How to switch to renewable energy

Generating biomass energy and anaerobic digestion


Biomass energy accounts for around 85 per cent of the UK's renewable energy supply. Biomass refers to organic materials, such as wood, straw and energy crops, which can be used to generate electricity, heat and motive power. The energy is released by burning and fermentation.

The payback period for biomass systems is generally five to 12 years, though this can be significantly shorter if free waste wood is available.

Anaerobic digestion is another method of converting biomass into energy. In this process, organic material is broken down by bacteria, in the absence of oxygen, to create methane-rich biogas. This can then be burned to generate heat and electricity. The solid waste from the process is called digestate and can be used in a similar way to compost.

The payback periods for anaerobic digestion plants vary widely, but could be between five and ten years.

Advantages of biomass energy and anaerobic digestion

  • You can use waste by-products to generate energy and reduce your waste disposal costs.
  • It can be used in combination with a combined heat and power plant to generate both electricity and heat.
  • Burning biomass fuels releases lower net carbon dioxide emissions than burning coal and gas.

Disadvantages of biomass energy and anaerobic digestion

  • You need to control emissions from burning biomass materials to prevent local air pollution. Any system you install must comply with legislation such as the Clean Air (Northern Ireland) Order.
  • Storing biomass fuels can require a large amount of space.
  • It can be difficult to find a secure supply of fuel. If you intend to use by-products from your business you must ensure that suitable quantities will be available.
  • If you're having fuel delivered, you'll need to consider the environmental impact of fuel transportation.

Complying with waste controls

If you anaerobically digest waste to generate gas for heat or electricity you must have a pollution prevention and control permit or waste management licence.

You must comply with waste regulations including the duty of care. If you are collecting and transporting other people's waste you will need a waste carriers licence.

The Northern Ireland Environment Agency (NIEA) and the Waste & Resources Action Programme have created a quality protocol for anaerobic digestate. If you follow the protocol, you can produce a high quality digestate which can be sold without waste handling controls. For example, if it is not classed as a waste, you do not need to transport it using a waste carrier or with a waste transfer note.

Download the quality protocol for the production and use of quality compost (PDF, 180K).

If you use parts of animals, products of animal origin or food and catering waste you must comply with animal by-product controls.

Prevent odour from your anaerobic digester

You must prevent your anaerobic digester causing an odour nuisance to your neighbours. You must design your digester, storage areas and delivery areas to minimise the escape of odour and liquids.

Reduce your digester's operating temperature and use a two-step digestion process by pasteurising your material first, to reduce odour problems.