The foundation has lent environmental charity Global Action Plan about £250,000 in a quasi-equity deal. Loan repayments are based on how much revenue the charity earns, in the same way that share dividends depend on company profits.
Gap will use the money to develop its environmental consultancy, which advises businesses on how to improve their green credentials and uses the profits to provide the same service to schools and disadvantaged communities.
Jonathan Katz, the charity's commercial director, said the commercial business was growing fast but needed investment.
"There's been a lot of talk about using this idea to bridge the funding gap, but there's not been much work to try it," he said. "The attraction from our point of view is that this investment is not a straight loan. It's flexible in relation to our performance.
"If we hit our projections, then it will give Esmee Fairbairn a better rate of return than it gets from an ordinary loan. But if we don't, we're not repaying money we can't afford. It's similar to a private sector equity transaction - but with much less legal trouble."
Esmee Fairbairn is also testing a number of other schemes to help charities to raise money, using its newly allocated £15m finance fund.
Dawn Austwick, chief executive of the foundation, said: "We're aiming to try out a wide range of funding options with about 10 organisations.
"If the trials work, we'll offer them to more charities," she said.