SunPower last year verified 25.2% efficiency in a manufactured silicon-based PV cell. This year, they have integrated that cell into a manufactured PV module which attains 24.1% efficiency. When making efficiency comparisons, the cell-level efficiency is less relevant as in order for us to utilize that power, we need the cells built into a module, which will necessarily be slightly less efficient due to the space between cells, and the small area occupied by the frame.
When we are designing a system for a home’s roof, we usually need to make as much power as we can on the available roof space in order generate the largest percentage of the home’s annual energy. So using the most efficient modules available is important to us. While these SunPower modules are not the least expensive on the market, when we can put up an array with higher power rating in the same space as an average array, we can recognize relatively lower $/watt installation costs on all the other aspects of the system.
We are now commonly utilizing SunPower X-21 345 watt modules, which are 21.5% efficient at the module level. Their high efficiency, finish quality, and industry-leading warranty make SunPower an excellent choice for almost all of our clients. For example on the installation from last winter pictured above, we used the SunPower 327 watt modules to get 7.85 KW in the available un-shaded space. If we had used an average module, running ~290 watts in this size right now, that would be a 6.96 KW array in the same space, 12% less power installed for the same amount of work.