Originally Posted by

**rintelen** Recently the British govt decided to force energy companies to pay people who installed photovoltaic solar panels on their roof. The rates are as follows:

Main Tariff: 41.3 p/kWh for everything you generate plus

Export Tariff: 3 p/kWh for what they deem you export, e.g. they might say you use 50% and you export 50% of what the panels generate.

Both tariffs rise by inflation rate r = 2.4% each year.

A typical 1kW system in the UK generates 850 kWh per year. A 2.0 kW system will generate twice this and so on, whatever the size. Anything under 4 kW qualifies.

Okay, so far, so good. I want to work out three short formulas that will predict my earnings from

Main tariff (m)

Export Tariff (e)

for any given year 1-25

rate rise = 2.4% (r)

For example, year n=1,2,3,4....25 (the last year they'll pay).

I can do this on a long complex spreadsheet, but I'm sure that there is a shorter formulaic way to do this.

It's a good problem to solve actually, so I hope someone can provide the formulas.