I don't think the issue is lack of an energy source. The problem is that no one wants to spend 100 million kilojoules to capture 50 million kilojoules.

The key is to use a truly renewable, otherwise unusable energy source (like hydrothermal) to power the reaction so we can convert energy from usable to unusable forms.

Of course the sad truth is that we'll always have environmental effects, because even of we have a net gain of energy, we won't replenish it equivalently. Just don't ask the dipshits who think wind turbines and solar energy aren't environmental disasters.