When comparing solar panels, concentrate on power and efficiency. The most common power range available is between 200 and 350 watts, but critics almost always consider higher panel nameplate output ratings more favorably than lower. Regarding efficiency, the best panels have efficiencies of 20 percent or slightly more, whereas the market average falls between 14 percent and 16 percent, as of 2015.
Other aspects of comparison may concern the climate or region in which the buyer resides. For instance, someone living in the northeast should compare brand assurances regarding snow load, particularly the panels' pressure rating and the excess weight they can handle while maintaining structural integrity. Similarly, residents of most regions should ensure their panels have some measure of wind resistance, as gauged in their wind load rating.
Shoppers should compare long-term guarantees. While solar panels are expected to lose efficiency over time (called panel degradation), expectations should not be worse than 10 percent to 20 percent loss in the first 25 years. Thus, seek manufacturers willing to offer a 25-year output warranty. Comparisons for aesthetic qualities are more subjective, with possible details including panel or frame color, surface lines and dots and the degree to which the homeowner desires a homogeneous appearance of all materials.