Home Electrification Calculator

Sizing solar for an all-electric home

Home electrification — swapping gas heating, hot water and a petrol car for a heat pump, heat-pump water heater and an EV — dramatically cuts emissions and running costs, but it also reshapes your electricity demand. An all-electric home uses far more power than a gas-and-petrol one, so if you're planning solar alongside electrification, you need to size the array for the future all-electric load, not today's bill. Done well, your roof can power your home, your heating and your driving from the same panels.

Electrification is one of the biggest shifts a household can make, and it changes the solar question fundamentally: you’re no longer just offsetting an electricity bill, you’re planning to power your heating and your driving from the same roof. That’s an exciting prospect — it can take a home almost entirely off fossil fuels — but it only works if the solar is sized for where the household is going rather than where it is today. The most common and expensive mistake is to size an array to the current bill, then add an EV and a heat pump a year later and discover the system covers only half the new demand. Planning the two together, as this tool does, avoids that trap and reveals both the array size and the storage strategy a fully electric home really needs.

This calculator adds your projected EV and heat-pump loads to your baseline use, then sizes the solar to match — so you plan for where you're heading, not where you are.

How electrification changes your demand

The two big new loads are transport and heating. An EV typically adds around 0.2 kWh per kilometre (about 0.3 kWh/mile), so an average driver adds roughly 3,000–4,000 kWh a year. A heat pump for space heating can add a similar or larger amount depending on climate and home size, though its high efficiency (delivering several units of heat per unit of electricity) keeps it far below what resistance heating would draw. Add a heat-pump water heater and you've electrified the three biggest household energy uses. Together these can double or more your annual electricity consumption — which is exactly why sizing to your old bill would leave you short.

Size for the future load

The sensible approach is to estimate your post-electrification annual kWh — baseline use plus EV plus heat pump — and size the array to that. Building the capacity in from the start is far cheaper per watt than adding panels later, when you'd pay again for scaffolding, labour and possibly a bigger inverter. If you're electrifying in stages, it's still usually worth installing the full future array now, or at least an inverter and roof layout that leave room to expand.

The timing catch: annual vs hourly

Here's the honest nuance. Sizing the array to match your annual all-electric load means you generate as much as you use over a year — but not necessarily at the same time you use it. EV charging and much heating happen in the evening and overnight, when there's no sun. So covering the load "on paper" annually isn't the same as running those loads on your own solar in real time. To truly self-power night-time charging and heating you need either net metering (banking surplus with the grid) or a battery (banking it at home). Where export rates are low, a battery or load-shifting — charging the EV and pre-heating during daylight — makes the difference between genuinely solar-powered electrification and merely offsetting the annual total.

Why electrify at all?

Beyond emissions, the appeal is running cost: heat pumps and EVs are so efficient that, powered by your own solar, heating and driving can cost a fraction of gas and petrol. The combination of electrification plus solar is one of the most effective ways a household can cut both its carbon footprint and its energy bills — provided the system is sized for the full load and the timing is handled with storage or smart scheduling.

Frequently asked questions

Often substantially — adding an EV and heat pump can double your electricity use. Size to your projected all-electric annual kWh (baseline plus EV plus heating), not your current bill. The calculator above adds these loads and sizes the array accordingly.

Over a year, an appropriately sized array can generate as much as they use. But because much charging and heating happens at night, truly running them on your own solar needs net metering or a battery to shift daytime generation, or scheduling those loads for daylight hours.

Usually now. Adding capacity later costs more per watt because you repeat scaffolding, labour and possibly inverter upgrades. If electrifying in stages, install the full future array up front, or at least size the inverter and roof layout to expand cheaply.

For most homes, yes — heat pumps and EVs are highly efficient, so powering them with your own solar makes heating and driving very cheap and low-carbon. The keys are sizing the array for the full load and managing timing with storage or smart scheduling.