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But after searching the web a bit it seems cheapest to buy individual cells
then tie them in series...No? thanks, My experience with tying together solar cells is that you'll probably destroy a few along the way (the pads lift very easily when heated with soldering iron), so either get extras or go with a solution which does not require you to solder cells together (or be more careful than I was, I guess). |
On Mon, 12 Apr 2004 13:02:38 -0700, "Watson A.Name \"Watt Sun - the
Dark Remover\"" wrote: Joerg wrote: Another option might be to use a different voltage panel, whatever has a good price, and then use a small switcher to run the cells at their optimum load. Regards, Joerg. Seems foolhardy to me, to use a boost circuit, and waste a lot of power. Just put more PV cells in series to increase the voltage. The solar cell operates as a (badly) regulated power supply with current limiting. At low load currents, the cell operates nearly as a constant voltage source, but after a specific current (for a given illumination) it operates nearly as a constant current source and deliver approximately that current even into a short circuit. The largest power from the cell (for a specific illumination) is obtained at the point it switches from constant voltage to constant current mode, in which both the voltage is quite close (within 30 %) of both the maximum voltage (as measured at open circuit) and maximum current (as measured at short circuit). This maximum power point varies with illumination, but if the switcher always loads the cell at this maximum power point, the largest available energy at a specific time is extracted from the cell independent of illumination. Even if the losses in the maximum power point tracker is 10-20 %, usually more energy can be obtained than running the module in some non-optimal constant voltage or constant current mode. Paul |
On Mon, 12 Apr 2004 13:02:38 -0700, "Watson A.Name \"Watt Sun - the
Dark Remover\"" wrote: Joerg wrote: Another option might be to use a different voltage panel, whatever has a good price, and then use a small switcher to run the cells at their optimum load. Regards, Joerg. Seems foolhardy to me, to use a boost circuit, and waste a lot of power. Just put more PV cells in series to increase the voltage. The solar cell operates as a (badly) regulated power supply with current limiting. At low load currents, the cell operates nearly as a constant voltage source, but after a specific current (for a given illumination) it operates nearly as a constant current source and deliver approximately that current even into a short circuit. The largest power from the cell (for a specific illumination) is obtained at the point it switches from constant voltage to constant current mode, in which both the voltage is quite close (within 30 %) of both the maximum voltage (as measured at open circuit) and maximum current (as measured at short circuit). This maximum power point varies with illumination, but if the switcher always loads the cell at this maximum power point, the largest available energy at a specific time is extracted from the cell independent of illumination. Even if the losses in the maximum power point tracker is 10-20 %, usually more energy can be obtained than running the module in some non-optimal constant voltage or constant current mode. Paul |
On Mon, 12 Apr 2004 13:52:35 -0700, "Joel Kolstad"
wrote: Watson A.Name "Watt Sun - the Dark Remover" wrote: Also the currewnt outputdepends somewhat on the latitude you're at. You won't get all that current at the arctic circle. The difference for panels perpendicular to the sun on the equator and the arctic circle in the summer noon is about 10-15 %, due to the atmospheric absorbtion. The difference between the equator and pole is about 30 % in the same conditions. If the panel is tracking the sun, the panel on the pole during the summer will produce electricity for 24 h each day, while the other panel on the equator will produce for less than 12 h. On the arctic circle about 18-20 h each day will give usable electric output. Exactly at the arctic circle, the midnight sunlight is strongly attenuated by the atmosphere, so you can look at it even with your naked eyes or ordinary sunglasses, thus the electric output is also minimal. He might actually have a better chance there during the periods when the sun never sets than at, e.g., the equator... solar cells are noticably more efficient when they're keep cold, which is typically a lot earier to do in the arctic than at the equator! The silicon cell behaves quite in the same way as a silicon diode which has a 0,7 V threshold voltage and -2 mV/C temperature constant, thus the cell output voltage (and hence power) drops with temperature. However, the cells are heated by solar radiation at nearly at constant flux on the equator and arctic circle, thus, the main issue is how well the heat will be removed from the cell to the environment. At the arctic summer the air temperature can be well over 20 C for longer periods of time, so this does not help a lot in keeping the cells cool. Paul |
On Mon, 12 Apr 2004 13:52:35 -0700, "Joel Kolstad"
wrote: Watson A.Name "Watt Sun - the Dark Remover" wrote: Also the currewnt outputdepends somewhat on the latitude you're at. You won't get all that current at the arctic circle. The difference for panels perpendicular to the sun on the equator and the arctic circle in the summer noon is about 10-15 %, due to the atmospheric absorbtion. The difference between the equator and pole is about 30 % in the same conditions. If the panel is tracking the sun, the panel on the pole during the summer will produce electricity for 24 h each day, while the other panel on the equator will produce for less than 12 h. On the arctic circle about 18-20 h each day will give usable electric output. Exactly at the arctic circle, the midnight sunlight is strongly attenuated by the atmosphere, so you can look at it even with your naked eyes or ordinary sunglasses, thus the electric output is also minimal. He might actually have a better chance there during the periods when the sun never sets than at, e.g., the equator... solar cells are noticably more efficient when they're keep cold, which is typically a lot earier to do in the arctic than at the equator! The silicon cell behaves quite in the same way as a silicon diode which has a 0,7 V threshold voltage and -2 mV/C temperature constant, thus the cell output voltage (and hence power) drops with temperature. However, the cells are heated by solar radiation at nearly at constant flux on the equator and arctic circle, thus, the main issue is how well the heat will be removed from the cell to the environment. At the arctic summer the air temperature can be well over 20 C for longer periods of time, so this does not help a lot in keeping the cells cool. Paul |
