I think you need to consider the Export Tariff of 4.77 p/kWh....

I think you need to consider the Export Tariff of 4.77 p/kWh. This is in addition to the generation tariff of 13.24 p/kWh.

Without knowing who the 3rd party is, there is extra value in the exported electricity. Consider an electricity retailer able to sell the exported power to other other grid connected customers rather than be charged for the electricity delivered from the TSO and centralised generator (it is metered as it transitions from transmission to distribution grid). Also same method could apply for an entity much like Alliander AG who can use the exported electricity for consumption by their own street lighting, again this electricity would offset what they would otherwise have to purchase.

So payback to the "3rd party finance" may come in a similar form.

I'm not saying I'm correct but it would help in extracting maximum value from the investment, however, someone who could use the exported electricity could benefit in the scheme. Just my hunch.