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Dedicated solar a better option?

Discussion in 'Prime Plug-in Charging' started by Diemaster, Dec 28, 2017.

  1. Diemaster

    Diemaster Active Member

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    Quick thought:
    Im liking this not having to put gas in my car every week. would it be practical to get solar components to make a small solar shack (perhaps in a storage shed) that the prime can charge off of?

    Basicly charging / driving the prime for free using the sun.i haven't done any calculations or engineering yet just want some feedback on the idea.

    Getting something like this connected to a few deep cycle batteries.
    Sun charges batteries while im at work during the day. come home and plug in; batteries charge prime during the night.
     
  2. bisco

    bisco cookie crumbler

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    likely not practical, or economical. but if you are an engineer type or serious electrical hobbyist, why not make it a fun project?
     
  3. fotomoto

    fotomoto Senior Member

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    You're not the first to ask and IIRC from previous discussions by solar owners it's best to install solar on your home where the most electrical use is and install enough capacity to also cover your car (if possible).
     
    jerrymildred likes this.
  4. Andyprius1

    Andyprius1 Senior Member

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    It’s much more complicated than that, there are companies out there that will sell you whole kits, either for DC storage or linked with your Electric provider. Doing anything on a small scale first is always a good idea.
     
  5. draheim

    draheim Member

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    I've done some quick calculations but I'm not so great at math, and I know folks on this forum are way better at this kind of thing than I am. So I just wanted to run some numbers by you folks to make sure I'm understanding this right. Sorry in advance for the long post.

    Main question (related to the title above) is whether installing solar panels for the sole purpose of charging my Prime's battery for EV-only driving makes economic sense, or if it would be almost only for the environmental benefits of powering my car with solar energy rather than hydropower (main source of electricity in my area, at 88%). I'm not going into whether hydropower or solar is a more environmentally friendly source of energy, that's another discussion. (Still relevant though)

    So below are the numbers I am working with.

    The Prime battery takes 6.1 kWh for a full charge, which gets me about 25 miles of EV driving.

    In my area, electricity averages about $0.10/kWh through the local utility (it ranges seasonally, with a low of $0.07 and a high of $0.13)--so let's say a full charge = $0.61, or $0.024 per mile in EV driving mode.

    In my area, the current estimate for a 6 kW solar system installed is between $10k and $14k. (And here is the crux of where I'm not sure I've got this right--how much power does a 6 kW system generate? More on that below)

    So assuming the higher end of that range (I realize prices are coming down, but if I wanted to do this today), the way I calculate this is that I would have to drive 573,770 miles in EV mode ($14,000 for solar system at $0.024 per mile) to break even on solar compared to what we currently pay for electricity.

    So this is where I need help. Is a 6 kW system not the same as a system that provides 6.1 kWh? This is where I get confused, and I'm not sure I've got my fundamentals right (or even close). I've seen a website saying that a 4.23 kWh solar system is adequate to cover an entire house's electrical demand in California (7.05 kWh in Arizona, 9.98 kWh in Florida etc.). I'm in Washington state, the site doesn't list us. But maybe I'd need only a 2 kWh or 4 kWh system to power the car only (or even less), which thus would reduce the break-even mileage to 191,257 miles or 382,513, respectively? (Both still unlikely, as I put just 31,000 miles on my last car, a regular Prius, over 8 years--so to get to just 191,257 miles would take me 49 years, by which time I'll almost certainly be dead).

    Put simply, if I charge my Prime every other day, that's just 100 kWh demand per month. Based on a year of electrical bills, we averaged 880 kWh/month--so maybe the Prime needs only 10%-15% of the full demand. And if that's the case, then the idea of a solar system paying for itself just to cover the demand for the car starts to make a lot more economic sense.

    Any fatal flaws to my math here? Or, better yet, does anyone out there have a dedicated solar system that they use only for charging their Prime? What size system is it and what did it cost?

    Our utility also had a community solar program, though apparently it is currently sold out. This seems to make a lot of sense, depending on the variables etc.

    Thanks for reading.
     
  6. bisco

    bisco cookie crumbler

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    i don't think it pays out. if you can install solar, why not put in a regular system and power your house and car?
    btw, iirc, your electrons are so cheap, solar isn't worth it.
     
  7. draheim

    draheim Member

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    I think you're right, though the numbers aren't as bad as I first thought (I wouldn't need anywhere near a 6 kW system).

    I found this site, which leads me to believe that if I wanted to fully charge the car every day (and I don't even need that, probably only about half that) I would need a ~2.2kW solar system.

    What I'd really be looking for is a system that's gradually expandable so maybe I can start by charging mainly the car (or offsetting that portion of the electric bill) but then eventually supply more of the house's power from solar too. If prices keep coming down it might make sense at some point to start with a 1 kW system, but I don't think we're there yet. The lower cost of power here does make the cost/benefit a lot less than in other areas for sure.
     
    #7 draheim, Mar 26, 2018
    Last edited: Mar 26, 2018
    bisco likes this.
  8. bisco

    bisco cookie crumbler

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    there are some great solar threads here, if you can find them.
     
  9. Blue-Adept

    Blue-Adept Active Member

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    Look at Get competing solar quotes online | EnergySage
    My solar array was at 7.275 kWh peak and generated over 1000 kWh per month from April to October. Then between 400 and 600 kWh per months in the winter. Pay off time was 6.5 Years at current electrical rates of $0.16 per kWh.
    The Pool and AC in the summer can use between 60-70 kWh per day.

    My new solar array in Michigan is a 10.675 kWh Peak. This will cover charging the Prius Prime and one more electric car in the future.
    Will get the next generation Tesla Power Wall next year.
    Remember just like gas is cheap now it will go up and so will electric costs.

    Blue