Solar Panel Efficiency

Efficiency is one of the most talked-about topics in solar, but also one of the least understood. So what does the efficiency of a solar panel really mean?


Solar panel efficiency is the electrical power output divided by the available solar power. For example, if a solar panel produces 400W of electricity from 2000W of sunshine, then it’s 20% efficient (400 divided by 2000 = 20%).

When Efficiency Doesn’t Matter

Consider this: John has 6 large solar panels with 16.7% efficiency, giving him a total of 2 kilowatts. Jane has 5 large solar panels with 20% efficiency, also giving her a total of 2 kilowatts. As this example shows, efficiency doesn’t really matter. What matters is the overall power of the system. In solar speak, “efficient” is not a synonym for “better”. Instead, it has a very specific meaning. At the end of the day, a 2 kW system is a 2 kW system whether it’s high efficiency or low efficiency. The only difference is that the high efficiency system will achieve the same power output with fewer panels. The highest efficiency panels are not always worth the price premium. Remember that high-efficiency does not automatically mean high quality!

When Efficiency Does Matter: Limited Roof Space

Sometimes you will have a limited amount of roof space to work with for installing solar PV panels. This is one time when the efficiency of your panels will be particularly important. In this case, higher efficiency will allow you to fit more power capacity per precious square meter of available space. A site survey can help you to figure out exactly how much space you’ve got to work with.

When Efficiency Does Matter: “Balance of System Costs”

Another benefit of high efficiency panels is that they make help to streamline your system in other ways. Fewer panels means fewer brackets, connectors, and less installation labour for the same power output. These savings can often tip the balance in favour of higher efficiency panels.


“High efficiency” is not simply a badge of honour for the best solar panels. It’s a technical term with a very specific meaning. Remember that “high efficiency” does not always mean “high quality” and “low efficiency” does not always mean “low quality”. The highest efficiency panel is not always the right choice. The decision comes down to the size of your roof and streamlined installation versus the extra cost of high efficiency panels. Often, it ends up being a 50-50 trade-off, so either option will be a fine choice.