Hacker News Reader

Comment by phkahler | Hacker News Reader

Did you know that the standard DC chargers communicate with the vehicle using PLC (Powerline communication) chips even though that communication is not over the high power conductors? I've always had the feeling the grid operators got that included because they thought they were going to communicate directly with the battery management system to control it as they wish. It never happened and now the standard is stupidly complex and they're still trying to use cars as storage without much consideration for what vehicle owners want.

Sure, offer variable rates. Offer interruptabke service. But stop wanting V2G, nobody actually wants it.

View on HN

>stop wanting V2G, nobody actually wants it.

Utilities really want V2G, so it's probably going to happen one way or another. It's probably less applicable to an individual homeowner, but commercial and other fleet operators are going to find this appealing at the right price.

For example: https://www.proterra.com/press-release/massachusetts-electri...

School buses seem like possibly the only real use case here, since they have a very seasonal usage pattern. For other commercial vehicles, the operators buy them to operate, not sit around and power the grid. When are they envisioned to be powering the grid?

Municipal buses are parked in depots overnight, right? That would kind of make sense - they already have to own the land for that, the vehicles already have to stay there in specific conditions, etc.

When are they supposed to charge if they're operating during the day and powering the grid at night?

I don't think that makes sense given that you'd probably want a full battery in the morning to start your day, and night-time is when you'd want to draw from the battery (assuming solar becomes a much bigger component of grid power).

It's possible I suppose that cities and school districts could have busses that have more capacity than they strictly need, and so it makes sense to use any surplus capacity for grid storage (while maintaining a reasonable margin in case a bus has to make an unexpected trip because some other bus had a flat tire or something).

Not just seasonal, the school busses are also not in use during the day while school is in session, which is unusual for mass transit busses.

Most buses do at least 4 trips a day, elementary then a middle or high school route in the morning, then repeat that in the afternoon.

There are only idle for 2 or 3 hours during the day.

(Field trips can add another usage in the middle of the day as well)

Yeah, but sequential charging will eliminate that and reduce the fleet owners costs.

Assuming V2G means Vehicle to Ground, this is something I would like to see for the following use-case.

I would like to use my car battery as a temporary home battery in the inevitable case of a grid outage. This opens the option to bring energy home from another location. Reduce or eliminates the need for a battery in a grid-tied house.

Am I crazy?

Edit: Granted that doesn't mean the energy company can use my car's battery at it's whim. I think compensation would be required and would actually make a lot of sense. It isn't like the electric company could build out a battery system for cheaper. It would need to be a higher compensation than to PV though. Batteries are more expensive and should be compensated as such.

V2G = vehicle to grid. It’s quite possible for this to operate as a backup battery, but like a Powerwall it requires extra “gateway” hardware to ensure that your house is isolated from the grid when the battery is discharging.

V2L (vehicle to load) is a simpler form that lets you power 115/230V appliances directly from the vehicle. Quite a few EVs (Hyundai, Ford, etc) already support V2L.

That's not crazy, it's actually a publicized optional feature on the F-150 Lightning, and the F-150 hybrid has an optional 240V 30A output that can be used as a home backup as well (although that'd be a bit more manual).

How could you plug a whole house into a 30A without immediately blowing the fuse?

Depends on your appliances. 30A @ 240V is 7.2 kW; which is plenty if you don't have AC or electric heating or cooling. If you do have those, you'll at least need to be sure not to run any two of those at once, if you can run them at all; you need to be careful with things like dryers, heaters, heat pumps, air conditioner, oven, stove, water heaters (especially tankless, but check your amps on an electric storage water heater too). Well pumps can be big loads too; mine is rated at 30A by itself, but many people have smaller pumps or utility water.

FWIW, the F-150 Lightning car to home option only goes up to 40A, which isn't that much more.

> I would like to use my car battery as a temporary home battery in the inevitable case of a grid outage. This opens the option to bring energy home from another location. Reduce or eliminates the need for a battery in a grid-tied house.

Question is "how long?" and "how much?"

Lets take a 100 kWh battery which matches a Tesla Model S battery option and is a nice number for doing conversions from.

https://shrinkthatfootprint.com/average-household-electricit...

