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How much less do solar panels generate in winter?

Short answer

A lot less. For a south-facing 35° roof in London, PVGIS 5.3 averages about 36 kWh per kWp in December against 123 in June and July, under a third. December is only 3–4% of the year's output. In Scotland the gap widens: near Glasgow, December is about a sixth of July.

Last checked 24 September 2026 · 2 sources

In more detail

  • Plan winter savings from time-of-use tariffs/battery charging, not solar.
  • Steeper panels (and vertical/wall mounts) lose less in winter but more in summer.
  • Annual MCS figures don't give monthly splits; use PVGIS monthly outputs for a seasonal chart.
  • Individual months vary a lot year to year (PVGIS 2023 Portsmouth December: 20 kWh/kWp vs 37 in the long-term average).

The facts, dated

  1. 01
    PVGIS London S35 monthly (kWh/kWp) Dec / Jun / Jul — 36 / 123 / 123 kWh/kWp

    market_data · England · checked 24 September 2026 · PVGIS (EU Joint Research Centre)

  2. 02
    PVGIS Glasgow S35 monthly Dec / Jul — 19 / 112 kWh/kWp

    market_data · Scotland · checked 24 September 2026 · PVGIS (EU Joint Research Centre)

  3. 03
    PVGIS Portsmouth S35 Dec 2023 (dull) vs long-term — 20 vs 37 kWh/kWp

    market_data · England · checked 24 September 2026 · PVGIS (EU Joint Research Centre)

What we saw in the field

[QA review 2026-09-24] C2-5 AGREES. I-11 UNVERIFIABLE (consolidated verdict; supersedes differing notes in and ). | Earlier notes: Ground-mount claim: 737 kWh in December vs ~6 MWh in July, a ratio of ~8:1. PVGIS long-term December/July for south 35° is ~0.26 in southern England and ~0.17 near Glasgow; in dull Dec 2023 Portsmouth it was 0.16. An 8:1 ratio is PLAUSIBLE only for a dull December, a northern site or a low tilt. The magnitudes imply roughly 40-45 kWp (July ~130-140 kWh/kWp), which is near the 50 kWp MIS 3002 ceiling and far above a typical home. Treat it as a farm/commercial-scale example, or check whether '6 MWh' was annual. If it was annual, December would be 12% of the year versus 2-4% expected, which is IMPLAUSIBLE. Customer 2 expecting negative net cost from late March to mid-October AGREES with the seasonal shape (Mar-Oct ≈ 80%+ of annual output).

Sources

Last checked: 24 September 2026