Homebrewed Electricity > Solar
Why 36 Cells per panel?
roosaw:
There is of course the boost converter.
With this device you could, in theory, wire all the cells in parallel (no bypass diodes) at 0.5ish volts and boost the voltage (and lower the amps of course) to whatever you wished to make it play well with other panels.
A boost converter is an inductor, a transistor (PWM driven duty cycle control of the transistor) and a diode (wiki has a good discussion). It uses the panel to "charge" the inductor with current then opens the switch and the inductor discharges to the load circuit via magnetic induction. By changing the duty cycle on the transistor you control the amount of voltage boost.
The same circuit can be run to control the the panel output voltage (MPP) and if yo put two back to back you can MPP the panel and boost the voltage to an acceptable level.
The advantage is that in the morning when either the panel is at a high angle or insolation is low the panel can still a) operate at its MPP and b) produce a voltage that can be used.
Course active tracking is still the best "watt improver" but that is not always an option.
Ungrounded Lightning Rod:
Remember that the voltage from a single solar cell is about the same as a diode voltage drop - because it's essentially the same mechanism. So the output of the first cell of your series string is essentially wasted pushing current through diode drops in your semiconductors. Putting all the cells in parallel won't get you ANY output unless you're using all FETs and Schottky diodes or the like.
This is one of the reasons that higher voltages is desirable: Lower percentages of loss in semiconductors in the associated electronics. (Another is lower current in the wiring.)
rain1224:
I agree with DanG's answer.
Yyrkoon:
Here is another way to look at it. The higher voltage you have( and smaller current ), the smaller size of wire you can use to transport it to where you need the power converted. This means, you can use smaller wire to transport the same amount of power, and save money on copper.
Take for example one type of panel we have here. 30v @ 6A. If you drop that voltage down to say 15v, you have to double the current in order to maintain the same power. Which means you need more copper to keep loses at a minimum. On top of that ( someone correct me if I am wrong here). I believe that the more current your transport, the more line loses you will have anyhow. So on the other end of the coin. Some panels like the one I described above can have a high series rating. The ones I described above can be run in series on up to 300V. Smaller wire yet, for delivering the same amount of power.
There can be downsides to this approach however. Such as regulating voltage down to working nominal voltage for your given system. Then when converting DC to DC you will have some efficiency loses as well.
Anyhow, there may not be such a thing as a free lunch. But sometimes, you can get a discount. All a matter of perspective.
Xan:
I think putting all cells in parallel would not be able to run a boost converter as you would not have enough voltage to overcome the characteristic voltages in the semiconductors. And it would also require pretty heavy wiring as you would be mainly getting your watts mainly from current, if it could work at all.
However, I do agree boost converters can be useful. I have half a folding panel set that has 24 cells and they are wired series/parallel for a 6 volt nominal output. Pretty much useless for anything, really don't know why it was made that way!? So, I made up a boost converter circuit and that works really well & means I can now feed the output of that panel into my 12 volt system and get some useful charging amps. :D
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