The seed assets are operational at sites in Llanwern in South Wales and Strensham, Worcestershire, which together will have an installed capacity of 115MW.
The UK farms will be managed by a new fund with NextEnergy Capital that aims to double the amount of subsidy-free solar power in the UK by raising £500m (€587m).
NextPower UK ESG (NPUK ESG), is a private 10-year solar infrastructure fund.
The UK Infrastructure Bank plans to invest up to £250m, half of the fund’s total target fund size, on a match-funding basis with the private sector.
It is hoped that this support will lead to significant investment into the UK subsidy-free solar sector.
It will be the largest subsidy-free solar investment fund in the UK, managed by NextEnergy Capital (NEC) a global leader in the solar infrastructure sector.
Once the fund is fully operational it will have an expected generation capacity of around 1GW of power from around 30 solar farms across the UK.
It will produce enough clean electricity to power the equivalent of 280,000 households or offset 370,000 carbon-emitting cars on the road each year.
The Bank was launched in June to support infrastructure investment to help tackle climate change and boost regional and local economic growth across the UK.
The investment marks a first private sector transaction for the Bank and a significant step in helping the UK government meet its net zero goals.
Exchequer Secretary to the Treasury Helen Whately said: "It’s great to see the UK Infrastructure Bank striking another deal, which will help power thousands of homes across the UK with clean energy and create green jobs.
"We are investing billions through the bank in important projects across the UK to drive growth and level up opportunities."
UK Investment Bank chief executive John Flint added: "As this is the first deal for the UK Infrastructure Bank to leverage private sector investment, it is an important milestone for us.
"I am delighted that the Bank is able to play a role in the development of subsidy-free solar energy for the UK."
NextEnergy Capital chief executive Michael Bonte-Friedheim said: "The launch of NextPower UK ESG marks an important milestone in bringing together capital from both the private and public sector to fund the next the phase of evolution in the UK solar PV sector.
"Unsubsidised new-build solar projects represent an attractive investment opportunity, both in financial investment returns and in the pursuit of societal objectives such as addressing climate change and improving biodiversity in the UK.
"NextEnergy, the preeminent participant in the UK solar market, is uniquely placed to do this and we look forward to now executing upon NextPower UK ESG’s secured pipeline of projects.
"This milestone is also a further recognition of the strength of the NEC platform."