In a recent blog post, I discussed energy efficiency.  The specific examples I used were my new furnaces (95% efficient) and a car (15% efficient). Now, I’d like to discuss solar panel efficiency.

Solar panel efficiency is a measure of how well a panel converts sunlight to electricity.

How efficient are solar panels? While scientists are working hard at improving efficiency and have achieved impressive results in the laboratory, the best commercially available panels are the SunPower X-22 Series panels. And yes, you guessed it, they are 22% efficient. Or, more precisely, the SunPower 345-watt panel is 21.5% efficient and the SunPower 360-watt panel is 22.2% efficient.

While this sounds like a low number compared to my new furnaces (95%), there is a key and fundamental difference between solar panels and a furnace or any device that burns fossil fuel.

Remember, my furnace takes in natural gas and burns it. Five percent of the energy generated during the burning process is lost and is unusable. For example, warm combustion products – the stuff that is unhealthy to breath – are vented to the atmosphere. So, although I may have had 100 units of energy delivered to my furnace, I only realized 95% of that energy when my furnace burned it.

Solar energy, on the other hand, is quite different. Even though the panel converts only 22% of the sunlight that hits it into electricity, the other 78% is not lost and unusable. Instead, that sunlight goes on and does what it would normally have done – it heats something up. But, unlike a furnace, it doesn’t add any combustion products to the atmosphere.

This difference is becoming more and more important as we learn about the record high carbon-dioxide levels in our atmosphere. A subject for another post.