Device to charge electric vehicle battery from PV during grid outage and draw from EV battery at night?
MarieMcM
| Posted in Green Products and Materials on
Has anyone heard of a manufacturer developing a device that would allow a homeowner to charge their electric vehicle battery from their PV array during the day and draw from EV battery at night during a grid outage, basically using the vehicle battery as one would on a off grid PV/battery-array system?
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Replies
Marie,
There are several ways to do this. The easiest way is to create a PV array with a voltage that matches (actually, slightly exceeds) the voltage of your car's battery bank. Then you need a charge controller to be sure that your car battery isn't overcharged.
To use the electricity at night, you would need to purchase an off-grid inverter with an input DC voltage that matches the voltage of your car battery.
This set-up would work with conventional lead-acid batteries, although there are plenty of ways you could mess things up. If your car has lithium-ion batteries, you have to be much more careful. These batteries have very specific charging requirements. Tinker at your own risk.
Off topic, but do you happen to be the Marie McMahon I met at a deep energy retrofit open house in Worcester, MA last weekend? (It's a common enough name I suppose, but...)
Dana,
Yes, that was me. To learn more about the Deep Energy Retrofit measures check out:
https://www1.nationalgridus.com/DeepEnergyRetrofit-MA-RES
Great to meet you!
I've read about car manufacturer's promising this feature in plug-in hybrids as a way to balance loads across the grid. Electrical component manufacturers like Leviton are working on home chargers as well.
I find battery technology pretty interesting and thought the California Plug-in Alliance or somebody would be addressing your issue, but I didn't really see much. But you might find this article by Chelsea Sexton interesting. http://www.wired.com/opinion/2012/09/ev-plug-wars/ If you emailed her, she might be able to give you the scoop on this issue.
Martin -
I think you are underestimating the difficulty and danger of using PV with an EV battery pack as a back-up energy source in a 'backyard mechanic' type of configuration.
Generally speaking, EV packs operate at higher voltages than battery-PV systems since the power needed to accelerate cars would result in expensive hardware to deal with high currents at lower voltages. Fit EV, LEAF, and Tesla batteries are around 350vdc, Prius 200 vdc; most PV charge controllers are designed for lower voltages like 48vdc, though Midnite Solar does reach 120vdc.
Handling high voltage/high current DC wiring / connections also isn't without risk, and integrating a DC charging arrangement into a lithium battery management system (BMS) is no small matter, especially considering that improperly charging Li batteries that are being used in production EVs can result in thermal runaway / fire.
Perhaps one day there will be collaboration among EV manufacturers, PV inverter manufacturers, and the utility folks to work out a system that uses PV systems and EV batteries for grid storage / back-up power. But I think that will be a number of years from now, given what looks to me like a relatively small application window, high capital and O&M cost per unit, and a difficult coordination effort required to bring the parties together, especially the utility folks who inherited a grid that wasn't designed for many small distributed generators.
At this point, I think the Toyota hybrid system and a ~$100 12v inverter is better suited to being used for a small amount of back-up power and high efficiency transportation. Look up "Prius as back-up power" and find information regarding the fairly straightforward (though also not without risk) 12v configuration.
Or, if you are considering PV and frequently lose power, look at getting a battery backed-up system - I initially thought of the battery back-up on my grid tied PV system as something of a toy, but have come to see it's "utility" during the seemingly more frequent and longer grid outages.
Mark
Mark,
Like you, I advised Marie that lithium ion batteries are a whole other kettle of fish compared to good old lead acid batteries.
Plenty of electric car aficianados are still converting cars to electric propulsion using lead acid batteries. (Home Power magazine is a good source of articles on these conversions.) Lead acid batteries have several advantages -- they are cheap, they are available, they are rugged enough to charge with your PV system -- and several disadvantages (namely, their high weight to amp-hour ratio).
Marie- It was great to meet you too! (And Synergy-Dave, who I'd heard about several times through the project but not actually met until Saturday). I was the guy who steered Jeff toward the Nat'l Grid program and doing a DER on the project in the first place, and shepherded him through the process helping him understand the building-science aspects, vetting the HVAC proposals, find him the low-cost reclaimed foam, etc. ( It's a great program yer runnin' there ma'am- good on ya! )
Is the PV-Prius question of personal or professional interest (or both)? There have a number of wonks at the Rocky Mountain Institute with deep knowledge & interest working smart-grid tied EV issues. It wouldn't surprise me if somebody there could answer what the state of the existing hardware solutions are that might get you to a PV-Prius grid backup solution. I'm not sure exactly who the right insider to ping about it would be though. See: http://www.rmi.org/Autos
http://www.voltwerk.com/en/voltwerk/
and many more. Search the web.