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Solar

Solar production in winter vs summer

Annual production is a comforting number. The monthly shape is the one that decides whether solar covers your winter bill.

Published 23 August 2026 · Published by SnapEnergyLab. Methodology and default assumptions are documented separately.

The same house with rooftop solar seen with a snow-covered winter garden on one side and a green summer garden on the other

Quick answer

At mid to high latitudes a solar array produces roughly six to nine times as much in its local summer month as in its local winter month — June versus December in the northern hemisphere, the reverse in the southern. The four darkest months together typically deliver about a tenth of the annual total.

This is why an annual figure — the number every quote leads with — can be perfectly accurate and still mislead. Annual output tells you what you generate. The monthly shape tells you whether it arrives when you need it.

How to read the numbersIllustrative modelCalculated resultSite default
Modelled annual output
5,380 kWh
Illustrative model
Nov–Feb share
11%
Calculated result
June vs December
8.3×
Calculated result

Three effects, all pulling the same way

Day length. At 52° north, a June day offers about 16.5 hours of daylight against 8 hours in December. That alone is a factor of two.

Solar elevation. A low winter sun means sunlight strikes the panel at a shallow angle and passes through far more atmosphere. Both reduce the irradiance reaching the cells, and the effect is strongest exactly when day length is shortest.

Weather. Winter cloud, fog and short-lived snow cover cut further into what geometry already reduced. Unlike the first two, this part varies enormously year to year.

Cold weather itself is the one factor helping you: panels are more efficient cold. It is nowhere near enough to offset the other three.

Illustrative monthly production for a 6 kWp array at about 52° north0200400600JanFebMarAprMayJunJulAugSepOctNovDecMonthly production (kWh)
Illustrative monthly shape for a south-facing 6 kWp array at roughly 52° north with a 0.85 performance ratio, totalling about 5,400 kWh a year. Use PVGIS or PVWatts for your own coordinates, tilt and azimuth — the shape shifts substantially with latitude and local climate.
Show the plotted values
PeriodMonthly production (kWh)
Jan130
Feb220
Mar420
Apr620
May760
Jun790
Jul780
Aug660
Sep470
Oct290
Nov145
Dec95

What the shape means in practice

  1. winter share = Nov–Feb production ÷ annual production
  2. example: 590 ÷ 5380 = 0.110 → 11%
  4. winter daily average = Nov–Feb production ÷ 120 days
  5. example: 590 ÷ 120 = 4.9 kWh/day

Compare that daily average against your winter consumption, not your annual average consumption. In a home with electric heating the two are very different numbers.

Worked example: can solar cover a December bill?

  1. December production95 kWhIllustrative model
  2. Daily average in December95 ÷ 31 = 3.1 kWh/dayCalculated result
  3. Household December consumption900 kWh (heat pump running)Illustrative model
  4. Share covered, before self-consumption95 ÷ 900 = 10.6%Calculated result
  5. Realistic self-consumption of that output≈ 80% in winterSite default
  6. Bill actually offset≈ 76 kWh, about 8%Calculated result
December bill offset by solar≈ 8%

Designing for the shape you actually get

Size against annual consumption, then sanity-check the summer surplus. Oversizing to chase winter output produces enormous summer export at whatever low price your market pays for it.

Consider a steeper tilt if winter matters most. A tilt near your latitude plus 15° favours low winter sun at the cost of some summer yield. It flattens the curve; it does not level it.

East–west arrays spread output across the day. Lower annual total, but often higher self-consumption, which is what actually determines the financial result.

Match flexible loads to the season. EV charging, water heating and dehumidifying are worth scheduling around production in the eight good months and simply paying for in the four bad ones.

See the monthly shape for your own system

The calculator reports monthly as well as annual production, so you can compare the winter months against your own winter consumption instead of against an annual average.

Open the solar output calculator

Assumptions and limitations

  • The monthly profile is an illustrative model for a northern-hemisphere mid-latitude location (roughly 52°N), not measured data. Southern-hemisphere readers should mirror the calendar: December and January are the high-production months, June and July the low ones. Yours will differ with latitude, tilt, azimuth, shading and local climate.
  • Year-to-year variation in winter months is large: a cloudy December can be half a sunny one, and the percentage figures move accordingly.
  • The self-consumption assumption in the worked example is a default, not a measurement of any household's behaviour.

Sources

  1. PVGIS — monthly and hourly PV performance data — European Commission Joint Research Centre

    Supports: Month-by-month modelled PV output showing the seasonal distribution of annual yield.

  2. PVWatts Calculator — monthly results — U.S. National Renewable Energy Laboratory

    Supports: Monthly production estimates for a specified system and location.

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