31 October 2006

Useful information for decision makers

LCA Study Provides Comparison of Different Energy Systems

World Energy Council's LCA (Life Cycle Analysis) study, completed
under leadership of Finnish experts, gives relative characteristic
features of various primary energy sources related to decision-
making. The comparison is based on results of LCA studies during
last 10 – 15 years.

Factors important for 
                                    Coal   Oil   Gas   Biom. Nuclear Hydro Wind Solar

Energy accessibility      F     M     M        M            F           F         D       D   
(related to the direct
costs of energy)
Energy availability         F     M      M        M            F           F         D       D
(related to the security/
reliability dimension)
Energy acceptability     D      D     M          F            F           F         F        F

Relative rankings in the perspective of factors for decision making:

F = energy source in favourable position
M = energy source in medium/neutral position
D = energy source in disfavoured position

Payback ratio - a useful way to compare energy efficiency 

An interesting way to compare different energy systems for producing electrical energy is to calculate the payback ratio (or net generation ratio) of the systems.

The energy payback ratio is the ratio of the net electrical energy produced over a plant's lifetime to the energy required to build, maintain and fuel the plant over its lifetime, converted to the corresponding amount of electrical energy.

Following table is collected from different sources:

Production form                               Payback ratio

Coal burning plants*                            5-11
Combined cycle gas power plants*   2-4
Nuclear power*                                      16
Bioenergy**                                           4-16
Wind power*                                         9-20
Solar power*                                           6
Hydro with reservoir***                      50-260
Hydro run-of river***                           30-270

Some of these results are very case-specific. For instance, the payback ratio of gas power plants depends on the needed infrastructure or gas pipeline system. 

Bioenergy means in different areas using of different fuels ranging from straw, canary reed and willow to forest residues and waste fuels.
Thus, the payback rate may vary a lot. The table ratios 4 – 16 for  bioenergy are based on different production and conversion
scenarios of a short rotation willow. A poplar biomass crop gasified for electricity production gives a payback ratio of around 16.

The payback ratio of hydropower varies strongly depending on the used technology and ambient conditions.   


*Comparison of Energy Systems using Life Cycle Assessment, A
Special Report of the World Energy Council, London, 2004

*WEC's LCA study, LCA-based Comparision of Energy Systems, 
Ami Rastas, Chairman of WEC's LCA Study Group, Energia 2/2005,
p. 36-38 (in Finnish)

**A Master's Thesis Life Cycle Assessment study in Sweden by Erik
Daugherty found net energy ratios between 4 and 16 for different
production and conversion scenarios of a Short Rotation Willow to
electricity system.

**NREL's Life Cycle Assessment of a poplar biomass crop gasified
for electricity production conducted by Rafaschieri et al. found a net
energy production ratio (electricity to the grid divided by total fossil energy consumed by the system) of around 16.

***Life-cycle assessment of electricity generation options: The status
of research in year 2001, Luc Gagnon, Camille Belanger, Yohji
Uchiyama; Energy policy 30 (2002) 1267-1278
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