Keep in mind that a traditional 100 amp service for the house can theoretically provide 100 amps * 240 volts == 24,000 watts == 24 kilowatts, instantaneously. You multiply by 240V because you have two input legs, each providing 120V service to ground, on separate phases.
That’s why whole-home generators are typically sized at 24kW, unless there are some circuits you’re not going to power while you are operating on generator.
Now, most homes don’t use that much power 24x7. Most homes use a lot less than that. But, they need to provide that much power, in case all the electric devices inside the house are all running at the same time. And in Texas, newer homes usually come with 200 amp service, because HVAC draws so much, plus electric hot water, electric cooktops, etc….
So, to get a real idea of the amount of power you need from batteries, you need to look at how much power your house actually requires on those critical circuits, on the worst day. If you can’t deliver that much peak power, then you need to increase the size of your inverter stack, or you need to reduce the number of critical circuits you’re powering. Most battery solutions for powering a house will give you some options here, and then combine all the output power from each stack into a smart breaker box.
Then you also need to look at how much total power you pull over a full day. That’s your minimum kWh rating that you need from the battery pack. And again, most whole-home type battery solutions will give you multiple options here. These are companies like Bluetti, Anker, EcoFlow, etc….
For example, the Anker SOLIX E10 Power Dock can do a max of 7.6kW sustained and 10kW turbo output with 12kWh-90kWh storage, depending on how many battery units you connect to that inverter. But to get 20kW total turbo output, you’d need two inverter stacks, each with their own chain of batteries. And you would need their Smart Power Dock to combine those two stacks. Each power dock can handle a total of three input stacks, for a total maximum of 22.8kW combined max sustained output, with 30kW combined turbo output. That gets you their 200-amp equivalent service.
In comparison a Tesla Powerwall does about 11.5kW maximum output for one unit, but has much less battery capacity per unit (only 13.5kWh). And you would either need to trim down your critical loads to get under that 11.5kW maximum output, or have a pair of such units that each talk to their gateway device. And the Tesla Powerwall doesn’t have any additional battery units that I know of that you can connect to that same inverter. So, you would end up buying a lot more inverters if you want longer runtimes with Tesla.
Either way, you can pair these with solar panels on your roof, to get either total or partial fill of these units from the sun, and the rest from the grid. The same is true for all of the major whole-house battery backup units I know of.
Now, if the batteries in your car can sustain 100kWh of power, and you’re using 30kWh per day, that would last you just over three days before you’re completely drained. Then you would have to look at the maximum amount of instantaneous power that the vehicle can provide. Is that just 10kW? Can it do 20kW? 30kW? Note that this number is usually a lot lower than the rate that the vehicle can charge at, when it is at a supercharger facility. Usually, they can suck down the power a lot faster than they can push it up. And many BEVs today are still pretty slow at being charged up.
I look forward to the day when all BEVs can charge quickly at high voltage, and also discharge V2L and V2H at high rates of speed, with large battery capacities. But I think it’s going to be a while before we get there.
Meanwhile, I feel like I need to have the power service at my house upgraded to 200 amp, before I can realistically buy a BEV. We just don’t have the spare power capacity available to us to be able to charge the vehicle at reasonable speeds, which would require a level 2 charger at home.