Estimate solar panel output and payback

Estimate annual PV generation and simple payback from the specific yield in an MCS assessment and the household’s actual import and export rates.

freeworks offlinenothing uploaded
ToolSolar Panel Calculator
Input
Output
—
Put this on your own site

The frame below runs the same code as this page, in the reader's own browser. Nothing is sent to us, and nothing is sent to you.

Pick a dark background and the text and panels follow it, so the frame stays readable on a dark page.

Preview

How it works

MCS annual output multiplies array kWp by a postcode-, pitch-, and orientation-specific kWh/kWp value and a shading factor. The resulting energy is split by self-use percentage, valued at avoided import cost or export tariff, and divided into installation cost to give simple payback.

Formula
annual kWh = array kWp × specific yield kWh/kWp × (1 − shading loss ÷ 100)
simple payback years = installation cost ÷ annual self-use and export value
  • A zero shading loss is appropriate only for the clear-horizon case that MCS permits to use a factor of 1.00.
  • Specific yield, self-use, capital cost, and both tariff rates are required because roof location, demand, quote, and supplier determine them.

Worked example

A 4kWp array with a 950 kWh/kWp specific yield
6,000 install cost, half the power used in the home and no measured shading loss
Input
											Array size kw: 4
Specific yield kwh per kwp: 950
Shading loss percent: 0
Install cost gbp: 6000
Self use share percent: 50
Electricity rate pence per kwh: 25
Export rate pence per kwh: 15
Output
												Annual generation kwh: 3800
Self used kwh: 1900
Exported kwh: 1900
Annual saving gbp: 760
Payback years: 7.89

When to use this

MCS installer quotes provide the specific yield, Smart Export Guarantee comparisons supply export rates, and home-battery scenarios change the self-use share.

Edge cases

  • A 100% shading loss leaves no generation or annual saving, so no finite payback is returned.
  • At 100% self-use, exported energy is zero and the export tariff contributes nothing to the annual value.
  • A specific-yield value from another postcode, pitch, or orientation is used exactly as entered; those roof factors must come from the matching MCS assessment.

References