All those same concerns apply to the existing Tesla virtual power plant's (VPP) in California and Texas. People buy Tesla power-walls to have emergency power

All those same concerns apply to the existing Tesla virtual power plant's (VPP) in California and Texas. People buy Tesla power-walls to have emergency power that would be useless if their battery has been emptied by the VPP. And those PowerWalls are more expensive per kWh than a car is. The solution for the first is a simple power limit, typically 50%. So the VPP never drains the battery below 50%, leaving a nice margin for emergencies. The solution for the second is pricing: the VPP typically pays 50 cents per kWh, in return for about 0.1 cents/kWh of wear and tear on the battery.