It is also possible to combine modes. To do this, set a reserve percentage – this is the amount of energy your Powerwall will keep stored in case of an outage. First, select the mode you want to use (self-powered or advanced). After you have selected that mode, you will see the reserve for outages option. To adjust the reserve percentage, use the ‘+’ and ‘-’ icons. We recommend setting the reserve percentage to 20%.
For example, you can set a reserve of 20% for Backup-Only mode and select Self-Powered for the remaining 80%. This ensures that during an outage you have 20% of your Powerwall energy saved, while 80% of your Powerwall energy is used to power your home daily.
Selecting a reserve percentage of 100% is the same as being in Backup-Only. If 100% is selected, you will not receive Self-Powered or Time-Based Control benefits.
You can change modes as often as you like, but keep in mind that changes can take up to an hour to take effect. Learn more about each mode below. If you've selected the Self-Powered or Advanced modes, you will see the Reserve for Power Outages box below the mode you've selected:
While we can't tell you what your reserve should be set to, we can offer general guidelines that will help set you up for success. Opt for a higher reserve (50%-100%) if:
- your main priority is to ensure you never go without power
- you have critical equipment/appliances
- you have unplanned outages often
Opt for a lower reserve (20%-50%) if:
- your main goal is to lower your energy bill
- you rarely have unplanned outages
Remember, these are just guidelines and you should evaluate your circumstances to set a reserve that suits your needs. You are most protected from grid outages if you set the reserve to 100% (which is the equivalent of setting your battery to backup-only).
If you want to make sure that your system can run off-grid indefinitely, you should probably set your reserve so that you can run for around 12 hours off-grid. This will provide enough energy to power your home from sun down to sun up for the majority of the year. Here is a more technical way to consider your reserve for outages:
- If you have 2 powerwalls (27 kWh) and your home typically uses 1 kW, that means you would need 12 kWh to power your home for 12 hours (1 kW x 12 hrs = 12 kWh), which is 40% of your total battery capacity (12 kWh/27 kWh = .40 = 40%)
- If you have 2 powerwalls (27 kWh) and your home typically uses 1.5 kW, that means you would need 18 kWh to power your home for 12 hours (1.5 kW x 12 hrs = 18 kWh), which is 67% of your total battery capacity (12 kWh/27 kWh = .67 = 67%)
Generally, the formula to calculate a reserve is:
(runtime x average consumption) ÷ (# of Powerwalls x 13.5)
- Runtime is in hours
- Average consumption is in kW
Here's another example using this formula:
- Your runtime goal is 10 hours
- Your home's average consumption is 1.4 kW
- You have 3 Powerwalls
(10 hours x 1.4 kW) ÷ (3 x 13.5 kWh)
= 14 kWh ÷ 40.5 kWh
Keep in mind that your Powerwall system will power down when it reaches 10% (if your are running off-grid) to keep some energy in reserve to restart the solar in the morning, so you should add 10% to your calculation to ensure you have sufficient energy in reserve for an outage.