Monday, January 24, 2022

Solar Panels or an Electric Vehicle?

Last week we noodled over which electric vehicle might replace one of the two gas burning cars in our garage right now. But I was underwhelmed by how little cost or even environmental savings would be gained from most of the options. 

The new EVs wouldn't break on costs for hundreds of years. Okay, fine: we're not really trying to save money with a new vehicle. We're trying to save the atmosphere from having even more CO2 dumped into it every year. 

But even on that front, a new Tesla would take five years just to break even from the environmental impacts of building the car. Mining the steel & lithium to make a new vehicle, and shipping that stuff all over the globe, has some pretty material environmental impacts.

The catch is that we just don't drive that much. While neither of our cars gets great miles per gallon, a fill up lasts each car about two months. So we use about 7 gallons of gas per car per month: or 14 gallons per month total. That tilts the math on EVs for our household more than it would for a family that, you know, drives to work. *

But what about the environmental impacts of just living in our home? Might we get a bigger environmental (or economic) bang for our buck by using that money to put solar panels up on the roof instead?

Let's look at one estimate of what it would cost to install solar.

Click for bigness. Source:

So, twenty two thousand dollars if we bought the system outright. We might get some tax incentives but, now that our household income is lower, we might not want to count on those just yet. And the system would hypothetically generate 13,600kWh in a year. 

Here is some more data from the estimate. Please take it all with a big grain of salt. Actual quotes would have to come from contractors, which we're not going to bother with in the middle of a pandemic. And the true energy generated, as well as any savings, will likely be different than those estimated. (Especially as our utility company can, and has, changed rates charged to customers with solar, to cover costs associated with the grid.) 

Some initial takeaways from these figures:
  • The estimator is saying our electricity bill would be reduced to nothing, but I'm sure that's not the case. For one, SRP charges a "demand charge" to customers with rooftop solar who still draw electricity from the grid at any point (which is just about everyone, due to the need to run the air conditioner at peak hour prices in the summer). 
  • On top of that, the system size wouldn't seem to cover our entire energy usage over the course of the year (likely for the same reason: using the air conditioner/heat pump in the summer).
Here is what our actual energy usage looked like in 2021:
Click for bigness.

Our energy use peaks in the summer, when both the AC and the pool pump are running. We don't have any natural gas or any other power source like heating oil, so everything in the home runs off of electricity. Some summary figures:
  • Our total electricity usage in 2021 was 18,892 kWh
  • The annual cost was $2,310
  • The costs were atypically high this year as we had Baby JC, who can't have a blanket or anything else in the crib. We kept the thermostat low in the summer and high in the winter, and we didn't play any of the games we used to, like letting the temp creep up in peak hours in the summer to save a few bucks. Not worth it.

So, if we were to believe the figures in this estimate, what sort of savings would we see? How long until we broke even? 

A breakeven analysis that contemplates environmental impacts is complicated by the fact that our utility company, SRP, is reducing its carbon impact over time, and is set to more than double its solar production by 2025

Source: SRP

Regardless, we can at least work with today's figures. With its current mix of power plants & renewable energy, SRP claims to be releasing 922 pounds of CO2 per MWh of electricity generated (1MWh = 1,000 KWh). Would spending on solar have a better impact than spending that money on an electric vehicle? Time for some math. 

  • As we used 18,892 kWh of electricity in our house in 2021, that would mean we're responsible for 18,840 pounds of CO2 released into the atmosphere.
  • Using the estimates above, a solar system could generate 13,600 kWh in a year, hypothetically preventing 12,539 pounds of CO2 from being generated per year, at a cost of $21,675.
  • Going back to the post on electric vehicles, we currently emit 1,645 pounds of CO2 per vehicle, per year. 
  • A new EV would actually take five years just to break even on the environmental impacts, given how little we drive. But from that point forward, an EV would prevent those 1,645 pounds of CO2 from coming straight out of the tailpipe...but without solar panels, more CO2 would now be generated again by the increased electricity usage needed to charge the car. 
  • A used EV would start saving on net emissions immediately, as any environmental impacts from the car are sunk costs.

The big takeaway for me is that our house generates way, way more CO2 than our cars do, even if it does so indirectly. Even if a solar array wouldn't completely cover all our energy usage, the 12,539 pounds of CO2 such a system would keep out of the atmosphere every year is roughly 8 times the amount of carbon dioxide emitted from one of our cars in that timeframe. 

And while twenty two thousand dollars is a lot of money, it's still a fraction of what a new EV costs.

So, at least for our house, it looks like solar panels give a better bang for the buck. Which is kind of a bummer, because electric cars are really fast and a rear wheel drive Tesla is a good bit more fun than solar panels that just, you know, sit there.

Of course, this is a false dichotomy. While solar is maybe a better value prop than a new car, there's no reason we couldn't buy both.

