What Is Predbat? Solar Battery Optimisation Explained
Predbat is the open-source Home Assistant add-on that automates battery charge and discharge decisions on UK time-of-use tariffs. Every half hour it pulls Octopus Agile prices, forecasts your home’s next 24-48 hours of solar generation and electricity consumption, and tells your hybrid inverter when to charge from solar, charge from grid, discharge to home, or export. Result: 30-50% more savings on a battery-storage home than running the same kit without Predbat. Free software, running on a small always-on host such as a Mac mini or a Raspberry Pi, supported across Solis (default) and other major hybrid brands.
Predbat is the single biggest reason Spectrum recommends Solis hybrid + Fogstar to customers on Octopus Agile. Without Predbat, a battery on Agile saves perhaps 60% of what it could. With Predbat, it gets close to the theoretical maximum. The maths only works if the software is there.
What Predbat actually does
Predbat is a half-hourly battery scheduling optimiser. Every 30 minutes it:
- Pulls the next 24-48 hours of Octopus Agile half-hourly prices via API
- Forecasts your home’s solar generation for those 48 half-hours (using location, panel orientation, weather forecast)
- Forecasts your home’s consumption for those 48 half-hours (based on recent metered data)
- Calculates the optimal battery charge/discharge schedule to minimise total cost
- Issues commands to your hybrid inverter for the next 30-minute interval
The algorithm balances three things: minimise grid import cost, maximise grid export revenue, respect battery cycle limits (don’t over-cycle if the arbitrage doesn’t justify the wear).
What you need to run Predbat
- Home Assistant, free open-source home automation platform; it runs on a Mac mini or a Raspberry Pi 4/5 (~£100)
- Predbat add-on, free, installed from the Home Assistant Community Store (HACS)
- A compatible hybrid inverter, Solis (LV/HV, the Spectrum default), Sungrow, Sunsynk, SolarEdge (partial) all supported. Closed-ecosystem inverters like older Tesla Powerwall firmware don’t expose the control hooks Predbat needs.
- An Octopus Energy account, for the Agile API
- Optional but recommended: an Octopus Mini, a small device Octopus supplies that streams your smart meter’s readings to Home Assistant in real time (replaces the standard 30-minute meter feed with sub-second data)
How Predbat compares to manufacturer apps
| Feature | Predbat | Inverter app (SolisCloud) | Tesla app (Powerwall) |
|---|---|---|---|
| Half-hourly price awareness | Yes (Agile API) | No | Partial (Octopus integration) |
| Solar generation forecast | Yes (per-roof) | No | Partial |
| Consumption forecast | Yes (learns from real data) | No | Partial |
| Battery cycle optimisation | Yes (tunable) | No | Partial |
| Export arbitrage | Yes | No | Partial |
| Cost | Free | Free | Built-in |
| Complexity | Moderate (one-time setup) | Low | Low |
What the Predbat add-on includes
Spectrum customers on Octopus Agile who take the optional Predbat add-on get the following alongside their solar and battery install:
- Solis 5/6/8kW LV hybrid inverter
- Fogstar 16.1kWh battery
- A Mac mini or a Raspberry Pi 4/5 running Home Assistant, supplied and configured by us
- Predbat add-on configured for the customer’s tariff, roof orientation and consumption profile
- Octopus Mini (where available) feeding real-time consumption data into Home Assistant
- First Predbat tuning after commissioning
The add-on is priced separately on your quote and usually pays for itself within months once the system is running.
Want Predbat as part of your install?
Spectrum offers Predbat as an optional add-on on our own installs, for customers who ask for it on Solis and Fogstar systems we fit, with the setup and first tuning priced on the quote. We do not add Predbat to systems fitted by other installers. Or send us your property details and we will design and price a system from them.
Request a QuoteThe savings, quantified
For a 5kWp solar + 16kWh battery domestic on Octopus Agile:
- Battery + Agile, no Predbat: ~£1,200/year savings vs flat tariff (basic time-shifting)
- Battery + Agile + Predbat: ~£1,700/year savings vs flat tariff (full optimisation)
- Battery + Agile + Predbat + Agile Outgoing export arbitrage: ~£1,900/year savings vs flat tariff
The Predbat uplift is typically £400 - £600/year. Pays back the hardware and setup time in 3-6 months.
