Now I know that the financial return is not the only factor here (enabling green power & a buffer against price spikes being the other two main ones), but can I just check my calculations are correct on the ROI?
For the low estimate, I'm seeing it as the equivalent of a savings account getting 1.36% return per annum after 20% tax (for an investment of £1000 in 567W, the low estimate being a return of £1658 over 30 years, which is the equivalent of getting 1.7% interest on a savings account, compounded over 30 years and paying 20% of that in tax)
Doing the same calculations for the high estimate, it's 3.04%.
Does that sound about right, or have I got a detail wrong somewhere?