Time-Based Control User Guide
Time-Based Control maximizes savings by optimizing how your Powerwall provides power to your home. With Time-Based Control, your Powerwall will charge from and discharge to the grid at certain times to take advantage of changes to utility rates that occur throughout the day and season.
How Your System Will Work
When Time-Based Control mode is enabled, Powerwall uses a technique called energy arbitrage. Energy arbitrage allows Powerwall to store energy when energy prices are low and to sell that low-cost energy back to the grid when energy prices are higher. Powerwall optimizes your charging and discharging behavior for this arbitrage with an energy forecast tailored to your home.
Note: Grid charging and discharging are not available with all utilities. Refer to your Powerwall ‘Settings’ menu to show specific options available to your site.
What is Energy Forecasting and How Does It Work
Powerwall continuously runs an energy forecast, which means Powerwall learns and monitors the patterns of your seasonal energy use and solar production. When there is not enough sun available for your solar production and the forecast shows that you are likely to use energy at a high-cost time (peak period), your Powerwall prioritizes charging during a low-cost time (off-peak period) and discharging during a high-cost time (peak period). This may lead to instances where your Powerwall is idle, as it waits for an optimal opportunity to discharge, resulting in the use of solar or the grid to power your home. This method enables you to keep your energy costs down and to support the grid when energy imports are needed.
Solar Forecasting
Powerwall also uses a solar energy forecast produced using satellite weather data. This forecast is used to predict your solar energy production as the weather changes and also helps Powerwall make better decisions about when to charge and discharge while Time-Based Control mode is enabled. For example, if a forecast predicts significant cloudy weather tomorrow, your Powerwall may be programmed to charge earlier from the grid during a low-cost time period instead of normally charging from excess solar.
Note: Because this smart forecasting needs time to learn about your energy usage, Time-Based Control may not behave as you would expect for the first seven days following installation.
How Time-Based Control Looks in the Tesla App
When in Time-Based Control mode, you can refer to the visuals on the home screen of the Tesla app to better understand how your solar and Powerwall are operating throughout the day. The home screen of the Tesla app for Powerwall and solar displays a live view of power at your home, including solar, Powerwall, grid-use and home power consumption.
The following sequence of screenshots demonstrates a day for a typical Powerwall owner when using Time-Based Control mode. This example shows a home in the summer, where there is excess solar production to be stored in Powerwall for later exports to the grid during peak demand periods.
Note: The exact times and power numbers may differ for your home, but the same concepts still apply.
8 AM – Sunrise
The day starts in an off-peak period, when energy prices are low. Tesla Solar Inverter is now providing power to this home while Powerwall is charging from excess solar and storing energy for later use.
12 PM – Noon
Powerwall has now fully charged, so excess solar is exporting to the grid.
3 PM – Shoulder (Partial Peak)
This home's energy costs have partially increased during the shoulder period.
The homeowner has scheduled their air conditioning to start cooling their home before peak. Powerwall is programmed through energy forecasts to discharge energy to avoid higher grid costs. Powerwall isn’t exporting any excess energy to the grid yet.
If your home doesn’t have enough energy to cover all your home energy consumption, you may see Powerwall allow your home to use energy from the grid during the shoulder period.
5 PM – Peak
It's now peak period, where energy costs are the highest, so Powerwall is programmed to discharge to support this home's energy consumption. Any excess energy is exported to the grid to maximize economic value.
9 PM – Shoulder
Powerwall has now fully discharged down to the configured backup reserve after peak. It’s now programmed to allow some energy imported from the grid during this partial peak period, because this home’s consumption after the peak period is typically low.
If your home typically consumes a lot of energy after the peak period, and your shoulder period has high rates, Powerwall may be programmed to reserve energy to use towards powering your home during this period, too.
Midnight – Off-Peak
This home’s off-peak period starts at midnight. There’s a Tesla vehicle now charging based on set charging schedules to maximize the use of low-cost energy. Even if Powerwall had stored energy available, Powerwall would not be programmed to discharge, even to help charge the Tesla vehicle, during the off-peak period.
While Powerwall is not currently charging from the grid, if there is low excess solar production forecast for tomorrow, then Powerwall programming may initiate charging from the grid during this off-peak period to prepare for the next peak period.
Understanding Energy Flows
The Energy tab in the Tesla app allows you to review system production. You may select each reporting-meter separately or overlap data displayed by tapping the bar-icon next to ‘Day.’ By tapping ‘Day’ you can also change the timescale between ‘Month’, ‘Year’ and ‘Lifetime’ views.
The examples below show what energy usage history could look like for your home with grid and Powerwall to help understand the behavior of Time-Based Control. However, the actual results you see within the Tesla app may differ depending on your energy costs, home energy consumption and daily solar production.
The Energy Graph screenshots show solar and grid components. The grid view shows home usage as a positive value and grid exports as a negative value. The Powerwall view shows discharging to power your home or the grid as a positive value and charging from grid or solar as a negative value.
Time-Based Control: Summer Solar Production
The summer season brings high periods of solar production. Your Powerwall can be seen prioritizing charging from solar to offset peak usage, most often during off-peak.
Solar-Only Without Powerwall
Net Grid Use
During the day, solar is consumed by the home and any excess solar is sent to the grid. The grid covers the remainder of your home energy use, including grid imports during peak hours.
Solar-Only With Powerwall
Net Grid Use
Powerwall charges in the morning from high solar production, reducing your need to draw from the grid during evening peak periods.
Powerwall Discharge
Powerwall is seen below discharging to power your home and grid during the peak window. Stored energy is used to offset home consumption needs.
Time-Based Control: Winter Solar Production
With Time-Based Control, Powerwall always tries to maximize your home’s energy value, even during low winter seasonal solar production, which could be less than half of your solar production during the summer. During winter, Powerwall may need to charge more often from the grid to offset your home usage during peak periods, and this charging may occur at different times throughout the day than if it were during summer.
Powerwall takes advantage of low cost, off-peak energy to offset your home’s exposure to peak pricing. This gives you a level of flexibility to select utility rate plans with time-based periods with increased value for your system during all seasons – a value that traditional rate plans don’t offer.
Solar-Only With Powerwall
Net Grid Use
Powerwall charges from the grid and solar ahead of peak periods to offset forecasted home usage during peak periods. Powerwall does not discharge to the grid during peak.
Powerwall Discharge
With low solar production, Powerwall charges earlier in the day with low-cost energy from the grid and discharges to offset anticipated home energy consumption during peak periods.
