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Comment by crdoconnor | Hacker News Reader

Powerwall doesn't make a lot of sense. It's about 30-40% more expensive than other batteries that were on the market when it came out.

And, while Tesla cars might be bragworthy and worthy of showing off to your friends, house batteries are not. All that really matters is cost and efficiency.

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If you already have a Tesla you effectively have a powerwall too. All you need to do is plug it into your home circuit and store whatever energy you want. If the car isn't moving it's just a huge battery. The extra hardware required to convert the energy in the batteries back to household power is pretty trivial, and it shares major characteristics/components with the electronics in the power module of the inverter driving the electric motor in the car.

I don't see the point of that either. It'll just wear out your expensive battery more quickly. And to what end?

One thing that doesn't wear out your battery at all is a smart controller that charges your battery when energy is cheapest. So all that excess night-time wind energy can be sopped up, not to mention that day-time excess solar energy for cars that plug in at work.

It's like storage, only it costs almost nothing: all you need is a lot of cars with overly-large batteries plugged in, and a little predictive software.

In addition to the sibling comment, I'll add that I don't want to have think about whether my EV is at 100% or 30% despite it being connected to the charger for the last 12 hours since I got home from work the day before.

Also, existing EV owners don't have an EV <> Household bidirectional interface connected, and I'm not aware of any serious vehicle manufacturers claiming they will do this. Probably because if the battery has an X kilometer / Y year warranty, how does using it as a household power reserve affect that warranty?

Obviously if you need a full tank you'd unplug your house from the car. But the point of the Tesla car is that, like a gas car, 30% tank is enough for 99% of the days of the year.

An X Km warranty is just an X KWHr warranty in different units.

> I'm not aware of any serious vehicle manufacturers claiming they will do this.

Here in Japan, Nissan has been advertising the capability on TV, and the equipment is available for general sale

http://ev.nissan.co.jp/LEAFTOHOME/index.html

Some Tesla cars have more capacity built in than you can use. You can unlock the extra capacity by paying more. They could use that as distributed storage.

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