Stick with us here.. some of these product nuances can be a bit bland, but solar panels are a big purchase!
Solar panel efficiency defines a panel’s ability to convert sunlight into usable electricity. Solar panels range in efficiency from about 15-23%, and in a panel with 20 percent efficiency, 20 percent of all the light that hits it will be translated into electricity. Solar panel efficiency is determined by the production of electricity by solar cells, which is in turn influenced by the cells’ composition, electrical configuration, surrounding components, and more.
A less efficient panel can produce the same wattage as a more efficient panel, it would just need to be bigger with more solar cells.
(On a side note, you’ll need a battery monitor to get a reasonably accurate reading on how many watts your panels are we generating. We’ve got the rundown on battery monitors.)
Solar panel voltage will be fed by the panels to your charge controller, which then charges the batteries. As long as you get an adequate charge controller (MPPT, not PWM), then the controller regulates the incoming voltage from the panels to charge the batteries based on their voltage.
No need to worry about the panel voltage (most common are 12v, you will see some 24v), because the voltage has no impact on the performance.
Solar panel warranty is based on power output. Solar panels are expected to degrade over the years. The National Renewable Energy Laboratory found in a 2012 study that solar panel output falls by an average of about 0.8 percent annually. In other words, after 10 years it will produce 92 percent of the energy it did when it was new; and so on.
Manufacturers guarantee that their panels will still offer a certain percentage of their original output. Warranty periods generally range in length from 10-25 years. Renogy warrants panel output at 80% efficiency rate at year 25. Hightec and SunPower offer similar warranties.
For life span of flexible panels, be sure to purchase flexible panels coated with ETFE, as opposed to PTE. PTE will yellow and degrade much quicker. All Renogy panels are coated with ETFE (we checked with Renogy).