> The recent figures, as of 2021, show that the average annual electricity consumption for a U.S. residential utility customer is 10,632 kilowatthours (kWh). If you divide that by 12 months, the average monthly electricity consumption is 886 kWh per month. What about in a single day? That would be 10,715 KWh divided by 365, or 29 kWh. Then the average daily electricity consumption is 29 kWh.

So, hypothetically, 100 kWh would give you 3 and almost 4 days. This can be improved by unplugging things that consume more power. The other part with this is a "once that 100 kWh is drained, you're stuck stuck."

You're going to still need something between the mains power and the circuit breaker box. I'm also going to note I don't know what rate it can discharge.

You might also want to look at a system that is a dedicated whole house battery backup ( https://www.zdnet.com/home-and-office/energy/best-home-batte... )

The zdnet article links to a Lowes worksheet - https://www.lowes.com/pdf/portable_generator_wattage_chart.p...

And from that, look at the "this is what we want" and the question of "generator or battery" becomes interesting.

Then consider also, you can get a 10,000 watt generator (that does a cutover in event of a power outage in 7 seconds) for about $3000 which can provide 10 kW at 40 amps.

Anyone expecting regular 4+ day outages is already going to have a generator. What people want is for the car which is already plugged into their house to kick in when the power goes out for an hour or two.

At an hour or two, that's ballpark 3kWh of power you'd need. There are battery backup solutions in this range that are $3k to $6k (that are frankly quite interesting.

Those have the instant on design so that if the power is lost to the house you have a few seconds and its back up and running.

But why would I waste an extra $5k and floor space in my garage if _I already have an EV that should be able to do this_.

You may not be at home during the power outage. This could impact things such as aquarium support, home security, or cold food storage.

You may need additional equipment or an upgrade to existing equipment to do the power outage cut over. To do this (and not just support an outlet from the vehicle), it is necessary to remove the house from the grid for the duration - suddenly changing phases can damage equipment (e.g. when the power comes back on). Additionally, if you were still connected to the grid, it would mean that your batteries are trying to support the portion of the entire grid (which it will fail badly at).

This also depends on the equipment that you currently have. Not everyone has a battery backup Tesla power wall. If you are plugging the car into 120v or 240v outlets, that doesn't have the circuitry to support isolation of the house from the grid after a power outage and the wiring for the 120v or 240v outlet isn't heavy enough to support the current draw for the rest of the house even if it was isolated.

You may also decide that trying to do it from the car, while possible, is a bad idea. https://electrek.co/2021/02/23/tesla-voids-your-warranty-pow... and https://www.tesla.com/sites/default/files/downloads/tesla-ne...

> This New Vehicle Limited Warranty does not cover any vehicle damage or malfunction directly or indirectly caused by, due to or resulting from normal wear or deterioration, abuse, misuse, negligence, accident, improper maintenance, operation, storage or transport, including, but not limited to, any of the following:

> ...

> Using the vehicle as a stationary power source

There's two ways to power your house off your car battery. You could have your car act as a mobile electrical outlet that you can run extension cords off of to plug things into, or you could have it tie in directly with the wiring of the house so all your electrical outlets work.

The former is pretty straightforward. The latter would need a lot of electrical upgrades to the house. (I'd expect you'd need to do about the same thing that people do when they get solar, which is to replace the meter with something that can measure power flows in both directions, and is smart enough to disconnect the solar panels from upstream power when the power goes out, so you don't electrocute people trying to fix the power lines. If you don't have a local battery, that means basically turning the solar system off in a power failure.)

If you aren't planning on selling storage capacity to your local utility, maybe all you really need is an automatic shutoff switch to disconnect your house from the grid when the power goes out.

Either way you'd need some sort of power inverter to convert DC to AC. That could be built into the car, or it could be attached to the house.

it is called V2H (to Home)

these are already available.

Pay the right price for V2G energy supplied and a lot of people will want it.

Plenty of people are willing to drive 200 miles of Uber as a second job. V2G is a lot more appealing than that I think.

Reply on news.ycombinator.com