There is a lot of hype by solar panel manufactures about how more efficient their solar panels are over competion. That may be true by the numbers in many cases all other things being even, but solar panel efficiency is actually of little practical importance. Solar panels with lower efficiencies will simply have to cover a greater area which is usually not a problem except for those applications with limited space.
Recently I compared a leading solar panel company’s 235 watt 18% efficient panel against a competitor with a 235 watt solar panel that was 15.6% efficient. It was a substantial project with 108 panels. Both panels were compared with identical orientation, angle and using the same zip code. The 18% solar panel did out perform the 15.6% panel yes that’s true. But the performance difference amount to about 650 kWh per year. Now that may sound like a substantial increase in power but lets not forget the most important part of that comparison which is cost. The 18% efficient module’s cost was about 3X that of the 15.6% panels cost. That number is HUGE! compare to the 3% efficiency pick up.
In terms of dollars, it cost nearly $800 for the 18% efficient solar panel as compared to $341 for the 235 watt panel at 15.6%. Considering the payback the decision to go with the cheaper panel was far a better choice since there was no restrictions on space in this application.
System cost is expressed in terms of the energy yield of the panels that make up the solar system over a period of time, typically 25 years. Lower efficiency simply means that an array consisting of lower efficiency will have a larger surface area. The cost of the solar panels is the true variable in this equation that will increase the return on investment. When searching for the right solar panel for your project you may want to look closer at this factor.