Community energy: A practical guide to reclaiming power

Biomass can be a renewable fuel when it comes from sources such as forest residues, tree surgery waste, food waste, agricultural waste and other wood residues (such as sawdust).

In theory you are emitting CO2 by burning wood, but the idea is this carbon will eventually be absorbed by new growth that replaces what you have burned.

However, it is not always a given that this new growth will take place. And we know we are in a crucial decade for the climate, and we need to take carbon out of the atmosphere! This is why biomass is not suitable for large-scale deployment, but for some communities, it can be part of the solution, in particular when local resources are sustainably managed.

Biomass is a versatile material that can be used to produce:

• Heat, for space or hot water,
• Electricity
• A combination of heat and power (electricity) in a Combined Heat and Power (CHP) plant.

Types of biomass

1) Wood

Wood can be used in the form of logs, wood chips and wood pellets, for wood stoves or wood-chip boilers used for space and water heating. Wood chips are generally only used in larger boilers, such as those used in schools, community buildings and offices.

On a larger scale, wood can be used for the production of electricity. The main method for this is combustion plants (where wood is burned to produce steam). However community projects should never be involved in the burning of whole trees, or other activities that participate in deforestation.

2) Agricultural waste

Other methods using biomass taken up by farmers are by-products of conventional agricultural activity. They include:

• “Dry” agricultural wastes, such as straw that can be burned to produce energy.
• “Wet” wastes such as green matter or slurry can be “digested” to produce methane in a process known as anaerobic digestion. This can be used to fuel a gas engine to produce electricity and heat.

There are already examples of chicken litter combustion, animal slurry digestion and straw combined heat and power projects working well in this country. In many cases, however, these projects are only economically viable if an outlet can be found for the heat produced such as nearby factories and the by-products fertilisers for farms.

Keep in mind that large-scale animal farming also comes with many ecological issues — if you are increasing their profits with bioenergy, you may be supporting and perpetuating an exploitative and unsustainable system.

3) Municipal and industrial waste

Municipal waste products need to be minimised or recycled wherever possible. However, there will always be some requirements for disposal. Some forms of municipal and industrial waste can be described as biomass — such as waste food and wood waste (from the construction industry, for example).

Many local authorities now operate a waste food collection service. The waste food is recycled and used to produce compost, or used for the production of electricity in an anaerobic digestion plant (a biogas plant).

Whether the burning of other types of municipal waste to produce energy can be described as renewable is a matter of some debate. There can be environmental benefits if waste is used to generate electricity and/or heat, such as reducing demand for landfill space. However, emissions and residues can cause environmental problems.

What is important to avoid creating a demand for waste. If there is unsustainable food waste in a community, setting up a power plant to use that waste makes tackling the original problem unlikely. Often, biogas plants are a better way of treating organic waste when they can produce energy as well as organic fertiliser.