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Using Solar Power to Charge Electric Vehicles

Using Solar Power to Charge Electric Vehicles

One of the holy grails of renewable energy is to charge an electric vehicle off a solar power source - AND make it efficient and convenient enough to suit the needs of the average driver. This is easier said than done. But it is a tantalizing prospect; some 40-50% of global CO2 is emitted by transportation alone. Electric vehicles (EV) by themselves simply shift the load to the power grid, which doesn't help much if you're charging off fossil fuel. But add solar power into the equation, and you're now basically running a car on air.

It's not quite so simple, but it is very possible.

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Challenges to Solar EV Charging

The chief bottleneck is charging time. Most EVs come standard with a 120-volt outlet charger. That uses the same plug that fits the outlets in your standard home. Everybody has that (as far as the US in concerned), so it's the default.

The problem with 120-volt charging is the time factor. An hour of charging at 120 volts will only provide a few miles' driving range for the car. To fully charge an EV from empty to full might take more than one day. Typically, you'll get 20-50 miles of range out of an overnight charge (figuring ten hours).

This is suitable for in-city driving, especially if you have a dedicated place to plug in while parked at work. It's also ideal for households with limited driving needs - retirees, those working from home, and such. But it's not quite feasible for the household with, say, two working and commuting adults plus kids to drop off at soccer practice.

Things improve dramatically with the installation of a 240-volt outlet. These are easily recognizable to most of you; it's the larger "claw" shaped plug that is most often seen in commercial appliances but occasionally shows up in the garage or utility room for a washer / dryer hookup.

Using a 240-volt charge setup cuts our charging time. A mere hour of charge time provides up to 30 miles' driving range, while an overnight charge of eight hours is enough to top the EV off to 200 miles. Federal Highway Administration data tells us that the average US citizen drives 35 miles per day. But even if you're at the top end of that average, 200 miles per day would have to be sufficient.

There is also DC Fast Charging (DCFC), an even more specialized hookup which can charge up to 250 miles in a single hour. However, most EVs aren't capable of DCFC, and it also takes special charging setups that aren't feasible for the average home.

How Much Solar Power to Charge an EV?

As a rough back-of-the-envelope calculation, it would take between four and eight standard solar panels, given that the panels are rated about 350 watts each. That's a lot! Standard household installs already take around 20 to 25 panels, but charging up an EV draws a lot of extra power.

You have to also take into account, if you are currently getting solar power credits or net metering from your utility for your excess electricity, some of that will be diverted to charging now. There's a lot of math involved in charging an EV.

You can also mitigate solar panel charging in two ways: by using a smart charger, which will only divert energy to the EV when it's available, or by installing power storage batteries, so that excess power can be stored and then used for the car when you plug in. However, power storage batteries can run up to five figures, so that's a hefty cost to tack on.

One more fudge factor to consider is the wear and tear on the battery. Your average EV has an eight year warranty on batteries, but as batteries wear down over time, they take a charge slower and run down faster. So you want to be extra generous in figuring electricity usage for the EV, if you're planning on doing this long-term.

Progress Marches On

US President Biden recently tweeted "We’re building 500,000 electric vehicle charging stations across the country. The great American road trip will be fully electrified." EVs are growing in popularity every day, spurred not only by climate change concerns, but the high price of gasoline and our crippling dependence on foreign oil. Charging your electric car from solar power is well within the realm of possible now, and can only get easier as market demand drives innovation.

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