Biomass power in essence means extracting energy from plant matter. This can be done either by burning it, or digesting it with enzymes to release methane that can be burned.
It can be used either to generate electricity, to heat buildings or even both. Biomass has the advantage of being ‘carbon neutral’. Any carbon released to the air by burning is the same amount that was absorbed by the plants as they grew. No additional gases are added to the atmosphere.
Biomass energy may add an extra way that clean electricity can be generated, but it is unlikely to become a major source of power by itself. Too much land would have to be devoted to growing crops for power instead of food. Wind and wave power are more likely to deliver electricity on a scale that would make an alternative to fossil fuels.
Where biomass is likely to be very useful is in heating individual homes, or as part of combined heat and power systems. Equally it can be a way to retrieve energy from waste products, such as stubble in fields after harvest, or using up methane produced by landfill waste dumps.