Solar panels

What do the ratings mean on the solar panels? I suppose the maximum output is easy to understand, but is it rated to a specific solar radiation measurment? How does it relate to actual performance?

 

One takes a certain percentage of the actual maximum output. In Holland is that 60%, measured over a day; southern countries might have better numbers.
It is a solution for small applications, or in situations where a low E-balance is applicable IMO. In Norway those weekend cabins in the moutains do use this technology succesfully, using 12/24 V apparatus and lighting.

 

If you look at the site of Mastervolt, they have some Exel sheets to calculate performance. Hope that wil help you.

 

PV ratings

Ratings are all referenced to a theoretical 1000 watts of solar energy per square meter of surface area. That is generally what you might see on a perfect day at high noon, pointed at the sun. There are many things that affect this and you could see even up to 30% more energy under special circumstances, and obviously less under worse conditions.

So when they say a panel is 12% efficient they are saying it converts about 12% of that 1000 watts into electricity. Its a theoretical yardstick to evaluate the efficiency of different technologies. For instance amorphous modules (solid in color & inexpensive) are from 4-9% efficient, some say more but that's a good general yardstick. Polycrystaline (individual cells with a fractal type surface) are 12-14% efficient. Single crystaline (dark colored individual disks or squares) are 14-17% efficient. Don't get caught up in the numbers but you get the idea, higher efficiency, more power per sq.mtr, higher cost, but less real estate.

Isc is the short circuit current if you were to short the 2 leads together. Its the maximum current output, again a yardstick for comparision, but nothing practical.

Voc, Open circuit voltage, tells you how many cells you have in the module. A yardstick, but not the money question.

Where the rubber meets the road ($$ question) is the I-V curve or the current versus voltage curve. A plot of the output current at specific voltage. You want the most current at your typical charging voltage (plus whatever voltage drop for a blocking diode or voltage regulator you have) that you can buy.

Remember, PV (photovoltaics) is DC and you are paying good money for the power. You get the most for your $$ by minimizing your losses beteween the PV panel and the battery. Large wire, minimize # of connections, clean soldered (yes, I said soldered) connections, corrosion protection, will all go a long way.

This explanation could go on forever, if you have a specific question I will be glad to answer them. You could try this link, they have some educational stuff that might be able to do a better job and go deeper that a forum diatribe. http://www.fsec.ucf.edu/pvt/

I also think you may find other educational links if you search under "standalone PV systems".