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How do I read the generation curve in my solar app?

Short answer

A south array draws a bell curve peaking around 1pm (BST). East arrays peak mid-morning and west arrays late afternoon, so an east-west system shows a wider, flatter hump. Clouds cause jagged spikes. A flat top at the same value on sunny days usually means the inverter or an export limit is clipping output.

Last checked 24 September 2026 · 1 source

In more detail

  • Plot kW (power) through the day; the area under the curve is kWh (energy).
  • Compare a clear day with the same day last year, or with PVGIS hourly output for your orientation.
  • Sudden zero midday on a sunny day = fault/trip: check app for an error code, check AC isolator and consumer-unit breaker are on.
  • Hourly-mean PVGIS peaks per kWp (Portsmouth 2023): south ~0.89, east/west ~0.8, north ~0.4 of kWp.

The facts, dated

  1. 01
    PVGIS 2023 hourly-mean peak per kWp, south 35°, Portsmouth — 0.89 kW/kWp

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

  2. 02
    PVGIS 2023 hourly-mean peak per kWp, north 35°, Portsmouth — 0.41 kW/kWp

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

What we saw in the field

[QA review 2026-09-24] C1-1 AGREES (E/W curve shapes). H-10 AGREES (1.5-2 kW snapshots plausible). | Earlier notes: Customer 1's east ramp from ~8am fading early afternoon and west to ~8pm in August AGREES with expected E/W shapes. Homeowner's '~2 kW on cloudy summer days, ~1.5 kW on clear winter days' from 5.6 kWp (4.0 kWp SW): PVGIS 2023 hourly maxima for the SW array are 1.99 kW in December and 2.25 kW in January, so 1.5 kW on a clear winter day is PLAUSIBLE. ~2 kW (≈35% of kWp) under summer cloud is plausible for bright overcast.

Sources

Last checked: 24 September 2026