How feasible/costly is solar roof (house) charging for the Model S. ?

Panoz

I'm new, it's late, sorry I haven't searched this forum.

I'm a wannabe Model S owner and am wondering how practical it is to charge a Model S using rooftop solar panels - rooftop as in house/garage, not car. Has anyone done a payback calculation? I live in sunny Colorado, and think solar charging would be as practical here as anywhere.I'm curious if many Tesla owners have gone solar on their charging options.

I did see one set of photos on this site showing an entire garage roof of solar panels...I wonder what that cost and how it works. You have to have some sort of batteries to store the collected energy, correct?

scottch

There are probably a million sites on the web devoted to solar power, but to answer your questions:
1) Payback -- depends very highly on your usage patterns (hourly as well as monthly) as well as your utility rates. There is honestly no good way to accurately calculate your payback without knowing those two things, and the first ( your hourly usage pattern) may not be trackable without "smart metering". A local solar installer will be able to give you some estimate figures, although they may not be unbiased.

2) You do not need batteries if you are on a reliable grid connection. Batteries are expensive, require charging electronics, and need to be maintained, so they're mostly for off-grid homes. Most suburban homeowners just sell power to the grid during the day and buy it back at night. If your utility has "time of use" rate structure, this is perfect for generating solar by day and charging EVs at night.

3) I was quoted by a contractor that it costs roughly $4-5/watt installed for a system of at least 3kW. Materials are about half of that. A 3kW system is typical for a residence, but charging an EV will eat up most of that power. I believe there is a 30% federal tax credit for solar installation, so the net cost is less.

nwdiver93

I own a house in Bremerton, WA (Worst place for solar) my 8.4kw system there will pay for itself in ~8 years

I live in Eunice, NM (Best place for solar) my 8.4kw system here will pay for itself in ~5 years

Some great resources:
http://www.dsireusa.org/
http://www.nrel.gov/gis/solar.html

Dirt cheap solar:
http://www.sunelec.com/

and of course:
http://www.solarcity.com/

reitmanr

We have had solar here in Menlo Park for many years. Last year our total electric bill was $15 plus mthly service fee. It used to be hundreds of dollars. We added 5 new panels which should cover our MS charge expenses. Obviously it depends on how much energy you use, and we use the Superchargers when ever possible, especially on trips south, stopping at the Gilroy SC station. We have been motivated to use renewable energy as a matter of national security and to do what we can to stop global warming. Just one small piece of the problem. Good luck on your journey.

Panoz

Thank you all for your responses. Let me be specific - I'm curious about solar panels ONLY to recharge a Tesla. You would, in fact, need batteries to store captured solar energy during the day so that you could charge your car at night when you're home.

Anyone thinking of doing that?

SonomaDriver

Solar systems in a residential setting won't be powerful enough to entirely take up the charge demand for your car. With a single charger, 10kWh is needed. Most systems are smaller than 10kWh.

We had a system installed by Vivant Solar. They pay the costs of install, maintain the system etc. The deal is you buy the power the roof produces (less the 20% our local utility must be allowed to sell to you). It's an 8.1kWh system and is more than enough to power our home. Adding an EV will result in charging from the grid but you'd still save $$.

I haven't convinced the wife we should get a $80k Tesla yet but we are set up to charge an EV for a lot less cost than off the PG&E grid.

Panoz

So no one is just going solar to just charge the car? I guess all the responses center around NOT having an energy storage system to charge the car at night. They seem to focus on using solar during the day to defray your overall electricity costs, thereby reducing the grid demands for the car. Unless you work at home and use electricity during the day, a storage system would add to the payback time and have its own maintenance issues, I would assume.

frmercado

What you are asking doesn't make any sense at all. The only reason to set up a system like that would be if you lived off the grid in the middle of nowhere, mainly because you couldn't sell the electricity back to the utility company so you would be forced to store it. You would need a giant solar array plus pretty big battery storage capacity.

I don't think you will find anyone who is planning that in here, unless, maybe, if they live in the middle of nowhere, and I don't think the Model S would be the ideal vehicle to have under those circumstances.

Vawlkus

Expenses plus upkeep argue against a grid isolated system, for now at least.

mdemetri

Panoz

What you need is called 'net metering' with a "time of use plan". The grid is the largest possible energy storage system you can have. You sell your electricity generated from solar during the day to the grid and charge the car at night (when there is no solar) by buying back from the grid. As electricity is much more expensive during the day then at night, you can make money if you have a time of use plan. To illustrate the point, here is a comment I made on another thread:

"... lets say during peak time (10am-6pm) I over-generate 30 kwh above baseline and during off peak I use 30 kwh above baseline (in reality there are three timed rates, but for simplicity I will use just two: peak and off-peak). Using revised SCE summer tier two rates (which kick in after baseline) we get -30 x 0.47 per kwh gives -$14.1 for peak time and 30 x 0.09 per kwh gives $2.7 for a net -$11.4. Multiple this by 30 days and you get -$342!!! Thus, even though there was no net generation/use, you still make significant positive cash flow. This is because you are selling high and buying low. Note that the math is more complicated than this and needs to account for the basline usage, but this is essentially the way it works."

I hope this helps.

kilimats

Elon tweeted few weeks back, solarcity panels will cover many times what model S consumes in a year

scottch

This has probably been done on this site already, but lets do some math, assuming 12,000 miles a year driven, 0.35 kWh/mile, and 5.5 hours of insolation per day (Avg USA for fixed roof panel, accounting for weather, and daily and seasonal solar angles)

12,000 miles/year X 0.35 kWh/mile = 4200 kWh/year , or 11.5 kWh/day consumed by your car

At 5.5 hours a day of insolation, you would need a system of 2.1 kW net rated power to generate 11.5 kWh.

2 -4 kW systems are typical roof system in the suburbs.

Your mileage may vary.