Powerwall's Time-Based Control: what it is
Time-Based Control is Tesla's scheduling mode for the Powerwall. Instead of letting the battery respond reactively to home consumption demands, Time-Based Control lets you specify exactly when the Powerwall should charge from the grid and when it should reserve its stored energy for home use.
You set a preferred charging window, typically overnight. You set a backup reserve percentage, the minimum charge level the Powerwall should always maintain for emergencies. You set a discharge period, the window during which the Powerwall should actively supply the home and avoid grid draw. Once configured, these settings run automatically every day.
The key insight: Time-Based Control does not require dynamic price data from Octopus. It simply follows the time windows you give it. Your job is to align those windows with Agile's cheapest and most expensive periods. Once aligned, the Powerwall executes the strategy without you needing to do anything further.
Configuring Powerwall for Agile pricing: step by step
The initial configuration takes approximately five minutes in the Tesla app. Here is the exact process.
Step 1: Open the Tesla app on your smartphone. Navigate to the Energy tab at the bottom of the screen. Select your Powerwall from the device list.
Step 2: Tap on the Powerwall tile to open its control screen. Select the operating mode at the top. Choose Time-Based Control from the three available modes (the others are Self-Powered and Backup-Only).
Step 3: Set your preferred charging window. Tap Add Time-of-Use Period. Set the start time to 1:00am and the end time to 6:00am. Select Grid Charging as the action. This tells the Powerwall to draw from the grid during this window to top up the battery.
Step 4: Set your backup reserve. This is the minimum charge percentage the Powerwall will maintain at all times for grid outage protection. A reserve of 20% is appropriate for most households, keeping 2.7kWh in reserve while allowing 10.8kWh for daily cycling.
Step 5: Set your peak avoidance window. Add a second Time-of-Use Period from 4:00pm to 9:00pm. Select Battery Discharge as the priority. This tells the Powerwall to power the home from battery storage during this window rather than drawing from the grid.
Step 6: Save settings. The Powerwall now runs the Agile-optimised schedule automatically every day. Revisit these settings seasonally: in summer, the peak window may need extending as consumption patterns shift.
The overnight charging window: settings to use
The 1am-6am window captures the cheapest Agile periods on the majority of nights. Agile price data for 2025-2026 consistently shows the overnight low point falling between 1am and 5am in most UK regions, with occasional nights where the cheapest period is earlier or later.
The fixed 1am-6am window is a practical default that requires zero daily management. Over a full year, it captures approximately 80-90% of the maximum possible overnight saving compared to a perfectly optimised dynamic schedule.
For the remaining 10-20% of saving, check AgileAlert's live price dashboard each evening around 9-10pm when Octopus publishes the following day's half-hourly prices. If you see that the cheapest block is concentrated between 2am and 4am, adjust your charging window start time to 2am in the Tesla app. If prices are cheapest from 11pm, shift the window to start at 11pm. This takes 60-90 seconds and meaningfully improves your annual capture rate.
On nights when you notice a plunge pricing event (prices going to 0p or below), consider starting the charge window as early as the negative-price period begins. Every unit the Powerwall charges at negative prices is literally free electricity, and charging during that window eliminates the grid import cost for that day's battery cycle entirely.
Peak discharge programming
The discharge window tells the Powerwall to stop drawing from the grid and instead power the home from battery storage. On Agile, the most expensive periods reliably fall between 4pm and 9pm, when domestic demand peaks and grid stress is highest.
With a 13.5kWh Powerwall and a 20% backup reserve, you have approximately 10.8kWh available for discharge. Average UK household consumption between 4pm and 9pm runs to approximately 3-6 kWh depending on household size and season. The Powerwall comfortably covers this window without running below reserve on most days.
In winter, consumption is higher due to lighting, heating top-ups, and cooking. On cold evenings with high household loads, the Powerwall may fully discharge before 9pm. If you find this happening regularly, extend the backup reserve slightly to 25-30% to ensure you always have emergency power, and consider whether you need a second Powerwall or a larger capacity battery for full winter evening coverage.
During summer, Agile evening prices are generally lower than in winter, sometimes only 8-15p/kWh during the 4pm-9pm window. On these days, the value of the discharge is smaller, but the system still works correctly. Your electricity is coming from battery storage that was charged at 2-4p, regardless of what the Agile price is at discharge time. The saving is the difference between your overnight charge cost and whatever the grid would be charging at that moment.
Solar integration: letting the Powerwall prioritise solar first
If you have solar panels alongside your Powerwall, the optimal priority order for electricity flow is as follows.
Priority 1: Power the home directly from solar generation during daylight hours. No battery or grid involvement required. Free electricity consumed the moment it is generated.
Priority 2: When solar generation exceeds home consumption, direct the surplus into the Powerwall. The battery charges from free solar electricity rather than from the grid during the cheap Agile window.
Priority 3: If the Powerwall is not full at the end of the solar day, top it up from the grid during the cheap Agile overnight window (1am-6am). This grid charging supplements whatever solar has already contributed to the battery.
Priority 4: Discharge the Powerwall during the peak evening window (4pm-9pm) to cover home consumption without grid import.
Tesla's Time-Based Control handles this priority sequence automatically when combined with a solar Powerwall Gateway installation. The gateway sees solar generation in real time and directs it to home consumption first, then battery charging, then grid export (at SEG rates). Overnight grid charging via Agile tops up whatever the solar day could not fill. The result is a system where the Powerwall is almost always full by the start of the morning solar window, and almost always full again by the start of the evening peak window, at the lowest possible charging cost.
Real-world saving data from UK Powerwall and Agile users
Reported outcomes from UK households combining a 4kWp solar system, Tesla Powerwall 13.5kWh, and Octopus Agile paint a consistent picture.
Annual electricity bill: approximately £150-250. The equivalent household on a standard tariff consuming around 3,200 kWh per year at 26.11p/kWh would pay £836. Add standing charges of roughly £110/year and the standard tariff bill reaches £950+. The Agile and Powerwall household saves approximately £700-800 annually on electricity running costs alone.
Households with slightly larger solar (5kWp) and higher self-consumption report annual electricity bills under £100, essentially covering only the standing charge and minimal grid import. Several users in favourable regions with good wind resources and regular plunge pricing events have reported net-zero or net-positive electricity accounts over summer months.
At a saving of £700-800 per year, the Powerwall's installed cost of £10,000-12,000 produces an electricity-cost payback of approximately 13-17 years. Combined with the value of the Powerwall as a backup power source during grid outages, the warranty confidence of the Tesla brand, and continuing electricity price volatility, most solar homeowners who purchase a Powerwall regard the economics as acceptable rather than compelling. The technology represents resilience and independence as much as pure financial return. As Powerwall costs fall toward £8,000-9,000 installed in the coming years, payback periods will drop below 12 years for solar Agile households.
Check AgileAlert's price dashboard regularly to understand your regional overnight price patterns and confirm your charging window is targeting the cheapest periods in your area.