Future Tense

The One Question I Hate Getting About My Home’s Solar Roof

Yes, it can power my home and two cars. No, that isn’t the point.

A beige concrete house, in dusk, under a gray sky, with sun reflected in its windows and solar panels on its roof.
Think of these panels as peer pressure. Giorgio Trovato on Unsplash

Climate change. The electric grid. Renewable energy. There is a pervasive fiction that these are all topics for another time, that these issues can be addressed when some new unforeseen technology presents itself. It is a fiction I encounter all too often as an environmental science educator, and a desire to contradict these myths was one of the main reasons that my wife and I decided to add solar power to our home. We wanted to demonstrate that it is completely feasible to power one’s home and cars using 100 percent solar energy. Not next year. Not a decade from now. Today, in 2021.

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It’s not uncommon for friends, family, and neighbors to ask us about our home’s solar power. And I love most of the questions. It’s a chance to talk about a subject I enjoy, while encouraging people to think about adding solar to their own homes. Most questions are pretty straightforward: How much energy does it produce? Does it produce enough electricity to power your cars? What happens when it is cloudy? (There is one question that really irks me, but I’ll get to that shortly.)

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It’s been fun telling people that we produce more than 100 percent of the electricity we need to power our entire house and both our cars. I know that some may wonder whether we are being extremely miserly about our own electricity usage or whether there is some secret to our specific home. But there’s no secret and nothing unusual going on. We have a solar roof (the tiles themselves produce the electricity, as opposed to panels added to the roof), but other than that, everything is quite normal. We use our appliances, run the air conditioner, and drive to the park to play with our daughter.

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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.

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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.

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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.

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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.

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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.

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But that’s not the only benefit. The quantifiable benefits of solar go far beyond the direct impact of just one home. Something else happens when you put solar on your roof: You influence the people around you. Neighbors notice your roof and, whether it is conscious or unconscious, they themselves are now more likely to put solar on their roof.

This might sound odd, but it is not without precedent. Cornell University economist Robert Frank outlines this phenomenon in his book Under the Influence: Putting Peer Pressure to Work. One example from the book that stuck with me is the case of secondhand smoke. Smoking was banned from many restaurants across America based on the reasoning that there was a health-related cost associated with secondhand smoke. This is undoubtedly true. Yet it is not the only cost. Smoking in restaurants “normalizes” the behavior of smoking and makes other people ever-so-slightly more likely to smoke. But, if you ban smoking, this influence goes away. The people that go to restaurants no longer see their peers smoking. They are no longer subtly influenced by the act of smoking. The impact of this “peer effect” is that the number of smokers decreases, health costs go down, and lives are saved, far beyond the people protected by the lack of secondhand smoke.

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The same effect has been shown to be true for solar installations. Study after study has shown that when one home adds solar to their roof, it increases the likelihood that surrounding homes will add. When you add solar to your house you are not only responsible for the good that your own roof will unleash, but you are now partly responsible for the benefits derived from other roofs in your area. The direct environmental benefits of solar are clear, but one could make a case that the most beneficial aspect of installing solar is that you will influence your neighbors to do the same.

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Much of the conversation around solar power is about saving money—energy from the sun is free! But I want to believe that most people also care about the health of someone who lives one town over, and that even a random person’s well-being has definable value. I believe that the issue isn’t a lack of caring, but a lack of information. And can we blame anyone? We live in a society that inundates our every moment with consumerism and obfuscates any costs or benefits that aren’t intuitively obvious. It only makes sense (sadly) that external costs and benefits wouldn’t factor into most of our calculations. But once we shine a light on these calculations and understand that the social costs are just as real, then the calculus starts to change.

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So, when will rooftop solar pay for itself? It’s definitely not as simple as dividing the cost of the system by the value of electricity generated each year, that’s for sure. The true calculation is complex, and each home is different, but there are two things we can be quite confident about: that the benefits are vast and that the true payback is much quicker than any simple calculation will indicate. And did I mention that it is really fun to look at your phone and see how much energy you have generated each day? So, there’s that, too.

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.

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