Newbie wanting to size a panel array and battery bank to charge my electric car, and....

Re: Newbie wanting to size a panel array and battery bank to charge my electric car, and

Welcome to the forum.

A few people here have electric vehicles 'charged from solar'. I put that in quotes because it's not quite as simple as it seems.

For one thing, using panels to charge a battery and then draining that battery to charge your electric vehicle is very inefficient. Charging the car directly from panels is much more efficient, but chances are the car is not at home when those panels are making power, yes?

Therein lies the standard solution: install enough grid-tie PV to offset the charging demands of the car when it is at home. During the day the panels sell power to the grid, and at night the car charges from the grid. In other words the grid is your battery.

Otherwise you end up needing a lot of PV and a big battery because you have to make up for the losses inherent in charging a battery and then using it to charge another battery.

Re: Newbie wanting to size a panel array and battery bank to charge my electric car, and

Seventeen cents per kW hour is really cheap compared to what off-grid power costs. About one fifth as much.

605 kW hours in a month is quite a bit, but not unrealistic. About 20 kW hours per day. In order to produce that with PV you'd need about 7 kW array and 4 hours of good sun (every day). For an example of how it works out try PV Watts with information relevant to your location: http://www.nrel.gov/rredc/pvwatts/

That would be for grid-tie. If you take the same power requirements off-grid it needs to be larger and it becomes much more expensive due to the battery need. For example 20 kW hours per day looks like this:

20,000 Watt hours / 48 Volts = 417 Amp hours used. Multiply by 4 for 25% DOD limit = 1,668 Amp hour 48 Volt battery bank. That is not small or cheap. To recharge it you'd need 166 Amps of current, meaning two charge controllers connected to 10,348 Watts of array. Consider that those panels would be at $1 per Watt if you're lucky: there's $10,000 right there. The two controllers will eat up another $1,200. The huge battery bank about another $6,000. The inverter will need to be a pretty large one too, like a Radian 8kW for another $4,000. Add in the hardware, wiring, and miscellaneous and you are in the $25,000 range. That's enough to buy 147,058 kW hours from your utility, or 20 years worth of power. Trouble is that's about the lifespan of the solar equipment, not including having to replace the batteries two or three times.

Not very economical is it?

Oh tax incentives and such can make it better, but on the whole off-grid power just isn't cheap and doesn't make sense in most places. Grid-tie can be had for a fraction of the cost, but even so against your low utility rate it's pretty expensive.

As for how much you need for charging your car I couldn't say as I don't know what the charging needs of the car are.

BTW one fellow here has done an interesting job of adapting his Prius to power an inverter for power outages: the car operates as an auto-start generator and battery bank to power the inverter which runs the critical loads in time of need.