Among hundreds of the so-called "gree hosts" imountain seems to be providing really environmentally-friendly hosting. Any experience with them?
Any difference in performance of the server using the ordinary power supply and that on the sun or wind power.

Can't see there being any difference in power supply.

Some power suppliers here in the UK offer green tarriffs. The energy you receive isn't always wind-generated, you get your power from the nearest power station but every watt you use the energy company provides onto the "national grid" so people near to the wind turbines receive the actual green power - even if they're not on a green tarriff.

iMountain does use solar power for the power in it's facility. I've seen pictures of their facility, and have a friend who is also good friends with the owner. They are one of the truly green hosting providers in the United States.

I can't see them relying on 100% Wind and Solar for resources of power. California Winds aren't always strong enough. If they also have a Water Turbine hats off to them.

Usually the regular grid is used as temporary backup or supplemental source of energy. It's probably the case here as well.

I think on WHT it was revealed they don't actually use Solar power at the current time, just that they are planning on it at some point in the future.

I would imagine that would be the case too although a true green provider should invest in generating cycles for it's staff to pedal away when the sun goes down and wind stops.

What web site do you host with 'em?