May 3, 2021


The One Question I Hate Getting About My Home's Solar RoofYes, it can power my home and two cars. No, that isn't the point. (RYAN CORNELL, APRIL 26, 2021, Slate)

The fact that it is possible to power an entire house and two cars with today's technology seems to intrigue most people. It also inevitably leads to another question. The question that drives me a little bit crazy:

When will the roof pay for itself?

I can hear the comments coming my way: What's wrong with that question? Why wouldn't someone want to know the payback? So, before I dig too deep of a hole, let me state that I don't begrudge anyone that asks it. It is a completely valid question, and while there are problems with the question itself, I still understand why someone wants to know.

The problem with the question is that it is a gross oversimplification. It's a bit like making a yearly budget, but only tracking purchases made on your debit card and ignoring those made with cash. You're tracking, but you'll miss out on the bigger picture. The standard payback calculation for solar is no different: You learn something about some of the benefits of your system, but you completely ignore the environmental benefits and other factors. Many rooftop solar systems will pay for themselves in five to 10 years using a simple cost-benefit calculation, but that only tells us part of the story. We need to factor in a variety of other costs and benefits, which might be a little less obvious but are still just as real.

The environmental impact of electricity generation is a complex calculation that involves a host of variables. But, if we simplify it down, you are essentially replacing a kilowatt hour of electricity (kWh) from the grid with a kWh that comes from your roof. We can then ask: How much pollution is caused from a kWh of coal or natural gas? What are the health and climate costs? How much are these costs reduced if we replace that kWh from fossil fuels with a kWh from solar? The answer: a lot.

A study by the Harvard School of Public Health demonstrated that a single kWh from a coal power plant costs society between 9 cents and 26 cents (taking into account health costs, climate costs, and other damages). Another study found that the health costs of fossil fuels represented 14 cents to 35 cents per kWh. These types of studies are essential, as they tell us about the "social cost" of electricity generation. The social cost gives us a true understanding of what something actually costs, as it factors in the real impact to the climate, human health, and other costs that are outside the normal market transaction.

If we take into account the fact that an average American household consumes more than 10,000 kWh of electricity per year, we can see that a single household could correspond to thousands of dollars in costs to society (if those kWh are coming from fossil fuels). That is incredibly significant. Now, a kilowatt hour produced from solar power has its own costs; the panels aren't made with magic and fairy dust. But the social costs are undeniably far less than combusting fossil fuels.

How much less? Well, that is going to vary from home to home and region to region. But even a 10 cent per kWh reduction in social costs would represent a yearly decrease of over a thousand dollars of damages to our climate, our collective health, and our environment. That's a big deal and it's imperative that we take it into account.

But that's not the only benefit. 

Posted by at May 3, 2021 12:00 AM