What is biomass?
Biomass is a scientific term for living matter, and is also used for products derived from living organisms. Biomass used for heat and electricity production comes from recently grown plants and the waste from animal husbandry and includes agricultural and forestry residues, energy crops, and the biodegradable components of municipal and business wastes.
Biomass can be used as a fuel to provide heat, electricity or fuels for transportation. Although biomass releases carbon dioxide (CO2) when burned it differs from fossil fuels in that the CO2 was recently absorbed from the atmosphere when the plants grew.
Is biomass really a renewable source of energy?
Renewable energy is any energy source that can be either replenished continuously or within a moderate timeframe, as a result of natural energy flows.
If biomass is cultivated and harvested in a way that allows re-growth without depleting nutrient and water resources, it is a renewable resource that can be used to generate energy on demand, with little net additional contributions to global greenhouse gas emissions.
Burning biomass efficiently results in little net emission of carbon dioxide to the atmosphere, since the bioenergy crop plants actually took up an equal amount of carbon dioxide from the air when they grew. As with all combustion processes some nitrogen oxides are produced but these are comparable to emissions from natural fires, and generally lower than those from burning fossil fuels. Utilisation of biomass residues which would have otherwise been dumped in landfills greatly reduces greenhouse gas emissions by preventing the formation of methane.
The DTI estimates net life-time CO2 emissions in grams per unit of electricity power generation (g/kWh) are as follows:
- Energy crops (65)
- Unsorted municipal solid waste (348)
- UK current generation mix (460)
- Coal (1200)
How much biomass exists?
Worldwide, total biomass is a huge resource estimated as 1,250 billion tonnes of dry plant matter, containing 560 billion tonnes of carbon, and equivalent to about 60 years of world energy use. However, the Earth actually grows every year about 130 billion tonnes of biomass on land and a further 100 billion tonnes in the rivers, lakes and oceans. The energy content of this annual biomass production is estimated to be more than 6 times world energy use.
Estimates of how much of the Earth’s land-based biomass production is used by the human population worldwide range from 2% to over 30% including food, animal fodder, timber and other products, as well as bioenergy. The higher estimates include a lot of wasted material and activities such as forest clearance.
How much of our energy supply comes from biomass today?
Worldwide, biomass is the fourth largest energy resource after coal, oil, and natural gas – estimated at about 14% of global primary energy (and much higher in many developing countries). Biomass is used for:
- Heating such as wood stoves in homes and for process heat in bio processing industries
- Cooking especially in many parts of the developing world
- Transportation fuels such as ethanol
- Electric power production; installed capacity of biomass power generation worldwide is about 35,000 MW
How do plants store energy?
During photosynthesis, plants use sunlight to combine carbon dioxide from the air and water from the ground to form carbohydrates, the biochemical building blocks of biomass.
The solar energy that drives photosynthesis is stored in the chemical bonds of the carbohydrates and other molecules in the biomass.