Home editor's blog on going solar Solar delivers 10,000 Sun Miles® for an EV

Solar delivers 10,000 Sun Miles® for an EV

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Our 5.59 kW solar system has produced 2,500 kilowatt hours more than we've used since being installed at the end of June.

editors-blog-entry3Not that we’re counting obsessively or anything – OK, so we are ;-) – but we hit 10,000 miles worth of banked Sun Miles® this week.

Sun Miles® are miles driven by an electric vehicle (EV) or plug-in hybrid electric vehicle (PHEV) whose batteries have been charged using solar energy and/or using electricity credits amassed via solar offset generation.

As I’ve noted elsewhere, not everyone could be doing what we are – using a home solar system to overproduce electricity at a high rate in order to save that electricity as fuel for a future electric car. But I suspect quite a few people could be, certainly far more than who are doing so right now.

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And, if they were able to achieve our solar overproduction – pumped out by, in our case, a 5.59 kW system, they, like we, would have saved the equivalent of $1,500 worth of gasoline ($3 per gallon, 20 m.p.g., 1 kWh = 4 miles) in a little more than four months – 134 days to be exact.

That’s about 75 miles of driving per day -- far more than we drive our two cars per day. It’s $11.20 in “gasoline” savings per day, that’s right, per day!

$10,000 worth of energy in two years
And, we’re covering 100-percent of our admittedly pretty low home electric use, usually around 250 to 300 kWh per month, with the energy generated by our solar system as well, meaning we need to add about $135 to that $1,500 savings total.

At this rate, we’ll hit $10,000 worth of power production in about two years. That, by the way is $2,000 more than the out-of-pocket cost for our solar system.

But let’s say you installed a 5.59 kW system without any utility rebates. Our system was around $32,000 prior to the Xcel Energy Solar Rewards Rebate. A 30 percent Federal tax credit brings the price down to $21,334. Using our formula above ($3 per gallon, 20 m.p.g., 1 kWh= 4 miles, plus an 11 cent per kWh electric rate) and assuming you can overproduce by about a 2 to 1 ratio as we are, you would still hit solar payback without any utility rebates or state or local rebates in a little over four years.

But even if you don’t manage to secure the same deal as we did for our solar system (we hit the utility rebates at just the right time, got a great deal from REC Solar, and we saw the City of Aurora offer an additional $500 rebate on top of it all), if you’re able to overproduce at the rate we have been able to -- we’ve been producing roughly two times as much electricity as we have used on a daily basis -- you could see solar payback rates like those below:

  • 5.59 kW system with an out-of-pocket cost of $9,810 pays itself off in two years;
  • 5.59 kW system with an out-of-pocket cost of $14,715 pays itself off in three years;
  • 5.59 kW system with an out-of-pocket cost of $19,620 pays itself off in four years

Most people in the U.S. will not pay $19,620 out of pocket for a 5.59 kW system. In fact, an out-of-pocket cost of approximately of $10,000 to $12,000 is more likely.

There are other limiting factors as well. Not everyone would be able to over-produce at the rate that we have been so far with a 5.59 kW system, though certainly more than a few people could, especially if they live in a sunny location like we do and they’re focused on conserving electricity, as we are.

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The REC Solar crew that installed our 5.59 kW solar system in June of this year.

System size restrictions
Additionally, utilities– including our utility, Xcel Energy – often seek to limit homeowners’ ability to over-produce electricity via a home solar system by capping the system size for which they’ll provide a rebate.

But let’s say you installed a 5.59 kW system without any utility rebates. Our system was around $32,000 prior to the Xcel Energy Solar Rewards Rebate. A 30 percent Federal tax credit brings the price down to $21,334. Using our formula above ($3 per gallon, 20 m.p.g., 1 kWh= 4 miles, plus an 11 cent per kWh electric rate) and assuming you can overproduce by about a 2 to 1 ratio as we are, you would still hit solar payback without any utility rebates or state or local rebates in a little over four years.

In the U.S., most folks are going to be able to get some kind of rebate beyond the Federal tax credit, putting even those worst off in terms of low solar rebates to realistically hit solar payback in three to four years.

Again, this is applying the same formula we’ve used above and assuming one can overproduce electricity with a home solar system at a 2 to 1 ratio, and assuming that one can bank extra kWh one produces or assuming that one already has an electric car, or soon will have one, to fuel with the extra electricity produced.

Basically, PV+EV would seem to pay off -- potentially hugely and extremely quickly -- in what, given the above calculations illustrate, are likely millions of households across America.

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