Hacker News Reader

Comment by eloff | Hacker News Reader

I would like to see the ability to use a Tesla as a Powerwall. A backup battery for the house of the grid goes down, and a way to smooth demand so I draw more on the grid when the price is low and less when the price is high. That of course would depend on your electric company, if they charge consumers variable rates.

It would reduce the life of the batteries, but it would also save needing a Powerwall or a generator. It might complement rooftop solar well.

It would be less useful if you use the vehicle to commute and it's parked at work all day.

My parents live in a remote area and suffer frequent power outages. They'd love something like that.

View on HN

The cybertruck should be able to do this "out of the box". It has a 240V output (though they did not reveal the amperage, it must be at least 30), so your house should not care whether it's running off a small generator or the truck, nor should the truck care whether it's running a tool or a house.

People have tried to estimate the truck's battery size from it's drag coefficient (via it's watts per mile consumption) and it seems the 500 miles version should have like 150-160kWh of storage. You can run your house for a long time on that.

150kWh it my my montly consumption for my apartment. Sure, you use more on a house, but would be more than enough for a serious outage in the country side (like my parents have in the winter, lasting even 2-3 days)

Look at the software defined intelligent power inversion pioneered by Enphase (https://enphase.com). These systems will ultimately be the lynchpin of the dream-world you describe, which I very much believe will come to pass. You'll even be able to connect to neighbors.

Disclosure: we're investors and I'm on the board.

Fantastic. The thing is a 100kwh in a car battery is a fantastic amount of power - our condo ranges from 50kwh to 125kwh usage per month.

I would love if my smart charger could be wired with a transfer for switch or similar to send 40Amps back into the house. This would make a major difference in the decision to buy an EV.

Imagine also load balancing if, say, 3 of your immediate neighbors have EVs or home batteries.

Nissan's Leaf has the ability to do this (V2G or V2H) and the devices needed to enable it are starting to become available[1]. It's a shame they're not more widespread though. A lot of 1st generation EVs are available secondhand for much less than the cost of a Tesla PowerWall, despite larger batteries.

[1] https://www.greencarreports.com/news/1127590_nissan-leaf-as-...

The issue I have with it is that you can find yourself with an empty battery when you need your car the most.

Not as much a problem if you also have a gas car, something that many people recommend if you have an EV. Many families have two cars anyways.

But otherwise, maybe if with a mode that lets you use just a small part of the battery capacity. For example keep at least 50% charge, do not charge over 75%, use the 50%-75% range as a buffer. Lithium batteries last a while when used in that limited range, full charges and full discharges is what tends to wear them out. And on a Tesla, 50% is still plenty of range.

You can buy a 1000W inverter for < $100 and use that with a normal car. [1] A true sine wave inverter is more than double that.

Presumably this is very inefficient, but a lot of power needs can be satisfied by running it for shorter periods of time to run compressors on refrigerators and charge batteries. I would imagine this should work very efficiently for a Tesla as long as the computer doesn't stop you.

In either case though you want to have a full tank/battery. If your Tesla is low it won't help much, so although it would work really well most of the time it would be difficult to rely on it. In a remote area it is usually relatively safe and relatively cheap to store some gallons of extra gas.

Perhaps what they are hinting at here about having cheaper recycled batteries (not in cars) will make more sense for these kinds of applications: cheaper powerwalls. But I agree it would be nice to be able to put power back into a power wall from a Tesla. Particularly given that the default setting will assume a temporary outage and start charging the Tesla from the powerwall.

[1] https://www.consumerreports.org/cro/2012/02/can-a-pint-sized...

200$ for a 1000W pure sine wave inverter? That's a ripoff. Motor controllers are essentially three-phase variable frequency intelligent inverters, and you can get a 2340W ESC for less than 60$.

You can definitely find this for a bit < $200, its just kind of hard to find a trustworthy brand (maybe you know of one)? I think these may be reasonable markups to actually run a business with a finished safe product, to pay employees, ship these things, and offer warranties and handle returns.

Kelly controller is a pretty reputable brand.

For example, here is a reseller [0] that sells a 72V 120A (8640W peak, 4320W continuous) three phase pure sine wave motor controller for 126$, with warranties, logistics (plus shipping). I'm fairly certain that you could get a similar, or even lower price for only two phases and a fixed frequency at the same wattage. If you really want to use them as inverters though, they are programmable so you could set a fixed frequency, though I don't recommend it. I've heard of people running some other models at 120V, but I really don't recommend it :)

In any case, I think this shows that a 4320W inverter can be built and sold profitably for a lot less than 200$, if a 4320W+ three phase multi-frequency programmable inverter can be.

I should that 4320W is with passive cooling. With active cooling (from sticking a fan in the box to water cooling) you can get away with >12kW continuously.

[0]: https://www.aliexpress.com/item/32892079337.html?spm=a2g0o.p...

The problem is your alternator is going to be pissed off if it's running at idle speeds all day, and still trying to keep the battery charged while you're pulling an 80 amp load on it. Most alternators are designed to operate above idle speeds. Sure they can work at idle, and it might get you by in a short emergency... but it's probably not a great idea.

Wonder if it would work a lot better on a hybrid with a big beefy motor-generator instead of an alternator.

It does.

http://priups.com/others/index.html

https://forum.solar-electric.com/discussion/11546/using-a-pr...

https://www.bizjournals.com/boston/stories/2008/12/22/daily2...

I would like to see a general purpose DC-DC connector that could be used to hook up your car to other battery power equipment. It would be nice to be able to recharge your battery powered lawn mower / string trimmer / chainsaw without having to go through an AC/DC converter.

In a perfect world it would be great to be able to share your juice with another car. This would come in really handy for places that you aren't familiar with or don't have great charging station coverage. Imagine your on vacation and your hotel doesn't have charging; borrow some charge from a fellow traveler. Or your on a road trip and see a fellow electric car owner stranded at a rest stop; slip them some of your charge.

It might make more sense to get a Powerwall if it becomes cheap enough. The batteries that go into a Tesla car are the same batteries that go into a Powerwall. This implies that improvements in battery cost posited by the article will mostly likely apply to Powerwalls as well as to cars.

A Powerwall would be always available. What if your car isn't there when there is a power outage? What if your car isn't there when you are collecting solar energy? You wouldn't have to lose power when you drive your car during a power outage.

A Tesla with this ability could definitely serve as a supplement but the cheaper batteries are, the more it makes sense to have one permanently wired to your house. This ability would be an interim technology assuming battery costs go down enough.

I think it's too expensive to justify currently. I hope that changes.

Using the Tesla is interesting if you've already purchased it. It has the drawbacks you mention.

Renault is experimenting that with the Zoé. Probably others manufacturers are doing it as well.

https://easyelectriclife.groupe.renault.com/en/outlook/energ...

For occasional power outages, it definitely makes sense. But what toll that would take on the batteries?

Not much.

As car’s start hitting 300+ mile ranges battery lifespan is less about charge cycles than physical age. ~800+ charges X 300 miles = 240,000 miles.

Absolutely - the question is if it makes sense as a business move for Tesla, it would basically destroy the Powerwall as a product (though I am skeptical they sell a lot of them, compartively). And if they could also overcome the regulatory hurdles, electrical code is fairly strict (for good reason!) I have a roof full of PV I'd love to use during power outages, and a PHEV in the driveway I'd happily swap for a Tesla if they could connect the dots.

It would probably increase warranty replacement and be bad PR for Tesla batteries when capacity takes a hit. But yeah, it would be great.

Reply on news.ycombinator.com