Sir:
I had an epiphany a few years ago when I first viewed “Who Killed the Electric Car?” Since then, I’ve acquired several cars converted to electric and a Nissan Leaf. We bought our last tank of petroleum fuel in May of 2011.
Recently, I’ve been pondering how the electric cars might be used as a backup source of electric power. The battery packs of the conversions are readily accessible and can provide almost 100 kwh of energy. The Leaf’s battery is not accessible at this time. Inverters that use the car’s DC voltage (120-156v) as input are available but pretty rare. Ideally, I would like to find a source for a PV system where the car batteries could temporarily replace the PV panels in driving the inverter.
[JWR Adds: Nearly all home PV power systems have the inverter connected to a battery bank, rather than directly to PV panels. This eliminates the peaks and valleys of production caused by varying cloud cover.]
A higher cost solution would be to have two inverters, one for the PV panels and one for the car batteries. That would allow me to use electricity while the sun shines to charge cars as well as meet other demands and then supply energy from the car batteries when the sun isn’t shining. Commonly available battery backed PV systems use 24-to-36 volt battery banks which are charged from PV panels [through a charge controller]. My car batteries need to be charged through charg[ing transform]ers that have 220 VAC input. That is, the charger’s input must come through a transformer.
Our electric utility power is pretty reliable; I don’t think I have seen it down more than two hours. ~1 hour outages only occur once every year or two. We might see outages of a few minutes several times a year.
The primary function of a PV system would be to pump power into the grid. That is how it would be used 99% (or 99.99%) of the time. At this time, PV is not cost effective in my region. With electric utility cost of 10 cents to 11 cents per kwh, it takes many decades to pay for a PV system. So, I would have to justify PV cost with emergency or grid-down functionality.
I’ve been speaking here of lithium iron phosphate batteries here. When treated well, they are far more cost effective, long-lived, and trouble-free than lead-acid batteries.
My most recent electric vehicle purchase was a Prodeco bicycle. A lithium battery “ebike”, such as the Prodeco, is a great low maintenance people mover. Range is more than 10 miles without peddling. A great asset for when petroleum fuel is not available.
JWR Replies: Several of my consulting clients have Bad Boy Buggy electric ATVs. In addition to their quiet operation and utility as farm and ranch vehicles, they also provide a very portable battery bank. (They have eight large 6-volt deep cycle batteries.)