The Law of Conservation of Energy is a basic recognized law of physics, and one I occasionally forget when writing and speaking about solar energy. Solar power does not “create energy.” It simply converts energy to usable forms in our everyday lives. For example, solar thermal technologies move heat to where we want it. Photovoltaic systems convert solar radiation into electrical energy that we can use to power electronic devices.

If you catch me saying the phrase “create energy,” please pinch me or something. It’s a bad habit that I’m trying to break.

I was reminded about this as I spoke to an employee about how solar panels affect roof temperatures. Black panels on a roof can’t be a good thing, right? Well, solar pool heating panels can approach 85% efficiency, meaning that 85% of the sun’s radiation hitting them is transferred to pool water and the energy (latent heat) is moved into the pool. As a result, the roof under the panels is only subjected to 15% of the sun’s radiation (heat). I’m oversimplifying this, but common sense tells us that as we move heat from the roof to the pool, the roof underneath the panels should be cooler.

Similarly, solar electric panels, which are about 20% efficient with today’s commercialized technology, convert some of the sun’s radiation to electricity. Consequently, 100% of the solar energy landing on the solar panels cannot be radiated onto the roof’s surface.

I know some astrophysicist will send me an email about some obscure technical faux pas in the above analysis, but that’s okay. I’m not a physicist. The important thing to remember is that solar energy systems do not create energy – they just allow us to use the energy made available to us from the sun.