Features
Wonder Watt turns a solar battery into something that makes its own decisions. It reads your solar forecast, your tariff and your battery, then tells your inverter what to do, every day, without you touching it.
It runs in the cloud. There is no hardware to buy, nothing to install at your property, and no Home Assistant required.
Supported inverters
Wonder Watt works with Growatt, GivEnergy, Solax, AlphaESS, Solis and FoxESS hybrid systems, connecting through each manufacturer’s own cloud API.
See the supported inverters page for what works with each brand.
Solar forecasting
The reason Wonder Watt exists. Most battery automation only looks at price. Ours looks at the sky first, so you stop paying to fill a battery the sun was going to fill for free.
Built around your actual roof. Enter each array separately with its own direction, tilt and size. If you have east and west panels, or a garage roof facing somewhere else entirely, the forecast adds them together properly instead of pretending you have one big south-facing array. Forecast charts show each array in its own shade so you can see what each one contributes.
Used to make decisions, not just displayed. Schedules can require a minimum forecast before they charge, so a sunny tomorrow automatically cancels tonight’s top up.
One-time setup. Enter your panel details once. Nothing to do afterwards, and single-array systems need no changes at all.
Octopus Agile
Wonder Watt reads the half-hourly Agile prices for your region and picks the cheap slots for you.
- Selects the cheapest slots inside the window you choose
- Re-plans as each day’s new prices are published
- Handles negative pricing
- Live price view so you can see today and tomorrow at a glance
Intelligent Octopus Go
If you are on IOG, your battery can charge at the same cheap rate as your car.
- Uses the standard 23:30 to 05:30 off-peak window
- Picks up the ad-hoc smart slots Octopus assigns when you plug in, which is the part manual schedules always miss
- Reads your schedule straight from the Octopus API, so nothing needs updating by hand
You will need a compatible EV or charger, so that your smart charges appear in the Octopus app.
Schedules
If you would rather set the rules yourself, schedules give you conditional logic instead of a blunt timer.
- Charge to a target state of charge, or charge at least a set amount
- Only run if the solar forecast is below a threshold
- Conditions on required state of charge before a schedule fires
- Automatic or manual charge rate, with separate charge and discharge rates
- Stop export at a chosen state of charge
- One-off schedules for a single night, or repeating ones
- Multiple schedules working together
There are also rate limits and a global pause, so you can hand control back to yourself at any time without deleting anything.
Axle export events
Your battery can now earn money by supporting the grid.
Paste your Axle token into Advanced settings to join in. When an Axle export event starts, Wonder Watt exports for you automatically.
The part that matters is how it fits with everything else. Axle events take priority over everything. Intelligent Octopus Go, Agile and Wonder Batt all stand aside during an event, so nothing is charging your battery while you are being paid to empty it. Wonder Batt also tops the battery up ahead of an event, so there is more to sell when it starts.
That coordination is the difference between running an optimiser and a grid service side by side, and running them as one system.
Wonder Batt (beta)
Wonder Batt is full automation with no schedules to configure at all.
It builds a 48 hour plan at half-hourly resolution from your solar forecast, your tariff prices, your typical household load and your battery’s state of charge, then re-plans as conditions change. It decides when to charge from the grid, when to run the house from the battery, and when to sell.
Three strategies to choose from:
- Self use puts the bill first
- Balanced takes clear arbitrage opportunities and skips thin ones
- Minimise wear counts battery degradation as a real cost and declines the marginal cycles
You can see exactly what it intends to do. The plan view charts import and export prices, solar, household load, grid flows and the state of charge trajectory across the whole horizon, with the charge and export windows shaded in.
Wonder Batt is in beta and rolling out to users now.
Watt’s On
An in-app support assistant that answers questions about your own setup, so you are not waiting on an email reply for something the system already knows.
Battery care
Wonder Watt manages charge and discharge rates rather than always running flat out. A six hour overnight window trickles slowly, while a single cheap half-hour slot runs at full rate. You can set a minimum state of charge that is never breached, and Wonder Batt’s minimise wear strategy treats each cycle as having a real cost.
Fewer unnecessary charges also means fewer cycles, which is the simplest thing anyone can do for battery life.
Pricing
A 14 day free trial, with no payment details required. All you need is a Google account to sign in.
| Plan | Billing | Monthly equivalent | Total |
|---|---|---|---|
| 3-monthly | Every 3 months | £6.00 | £17.99 |
| Annual | Yearly | £4.50 | £54.00 |
Equivalent pricing in USD is available outside the UK. You can turn automatic renewal off at any time and keep access until the end of the period you have already paid for, then turn it back on again before it ends. Payment cards can be updated yourself in the app.
Refunds are no-quibble and in full within 7 days of purchase. Between 7 days and 6 weeks, refunds are proportional to the time left in the subscription.
Frequently asked questions
Do I need Home Assistant, a Raspberry Pi or a home server? No. Wonder Watt is a hosted web app that talks to your inverter through the manufacturer’s cloud. A browser and a Google account is the entire setup.
Do I need a smart meter? No. Wonder Watt controls your battery through the inverter, not the meter.
Will it work with my solar panels? Yes. Panel brand does not matter. What matters is the inverter, since that is what Wonder Watt sends instructions to.
Can I override it? At any time. Pause everything, turn individual features off, or drive the inverter from the manufacturer’s own app. You are never locked out of your own hardware.
What happens if Wonder Watt goes offline? Your inverter carries on with the last schedule it was given. Nothing in your home stops working.
Can I use Agile and Intelligent Octopus Go together? No, because you can only be on one Octopus tariff at a time. If you switch, Wonder Watt adapts.
How accurate is the solar forecast? It is a weather forecast, so it is approximate, and it is more useful for the size of a decision than the exact kWh. We measure it against real telemetry and keep working on it. Wonder Batt re-plans as the day develops rather than committing to the morning’s guess.
Is there a contract? No. Cancel automatic renewal whenever you like.
My inverter is not listed. Will you support it? Tell us in the community forums. It depends entirely on whether the manufacturer offers a cloud API that allows a third party to send control instructions. Solis and FoxESS both got built because users kept asking.
No payment details required. Cancel any time.
Wonder Watt is an independent service and is not affiliated with or endorsed by Octopus Energy, Axle Energy, Growatt, GivEnergy, Solax, AlphaESS, Solis or FoxESS. All trademarks belong to their respective owners.