Humans have always relied on plants for fuel. It is only in the last 200 years that we have utilised fossil sources to provide our heating needs, drive our industrial processes, give us light and power our vehicles. In this short time the world has changed immeasurably but these sources of energy which have taken millions of years to form are now already beginning to diminish. The tremendous changes that fossil fuels have afforded have also bestowed an unfortunate legacy. We are now facing climate change at an unprecedented rate and to halt the onset of global warming we must attempt to turn the clocks back.
Growing crops to provide energy is not a new phenomenon. In the days before trains and motor cars we relied on transport by horses and these organic vehicles were powered by oats! The energy crops of today include some that are familiar such as oilseed rape and sugar beet for transport fuels and others that are less so such as willows and poplars grown as short rotation coppice (SRC) and miscanthus for heat and electricity.
Producing energy from the land has several advantages. Home grown sources are more secure than fossil fuel imports that tend to originate from volatile areas of the world. Additionally, unlike other renewable energy sources biomass supplies are not intermittent. Whereas the sun needs to shine for solar power and the wind needs to blow for wind power, biomass can be stored and used as and when required.
Types of biomass
Biomass energy is the most diverse and versatile form of renewable energy. It involves plant and animal material that can used to provide heat, electricity and transport fuels. Below are some examples of how different types of organic matter can be converted to useful energy.
|Energy conversion method||Useful energy produced||Feedstock|
|Combustion (also advanced technologies such as gasification & pyrolysis)||Heat and electricity||Wood, straw and other forestry and agricultural bi-products|
|Anaerobic digestion||Biogas (a mixture of methane and CO2) which can be burnt to produce electricity and heat, used as a vehicle fuel or injected into the gas grid for heating buildings.||Animal manures, food wastes, non woody crops & bio-degradable matter in landfill sites & sewage farms|
|Fermentation||Liquid fuels for vehicles||Wheat and sugar beet to produce bioethanol (similar to petrol) or oilseed rape to produce biodiesel|
Woodfuel is one of the most important sources of biomass energy. This is used in both large and small projects to produce electricity and heat. For instance, in many coal fired power stations wood dust is mixed with coal and co-fired to produce electricity. In addition, there are a number of dedicated biomass power stations such as Stevens Croft and Wilton 10 which use a number of different sources of wood. In these large plants it is virtually impossible to use the low grade heat produced. As a result a great deal of the energy content of the wood is not utilised.
Greater efficiencies can be achieved when woodfuel is involved in small to medium scale projects on the local level. Biomass combined heat and power (CHP) schemes can be as much as 85% efficient but there are currently only a few examples in the country. However, with major new housing developments planned this is unlikely to be the case for long. The use of woodfuel as a feedstock for biomass boilers for heating schools, social housing, hospitals, glasshouses and estates is currently the most sustainable market for woodfuel as this tends to use locally sourced wood which reduces the distance the fuel needs to be transported. Small–scale heat markets provide the potential for growers to add value to their crop. In many cases the wood chip can be sold for a higher price than for larger electricity projects. Some examples of biomass energy production and case studies are listed below:
|Scale||Biomass facility||Feedstock||Energy product||Examples/ Case studies|
|Macro||Co-firing with coal in a large power station||Energy crops, palm kernels, olive stones etc||Electricity only||Drax Power Station|
|Large||Dedicated biomass plant||Waste wood, forest co-products, straw, energy crops||Electricity only||Steven’s Croft; Wilton 10; Eccleshall|
|Medium||Combined heat and power scheme||Waste wood, forest co-products, energy crops||Heat and electricity||Aberdeenshire Housing Association|
|Medium||Large scale woodchip boiler||Wood chip from forestry, arboricultural arisings, energy crops||Heat only||Strabane Mills; Royal Cornwall Hospital; Lanoyce nurseries|
|Small||Small scale woodfuel boiler||Wood chip, logs, pellets||Heat only||Ansty Manor|
|Micro||Household scale woodfuel boiler||Logs, pellets||Heat only||Priors Farm|
|Pico||Room heater||Logs, pellets||Heat only||Yeo Valley|