18 December

A few people asked me to say a bit more about home batteries. I’ll talk about the Tesla Powerwall 2, because it’s what we have, but there are multiple brands out there now. But the Powerwall is probably still the best battery on the market. Unlike solar panels, generally batteries at their current prices won’t pay for themselves inside their warranty period (usually 10 years). But it’s like buying a car, you can buy it for its functionality and not expect it to pay for itself too (though it will for us, in the 10 years). In our case we use nearly all our power mornings and evenings, so this way electricity generated during the day can be used when we get home at night. Batteries will also come down in price as the industry scales up, and government incentives may also increase. But there’s more to these. - You don‘t need solar to have a battery, it will charge from grid power alone too. So you could set it to charge at off peak rates overnight for example, and use that cheaper electricity the next day. - With solar panels, you can set it up to provide a backup if there are blackouts. People with only solar panels lose power in blackouts like everybody else, but a Powerwall lets you charge from your panels even if the grid is down, and use the panel power as well directly, and use that power during the blackout. - The software is very smart and very powerful. For example you can have the battery charging from both solar and the grid, and the battery will figure out by itself which is cheaper for you in your usage pattern, and charge from that. If you’re using a lot of power during the day, it might put off charging from your solar panels so you can use cheap solar for that usage, and then charge itself overnight at cheaper time of use rates. - It also has in-built ‘storm watch’, where it uses your current location and monitors the weather data for storms. If it sees one coming, it will automatically prioritise charging the battery, so you have power in reserve if there’s a blackout. - You can also let it calculate for you the best use of ‘time of use’ electricity rates (peak, off-peak, shoulder), and change its storing behaviour to make best use of the rates. - It has AI built in which learns the pattern of your household’s power use, and then optimises its storage to minimise costs of electricity to you.