# energy.solar-generation

The estimated annual electricity (AC) a solar PV system generates, by the
standard estimation method of the MCS Solar PV Standard (MIS 3002), the one
every MCS-certified installer quotes to customers:

```
Annual AC output (kWh) = kWp x Kk x SF
```

- **kWp**: the sum of the module data-plate ratings (Wp at STC), passed in
  watts.
- **Kk**: kWh per kWp, looked up in MCS's table for the site's postcode zone
  (the SAP zones), the array pitch (to the nearest 1°) and its orientation
  from due south (to the nearest 5°). It carries the irradiance and the
  orientation and pitch factor together.
- **SF**: the shade factor, 1.00 with a clear horizon, otherwise
  1 - estimated shading loss (for example 0.89), to two places.

## Why the Kk table is an argument

MCS publishes Kk as downloadable tables: 21 postcode zones, each a grid of
pitch 0-90° by orientation 0-180°, drawn from the European Commission's
PVGIS dataset (multiplied by 0.8). That is tens of thousands of values, and
MCS updates them with the standard. Shipping a partial copy would invite
silent use of the wrong zone, so the caller looks Kk up (from the MCS tables
or their design software) and this capability does the arithmetic and the
rounding the same way everywhere.

## Several arrays

MIS 3002 estimates an east/west or multi-roof system array by array, each
with its own Kk and SF. Each array is rounded to a whole kWh, **half-up**,
and the total is the sum of those rounded figures, so the total always
equals the lines on the estimate. (Rounding the unrounded sum instead can
differ by a kWh or two.)

MIS 3002 does not state a rounding rule; whole kWh, half-up, matches the
estimates installers print.

## Sources

MCS, "MIS 3002: The Solar PV Standard (Installation)", issue 5.0,
10 May 2023, Appendix B "Standard estimation method" and section 4.1.6,
https://mcscertified.com/wp-content/uploads/2025/02/MIS-3002_Solar-PV-Systems-V5.0-Final-for-publication.pdf