Greencoat initially agreed to buy the 75% stake in the 13-turbine farm from Belltown Power last autumn.
As well as the headline fee, the FTSE 250 group has prepaid the remaining £19mln of project finance debt, taking its total investment to £145mln.
Tom nan Clach is brand new, with work due to finish this month.
Its 13 Vestas V112 turbines are capable of generating 39.1 megawatts of electricity, while the load factor is expected to be 48%.
Interestingly, the project will benefit from a 15-year contract for difference (CFD).
These are long-term deals that enable generators such as Greencoat to stabilise revenues at a pre-agreed level for the duration of the contract.
The purpose of CFD is to incentivise investments in new low-carbon electricity generation by providing predictability of future revenue streams.
They are an alternative to existing green incentive scheme based around renewable obligation certificates, or ROCs.
Greencoat shares edged 0.1% higher to 140p on Tuesday afternoon, valuing the company at £2.1bn.