How Green Are Solar Panels?

We get asked this question a lot, given that solar panels (aka “modules”) require intensive energy and other resources to manufacture. A subset of environmentalists question how clean and green solar actually is. In fact, Rep. Matt Manweller (R-Ellensburg) asked this question during recent testimony over the proposed solar bill HB 1048 that is working its way through the Washington State Legislature.

To unravel this mystery, let’s first take a look at how solar panels are made.

To create the cells for the modules, silicon is melted in electric furnaces and transformed into solid rods or bricks called ingots. If you figure that most electricity in the country is still produced by fossil fuels, well, this part of the manufacturing process does emit a not-insignificant amount of carbon dioxide.

In addition to the energy required to produce solar cells, other module components like glass, aluminum, and wiring components also require energy in their production. There is fuel used in transporting the modules as well, whether that’s from Bellingham to Seattle or China to Texas.

So a shiny new solar panel begins its life with a “carbon debt” that needs to be paid back before we can say that it’s contributing positively to carbon reduction. But how long does that take, exactly?

For a long time, we’ve pointed people to this NREL report, which suggests the “energy payback” for a crystalline PV module is about 3-4 years. However, this was published in 2004, and obviously a lot has changed since then.

There’s a new study that updates those estimates and provides some additional insights into how the energy that goes into making a module “pays for itself” as it generates energy in the field over time, depending on where it was manufactured and where it’s installed.

Exactly how much carbon dioxide was emitted during the manufacture of a panel will depend on where it was made, as well as when. How much emitted gas it has saved will depend on where it is installed. A panel made in China, for example, costs nearly double the greenhouse-gas emissions of one made in Europe. That is because China relies more on fossil fuels for generating power. Conversely, the environmental benefits of installing solar panels will be greater in China than in Europe, as the clean power they produce replaces electricity that would otherwise be generated largely by burning coal or gas.

The study concludes that the energy payback for PV modules is now two years or less, and that number is expected to continue to decline as technology and efficiencies improve.