Final answer:
Bio-digesters produce renewable energy by converting the solar energy stored in biomass through photosynthesis into biogas for various energy needs.
Step-by-step explanation:
The energy source generated by a bio-digester is renewable energy. Bio-digesters utilize organic material such as plant waste or animal manure to produce biogas through anaerobic digestion. This biogas can then be used to generate electricity, heat, or transportation fuels. Bio-digesters are a means of converting the solar energy stored in biomass through photosynthesis into usable energy. Therefore, the correct choice for the type of energy produced by a bio-digester is (a) Renewable Energy.