Biomass is the use of energy crops. Sunlight is used by plants to convert carbon dioxide (CO2) into carbon rich plant material, thus during the growing cycle CO2 is removed from the atmosphere. When the crops are harvested and burnt their stored carbon is combined with oxygen in the air to create CO2. The whole process can be close to carbon neutral.
Biomass boilers burn wood chips and pellets made from sawdust or other energy crops. This produces heat which can be used directly or to power a generator to produce electricity. These can range from small domestic central heating boilers through to commercial and district heating schemes.
Cereals such as maize and sugar cane can be fermented to produce ethanol and biodiesel. The process is typically fairly energy intensive so not truly carbon neutral. New processing methods are being refined that are more efficient.