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Solar Modules

Although we have a preference for Sanyo HIT Power solar modules, Rancho Solar spends time with each customer to discuss the various equipment options for their system. Solar modules account for approximately 60% of the total system cost, are very low maintenance and extremely durable. Solar modules differ not only in size and nameplate rating, but also in performance, power tolerance and high-temperature power loss.

The following are several key characteristics we consider when selecting a solar module.

STC Rating  Also known as the “nameplate” rating. (Watts DC)

PTC Rating  This is considered a real-world estimate of power production, and is the basis for which California rebates are paid. (Watts DC). This rating is not published by manufacturer’s, but can be found at:
http://www.gosolarcalifornia.ca.gov/equipment/pvmodule.html

PTC/STC Ratio   This is a very important indicator of module performance. This value will vary between 83% to 93%, the higher the better.

Power Tolerance   Not all 200 Watt (STC) solar modules actually produce 200 Watts during factory testing. The average power tolerance is +5%/-5%, which means that a manufacturer may sell a 200 Watt solar module that produces as few as 190 Watts.

Power Guarantee   When a manufacturer states a –0% power tolerance, they are guaranteeing their module was factory tested to meet or exceed the nameplate rating. Only a few manufacturers offer a power guarantee.

Module Efficiency   This is an often-touted number and is a measure of STC Watts per square meter. However because it’s based on the STC rating, this is not necessarily a meaningful statistic.

PTC Watts per Square Foot   This is a much more meaningful comparison of solar modules than efficiency, since it’s based on the real-world power estimate.

Temperature Coefficient of Power   All solar modules will produce less power as temperatures rise, however some modules fair much better than others. This value varies between –0.336%/ºC to –0.5%/ºC, the lower the better.

Warranty   Although 20-25 year power warranties are common in the industry, consider selecting a manufacturer that is a large diversified corporation.  Others, who’s sole business may be solar, may not outlive their warranties.