Two or three weeks ago we launched a 'Back-of-Envelope' Solar PV Calculator.
You can access it here:
I have been using the calculator to get a rough idea of what the returns from solar PV look like in a post-subsidy world, without bothering our Estimating team (who, as you can imagine, are pretty busy in the run up to the Feed-in Tariff closure on 31st March 2019).
Here's an example of what 75kWp of un-subsidised solar PV looks like, retro-fitted to a factory roof...
