SolarpunkHomes
Sign inCall us · +44 7510 081687
Solar
Solar · Maintenance

What should my solar generation graph look like, and what do odd shapes mean?

Short answer

A clear day on a south-facing roof gives a smooth bell curve peaking around 1pm. A flat top at the same kW every sunny day is inverter clipping. East-west roofs give a wider, flatter or double-humped curve. A sharp dip at the same time each day is shading. A flat zero on a bright day means a fault or outage.

Last checked 24 September 2026 · 1 source

In more detail

  • Normal (south): smooth symmetric bell centred near solar noon (about 13:00 BST); cloudy days are jagged versions under the same envelope.
  • Clipping: flat plateau at the inverter's AC rating (e.g. 3.68 kW or 5 kW) on bright days, common with deliberate DC oversizing; small energy loss, not a fault.
  • East-west: east side peaks mid-morning, west mid-afternoon; combined curve is broad or double-humped with lower peak and longer day.
  • Shading dip: notch at the same clock time on sunny days that moves slowly with the seasons (chimney, tree, dormer, neighbour).
  • String missing: whole curve roughly halved or reduced by one string's share on sunny days; app may show one MPPT at 0 V.
  • Zero generation on a sunny day: inverter off/tripped, DC isolator off, grid outage (anti-islanding), or monitoring outage (check the inverter display vs the app).
  • Export limit: flat top at the DNO export limit on the export graph while generation continues to battery/house.

The facts, dated

  1. 01
    PVGIS London south 30 degrees: June 125 vs December 34 kWh/kWp — 125/34 kWh/kWp/month

    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. C2-3 CONTRADICTS as an AC figure: a ~12 kW peak exceeds one Powerwall 3's 11.04 kW AC rating; treat as DC/combined reading unless shown otherwise. | Earlier notes: Agrees with Customer 1 (east ramps ~8am, fades early afternoon; west generates to ~8pm in August) and Customer 2 (13.5 kWp DC on ~11 kW AC = deliberate oversizing; clipping plateau expected on best days; peak ~12 kW late June suggests multiple inverters/AC capacity or the figure is DC-side).

Sources

Last checked: 24 September 2026