Note: The information contained in this periodical weblog may be outdated. This was my personal weblog published before January 1, 2015. Since then I have been the co-owner and Principal Solar Designer at Florida Solar Design Group.

It all Boils Down to Dollar-Per-Watt

I’m asked quite frequently, what is the most efficient solar electric module on the market? That question has multiple answers. It depends on what you are trying to accomplish!

In the photovoltaic module industry, the term efficiency refers to the amount of rated power that a solar module can produce within a certain area (its size). More accurately, it seeks to explain how much of the available solar radiation is turned into usable electricity. You will hear efficiency ratings from 13-21% these days for commercially available modules. Most people jump to the conclusion that a more efficient module is the best.

Don’t fall into the trap!

It is typically more important to focus on how much rated energy a solar module produces relative to it’s COST! Let’s look at an example:

The Sanyo HIT-240HDE4 is an excellent module that is 17.3% efficient and 14.93 square feet in size. It produces maximum rated power of 230 watts. The Canadian Solar CS6P-230P is “only” 14.3% efficient and it is 17.33 square feet. It produces the exact same 230 watts of rated power. In other words, the Canadian Solar module is 16% larger, or 16% less “efficient.”

Now what if I told you that the Canadian Solar module was half the price of the Sanyo module? If space is not critical, who cares what size the module is? Buy the module with the lower price! This is known as dollars-per-watt ($/w) efficiency. Would you want to pay twice as much for the same amount of energy?

There are some other factors to consider, which are typically much less important. If aesthetics are important, there are some modules that are made to look great. Some are even semi-transparent. Warranty is also a factor. You want your manufacturer to stand behind the product. And some people are concerned with the product origin. There are fewer and fewer domestically produced module options in the United States.

Some module manufacturers claim that their modules actually produce closer to the rated amount of power than others. There is another rating called Practical Test Conditions that attempts to provide a more realistic power output under practical situations. In most cases, the PTC differences are negligible, and conditions at your site may not reflect either rating. There are no guarantees, so I usually discount this factor entirely.

The bottom line is that it all boils down to dollars-per-watt. Don’t be fooled into thinking that a more efficient solar electric module is the way to go.


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