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Solar generation

Solar generation is an estimate, not a promise of weather.

A generation figure is a model of the future built from inputs. It can be careful, well reasoned and useful. It cannot be a guarantee.

Request a solar proposal What an estimate depends on
Conceptual image

Generation · Status

Annual figure
Estimated
Method
Stated in proposal
Weather
Varies year to year
Guarantee
None implied

Illustrative reading

01 Generation

Estimate generation. Don’t pretend to guarantee the weather.

A generation figure is a model of the future built from inputs. It can be careful and well reasoned. It cannot be a promise.
Illustrative seasonal pattern of solar generation, January to December A circular year divided into twelve months. Segments are shortest in December and January and longest around June, showing that UK solar generation is typically lower in winter and higher in summer. The drawing is qualitative, has no values, and is not a forecast for any individual home. JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ESTIMATE ONE YEAR
Illustrative seasonal pattern — not to scale, no values

What an estimate depends on

  • LOCATION How much sunlight a region typically receives over a year.
  • ORIENTATION The direction the array faces relative to the sun’s path.
  • PITCH The tilt of the modules, which changes with the roof angle.
  • SHADING Obstructions that block light at certain times or seasons.
  • EQUIPMENT Module and inverter characteristics and how they are matched.
  • WEATHER Cloud, haze and the variation from one year to the next.
  • SYSTEM LOSSES Temperature, cabling, conversion and soiling reduce output.
How generation estimates work

02 Orientation & time of day

Direction changes the shape of the day.

An east-facing plane peaks in the morning, a west-facing one in the afternoon, and a south-facing one around midday. That timing matters as much as the total, because it decides how much generation overlaps with household use.

Illustrative shapes only — not to scale, no values.

Illustrative daily generation shapes by roof orientation Three curves across a day. An east-facing plane peaks in the morning, a south-facing plane peaks around midday and is usually the tallest, and a west-facing plane peaks in the afternoon. Shapes only; not to scale. MORNING MIDDAY EVENING EAST SOUTH WEST

03 More inputs

Equipment, losses, weather and seasons.

Beyond the roof itself, these four inputs shape any generation estimate — and explain why actual output varies.

  1. 01 PANEL CHARACTERISTICS

    Panel characteristics

    Rated output, efficiency and how a module responds to heat and low light all feed into a model.

  2. 02 SYSTEM LOSSES

    System loss assumptions

    Some energy is lost to temperature, cabling, conversion, soiling and ageing. An estimate should say what it assumes.

  3. 03 WEATHER

    Weather variability

    No two years have the same weather. Models use long-term averages; any individual year can be higher or lower.

  4. 04 SEASONALITY

    Seasonality

    Long summer days produce far more than short winter ones. Monthly generation follows the seasons, not a straight line.

04 Method

How an estimate should be built.

  1. 01 Inputs Location, orientation, pitch, shading and the proposed equipment.
  2. 02 Assumptions System losses, weather data and any shading factors applied.
  3. 03 Model A recognised calculation method applied to those inputs.
  4. 04 Estimate An estimated annual figure — stated with its method and assumptions.

Next: savings and assumptions

Conceptual image of low sunlight across a tiled roof Conceptual image
Conceptual light study Generated imagery, not a real property or installation

Questions

Generation questions

How much electricity will solar panels generate on my home?

Only a project-specific estimate can suggest that, and it remains an estimate. It depends on location, orientation, pitch, shading, equipment, system losses and the weather in any given year.

Why do estimates from different companies differ?

Because they may use different inputs, assumptions or methods — for example, different shading or loss assumptions. That is why each estimate should be shown with the assumptions behind it, so they can be compared fairly.

Will my system generate the same amount every year?

No. Weather varies from year to year, and module output can change gradually over time. Actual generation varies with weather, shading, equipment performance, system losses and how the system is installed and maintained.

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