Two figures from the European Commission’s PVGIS model carry most of this guide. At a Hatfield town-centre point, a 4 kWp array facing due south at 35° is estimated at about 478 kWh in June and about 135 kWh in December. Over a whole year it comes to about 3,965 kWh, but nobody lives with panels a year at a time. You live with them a day at a time, and a Hatfield day in June and one in December are very different things.
That seasonal swing shapes how big an array is worth fitting and, more sharply, how big a battery should be. For the roof itself, planning in Old Hatfield and what a survey covers, see our page on solar panels in Hatfield. The figures below are for an unshaded, south-facing roof, so treat them as a guide to the pattern rather than a promise for yours.
A June day on a Hatfield roof
June’s 478 kWh works out at about 15.9 kWh a day, and July’s 484 kWh at about 15.6, on our arithmetic. Ofgem’s typical domestic consumption value from 1 July 2026 is 2,500 kWh a year, which averages about 6.8 kWh a day. So on an average midsummer day a 4 kWp Hatfield roof makes more than twice what a typical household uses, most of it between late morning and mid-afternoon. The Met Office’s Rothamsted station, west of the town, averaged about 209 hours of sunshine in July over 1991–2020, and the long days do the rest.
Most of that midday output either runs the house at the time, goes into a battery or is exported. Welwyn Hatfield Borough Council names the University of Hertfordshire as Hatfield’s largest employer, and for a household that is out at work or study through the middle of the day, the share exported can be large.
A December day
December’s 135 kWh is about 4.4 kWh a day, and January’s 154 kWh about 5.0. December comes to about 28% of June, and January about 32% of July, on our arithmetic. Rothamsted averaged about 56 hours of sunshine in December over the same 1991–2020 period. The sun is also lower in the sky in winter, so shade from neighbouring buildings and trees matters more then than in summer, especially on a terrace, the most common home across Hatfield’s four wards.
At 4.4 kWh a day, a Hatfield array makes less than the 6.8 kWh a typical household uses. In December the house takes nearly everything the roof produces as it is produced, and the grid supplies the rest.
What the gap means for a battery
The Energy Saving Trust says a typical home battery might be 10 kWh, and that there is no exact formula for sizing one. The December figures explain why the answer is not “as big as possible”. A battery bought to carry a Hatfield home through winter evenings on solar alone would sit mostly empty from November to February, because there is so little surplus to store.
In the sunnier months the picture reverses. On a June day with nearly 16 kWh coming off the roof, the surplus after daytime use can fill a battery that then runs the house through the evening. That is the job to size for: your evening use in spring, summer and early autumn, not your December shortfall. If your tariff has a cheaper overnight rate, a battery can also charge from the grid in winter, which is a separate calculation. Our guide to what size home battery you need works through both, and our page on battery storage in Hatfield covers placement and the network.
What it means for the panels
The same figures scale with array size: about 34 kWh per kWp in December and about 120 kWh per kWp in June, on our arithmetic. That matters in Hatfield because many roofs are small. Across the town’s four wards, 33.4% of households live in terraced houses and 27.5% in purpose-built flats, with 25.1% in semis and 11.8% in detached houses (our sum of the Census 2021 ward figures). A terrace roof that takes fewer panels than the national typical system makes proportionally less in every month, and an east- or west-facing slope makes less than due south.
Cloud is part of the December picture, not a reason to rule panels out. With only about 56 hours of December sunshine at Rothamsted, a south-facing 4 kWp roof in Hatfield still makes about 135 kWh that month, because panels generate from daylight, not only direct sun, as our guide to whether solar panels work on cloudy days explains. The yearly total, not the winter low, is what decides whether panels are worth it on your roof.
Using the figures at a survey
The most useful thing to bring is a year of electricity bills, ideally with monthly readings, so the survey can set your winter and summer use against the Hatfield pattern above. With 27.5% of Hatfield households renting from a social landlord and 26.8% renting privately, the landlord’s agreement comes before any of this. For eligible privately owned or privately rented homes, Welwyn Hatfield’s Warm Homes: Local Grant, £1.5 million delivered with the National Energy Foundation, funds a battery only alongside solar PV. For the rest of the county, see our solar panels in Hertfordshire hub.
Sources: PVGIS 5.3 (European Commission JRC), PVGIS-SARAH3 2005–2023, 4 kWp, 35°, due south, 14% losses, building-mounted, run 15 October 2026; Met Office, Rothamsted location-specific long-term averages, 1991–2020; Ofgem, Typical Domestic Consumption Values (from 1 July 2026); Energy Saving Trust, Battery storage (updated 19 August 2026); ONS Census 2021, accommodation type and tenure by May 2022 ward, Hatfield Central, East, South West and Villages (our sums); One Welwyn Hatfield Climate Hub, Warm Homes Local Grant Fund; GOV.UK, Warm Homes: Local Grant successful local authorities (updated 2 July 2026); DESNZ, Warm Homes: Local Grant guidance (updated 2 July 2026).