How many kWh per day should my solar system produce?

As a rough rule, in northern-European conditions a system produces around 2.5–3 kWh per kWp per day averaged over the year — but the honest answer is a range: a 5 kWp array might do 30 kWh on a clear June day and 3 kWh on a grey December one. Sunnier climates (southern Europe, most of Australia) sit closer to 4–4.5 kWh/kWp. A single daily number without weather context tells you almost nothing.

Why the range is so wide

Daily yield is driven by day length, sun elevation, cloud cover and temperature — all of which vary far more than most owners expect. Between midsummer and midwinter the same roof can differ by a factor of five to ten at mid-latitudes. Orientation and tilt shift the curve too: east-west arrays trade a lower peak for longer mornings and evenings, and shading can carve out chunks the averages hide.

This is why comparing your output with a neighbour’s, or with a generic per-kWp average, so often causes false alarm. The only fair benchmark is your own system’s potential for that specific day’s weather — which is exactly what a physics-based forecast computes from your location, orientation, tilt and the day’s irradiance.

What to do

1. Stop comparing single days with annual averages — check monthly totals against a typical-year estimate for your location and orientation instead.
2. Benchmark against a forecast for your exact setup — if actual output tracks the forecast within a few percent, the system is healthy even when the absolute number looks low.
3. Investigate a persistent gap, not a bad day — actual consistently 15–20% below forecast across different weather signals a real issue: shading, soiling, a string fault. See the answer on checking whether your system works properly.
4. Log the good days — your best clear-sky day each month makes a personal reference curve; a slow slide in that peak over the years is degradation you can measure.