The problem of replacing our dependence on fossil fuels is complex. In Thinking Critically About Sustainable Energy (TCASE) #12, a checklist was provided to allow assessment of energy transition plans. The sort of questions listed in TCASE 12 are critical for evaluating the feasibility of future scenarios, like the ones from the recent IPCC report on renewable energy.

However, we also need to assess the capabilities of individual technologies to mitigate CO 2 emissions, effectively (and economically). The following is a list of criteria that can be used to determine the relative viability of various alternative technologies. This comes from the work I had published recently in the peer-reviewed journal Energy (with colleagues Martin Nicholson and Tom Biegler):

Proven: Has the technology been used at commercial scale?

Scalable: Can the technology be built in sufficient quantity to replace significant proportions of existing fossil-fuel generators?

Dispatchable: Can the output be allocated by the system operator to meet the anticipated load?

Fuel supply: Is the energy source reliable and plentiful, even when, as with some kinds of renewable energy, it varies with time?

Load access: Can the generator be installed close to a load centre?

Storage: Does the technology require electricity storage in order to deliver a high capacity factor?

Emission intensity: Is the emission intensity high, moderate or low (as defined in the table below)?

Capacity factor: Is the capacity factor high, moderate or low (as defined below)?



For a technology to be considered fit-for-service (FFS) as a baseload generator (i.e., a direct replacement for coal or combined-cycle gas power plants) it needs to be scalable, dispatchable without large storage and have a reliable fuel supply, low (L) or moderate (M) emissions intensity and a high capacity factor as defined in the table above. Load access is considered to be desirable for transmission cost reasons but is not essential to meeting baseload demand.

The technologies that score well enough to meet the FFS criteria are pulverised fuel black coal with carbon capture and storage (PF Coal/CCS), integrated gasification combined cycle coal with CCS (IGCC/CCS), combined cycle gas turbine with CCS (CCGT/CCS), nuclear power, and solar thermal with thermal storage and/or hybrid gas (STE).

Engineered geothermal systems (EGS or hot dry rocks: HDR) could also qualify, but is only at the pilot plant stage of development and furthermore there are inadequate reliable cost data for it. At present, the use of large-scale electricity storage is prohibitively expensive in most networks. There are significant economic issues in deploying storage, stemming from the high capital costs and complexity of operating in liberalized energy markets.

In our Energy paper (cited above), we did a meta-review of of 14 authoritative peer-reviewed studies, published during the last 10 years, of electricity generating technologies (for those that met the FFS criteria, as listed in the table above) to determine their life-cycle greenhouse gas emissions (expressed in units of kg CO 2 eq/MWh). The results are tabulated below (references in footnote).

The results of this survey represent the scientific/engineering/economic consensus of the world-wide, authoritative, peer reviewed energy literature. As such, you should bear these criteria and life-cycle analysis (LCA) figures in mind when discussing various alternative energy technologies. For a related discussion about cost, see here.

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Footnote – references for LCA table:

Audus H, Freund P. Climate change mitigation by biomass gasification combined with CO2 capture and storage. UK: IEA Greenhouse Gas R&D Programme; 2005.

ExternE-Pol. Externalities of energy: extension of accounting framework and policy applications: new energy technologies. Final Report on Work Package 6, European Commission, http://www.externe.info/expolwp6.pdf; 2005.

Gagnon Luc, et al. Life-cycle assessment of electricity generation options: the status of research in year 2001. Energy Policy 2002; 30:1267e78.

IPCC. Carbon capture and storage, http://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf; 2006.

ISA University of Sydney. Life-cycle energy balance and greenhouse gas emissions of nuclear energy in Australia, http://www.isa.org.usyd.edu.au/publications/documents/ISA_Nuclear_Report.pdf; 2006.

Lechón Yolanda, et al. Life cycle environmental impacts of electricity production by solar thermal technology in Spain. SolarPACES; 2006.

Meier Paul. Life-cycle assessment of electricity generation systems and applications for climate change policy. University of Wisconsin; 2002.

MIT. The future of coal – options for a carbon constrained world, http://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf; 2007.

NEEDS. Technology assessment under stakeholder perspectives. Stefan Hirschberg. Feb 2009. http://www.needs-project.org/2009/16-02-2009/Hirschberg.ppt.

NREL. Biomass power and conventional fossil systems with and without CO2 sequestration, http://www.nrel.gov/docs/fy04osti/32575.pdf; 2004.

Succar Samir, Greenblatt Jeffery B, Williams Robert H. Comparing coal IGCC with CCS and wind-CAES baseload power options, http://www.princeton.edu/ssuccar/recent/Succar_NETLPaper_May06.pdf; 2006.

Tokimatsu Koji, et al. Evaluation of lifecycle CO2 emissions from the Japanese electric power sector in the 21st century under various nuclear scenarios. Energy Policy 2006; 34:833e52.

Weisser D. A guide to life-cycle greenhouse gas (GHG) emissions from electric supply technologies. Energy 2007; 32(9):1543e59.

World Energy Council. Comparison of energy systems using life cycle assessment, http://www.worldenergy.org/documents/lca2.pdf; 2004.