cells have an efficiency of 4.3 per
cent. And the Japanese cells are much greater than that! Many of the flexible
solar cell panels that you see today are screen printed.
Now lets take a look at what The Dupont Company is doing with there solar
cells. Dupont is involved in the development of solar cell metallisation since
the 1970's. Although all PV cell manufacturers use different processes to
make there solar cells, the metallisation of the rear and front sides is in many
cases DONE BY SCREEN PRINTING! Which has shown itself to be one
of the most economic way to produce solar cells.
Recently, Dupont achieved a real breakthrough in the formulation of front-side
contacts for silicon solar cells that has resulted in customers, such as
photowatt, to realize the screen printing efficiency by changing their antireflection
technology from titanium dioxide to silicon nitride. This came at
just the right time for the Photowatt solar cell company, Because they have
been using there own past material for the front side metallisation since it first
started manufacturing solar cells. The development of the metallisation from
Dupont for the back side, (p-side). These pasty inks are either silver pastes
containing Al, or pure Al pastes to secure a good ohmic contact with the pside
of the solar cell. We have told you all this to help you better understand
and leam the screen printing solar cell process and what others are doing.
Scientists in Arizona
Scientists in Arizona are using screen-printing, a
technique developed for printing fabrics, paper and
to produce plastic, glass and metal solar cells.
The basic materials of a photovoltaic cell (solar cell)
are inexpensive. The organic manufactured by
Ghassan Jabbour and colleagues at the University of
Arizona in Tucson have about 11/4 of the efficiency
of commercial silicon solar cells, which turn 10-20
per cent of light energy into electricity. But, being
cheap to produce, they can make up the loss in
quantity what they lack in quality. Now the Japan
screen printed solar cells are even better than that!
In conventional Screen - printing, a taut piece of
screen mesh fabric is stretched over a wood frame,
you can buy the screens already made and the materials
from any screen printing shop or screen printing supply
company in your area or on the internet. Also you might
want to check with your local art store, sometimes they
have full kits etc...
The screen is then masked off using masking tape,
For example: a 5" x 5" square area. the screen outside
of the masking tape is then coated with a block out
liquid or paint, this is so when you apply your semiconducting ink that you mixe, it will go
through just the area that you masked off when you apply a rubber squeegee to it. The
screen can then be placed on any table top and hinges attached to the back of the wood
frame and the table, this will insure the screen can move up and down. Then get a small
wood paint stick and using a small nail, hammer one end to the front side of wood frame.
This will be your kick leg and will help keep your screen in an upward position when
needed. Take a 5" x 5" piece of glass and place it right under the open 5" x 5" area of the
open screen mesh. When the leg is flipped back the screen comes down and you grab
your rubber and wood handled squeegee and with the ink in front of your rubber squeegee
pull toward you applying pressure so ink will go through screen, once you have passed by
the 5" x 5" area then flip the screen back up and reverse squeegee to flood the screen for
the next print
Cadmium Sulphide ( CdS )
Crystal properties
Crystal growth method : Seeded vapor phase growth
Crystal growth orientation: (0001)
Maximum size: Up to 50mm diameter
Variations: Doped crystals (on request)
Crystallographic properties
Crystallographic structure: Hexagonal
a= 0.4135nm, c= 0.6749nm
Defects structure: Inclusions with < lOu. in size
Color: Red
Physical properties
Density: > 4.82 g/cm3
Melting point: > 1748 °C
Hardness: > 4 Mohs
Thermal conductivity: > 15.9 W m -1 K-1
Dielectric constant: > 8.28 C, 8.64 | I C
Band gap > (@ 300 K ): 2.53 eV
Specific resistivity: > ~108 (Ohms cm)
Emmission wavelength: > 600 nm @ 300 °K
Optical properties
Transmission range: >>>>>> 0.5 um -15 urn (2mm thick)
Refraction index:>>>>>>>> No = 2.517, Ne = 2.548
Solar Cell Materials
The most important parts of a solar cell are the
semiconductor layers, this is where the electron
current is created. There are a number of different
materials available for making these semiconducting
layers, and each has benefits and drawbacks.
Unfortunately, there is no one ideal material for all
types of cells and applications.
In addition to the semiconducting materials, solar
cells consist of a top metallic grid or other electrical
contact to collect electrons from the semiconductor
and transfer them to the external load, and a back
contact layer to complete the electrical circuit.
Then, on top of the complete cell is typically a glass
cover or other type of transparent encapsulant to
seal the cell and keep weather out, and a antireflective
coating to keep the cell from reflecting the
light back away from the cell. A typical solar cell
consists of a cover glass, a anti-reflective layer, a
front contact to allow the electrons to enter a circuit
and a back contact to allow them to complete the
circuit, and the semiconductor layers where the
electrons begin to complete there voyages!
Turning Sunlight Into Electricity!
Solar Cells convert light energy into electricity at
the atomic level. It was first discovered in 1839, theprocess of producing electric current in a solid
material with the aid of sunlight wasn't truly understood
for more than a hundred years.
Throughout the second half of the 20th century, the
science has been refined and process has been more
fully explained. As a result the cost of these devices
has put them into the mainstream of modem energy
producers. This was caused in part by advances in
technology, where PV conversion efficiencies have
been improved.
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