Watt Options

tonyslogic

About this app

Will solar pay off on your roof? Would a battery save you anything? Are you on
the wrong electricity tariff?

Watt Options answers those questions using your own electricity data, not a
national average. Import your smart-meter readings, describe the setup you are
considering, and it simulates a full year at half-hourly resolution — then costs
that year against real supplier tariffs.

WHY YOUR OWN DATA MATTERS

Most solar calculators ask for one number: your annual kWh. Then they multiply.
But whether solar pays off depends on *when* you use electricity, not how much.
A house that runs the dishwasher at midday gets a completely different answer
from one that comes alive at 6pm — even with identical annual totals.

Watt Options works from your actual half-hourly readings, so self-consumption,
battery cycling and export all come out of your real behaviour.

GET YOUR DATA IN
• Octopus Energy — pull your own consumption and generation history, and browse
Octopus tariffs directly
• Home Assistant — read your existing energy statistics over the official API
• AlphaESS inverter cloud
• Solis and FusionSolar inverter clouds (experimental — switch them on in
Settings)

No account is needed to use the app. Where you connect a provider, those are
your own credentials, encrypted on your device.

MODEL WHAT YOU ARE CONSIDERING
• Solar PV — panel count, orientation and tilt, with irradiance for your
location from the EU's PVGIS dataset
• Home battery — capacity, charge and discharge limits, grid charging windows
• EV charging — scheduled or diverted from surplus solar
• Hot water — immersion diversion and scheduling
• Heat pump — demand modelled from your fuel use and local weather

COMPARE PROPERLY
• Cost any scenario against any supplier plan, including day/night/EV tariffs
and standing charges
• Import and export priced as separate contracts — so an export tariff from a
different supplier is costed properly, not assumed away
• Download a community-maintained list of GB supplier tariffs, import and
export, then edit any of them
• Compare scenarios side by side — no solar, solar, solar plus battery — and
see the difference in pounds, not percentages

TWO WAYS TO USE IT

Quick mode answers "would solar pay off?" in a couple of taps, using sensible
defaults.

The full interface takes you through it step by step — your usage, then your
inverter, panels, battery, hot water, EV and heat pump, one section at a time,
each showing a summary of what you have set. Fill in as much or as little as you
like; anything you skip simply stays out of the simulation. Run it when you are
ready, and the year is costed against every tariff you hold.

WHAT IT IS NOT

It is not affiliated with any supplier or installer, and it does not sell your
details to one. There is nothing to sign up for. One purchase, no subscription,
no ads.

Built for Great Britain — GB supplier tariffs, and import and export as the
separate contracts they are.

What’s new

Home Assistant bug fixes