Tesla is launching the “Powerwall”, a high capacity battery for powering a home. It’s designed to work with mains (household line) power, solar panels, or a mix of the two.
The basics of Powerwall are nothing new: each battery unit will actually be made up of multiple lithium-ion batteries of the type Tesla already uses to power its electric vehicles.
Instead it says the difference comes in the software used to control the charging and draining of the battery. It believes there’ll be three main uses for the batteries, depending on different home setups. The first is as a simple backup to protect against outages.
The second is to store surplus electricity generated by solar panels so that it can be used when needed. To be fair, several other firms have offered battery solutions to deal with the problem that the hours when you get the most energy from a solar panel are often the hours you least need to use power, either because you are out of the house during the day, or because you don’t need electric lighting. The question is whether Tesla can do this better than existing setups.
The third use Tesla suggests is for householders who can get energy plans where the price is cheaper during off-peak periods, something that power companies offer to spread their own load. Tesla’s idea is that users could charge the battery at the cheap rate and use it to run appliances during peak hours, thus cutting power bills. The question here is whether its setup proves as reliable and low-maintenance as it plans.
The Powerwall will come in two forms: a $3,000 7kWh version that’s optimised for daily use (storing from solar or peak-hour mains to use later in the day) and a $3,500 10kWh version optimized to use as a backup, meaning it needs to store the electricity for longer before use.
To put that into context, 2010 figures from the World Energy Council pegged the average US household as using 11,698 kWh a year, or 32kWh a day. That means there’s certainly some scope to use the batteries in the ways Tesla describes, depending on your normal pattern of electrical consumption during the day.
However, it does mean that, contrary to some excited media reaction, even using these batteries to go off-grid completely would still have to involve significant energy use reductions compared to an average household. That’s certainly doable, particularly in a smaller home: it’s just that Tesla hasn’t found a magic solution to making that trade-off.