wonder watt
Power your tomorrow, today!
wonder watt
Power your tomorrow, today!
Octopus Agile, Intelligent Octopus Go, Flux, Cosy, EDF, E.ON Next and British Gas, each paired with the export tariffs you can actually get. We run a full year of your local weather and real prices through your system, with your battery charged and discharged at the right times on every tariff, and rank them.
Free, takes about two minutes. An estimate, not a quote: standing charges are not included.
We're running a year of your local weather and real prices through your panels and battery, for every tariff pairing, with the battery planned half hour by half hour on each. This takes 10 to 20 seconds.
It estimates a year of electricity costs for your home on each tariff, with your battery run the way Wonder Batt would run it.
One week from each of the last 12 months is replayed and scaled to a year. Standing charges and exit fees aren't included. Wonder Watt has no commercial relationship with any of these suppliers; tariffs are ranked by cost alone.
There isn't one answer: it depends on how much you use, how much your panels make, your battery size and whether you have an EV or heat pump. Homes with an EV and smart charger often do best on Intelligent Octopus Go, while homes that export a lot often do well on Octopus Flux or Agile with Agile Outgoing. Wonder Watt's free solar and battery tariff calculator runs a year of your local weather and real prices through your own system to rank them for your home.
If you have an EV and a compatible charger, Intelligent Octopus Go's long cheap overnight window usually makes it cheaper, especially paired with a good export tariff. Without an EV you can't get Intelligent Octopus Go, and Flux often comes out ahead for homes that export in the 4pm to 7pm peak. The Wonder Watt tariff calculator compares both for your own panels, battery and usage.
Often, yes, because a battery lets you buy at Agile's cheap overnight and windy-day prices and avoid its expensive 4pm to 7pm peaks. The risk is winter, when peak prices can be high and solar is low, so a small battery may not cover the evening. Wonder Watt's calculator replays a full year of real Agile prices for your region to show whether it pays for your home.
The usual choices are a fixed rate (such as Outgoing Octopus, EDF Export or British Gas Export Premium), Octopus Agile Outgoing, which follows wholesale prices each half hour, and Flux export, which only comes with Flux import. With a battery that can export in the evening peak, Agile Outgoing or Flux often pays more than a fixed rate over a year; without one, a good fixed rate is usually safer. The Wonder Watt calculator compares them with your own solar and battery.
Yes. To be paid for exported electricity your system needs to be notified to your distribution network operator (DNO), usually with a G98 or G99 form your installer submits, and you need a smart meter that records export. Ask your installer for the confirmation if you're not sure. The Wonder Watt tariff calculator asks about this and shows what export would be worth to you.
No. Intelligent Octopus Go needs an electric vehicle or a compatible smart charger that Octopus can control; without one, Octopus Go is the closest alternative. Octopus Cosy similarly needs a heat pump. The Wonder Watt tariff calculator only ranks tariffs you can sign up to and shows what the others would be worth if you got an EV or heat pump.
Usually yes on a time-of-use tariff in winter, when solar won't fill the battery and overnight electricity is much cheaper than the evening peak. In summer it often isn't worth it, because your panels will fill the battery anyway and charging costs battery wear. The right answer changes day by day, which is what Wonder Watt's Wonder Batt plans automatically, and the calculator assumes the battery is run that way on each tariff.
It varies widely with battery size, usage and season: a battery that avoids Agile's evening peak and charges on cheap nights can cut a typical bill noticeably, while savings are smaller in summer when solar already covers much of the day. There is no reliable single figure for every home. The Wonder Watt calculator works out a yearly estimate from your own battery size, solar and usage.
Sometimes, but usually not by much: standing charges are similar between suppliers in the same region, though not identical. The Wonder Watt calculator compares unit rates and export only, so check each supplier's daily standing charge before you switch, especially if two tariffs come out close.
A common rule of thumb is enough usable capacity to cover your evening and overnight use, often 5 to 10 kWh for a typical home, and more if you want to shift cheap overnight electricity for a whole day or charge an EV. Beyond that, extra capacity tends to earn less per kWh. You can try different battery sizes in the Wonder Watt tariff calculator to see how the best tariff and yearly cost change.
For battery owners who can export in the 4pm to 7pm peak, Agile Outgoing often pays more over a year, although midday summer prices can be low. Without a battery, or if you mostly export at midday, a fixed rate is usually the safer choice. The Wonder Watt calculator compares both using real Agile Outgoing prices for your region.
Without a battery you mostly export at midday and import in the evening, so a good export rate matters most and a cheap overnight window matters less unless you have an EV. A strong fixed export rate with a competitive import tariff is often the best combination. Enter a battery size of 0 in the Wonder Watt tariff calculator to compare tariffs for solar alone.
It's an estimate, not a quote. It uses a year of real weather at your postcode, real Agile prices for your region and today's published rates for the other tariffs, with a typical daily usage pattern scaled to your figures, so your own pattern will differ. Standing charges are not included.
Wonder Watt plans your battery around your tariff and tomorrow's solar forecast, automatically. Works with Growatt, GivEnergy, Solax, AlphaESS, Solis, FoxESS and Sunsynk.