Which of the alternative energy sources do you think would have the least impact on the environment.

Solar Power, Microbial fuel cell. These two and I am sure other ways as well Solar power as you guess use the sun as a power energy source with non-waste and long lasting use. Microbial fuel uses the bacteria aka decomposers turn the sugars, nutrients into rich soil while also releasing electrons back into the soil and can be used as a energy source.