Paul Keinanen wrote:
At the arctic summer the air temperature can be well over 20 C for longer periods of time, so this does not help a lot in keeping the cells cool. ....and the windchill is also reasonably comparable? I didn't realize the arctic could be so 'balmy!' Thanks for the info. I suppose that if you wanted to push the issue, a heat pipe stuck in the ice going back to a metal layer on the back of the panel would be quite effective in cooling the panel... |
Paul Keinanen wrote:
At the arctic summer the air temperature can be well over 20 C for longer periods of time, so this does not help a lot in keeping the cells cool. ....and the windchill is also reasonably comparable? I didn't realize the arctic could be so 'balmy!' Thanks for the info. I suppose that if you wanted to push the issue, a heat pipe stuck in the ice going back to a metal layer on the back of the panel would be quite effective in cooling the panel... |
"Paul Keinanen" wrote in message ... On Mon, 12 Apr 2004 13:02:38 -0700, "Watson A.Name \"Watt Sun - the Dark Remover\"" wrote: Joerg wrote: Another option might be to use a different voltage panel, whatever has a good price, and then use a small switcher to run the cells at their optimum load. Regards, Joerg. Seems foolhardy to me, to use a boost circuit, and waste a lot of power. Just put more PV cells in series to increase the voltage. The solar cell operates as a (badly) regulated power supply with current limiting. At low load currents, the cell operates nearly as a constant voltage source, but after a specific current (for a given illumination) it operates nearly as a constant current source and deliver approximately that current even into a short circuit. The largest power from the cell (for a specific illumination) is obtained at the point it switches from constant voltage to constant current mode, in which both the voltage is quite close (within 30 %) of both the maximum voltage (as measured at open circuit) and maximum current (as measured at short circuit). This maximum power point varies with illumination, but if the switcher always loads the cell at this maximum power point, the largest available energy at a specific time is extracted from the cell independent of illumination. Even if the losses in the maximum power point tracker is 10-20 %, usually more energy can be obtained than running the module in some non-optimal constant voltage or constant current mode. Paul Yeah, I see what you mean, sort of like an impedance match, but at DC. But at the beginning or end of the day, or cloudy day, you can't pull any more energy out of the cells than there is there. What it looks to me is that you're adding circuitry to give a better match at the ends of the day or a cloudy day, and in return sacrificing a few percent overall. My attitude is that rather than try to do this (and in the process lose reliability), it's better to go supersize on the cells, add more area and overall capacity to get you thru the cloudy days, and have a higher capacity overall. |
"Paul Keinanen" wrote in message ... On Mon, 12 Apr 2004 13:02:38 -0700, "Watson A.Name \"Watt Sun - the Dark Remover\"" wrote: Joerg wrote: Another option might be to use a different voltage panel, whatever has a good price, and then use a small switcher to run the cells at their optimum load. Regards, Joerg. Seems foolhardy to me, to use a boost circuit, and waste a lot of power. Just put more PV cells in series to increase the voltage. The solar cell operates as a (badly) regulated power supply with current limiting. At low load currents, the cell operates nearly as a constant voltage source, but after a specific current (for a given illumination) it operates nearly as a constant current source and deliver approximately that current even into a short circuit. The largest power from the cell (for a specific illumination) is obtained at the point it switches from constant voltage to constant current mode, in which both the voltage is quite close (within 30 %) of both the maximum voltage (as measured at open circuit) and maximum current (as measured at short circuit). This maximum power point varies with illumination, but if the switcher always loads the cell at this maximum power point, the largest available energy at a specific time is extracted from the cell independent of illumination. Even if the losses in the maximum power point tracker is 10-20 %, usually more energy can be obtained than running the module in some non-optimal constant voltage or constant current mode. Paul Yeah, I see what you mean, sort of like an impedance match, but at DC. But at the beginning or end of the day, or cloudy day, you can't pull any more energy out of the cells than there is there. What it looks to me is that you're adding circuitry to give a better match at the ends of the day or a cloudy day, and in return sacrificing a few percent overall. My attitude is that rather than try to do this (and in the process lose reliability), it's better to go supersize on the cells, add more area and overall capacity to get you thru the cloudy days, and have a higher capacity overall. |
On Tue, 13 Apr 2004 09:18:00 +0300, Paul Keinanen
wrote: The solar cell operates as a (badly) regulated power supply with current limiting. At low load currents, the cell operates nearly as a constant voltage source, but after a specific current (for a given illumination) it operates nearly as a constant current source and deliver approximately that current even into a short circuit. The largest power from the cell (for a specific illumination) is obtained at the point it switches from constant voltage to constant current mode, in which both the voltage is quite close (within 30 %) of both the maximum voltage (as measured at open circuit) and maximum current (as measured at short circuit). This maximum power point varies with illumination, but if the switcher always loads the cell at this maximum power point, the largest available energy at a specific time is extracted from the cell independent of illumination. Even if the losses in the maximum power point tracker is 10-20 %, usually more energy can be obtained than running the module in some non-optimal constant voltage or constant current mode. Paul I have seen elegant ckts where a simple switcher was used, regulating the *input* voltage coming from the solar cell, keeping it in max efficiency mode at all loads. This obviously only works with flexible loads such as slow chargers or such. -- - René |
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