A life-cycle assessment of small to medium sized heat producing bioenergy systems
Marcelle C McManus,* University of Bath
David Lewis, Royal Agricultural College, UK
Climate change and energy security have become major concerns in recent times and many countries have agreed, under the Kyoto Protocol, to reduce emissions of greenhouse gases. One of the ways in which this is being done is through the pursuit of bio-energy. As the carbon dioxide (CO2) released when energy is generated from biomass is generally balanced by that absorbed during the fuel's production it is often regarded as a ‘carbon neutral’ process. However, there are impacts associated with various stages of bioenergy production (1), including, for example, the boiler production and transportation of feedstock.
Bio-energy is unique amongst renewable energy in that it is not immediately dependant on the weather (unlike, for example wind and solar). However, it is also unusual in that it requires a feedstock of often bulky materials which can limit its capacity and the geographical extent of its supply chain (2). The production of this feedstock can also be associated with environmental consequences, with some citing rising food prices and land use conflict as an unwelcome side effect of its use. This is due to the land required to grow specialist biomass crops such as miscanthus or oilseed crops. One way to over-come the issues associated with “land squeeze” is to use waste wood from urban environments in small to medium scale heating systems. This study examines two such biomass heating systems within an urban environment in the South West of the UK. Both systems provide heat – one to a local community centre and one to a plant nursery. Life cycle assessments of the systems have been undertaken in order to examine their environmental costs and benefits.
The study explores the impact of allocation within the LCA and the impact of boiler size and the sourcing of feedstock. The energy payback of the systems is examined and compared, briefly, with other small distributed energy systems including micro-wind and solar thermal. This enables an understanding of the wider issues associated with energy supply and the ways in which our energy might be best produced in the future.
(1) Hammond, G.P. Kallu, S. & McManus, M.C. (2008) Development of biofuels for the UK automotive market, Applied Energy. Vol 85, Issue 6, pp 506-515
(2) Upham, P & Speakman, D. (2007). Stakeholder opinion on constrained 2030 bioenergy - scenarios for North West England. Energy Policy Vol 35, Issue 11, pp 5549-5561
* corresponding author: M.McManus@bath.ac.uk