Will a Home Battery Fill Up in Winter? Derby Solar Output, Month by Month

ElectriFusion Solutions · 15 October 2026

The question behind most battery enquiries from Derby is simple: how much of the day's solar will the battery actually catch? The answer swings so far through the year that an annual figure hides it. Here is the whole year for a south-facing roof in Derby, from the European Commission's PVGIS model.

A 4.85 kW array in Derby, every month

PVGIS 5.2, SARAH2 radiation database, Derby town-centre coordinates, south-facing at 35°, 14% system losses, fetched 15 October 2026. Annual total 4,755 kWh (980 kWh per kW), within half a percent of Doncaster. Modelled averages, not a guarantee for any particular roof.

The best month here is May at 588 kWh (19.0 kWh a day) and the worst is Dec at 167 kWh (5.4 kWh a day), a ratio of 3.5 to one; that ratio, not the annual total, is what a battery has to live with.

For scale: PVGIS puts the in-plane irradiation on that roof at about 1,204 kWh per square metre a year, and the array converts it to 980 kWh per installed kilowatt; a Derby household with the regional average evening load would see the battery cycle fully on about 214 days a year on these figures.

What that means for the battery

A 5 kWh battery wants roughly 5 kWh of surplus after the house has taken what it uses during the day. On the PVGIS averages, a Derby roof clears 10 kWh a day in Mar, Apr, May, Jun, Jul, Aug, Sep, so those are the months a 5 kWh battery fills from the roof on an ordinary day. A 10 kWh battery needs about 16 kWh a day of generation to fill from solar alone, which this roof averages in Apr, May, Jun, Jul, Aug.

From November to January the average is 6.0 kWh a day. A house that runs a fridge, a router, a kettle and some lighting through the day uses most of that as it arrives, so the battery sees a few hundred watt-hours of surplus, not five kilowatt-hours. That is not a fault with the battery or the panels; it is the latitude.

That something else is the grid

Winter battery value in Derby comes from the tariff: charge at the overnight rate, run the house through the 4pm to 7pm peak, and the roof's contribution is a bonus. In summer the roles reverse. Either way the arithmetic is the difference between the two rates multiplied by what the battery shifts in a day, which is why the tariff is the first thing we ask about.

One caution: do not add grid-charging savings on top of solar savings for the same day. A battery that charged overnight is already full when the morning surplus arrives, so the summer saving is one or the other.

So what size for a Derby home?

Measure the evening. The kilowatt-hours used between the panels switching off and bedtime are what the battery has to cover, and a smart meter's half-hourly export tells you in a week. In Derby a typical three-bedroom semi lands at 5 kWh; a larger house with an EV or a heat pump justifies 10 kWh, mostly for the overnight charging rather than the roof. The sizing and registration details are on our battery storage Derby page, and the panels themselves on solar panels in Derby.

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