Reflections on Greenhouse Gas Life Cycle Assessment

Abstract

The amount of carbon dioxide equivalent greenhouse gas emitted per unit of electricity produced is an important consideration in the planning of future greenhouse gas reduced electricity supply systems. Useful estimates of emissions must also take into account the entire cradle to grave life cycle emissions of alternative systems. Thus emissions of greenhouse gases take into account all of the components of building, operating, and decommissioning facilities. This requires an accounting of emissions from production of all materials used to build the plants, transportation of materials to the site as well as fuels used for their construction, operation, and decommissioning. The construction of facilities may also have effects which tend to affect greenhouse gas emissions through modification of the local environment. A notable example, often cited, is the evolution of methane from the decay of organic matter submerged by dams built to serve hydro power facilities.In the long term, we anticipate that some kind of cost will be associated with the release of greenhouse gases. In that event it may be argued that the modified economic system established by inclusion of this cost will naturally control the emission of greenhouse gases from competing means of electricity production. Greenhouse gas emissions from all stages involved in the birth and retirement of electricity producing plant could be suitably constrained as the least cost method of production is sought. Such an ideal system is far from in place. At this point in time the results of life cycle accounting of greenhouse gas emissions are a needed means of comparing emissions from alternative sources of electricity.Many life cycle studies have been undertaken in the past. Many of the estimates are based on past practice which does not take into account any possible need to limit the production of greenhouse gas during the design of the plant and operational processes. Sources of energy used to produce materials and operate facilities vary naturally with geography and local economic constraints. Possibly greenhouse emissions resulting from materials or fuels which are produced in another country (or province) are not taken into account since it is assumed they are the responsibility of others. The studies thus show a wide variation in emissions from each primary energy source used to produce electricity.This presentation reviews results from some life cycle studies to show the range of emissions which have been estimated on the basis of past practice and which might be expected in the future when explicit attention to greenhouse gas emissions is factored into the system design process. The presentation depends on two earlier publications for technical data. These two papers are printed, with permission, for participants reference in the proceedings of the symposium.