Comparison of Energy Resources
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Unless you are manufacturing your generating technology completely with renewables, all electricity generation will result in some greenhouse gas emissions, whether they are the direct emissions from the smokestack of the powerplant, or the embodied emissions associated with manufacturing the generating technology. Exactly how much is emitted depends largely on your generating technology (both in terms of energy resource, and how the technology was manufactured.
Below is represented all of the readily available and reliable data on the subject that Lotus Live knows of. The values below have been derived by taking the lifecycle greenhouse gas emissions of the technology (stack and embodied), and dividing that by the expected electricity generation over the generator's lifetime to get a value for grams of greenhouse gas emissions per kWh. Emissions other than CO2 have been converted to an equivalent value of CO2.
As this graph indicates, there is quite a bit of variation in estimates. Some of this is due to variations in analysis methods, but much of it is due to how you manufacture the technology, how efficient it is, and where it is.
For each technology, an explanation (and a qualification of the accuracy of the data) is offered--derived from observations in the reports, and our own common sense.
- Hydropower: for run of river systems, there is little construction required and no expected vegetative effects, but for hydro dams, construction energy is high, and emissions from decaying plant matter in the reservoir may contribute markedly depending on location
- Geothermal: geothermal embodied emissions are not often investigated, and largely depend on what gases accompany the steam underground
- Wave: also not often investigated, depends solely on manufacturing and transportation energy
- Nuclear: depends largely on fuel enrichment method
- Biomass: depends on fuel source, if it is replanted, and processing energy
- Wind: depends mostly on the wind resource and utilization of the turbine
- Solar PV: depends on type of PV (thin film vs silicon, etc), what energy source was used to manufacture the cells, and insolation. High value is outlandishly high.
- The Fossil Fuels: depend on fuel quality, and efficiency of the conversion technology
For back of the envelope calculations, it is useful to have a single value that can be considered representative of the technology around the world. The following graph shows what we believe to be representative values, as they have been derived by averaging the midpoint values from each of the five studies. These values shouldn't be widely quoted, or taken as inherently true, as it really does vary quite a lot depending on the factors discussed above. For rough calculations, however, we hope these values will be very helpful.
For further reference, the primary sources:
- Greenhouse Gas Emissions from Energy Systems: Comparison and Overview (Swiss Paul Scherrer Institut 2003)
- Carbon Footprint of Electricity Generation (UK Parliament 2006)
- Table from "Hydropower-Internalized Costs and Externalized Benefits" (IEA 2000)
- Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis (UWM 2002)
- Assessing the Difference (IAEA 2000)
From EIA World Energy Overview 1995-2005
The following comparisons coming soon:
Author: Nick Enge
Special Thanks: Jane Woodward (Stanford), Gil Masters (Stanford), and Tony Kovcsek for introduction to many of these resources.
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