Will a battery like a Tesla Powerwall last for 3-5 days?

Q: How much can a Tesla power wall store? Will it be enough for 3-5 days in case of an outage?

A: One Tesla Powerwall stores 14kWh of electricity. If you are using fossil fuels for heating then you are probably using about 20kWh a day to run all the lights and appliances in your house. If you are using heat pumps to heat or you are using AC in the summer then you are probably using about double this. Hence it is not practical to use a Powerwall (or any other type of battery) to run your entire house loads. However, this is not how most people use a Powerwall (see my blog post on uses of batteries). Most people use them as an alternative to using a diesel or propane back-up generator. So the battery or generator is powering an emergency panel which is usually the fridge, the furnace burner circuit and the circulating fans or pumps, plus some lights and a few outlets. This is typically under 1kW in total continuous load so a Powerwall can last about a day. This is usually enough to get you through a power outage. To last 3-5 days you would probably need 2 Powerwalls and to reduce the load on your batteries to just the lights, the wifi, a few outlets and the fridge.

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