1. Solar panel power ratings
All solar panels receive a nameplate power rating indicating the amount of power they produce under industry-standard test conditions. Most solar panels on the market have power ratings in the range of 300 to 450 watts. A higher power rating means that the panels are more effective at producing power.
The nameplate rating represents the power output under ideal conditions, which most solar power systems will not experience for more than a few moments at a time. However, solar panel ratings are useful as a way to make consistent comparisons between panels.
2. Power tolerance
As solar panels are manufactured, some unavoidable variations that impact power output are introduced. Power tolerance indicates how the power output of a solar panel might differ from its nameplate rating. They are typically expressed as a plus-or-minus percentage. For example, a 300-watt panel with a +/= 5% power tolerance could actually produce anywhere from 285 watts to 315 watts under ideal conditions (as 15 watts is 5% of 300 watts). A narrower power tolerance range is preferable to a wider one, because it represents more certainty. Power tolerances should be viewed in tandem with solar panel ratings.
3. Solar cell efficiency
Solar panel efficiency represents how effectively a solar panel can convert solar radiation (e.g. sunlight) into electricity. The most efficient solar panels commercially available today have solar panel efficiency just under 23%.
A higher solar panel efficiency rating means a panel will produce more kilowatt-hours of energy per watt of power capacity. This is because one high-efficiency panel can generate more electricity than a similarly sized panel with a standard efficiency rating, efficiency is particularly important if you have limited roof space and large electricity bills.
4. Temperature coefficient
Although solar panels are designed to love the sun, high heat can actually reduce a solar panel’s capacity to generate power. The temperature coefficient quantifies how a panel’s power capacity decreases at temperatures higher than 25°C, which is the standard temperature at which tests are performed.
For example, many standard grade solar panels may produce 1 percent less electricity for every 2.7°C temperature increase above 25°C. Panels with less sensitive temperature coefficients will perform better over the long term. Check solar panel ratings and reviews carefully for the temperature coefficient, particularly if you live in hotter parts of the country.