I recently published a post about generating enough solar energy to drive a Tesla Model 3 around Earth 20 times.
I received a question: "What's the value of half a million miles of electricity, and how much CO2 does that offset?" Those are interesting questions. I thought this would be just a small update on the original post. As I began to figure out the answers, it became apparent that these questions were deep enough for a complete post of their own. So, let's figure out the answers.
The 20 laps were solar-powered, but what if they were grid-powered or gas-powered instead? This is what we'll compare.
Grid Electricity: Costs & Emissions
Since our PV system was installed in 2007, there have been many changes, both in prices and emissions from our local utility. Therefore, I cannot simply use today's price or emissions values and multiply. Luckily, I recently posted a history of my local utilities price changes and emissions from then until now. So, let's apply those values to our fictional intercontinental equatorial highway and see what pops out.
From 2007 to 2025, PGE’s residential electricity prices increased from approximately 8.19 cents per kWh to ~17.43 cents per kWh.
During this same period, CO2 emissions per kWh have decreased significantly, from an estimated 0.5 pounds per kWh in 2007 to approximately 0.05 pounds per kWh by 2025. This reduction is largely due to the closure of the coal-fired Boardman plant in 2020 and PGE’s increased use of wind.
Crunching the Numbers
Grid Powered
Taking each year's average utility cost and emissions, and comparing them with our corresponding generation, shows that our half a million miles of solar energy are worth $17,316, and we've avoided 14,605 kg of CO2 emissions by using solar rather than the grid.
What About a Gas Car?
Above, we just examined electricity generation, but this was framed in terms of vehicle miles traveled. For comparison, you could also view this as the cost and pollution associated with driving this distance in a gas car. So let's get some data for gas, then we can compare gas, grid, and solar.
First, we have to pick a gas-powered car for this comparison. Since we used a 2018 Model 3 for the EV, let's pick a popular 2018 gas-powered sedan. The average fuel economy for gas-powered sedans in 2018 was around 32-35 MPG. The 2018 Honda Accord has a combined MPG of 33MPG, which fits nicely in the average range from that time, and it was a popular model. So, for our comparison, we'll use the 2018 Honda Accord.
If you were to drive a 33MPG car for 500,000 miles, that would use 15,625 gallons of gasoline. If we spread this out over the same 18 years that we looked at above, that would be nearly 28,000 miles per year. A true road warrior value, but not impossible. Similar to how we didn't just take today's electricity price and use it for all of the EV charging, I'll be equally fair to the petroleum car and look at historic gas prices. And just as we used local electricity prices, we'll use local (Oregon) gas prices.
In 2007, regular gasoline was $2.27/gallon. The lowest-priced year during our time window was 2009, coming in at $1.86. Looking at the high price, the pandemic pushed the average price to $4.50 in 2022, with peaks over $5 in some areas.
Plugging in each year's average fuel cost, the half-million-mile drive comes in with a total fuel cost of over $39,000 and more than 134 metric tons of CO2 emissions.
Year | Avg. Gas Price ($/gallon) | Gallons Used | Cost ($) | CO₂ Emissions (kg) |
---|---|---|---|---|
2007 | 2.27 | 841.75 | 1,910.92 | 7,480 |
2008 | 2.66 | 841.75 | 2,237.99 | 7,480 |
2009 | 1.86 | 841.75 | 1,566.29 | 7,480 |
2010 | 2.28 | 841.75 | 1,919.38 | 7,480 |
2011 | 2.95 | 841.75 | 2,483.24 | 7,480 |
2012 | 3.03 | 841.75 | 2,550.72 | 7,480 |
2013 | 2.85 | 841.75 | 2,396.99 | 7,480 |
2014 | 2.69 | 841.75 | 2,265.52 | 7,480 |
2015 | 1.83 | 841.75 | 1,540.79 | 7,480 |
2016 | 1.49 | 841.75 | 1,255.26 | 7,480 |
2017 | 1.79 | 841.75 | 1,509.30 | 7,480 |
2018 | 2.13 | 841.75 | 1,792.44 | 7,480 |
2019 | 1.99 | 841.75 | 1,678.56 | 7,480 |
2020 | 1.47 | 841.75 | 1,238.75 | 7,480 |
2021 | 3.50 | 841.75 | 2,946.13 | 7,480 |
2022 | 4.50 | 841.75 | 3,787.88 | 7,480 |
2023 | 4.00 | 841.75 | 3,367.00 | 7,480 |
2024 | 3.50 | 841.75 | 2,946.13 | 7,480 |
Total | - | 15,151.515 | 39,393.29 | 134,652 |
To be clear, the CO2 emissions here are only considering the car's tailpipe emissions. To capture the true emissions related to burning gasoline, you need a complete well-to-wheel (drill & spill) analysis that looks at all the pollution created to pump, transport, and refine the crude into gasoline. However, we didn't do a well-to-wheel (or coalmine-to-atmosphere) analysis for the grid, nor did we look at the production and transport footprint for the solar panels. I'm not suggesting that this analysis isn't meaningful, just pointing out this limitation.
Gas, Grid, & Solar
So now we've looked at all three methods to fuel this 500,000-mile trek. Here's a summary table:
Energy Source | Fueling Cost | Emissions |
---|---|---|
Solar | $0* | 0 metric tons |
Grid Power | $17,316 | 14.6 metric tons |
Gas-Powered | $39,383 | 134.7 metric tons |
* after the solar is installed and paid off.
Conclusion
Unsurprisingly, solar is the clear winner; it has zero tailpipe emissions and (once the panels are paid for) zero ongoing costs.
Second across the finish line is grid power with a cost of $17,316 and 14.6 metric tons of CO2.
Coming in last is the gas-powered Honda Accord, costing more than twice as much as the grid-powered trip, while spewing out an order of magnitude more CO2.