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Off-grid power calculator

Pick what you're powering and where it is. We simulate a full year of real hourly solar data for that location and show your days off-grid, month by month — and if you run a generator, how few hours it actually needs to run once a 48V battery does the daily work.

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The December number is the one that matters

Anyone can promise off-grid power in July. The question that decides whether an off-grid system actually works in the UK is what happens in December, when a solar array produces a fraction of its summer output — and the answer depends heavily on where you are. The same system that sails through a Kent winter needs roughly three times the generator support in the Highlands.

That's why this calculator is location-based. It uses PVGIS — the European Commission's solar resource database — to simulate a typical year, hour by hour, for your area, rather than assuming an average British day. The result is an honest answer: which months run entirely on solar, how long the battery carries you in the dark months, and exactly how many hours a generator bridges the gap in a hybrid setup.

When you're ready to turn the numbers into hardware, explore our 48V off-grid systems or book a free call and we'll design it with you.

Common Questions About the Off-Grid Calculator

It runs an hour-by-hour battery simulation against a typical meteorological year of real solar data (PVGIS) for your area. Your daily consumption drains the battery on a realistic 24-hour profile, solar charges it as the sun actually behaves month by month, and the result is how long the system runs off-grid in each month of the year — including December, which is the number that matters in the UK.

How many days the battery lasts in that month before it runs flat, starting full, with solar topping it up as it goes. "All month" means solar covers your daily use in that month and the system runs indefinitely.

In a 48V hybrid system the generator does not power your appliances directly — it charges the battery through the inverter-charger, running for short bursts at high load. That is the efficient way to run a genset: a couple of hours at its sweet spot instead of all day at part throttle. The calculator simulates the generator auto-starting at 20% battery and charging to 80%, then compares those run-hours against your current routine of running it whenever you need power.

From roughly April to September, usually yes — most sensibly sized systems cover daily use entirely and the genset stays off. Through December and January in the UK, the honest answer for most loads is a hybrid: the battery carries the day and the generator tops it up for a few hours a week. The calculator shows you exactly how many hours, for your location.

Real 48V off-grid kit: Fogstar 48V lithium batteries (with self-heating and built-in fire suppression), Victron MultiPlus and MultiPlus-II inverter-chargers, Victron MPPT solar charging and Lynx distribution, monitored remotely with a Victron Cerbo GX. The charger power shown for each tier is the genuine Victron charge rating at 48V.

It is free and there is no sign-up. Solar data comes from PVGIS, the European Commission's solar resource database, and the battery maths is the same simulation our configurator uses. Treat the outputs as good planning estimates rather than guarantees — panel orientation, shading and unusual weather all move real-world results.