When the Tesla Powerwall is in Self-Powered mode, the Powerwall charges from the excess solar energy generated during the day, and discharges to power to your home at night.

When solar is producing more power than the home is using, the Powerwall captures and stores that energy. When the home is consuming more energy than solar is providing, the Powerwall discharges enough energy to offset the home usage. If solar is producing more than the Powerwall can store, or the home needs more than the Powerwall can provide, the remainder is automatically exported or imported from the grid respectively.

This means you store the energy you generate from your solar array for your own use and further offset your electric bill. Of course this also means you have a power backup system during a power outage that can run for 10 – 12 hours overnight (depending on your usage) with one Powerwall.

One Tesla Powerwall has a capacity of 13.5kWh and you can add multiple Powerwalls to your system to match your usage needs and solar array output.