Come back for a future post when I try to convince Mrs. Done by Forty that buying solar panels and a fancy, fast new car is what we need to do. You know, for the environment.

*(A small caveat: the pandemic is a weird time so who knows what the future holds for our driving. But our gas consumption in the past two years is remarkably close to what we did in the pre-pandemic times. With the Matrix, we drove 5,000 miles a year on average from 2011-2019. Assuming 30 mpg in mixed driving, that works out to 13.9 gallons a month.)

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  1. Went solar around a year and a half ago. My electric company charges ~$0.43 a day to be connected to the grid, so I'm paying about $12.50 a month. The nice thing is the excess energy just banks up credits so that when I use it I don't get charged. Summer and the bumper months tend to generate way more than I need, and that bank of credits gets drawn down a bit over the winter. Especially now that I just installed ductless mini splits/heat pump to offset my oil heat with electric. Would like to get an EV down the road when another car is needed, my wife commutes about 25mins each way to work, so getting her in to an EV, powered by the roof, would be nice. I think the path of "solar panels THEN a fancy, fast new car" makes the most sense. Once the solar roof was up, I spent a bit of time figuring out and optimizing where/when we were using the most electricity and ended up decreasing our usage quite a bit, now that extra capacity can do the mini splits and at some point an EV.

    1. Thanks for sharing that experience, Tom. I love the approach of solar first, then an EV: maybe I can buy a used EV at that point that isn't like 40 or 50k. (And hopefully the used market goes back to some sort of normalcy then, too.)

      We get sun year round here but our electricity use in the summer is just bonkers.

      I've seen some interesting DIY solar stuff on Youtube that I'm interested in, but to connect to the grid we need to use a small list of contractors approved by our utility. Maybe a small off grid system over the shed or garage, in addition to the main array connected to the grid, would be the ticket. :)

    2. That makes sense, a used EV is the most likely path here as well. In addition to the used market normalizing a bit, I think we'll have some more compelling options to choose from within the next few years. Some of the cars coming out now/soon look pretty great, like the Ioniq 5. Those should start hitting the used market by the time our '08 Accord gets to 200k. Maybe there'll be a used EV credit by then, but my confidence is pretty low on that.

    3. Also, just read the Noodling EV's post, same feelings on the Leaf. Even if it's been around the block and is losing capacity, it would still accomplish what we'd use it for. It could still work out numbers-wise even if it needs a pack swap. The problem is my wife doesn't like it. Small and ugly.

    4. I'm not a huge fan of aspects of the Leaf (slow, small range) but the looks are growing on me. I love a hatchback.

      You're the second person to mention the Ioniq5 in the past week. I'll have to check it out. Used might be the sweet spot on that one, for me. And yes, fingers crossed for a used EV credit (or maybe an EV conversion credit).

  2. Have you received multiple quotes for your solar system? I live in Los Angeles and I'm getting a 4.4kW system installed next week for around $14k without incentives. $21.6k for 8.7kW system seems really high.

    1. Hi there, Gilbert. Thanks for stopping by and commenting & congrats on your solar system.

      Nope, haven't even truly gotten one true estimate: this is just from the site, as noted in the post.

      "Here is some more data from the estimate. Please take it all with a big grain of salt. Actual quotes would have to come from contractors, which we're not going to bother with in the middle of a pandemic."

      I'm probably missing something with your comment on it being a high quote. Seems like roughly double the power for less than double the cost, right?

  3. Thanks for the welcome!

    Doh, sorry I didn't do the match correctly. Yes, your price per kW is actually a little better than what I got.

    Btw, I agree with your conclusion that solar is financially and environmentally a much better option than getting an EV, especially since you drive so little. But if you are trying to justify getting a fun new car, that is a different story... =)

    1. No worries at all, Gilbert.

      I think I'm both trying to justify doing a good thing for the environment and, as usual, trying to justify buying a different car. :)

  4. We did both. Our energy useage is less. But with $13k investment up front(after tax credits) - we estimate the break even at 10 years on 25 years of life. The estimates of energy produced by contractors has proved to be about 5% low annually. We were running a surplus, then we bought a Tesla Model 3 standard range. Cost (after state tax incentive) was about $39k. 2 years of no gas and $12 a month electric bills. Totally worth it.

    1. That's rad that you're doing both. And those incentives on the Teslas sure helped while they were around. Fingers crossed for more of that in the future.

      That's a great tip on the estimates from contractors being conservative. I would have guessed they'd shade in the other direction!

  5. I vote for solar panels first. That would make you pretty self sufficient in case of zombie attacks, civil war or coup. j/k!!

    1. Right?

      Though you have to wonder in the case of true disaster, if solar panels just end up putting a target on your house, too. May need to invest in other home defense. You know, just to be safe.

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