Toward the end of last year, I bought a solar array: 24 LG panels up on my roof paired with Enphase microinverters, transforming sunlight into 7.4 kilowatts of electricity. The company that installed them produced a fancy chart that showed my projected breakeven point, the moment when I'll have saved as much on my electric bill as I spent on the system. Saving on utilities is fine, but I had a more radical purpose in mind.

Modern electric cars are so good that they transformed the way I thought about solar. Those panels could be more than just a straightforward supplement to grid power. They could be a private gas station, a bottomless well of electrons to fuel my trips to the grocery store, to the kids' ballgames, to distant cities. Nobody gets ecstatic about saving ten cents per kilowatt-hour on the electric bill. But paying $0.00 per gallon, permanently, to drive anywhere you want? That would be supremely awesome. You'd want to sign up for that deal—if it exists.

My 310-watt LG panels (24 total) generate about ten megawatt-hours per year of power. Peter Taylor

The question, then, is simple: Can my modest solar array generate enough juice to cover all of my driving? To find out, I procured three electric cars of widely disparate prices and capabilities and spent a month logging mileage and kilowatt-hours. Your results would vary, of course, but the basic conclusions would hold whether you live in Dallas or Duluth, whether you drive a Model X or commute on a dangerously shoddy hoverboard. Let's take a look.

Subjects

To properly assess whether this gambit is both possible and practical, I need to sample a broad swath of the current EV spectrum, which is how my driveway has come to host a vehicular trio never before seen in a single cul-de-sac: (1) a GEM e4, (2) a Mitsubishi i-MiEV, and (3) a Tesla Model X P90D. The only trait they share is four wheels and a thirst for electrons.

The GEM is limited to 25 mph and allowed to drive only on roads with a posted speed limit of 35 mph or less. But in my dense suburban area, I can navigate to downtown via 25-mph side streets, a method that gets me almost anywhere I need to go. Driving the GEM is an elemental experience, with a fun factor all out of proportion to its 6.7 horsepower. People think it's cool. I know this because it has no doors and you're never going very fast. You can hear people say, "That thing is cool!"

To simulate winter months, when the Model X would outrun my panels' trickle, I use a public charger.

Further up the food chain is the Mitsubishi i-MiEV (eye-meev), the diminutive four-door that, at $22,995, holds the title of most affordable electric car in America. It's a funky little bargain, the i-MiEV. The rear-mounted 66-hp motor and rear-wheel drive make it something like a latter-day Baja Bug. I tear up my gravel driveway making power-slide exits out to the street. With a mere 62 miles of range, however, the i-MiEV probably wouldn't work as your only car.

But the Model X would. Tesla's ovoid people-mover has 250 miles of range and Supercharger stations around the country for fast highway fill-ups. It seats seven and can tow 5,000 pounds. Oh, and this one does zero to 60 in 3.8 seconds. The Model X is the closest thing yet to an electric car that's all things to all (well-heeled) people. But it's heavy, and sucks down a lot of juice when you're indulging in its 612 lb-ft of torque. My array will have to work hard to keep the Model X running.

Electric Driving Habits

On my busiest GEM day, I'm running into town and back home, coming up with excuses to run errands. Total mileage: 12 miles. As a low-speed vehicle, the GEM doesn't have EPA-rated specs, but based on its range and battery capacity, I can predict 128,412 miles that it uses about 18 kilowatt-hours of energy per 100 miles. Doing the math, a day's worth of solar power from my house could send the GEM on a 238-mile trip—which would take nine and a half hours, if the e4 could actually hold that much charge.

But most of the time, you're not driving flat out like that. Most of the time, you're probably not even driving at all. I realize this once I start tracking mileage in the Mitsubishi. On one representative day, I drive the i-MiEV to the gym and back. Then I hit the grocery store, the liquor store, and, because I have time, Bed Bath & Beyond. After all that, I retrieve my kids from day care and summer camp and circle back home. Total mileage: 10.5. In my section of North Carolina suburbia, the things I need are nearby, my daily orbit small. It always seems like I spend quite a bit of time driving, but it turns out I'm never really going that far. (Our primary family car averages just 6,000 miles a year.) The i-MiEV and the e4 have enough range for daily travels. Even if I added a daily 30-mile round-trip commute, the Mitsubishi would suffice.

Coincidentally, my busiest day in the i-MiEV (31 miles) coincides with the month's worst day for solar production. The sky is a cloudy muddle that pours forth a mere 24.2 kwh. But even that pittance is more than enough for the i-MiEV, which uses only about 7 kwh of energy. All my driving is covered, with enough solar energy left over to dent my home electric bill. So far, the rooftop perpetual fuel pump is working out better than I'd imagined. But will a Tesla outrun the power of the sun?

The Tesla Test

When you think about electricity like gasoline, free public chargers seem strange. Peter Taylor

Over nine days with the Model X, I cover 704.8 miles, using 281.4 kwh. That's a whole lot of driving in a big, luxurious, all-wheel-drive SUV doing 75 mph with the air conditioning on blast—a worst-case scenario for EV energy use. When I take the Model X on an interstate road trip and log 247.5 miles, I burn through 95 kwh of energy. I'd need twice as many solar panels to even get close to producing that much energy from a day of sunlight. Out of necessity, and to simulate the dim winter months when the Model X would outrun my panels' trickle, I supplement solar power with public infrastructure. In town, I use a 240-volt public charger, which gives the Tesla 16 miles of range per hour spent plugged in and charging—my garage's 110-volt three-prong outlet adds range at a rate of only three miles per hour. On I-95, I stopped at a 400-volt Tesla Supercharger station for a fill-up that, at one point, was recharging the battery at a rate of 296 miles of range per hour.

But when I drove the Tesla within my normal routine, the Model X coexisted just fine with my home-brewed power. The solar array plays a long game, punching in for its job day after day, whether you drive or not. On an average month, the panels generate enough energy to power the Tesla for nearly 2,200 miles—far more than I ever drive, even allowing for the occasional road trip. The sun eventually comes out ahead.

Free Gas

Having spent months paying close attention to my home solar production, and to the size of my grid electricity bill, I'm a little bit amazed that public chargers are still predominantly free. It's strange, when you think about it. Because electricity isn't free.

Sure, the power from your outlet is a lot less expensive than 87 octane, but can you imagine a Shell station with a public spigot dispensing fuel? The average U.S. household spends $2,000 a year on gas, and that's when prices are low. Even a ten-cent-per-gallon discount would cause lines around the block. There's just a different culture around electricity. We don't prize it. We're not trained to quantify it and obsess over it the way we do gasoline. But once you start thinking about electricity the way you think about a finite, labor-intensive resource like fuel, pairing solar panels with vehicles like these seems even more brilliant.

When my solar installer produced that financial chart, they pegged the payback day at 7.8 years out. But if I traded my gas-burning car for an electric one, and crude prices return to $100 per barrel, instead of saving ten cents per kilowatt-hour of electricity, I could be avoiding a four-dollar-per-gallon hit at the pump. In those terms, the payback horizon could go from eight years to three.

Would you prepay for three years of gas if it meant that you would never pay for it again? That's not magic, not a wild hypothetical. As it turns out, that's reality. There may be days when you outdrive your solar array. But it's like a casino. The house always wins.

*This article originally appeared in the November 2016 issue of Popular Mechanics.

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