Common Predbat misconceptions
- ‘Predbat is too technical.’ The first-time setup takes a couple of hours. After that, it runs in the background. Customers who take the Spectrum add-on get the setup done for them, so they don’t touch it.
- ‘You need to run servers in your house.’ A £100 Raspberry Pi tucked behind your router is the ‘server’. Silent, low-power, no maintenance.
- ‘Predbat doesn’t work with my inverter.’ If your inverter is Solis (the Spectrum default), Sungrow, Sunsynk, Sigenergy or any major brand with API exposure, Predbat works. The exception is closed-ecosystem firmware on a small set of older units.
- ‘Octopus’s own app does the same thing.’ Closer than it was, but Predbat’s granularity and tuneability still wins on the savings number.
Tuning Predbat across the seasons
Predbat’s parameters benefit from quarterly review. Summer solar surplus changes how aggressively you can lean on solar-charging vs grid-charging. Winter overnight cold-snaps change consumption patterns. Where a customer takes the Predbat add-on, the first tuning is part of the setup, and we show customers how to manage it themselves long-term.
FAQs
Is Predbat free?
Yes. Predbat is open-source software, free to download and run. You’ll need a small always-on host. The hardware is typically a Mac mini, or a Raspberry Pi (~£100) as a lower-cost option. Spectrum can supply and configure it as an optional add-on on our own installs, for customers who ask for it, priced on the quote.
Does Predbat work without solar panels?
Yes. Predbat can run battery-only arbitrage on Octopus Agile without solar PV. Charge from cheap import windows, discharge against peak import or export at Agile Outgoing peak rates. Less profitable than solar + battery + Predbat but still earns a meaningful return on a battery investment.
Which inverters does Predbat support?
Solis (LV and HV, the Spectrum default), Sungrow, Sunsynk, SolarEdge (partial), Victron, MultiPlus and a growing list. Closed-firmware inverters that don’t expose API control (older Tesla Powerwall firmware, some manufacturer-locked units) aren’t supported. Check the live Predbat compatibility list before committing.
Will Predbat break my battery warranty?
No. Predbat issues standard charge/discharge commands through the inverter’s normal API. It doesn’t over-discharge or push beyond manufacturer-rated parameters. Predbat’s cycle-cost parameter is specifically designed to respect battery warranty cycle limits.
Can Predbat handle Octopus Cosy and Octopus Go?
Yes. Predbat handles any Octopus tariff including Cosy (3-window), Go (overnight 7p/kWh), Intelligent Go (EV-focused), Agile and Flexible. It also handles Octopus Outgoing variants for export. Multiple-tariff setups (Agile import + Outgoing export) are explicitly supported.
Is there a non-open-source alternative?
Manufacturer apps (Tesla app for Powerwall, SolisCloud, Sungrow, Sunsynk dashboards) have built-in Octopus integration but typically deliver less granular optimisation than Predbat (Spectrum doesn’t install Powerwall; we offer Predbat as an optional add-on on our own battery installs). For self-hosters, pv_opt is an open-source Home Assistant alternative aimed at Solis inverters, though for maximum Agile optimisation in 2026, Predbat remains the strongest option.
Does Predbat need internet?
Yes. It polls the Octopus API for prices and the inverter’s cloud control endpoint. Most home broadband is reliable enough for Predbat’s half-hourly cycle. Short outages are tolerated, Predbat falls back to the last known plan and resumes when connectivity returns.
Related reading
- Home Assistant for Solar PV: 2026 setup guide
- Octopus Agile + Solar: 2026 guide to maximum savings
- Best solar battery for Octopus Agile in 2026
- UK solar export tariff comparison 2026
- solar in a smart home system
For the full Spectrum service overview see domestic battery storage.
Speak to Spectrum Energy Systems
MCS NIC200223. We design and install Solis + Fogstar systems for Octopus Agile across the East Midlands, with Predbat automation as an optional add-on. One quote, one warranty.
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