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Back of napkin PV payback period [NL]

Discussion in 'Energy, Environment, and Policy' started by keys, Jul 6, 2013.

  1. keys

    keys Member

    Jan 2, 2013
    The Netherlands
    #1 keys, Jul 6, 2013
    Last edited: Jul 6, 2013
    [Thread is in English for the general public, but I only regard Dutch prices]


    This might be already discussed heavily, but I just realized installing solar panels and having a model S is even more economical than I previously assumed. Nothing special, just wanted to share.

    When doing calculations on the so called payback period of solar PV, you are always referred to offsetting your domestic energy consumption. When I click Google's first hit using some obvious terms, I arrive at a website that offers a system delivering 4500 kWh yearly for an all-in cost of 7200 euro (ex install). Assuming I offset 100% and using an energy price of about 0.25 euro per kWh [source says even higher but I pay less actually], I have made back my full purchase after about 6.5 years. There are some purchase refund subsidies but I prefer to disregard those (they only save you about 6 months paypack anyway).

    Well, that's great. But, assuming I have a Model S, or any other electric car, and I am able to fully offset its energy consumption using my solar array, the napkin calculation is as follows. A car the size of the Model S would do about 12 km/L (that's about 28mpg, 'muricans :p) if you're lucky. That means you would be paying about 0.14 euro per km at a gas price of 1.70 euro per L (yes we are actually paying almost 9 dollars a gallon). Now assuming I use all of that 4500 I will generate on driving, that allows me to drive about 20000 km [I used this thread]: 350 Wh/mi].

    Now using that same 0.14 euro per km, I would have paid 2800 euro per year on driving, yielding a payback period of about 2.5 years.

    Conclusion: If you're spending 80k or so on a Model S, don't be an idiot and buy some solar PV with it ;). Because after those 2.5 years, you're driving for freeeeee.

    Critique requested and appriciated :)

    --edit-- Oops, used 1.60 for gas...

  2. Adm

    Adm Active Member

    Jun 7, 2010
    The Netherlands
    You've missed the charging losses in your calculations. Elon Musk has said the 3-phase charger will actually be a little bit more efficient than the US version, but I'd say your safe using 20%. Others please correct me if I am wrong.

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