How many kWh have I to produce with PV for 15'000 km/year

Probably a system rated at somewhere around 3kw to 3.5 kw should be enough to notionally power a Model S for 15,000kms / yr, allowing for losses in generation and charging.

This will vary slightly depending on many minor factors, from your driving style, to levels of solar insolation in your area.

Someone somewhere said that the charger is probably 85% efficient. Plugging in every night will not lead to more losses than plugging in less often. Use of A/C and heat will consume some energy. And if you have very hot summers, battery cooling during charging may use more. I'd suspect that if you used an overall 75% efficiency figure you'd be close. Then maybe 4,5 km/kWh? So very conservatively maybe 3 km per kWh generated? So for 15.000 km you'd want to generate 5.000 kWh.

I don't really know if my assumptions are valid, but as a first working estimate I'm comfortable with that. Of course, terrain and driving style will affect range. You've got lots of mountains over there.

Maybe you could ask a Roadster owner how many km per Wh they get in your terrain, and then assume that the heavier Model S will be 25% (???) less efficient. The Roadster tells you how much charge it takes each time, so that includes all charging losses as well as heat and/or A/C.

mdol said:

Hi there,

I'm planning to install some square meters of PV on my house to produce the electricity I'll need for my Model S (I know I have time to do that...). I plan to inject it in the grid. It's just a matter of philosophy : inject in the grid what I will use to drive.

Has somebody any idea of how many kWh I have to plan in one year if I'll do 15'000km ? I now the kWh/kilometer for the S but that theorical. If I plug it every night I think it will need more kWh... and for sure, there will be some losses somewhere...

Thanks for your help !

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Depending on how you drive and how good your sun exposure, 2 - 3kW should do it.

On the Model S Facts | Tesla Motors page, Tesla advises on dimensioning solar for Model S:

If you’re interested in installing a home solar system to charge your Tesla, we recommend working with a local solar installer to develop and install a system that supports your total daily energy demand. Assume average energy usage per mile is approximately 300Wh/mile (188Wh/km). Multiply 300Wh/mile (188Wh/km) by your daily driving distance to estimate your daily vehicle energy consumption.

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These number seem to include charging losses. In other words, it is the electricity consumption for wall-to-wheel. For 15,000km/year that gives 2820kWh. Neuchâtel has an insolation of ~1100kWh/year and square meter (source: Solar Bildergalerie - Strahlungskarten und Sonneneinstrahlung - Strahlungskarte-schweiz) which, after my experience, is good for a yield of 1000kWh for any installed kWpeak of an ideally oriented rooftop solar system. 3kWpeak system size seems OK. Snow cover in the months Januar to March can reduce yield up to 20%. I'd recommend a system of 4kWpeak and with one solar inverter. Or maybe a micro inverter system. Get some quotes from local installers and talk to some of their customers.

I've installed a system om my house last week producing 3800 Wp, which means about 3500 kWh per year. This will be what I need to drive my Fisker Karma for about 11,000 to 12,000 km per year.

A charge of 20 kWh at this moment gives me about 60 km of range, so 1 kWh for every 3 km. I think the Model S will definitely get more km per kWh, as the car is much lighter than a Karma (which weighs 2,400 kg) and has a better cw-rating. I'm guessing 4 km for every kWh at least.

So that would mean your pv-installation has to produce about 4,500 kWh for the 18,000 km you want to drive each year. Panels with a capacity of 5.000 Wp should be able to produce that in Switzerland, which I believe is somewhat sunnier than The Netherlands. Well, at least every time I'm climbing mountains in Wallis

It is all well and nice calculating the required nominal PV generator output. But have you considered the faint possibility that you might add another plug in car in the years to come? Might be "just" a hybrid, but... Or the kids come for a visit over the weekend later on and want a plug.
My point is, it's way cheaper to install 6kW now than to do 2 times a kW array, even with module prices dropping.
I plastered my complete roof with solar and am compensating for the electricity used since the house was erected. With a little luck my balance will be zero early next year, when my Model S should arrive. From then on, it will be interesting to see if I can keep my energy balance (PV minus residential+EV) on the plus side.

Honestly, everyone is guessing. The critical factor is the angle and pitch of your roof relative to the sun and your year-round average of sunshine hours. I have 190W panels on my roof and the best one produced 328.6kWh last year while the worst one (which catches shade from a palm tree at certain times of the day) produced 211.1kWh. That shows what the difference can be.

My advice is find a good local installer, talk it through with them and have the engineer explain his calculations.

BTW: I live in sunny Florida, your sunshine hours may vary.:smile: