Just be aware that the Merrill Lynch New Energy Fund is not a green fund. It invests in potential new energy sources & processes regardless of their environmental qualities. This includes coal and (possibly) nuclear. Just in case that matters to you.
There are various ETF funds available to cover different perspectives - non carbon, renewable, low to zero emission etc. There are mutual funds like ML available too.
PowerShares WilderHill Clean Energy includes the experimental technology type firms investigating alternative energy sources.
Sustainability type funds such as EasyETF GS Ultra-Light Energy, DJ Euro STOXX Sustainability 40 and social\ethical funds may provide some coverage.
I'm interested in investing into the DJ EURO STOXX Sustainability 40, but the Wilder Hill Clean Energy ETF sounds interesting too. What is the cheapest way to invest into these from Ireland? I also have a choice between Irish, French or German brokers.