WattFirst

Independent · UK · Numbers first

Electrify your home in the right order, for the right reasons.

Solar, batteries, heat pumps, EVs and tariffs interact. WattFirst helps you understand what to do first, what can wait, and when the best decision may be to buy nothing at all. This is an early prototype: its figures are illustrative, not verified.

What should I install first?Read the guides
Illustrative figures — not a verified calculation

Whole-home model

6 systems

Solar, storage, heat, transport, tariff and controls, assessed together

Transparent assumptions

By design

Every production calculation will show its inputs, assumptions, source dates and uncertainty. Current prototype figures are illustrative and remain clearly labelled.

Commercial stance

Disclosed

No affiliate links or partners today. Any future referral fee will be disclosed beside the action it relates to.

Know what to do first—and what not to buy.

  • No pre-ticked consent boxes
  • Production results will show their assumptions and sources
  • No affiliate links or partners in this prototype
  • We will publish the 'don't buy it' verdicts too

Start here

One questionnaire. A defensible answer.

Six short steps about your home, car, tariff and roof. You get a ranked plan, an indicative sizing range, a payback range and a clear statement of what would change the answer.

Model the whole house

Your heat pump changes the battery case. Your tariff changes the solar case. We assess them together, not as separate products.

Ranges, not false precision

Any tool quoting a payback to the decimal is guessing. We publish ranges and name the inputs that move them most.

Advice you can audit

Production results will show their assumptions and sources. If we are ever paid for a referral, that will be stated where the link appears — there are no such links today.

Run the calculator

The journey

Most households should do these in order

Each step makes the next one cheaper or better informed. Skipping ahead is the most common and most expensive mistake we see.

  1. 01

    Choose an EV

    Total cost of ownership, depreciation and charging access — before the showroom.

  2. 02

    Charge it cheaply

    Get the tariff and charger pairing right — normally the cheapest lever on what a mile costs you.

  3. 03

    Generate and store

    Work out whether solar, a battery, both or neither actually pays back in your home.

  4. 04

    Optimise the whole home

    Sequence heat pump, tariff and storage decisions so each one improves the next.

Topics

Pick the decision you are facing

Electric cars

Whether an EV saves you money depends far more on how you charge it than on which car you buy. We start with the running-cost arithmetic, then the purchase decision.

EV charging

Home charging is the single largest running-cost lever in electric motoring. The tariff does most of the work; the hardware just needs to be reliable.

Solar

Solar is the most quoted-for and least understood upgrade in UK homes. Generation is predictable; the value of that generation is not.

Batteries

A battery moves energy in time. Its entire financial case is the spread between the price you avoid and the price you pay.

Heat pumps

Heat pump running cost is decided by installation quality and tariff. Brand choice is a distant third.

Tariffs

Your tariff is the exchange rate for every other decision on this site. Change it and the payback on solar, batteries and EV charging changes with it.

Guides

Analysis with the verdict up front

No buried conclusions. Each guide opens with what we would do, then shows the working.

All guides
Batteries

Is a home battery worth it in the UK in 2026?

Batteries have become the default upsell on every solar quote. For some households they are the single best-value upgrade available; for others they are an expensive way to shift a small amount of cheap electricity. Here is how to tell which one you are.

11 min read · updated 22 July 2026

EV charging

The cheapest way to charge an EV at home

Charger hardware matters far less than the tariff behind it. Getting that pair right is where we would start, and we will publish the arithmetic once it can be sourced.

9 min read · updated 12 June 2026

Heat pumps

Heat pump running costs, explained without the marketing

A heat pump's running cost is decided by three numbers: your heat demand, the seasonal efficiency you actually achieve, and the unit rate you pay. Everything else is detail.

12 min read · updated 3 May 2026

Worked example

See how the analysis will work

An illustrative worked example using invented household figures, showing how case studies will be presented once real, consented households are involved.

All worked examples
Worked example

A new build with a heat pump and an EV — should they add solar and a battery?

An invented four-bedroom new build with an air source heat pump, one electric vehicle and no solar. Every figure below is made up to demonstrate how a case study will be presented once real, consented households are involved.

Ask the WattFirst Energy Agent — prototype

The assistant we are building — not yet available

The WattFirst Energy Agent is an interface preview: it is not connected to a model, so nothing you type is sent anywhere and no answers are generated. When it works, it will show its assumptions, use our verified calculators, and say when the honest answer is to spend nothing.

Interface ready — model connection pending configuration

Interface preview — not connected

Preview briefing signup

A preview of the briefing signup we intend to offer. It is not connected: nothing is collected, sent or stored.

Consent options (shown for illustration, not recorded)

This form is an interface preview. It is disabled: no email address, no consent choice and no other detail is collected, transmitted or stored, and nothing is passed to any third party.