The possibilities are dramatic. The whole thing starts with a fusion reactor, which isn't yet a viable technology. The reactor would combine helium-3 ions to produce helium-4 (the regular stuff found on Earth) and energized protons. According to Energy Bulletin, the process would release no greenhouse gasses. It would, however, produce a whole lot of energy. According to Artemis, the protons produced by a fusion reactor fed with the moon's available He3 could produce 10 times more power than the combustion of every bit of fossil fuel found on Earth.
Here's the rub, though. That He3 isn't exactly "available."
Many challenges face the potential lunar energy source. First, as of 2010, the United States, for one, isn't going back to the moon to establish a permanent colony. That most likely dampens, or at least postpones, any plans to develop an He3 mining project.
What's more, some experts say it's actually pretty difficult to mine He3. It would require heating lunar soil to extreme temperatures that may simply be prohibitive, as far as lunar-mining goes.
And then there's the fact that a large-scale fusion reactor is at least half a century away.
Still, the theory persists. He3 could provide more energy, and more-renewable energy, than current power sources. And all that energy would be so clean, energy credits would be a thing of the past.
At least once He3 replaced rocket fuel, anyway.