First, fusion's only bi-product is hydrogen, which cannot be radioactive (Its atoms aren't big enough to be unstable)- however, after billions of dollars of research, we've failed to produce 1kw from the thing.

The risk from nuclear powerplants isn't too bad if we take necissary precautions (like using deionized H2O instead of molten Na metal for the cooling process), and it's likely to be used more extensively in the future (the earth's supply of uranium is nearly limitless - not to mention the tons of radioactive materials in space).

Biomass is using alternative fuels that come from plants (mostly corn).

Solar power is clean, but not very efficient (or cheap). The most expensive part of solar energy generators, are the actual panels (or mirrors, depending on the process). Instead, I propose that it is actually possible to use plants to produce harnessable energy through photosynthesis.

The science checks out - H2O + CO2 + Solar Energy => C6H12O6 + 02 (photosynthesis). C6H12O6 + O2 => CO2 + H20 + Free electrons (aerobic respiration).

It is possible to harvest the glucose produced by plants, and break it back down into CO2 and H2O via micro organisms. Then, the free electrons can be picked up via carbon electrodes, and voila!

But wait!!! This produces CO2!!! CNN told me that CO2 is bad!!! WTF??? - No problem. The C02 and H2O is sent right back to the plants for more photosynthesis - thus providing a closed system with no by-products, which (according to CNN) is good. :p
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"We can categorically state that we have not released man-eating badgers into the area."

-UK military spokesman Major Mike Shearer