01
Monthly irradiation
Kilowatt-hours per square metre per day on a plane tilted 30° north — what a normal domestic array sees, not what a flat meter sees.
- Provisional, pending PVGIS
Calculator
What your roof does at noon.
The curve everything else on this site is measured against — and the one whose source is not settled yet.
- Feeds the pool and battery calculators
- Irradiance table still provisional
These irradiance figures are indicative and not yet sourced. They are reasonable monthly averages for a tilted array in the Helderberg and they are close enough to plan with, but they have not been pulled from PVGIS against real coordinates. Treat the shape as right and the last 10 % as unconfirmed — and tell us if your inverter says otherwise, because that is better data than ours.
1 kW20 kW
Panel count × panel watts. Sixteen 460 W panels is about 7.3 kW.
Which way the panels face
0.2 kW3 kW
Fridge, network, standby, somebody working from home. Generation below this line is not surplus — it is already spoken for.
Performance ratio 0.80: inverter, wiring, heat and dust between the panel rating and the kilowatt-hour that reaches a load.
Surplus above the house
17.9 kWh
Generated that day
24.5 kWh
Peak
3.5 kW
Over a kilowatt for
7 h 36 min
Over two
5 h 12 min
Over three
1 h 48 min
Usable window
09:12 – 16:42
That is about 2.5 geyser-days of hot water, in an average month, for the Helderberg. Saved to this browser, so the pool and battery calculators use your array rather than our guess.
There is no window here worth switching a heavy load into — the surplus never gets above a kilowatt. Either the array is small for the house, or the daytime load is already eating all of it.
South-facing, in the southern hemisphere. That is about a third of the yield of the same panels facing north. Worth confirming before you plan anything around the number above.
Generation
The house itself
Surplus is the gap
kWh a day
What the model does
Four numbers, and one of them is a judgement.
02
Orientation and pitch
North is the reference. East and west cost about 13 %, and they shift the peak an hour and a half either side of solar noon, which matters more than the loss does.
- The peak moves, not just the height
03
Performance ratio
0.80. Inverter, wiring, heat, dust. The number every installer quotes and roughly what a clean, ventilated array does.
- Judgement, and stated as one
What this leads to
The next question this one raises.
Start here
Your inverter already knows the real answer.
We read it during the assessment — generation, load and state of charge, minute by minute — and you keep the data either way.