Solar Panel Efficiency

I get quite a few questions about solar panel efficiency so I thought I’d dive into this topic again.

I understand why this comes up. It has been pounded into our brains throughout our lifetimes that more efficient is better. Whether we’re talking about a car, water heater or our time management skills; more efficient it better. Inefficient car = more costly to operate and more polluting. I get it.

Now, with solar panels that story is a little more nuanced because sunshine is free and likely to remain so. Let’s go back to our example of a car. Imagine that gasoline is free (and non-polluting). How would that influence your decision between the cheaper gas guzzler and the more expensive hybrid car that sips gas? Again, assuming gas doesn’t pollute, I might choose the cheaper car that is less efficient. I know this kind of turns the efficiency topic on its head, but if you think about it, it makes sense.

The Rocky Mountain Institute recently wrote an article about building efficiency and the exponential cost of incremental R-value increases. In other words, to get that triple pane window from R-6 to R-7 is much more expensive than from R-2 to R-3. One of their conclusions that struck me was that at some point it is more economically feasible to add more solar panels to the roof than chase more efficient insulation in the home. This coming from the Rocky Mountain Institute is surprising because they are all about efficiency.

There is a use case where more efficient solar panels makes sense. If you have a small roof (and nowhere to put the solar panels on the ground), and a large electric bill and a large budget for the project, then by all means go for the more expensive solar panels.

I personally don’t run into this situation too often in the Durango area. Most roofs are large and we get a lot of sunshine so the most efficient solar panels aren’t needed. Besides, the more efficient panels usually only knock off one or two panels from the total array. Its not like you need half the panels or something.

It does feel weird to push ‘less efficient’, but in the end an electron is an electron and your TV won’t be able to tell the difference of where it came from. If you want the best bang for your buck, look at the unit of production with respect to the cost per unit or $/Watt. This is the most common metric used to compare apples to apples when evaluating solar systems.