Mark Hoskin, a partner at wealth management company Holden Partners, was speaking in advance of the first National Ethical Investment Week, which runs from 18 to 24 May.
He said the divergence of research and opinion on ecological solutions such as wind farms and biofuels made many charities wary of investing in them.
"Charities are worried about having a PR disaster," said Hoskin, whose firm has signed up to show its support for National Ethical Investment Week, run by the UK Social Investment Forum to encourage investors to consider ethical options.
Hoskin said that focusing on negative screening rather than actively investing in companies that did good work could be costing charities money.
"Environmental markets are growing at 20 to 30 per cent a year, and make extremely good investments," he said.