How to choose: Photovoltaic modules

Photovoltaic modules or PV is composed of solar cells converting sun energy to electricity. There are abundance of different manufacturers to choose from, which can be a challenge in deciding the best PV module for you. There are 3 major factors in identifying what specifications are essential.

1. Efficiency

Ideally the sun produces 1 kWh per square meter at noon on a clear day at sea level. This is defined as the "full sun." Unfortunately, current technology is not very efficient. Most PV modules can only harvest 12-18% of the sun's energy. SunPower and Sanyo's HIT are the leaders of the industry on efficiency but that comes with a price. The benefit in getting higher efficient PV modules is if you are constrained with space. You can maximize the limited area you have with the most power you can get from the sun. This basically means the PV modules would be a little smaller with almost the same power you would get with the standard less costly modules. Sanyo and SunPower are about $200-300 more expensive (about $3.70/kWh).

2. Power Rating

Power is the product of voltage (V) and current (A). This probably is the first thing that is essential in looking for a PV module. PV modules are connected in series and/or parallel to attain the total required power. They range from 40 kWh to 230 kWh. Commonly 165-190 kWh modules are used due to cost. But due to loss from the heat of the sun and electrical connection of the solar cells, power ratings are categorized in 3 different standards. STC or Standard Test Conditions are based on laboratory test conditions. This is unrealistic but is a basis on maximum performance of a given module. This is also known as "template rating." PTC or Practical Test Conditions (usually 6-12% less than its STC rating) considers loss and more realistic environment conditions yet still not real world conditions.

3. Temperature Coefficient

This is the power that you would loose as temperature goes beyond the PV modules operating temperature. This is rated by percentage loss per degree centigrade (%/C). Again, Sanyo and SunPower market their products to perform better than others in higher temperature. SunPower claims -0.38% / C while Sanyo HITs at -0.34% / C. Less expensive PV modules like Evergreen is at -0.44% / C

Another specifications that is not commonly advertised is the PV module's performance degradation in time. Technically a brand new module should perform at 100% out from its packaging. Although modules last for a very long time (25+ years), its actual performance drops per year of use. Some manufacturers might have this in there spec sheet but if not expect from 0.25% to 0.50% degradation per year.

My 2 cents

I have done my own research on different manufacturers on their pricing, efficiency, and compared specifications side by side. First I was focusing on both leaders in the industry, Sanyo and SunPower but the cost difference is just not worth it. You would be better off getting 2-3 extra panels, if you have the space, and still save a huge chunk of cash since 60% of the cost for a solar power system would be on your PV modules. I would recommend going with Evergreen. They have been tested to perform well on the field and has the shortest payback time for return of your investment.