Ann: Half Yearly Report and Accounts, page-3

you should treat new like a bond, naturally the value of a bond will decrease over time. There will be more renewables added and lower electricity prices, but this doesn't matter for 7 years because of long term PPA's, after that 90% of the revenue will be from PPA's still.

So who cares, the total return should still be positive assuming you bought it under the NAV price at a considerable discount.