P.J. Meier, Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis, Ph.D. Dissertation, University of Wisconsin – Madison, 2002.

Abstract

Minimizing greenhouse gas emissions may prove to be the most significant technical and political challenge facing energy decision-makers today. The U.S. electric industry contributes over one-third of domestic emissions and is arguably the most important component for effective greenhouse gas mitigation. This research uses Life-Cycle Assessment (LCA) to better understand the energy and environmental performance of electricity generation systems. The results of the LCA are used to provide an effective and accurate means for evaluating greenhouse gas emission reduction strategies for U.S. electricity generation.

LCA is performed for two electricity generation systems, a 620 MW combined-cycle natural gas plant, and an 8kW building-integrated photovoltaic system. Consideration of life-cycle energy requirements significantly reduces the net energy performance of both systems. The modern natural gas plant considered in this thesis is nominally 48% thermally efficient, but it is only 43% energy efficient when evaluated across its entire life-cycle, due primarily to energy losses during the natural gas fuel cycle. The performance of an 8kW building-integrated photovoltaic system is also reduced significantly when evaluated over its life cycle. The module’s sunlight to DC electricity conversion efficiency is 5.7%; however, the system’s sunlight to AC conversion efficiency is 4.3%, when accounting for life-cycle energy inputs, as well as losses due to system wiring, AC inversion, and module degradation. The meaningfulness of efficiency comparisons between technologies is discussed and limitations are identified which make such comparisons of limited value due to the varying quality and availability of energy sources.

The LCA results drastically increase the greenhouse gas emission rate for the natural gas system. The emission rate for the combined-cycle natural gas plant life-cycle (469 tonnes CO2-equivalent per GWeh), was 23% higher than the emission rate from plant operation alone (382 tonnes CO2-equivalent per GWeh). This increase is due mainly to fuel-cycle emissions of which methane releases account for over half. There is a wide range of published estimates of fuel-cycle methane releases, with commonly cited estimates ranging from 1 to 4% of natural gas production. Because methane is a strong global warming agent, this uncertainty leads to a potential range of emission rates between 457 to 534 tonnes CO2-equivalent per GWeh for the studied plant.

The LCA illustrates that the PV system has a low, but not zero, life-cycle greenhouse gas emission rate of 39 Tonnes CO2-equivalent per GWeh. This value is higher than other nuclear and renewable systems studied previously, including nuclear fission (15 Tonnes CO2/GWeh), wind (14 Tonnes CO2/GWeh), and future DT fusion (9 Tonnes CO2/GWeh) technologies. The PV emission rate (39 Tonnes CO2-equivalent per GWeh) is insignificant in comparison to the natural gas plant (469 Tonnes CO2/GWeh) or a previously studied coal plant (974 Tonnes CO2/GWeh).

In addition to reducing emissions, effective climate change policy must also address the growing demand for electricity. This demand will likely be met with diverse energy sources, including coal, gas, nuclear, and multiple renewable technologies. Evaluating the total greenhouse gas impact from any combined electricity system is difficult, as it requires the assimilation of emission factors and generation from each technology. A ternary method of evaluation is developed that provides a simple means to compare greenhouse gas reduction alternatives. Life-cycle emissions, in particular from the natural gas fuel-cycle, are shown to add valuable insight in the evaluation of mitigation alternatives.

Three greenhouse gas mitigation alternatives are evaluated with the ternary method: 1) fuel switching from coal to natural gas for Kyoto-based compliance, 2) fuel-switching from coal to nuclear/renewable for Kyoto based compliance, and 3) fuel switching to meet the White House House’s Global Climate Change Initiative. In a moderate growth scenario, fuel-switching from coal to natural gas fails to meet a Kyoto-based emission target, while fuel-switching to nuclear/renewable meets the emission objective by reducing coal generated electricity 32% below 2000 levels. The White House’s Global Climate Change Initiative is shown to allow for a 14% increase in U.S. greenhouse gas emissions over 2000 levels and annual greenhouse gas emissions that are 54% higher than the proposed U.S. commitment under the Kyoto Protocol.

Full Text: meier-thesis.pdf

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