Size.Solar

    Solar yield in London

    Estimated annual solar yield is 905 kWh per kWp per year. A 400W panel is estimated to produce 362 kWh/year, or 0.99 kWh/day, after modelled system conversion losses.

    Provider-backed estimate

    NLR PVWatts 8.5.0, using TMY dataset (2022 release) weather data. The model assumes south-facing panels at 52° tilt, 180° azimuth, and 14% system losses.

    Retrieved . Compare tilt and direction.

    The estimate is before site-specific roof angle, shade, weather, and equipment factors.

    Solar Production Calculator
    Estimate solar production in London
    Adjust the controls to model annual output, monthly generation, and bill savings for a planned solar system.

    Current estimate

    Annual savings

    £1,636

    Use covered

    80%

    Plan 20 panels

    Draw panel areas next. No sign-in needed.

    Your system settings

    400 W
    200WDefault: 400W700W
    panels
    1 panelTotal size: 8.00 kW150 panels
    kWh
    100 kWhTypical: 600 kWh5000 kWh
    14%
    5% (high efficiency)14% (standard)30%
    Your roof orientation

    Choose the direction and slope your panels will actually use. We compare that roof with the ideal south-facing reference for London using the same weather model.

    0° is flat; 90° is vertical. The ideal reference here is 52°.

    Azimuth simply means direction: 0° north, 90° east, 180° south, and 270° west.

    South is the nearest compass direction.

    Annual bill savings

    £1,636

    Average monthly bill value of £136, based on monthly production and capped to the 600 kWh/month use you entered.

    Electricity use covered

    80%

    Surplus in higher-production months: 1,464 kWh/year. Export credits or batteries may add value.

    Annual output

    7,236 kWh

    Daily output

    ~20 kWh

    System size

    8.0 kW

    Panels needed

    20 panels*

    Will this system fit your roof?

    Keep these inputs while you outline usable roof space and refine the estimate. Compare installers when the roof plan is ready.

    Plan 20 panels

    Monthly production breakdown (kWh)

    Quote readinessThis estimate is strong enough for early planning. A supplier quote still needs roof space, shading, inverter limits, battery needs, and installation constraints.
    Planning notes* The panel estimate uses average monthly output; winter and summer production vary. Bill savings are capped at your entered use (600 kWh/month) and do not assume export credits.

    Next accuracy check

    Check this estimate against your roof

    The figures below are an example starting point for London: 20 panels at 400W, about 8.0 kW, and a 600 kWh/month electricity-use target. Review your current panel wattage, panel count, and electricity use in the calculator above before opening the roof planner or comparing installers.

    Review current inputsBrowse installers
    Example system
    ~8.0 kW

    20 panels for a 600 kWh/month home before roof, inverter, and battery constraints.

    Output per panel
    362 kWh

    Estimated annual AC electricity from one 400W panel after modelled system losses.

    Bill value/year
    £1,636

    Annual value at about £0.28/kWh, capped to the electricity use you can actually offset.

    Weakest month
    Dec

    10 kWh from one 400W panel; check this month before sizing essential loads.

    Roof fit

    Confirm usable roof planes, shading, inverter limits, and battery needs before accepting a final layout.

    Bill fit

    Adjust panel count and monthly use above so savings are capped to electricity you can offset.

    Quote check

    Ask suppliers to show winter output, assumed losses, and any export-credit value separately.

    Production evidenceShow monthly output and model assumptionsOpen this when checking winter production, irradiance, losses, or the source assumptions behind the quote handoff.

    Monthly model

    Monthly output and winter risk

    The calculator is useful when it shows the weak months, not just a flattering annual number. Use the table to check whether winter output still supports the loads you care about.

    Best month
    Jun

    45 kWh from one 400W panel

    Lowest month
    Dec

    10 kWh from one 400W panel

    Solar resource
    3.2 kWh/m²/day

    1155 kWh/m² annual irradiance

    Model checks
    10.3%

    Capacity factor, 78.3% performance ratio, 382 kWh DC before conversion

    JanFebMarAprMayJunJulAugSepOctNovDec
    14 kWh18 kWh29 kWh44 kWh41 kWh45 kWh45 kWh40 kWh38 kWh22 kWh16 kWh10 kWh

    Model basis

    The model uses south-facing panels at 52° tilt, true south orientation, and 14% system loss. Typical 600 kWh/month electricity costs are £93 - £273 (typically £170) using 2025 cost data.

    Solar production data provided by NLR PVWatts 8.5.0. Weather source: NSRDB PSM V4 Meteosat Prime Meridian tmy-2022 1.0.0; nearest source point 2.1 km from the city coordinates.

    Change the modeled city