A new study ranks alternative energy sources in terms of their overall impact on the environment and human health. The report offers guidance for policy makers making decisions on which emerging technologies to support.

Substantial investment in development of alternative energy sources is needed in order to meet greenhouse gas emissions targets. But policymakers must make tough choices when deciding which energy sources and emerging technologies to support.

The study assesses energy technologies not only for their ability to deliver energy, but also for overall performance in eleven different weighted categories, the most heavily weighted categories being CO2 emissions, mortality, resource abundance, footprint (land area required) and water consumption. Wind power emerges as a clear winner in the study, with other renewable technologies, including solar, geothermal and tidal power finishing ahead of nuclear power and coal combined with carbon capture and storage (CCS). Ethanol-based biofuels fared poorly. In addition to solutions designed to meet general energy needs, the study also considers twelve different combinations of energy sources and vehicles to meet transport needs.

Vehicle types considered are: battery-electric, hydrogen fuel cell and flex-fuel (able to run on a blend of petrol and ethanol). According to the results, wind, whether being used to power battery-electric or hydrogen fuel cell cars, offers the best all round solution.

In theory, all road vehicles in the US could be powered by less than 100,000 5 million watt (MW) wind turbines, resulting in dramatic reductions of up to a third in carbon emissions, as well as vehicle related air pollution deaths. Wind power is an 'intermittent' energy source and therefore the study also recommends combining a variety of other energy sources, such as solar and wave power, to ensure that supply meets hour-by-hour demand. In addition, well-informed grid planning and highly interconnected transmission systems could help avoid disruptions. Implementing the necessary changes will require cooperation at multiple levels of government.

Nuclear power performed badly in the study, ranking alongside coal combined with CCS in all the heavily weighted categories. But biofuels performed even worse - ethanol has a large land footprint and therefore reduces the land available for food crops, thus increasing mortality due to soaring food prices.

Energy and vehicle options, from best to worst, according to study's calculations: Best to worst electric power sources:

1. wind power

2. concentrated solar power (CSP)

3. geothermal power

4. tidal power

5. solar photovoltaics (PV)

6. wave power

7. hydroelectric power

8. a tie between nuclear power and coal with CCS

Best to worst vehicle options:

1. wind-BEVs (battery electric vehicles)

2. wind-HFCVs (hydrogen fuel cell vehicles)

3. CSP-BEVs

4. geothermal-BEVs

5. tidal-BEVs

6. solar PV-BEVs

7. wave-BEVs

8. hydroelectric-BEVs

9. a tie between nuclear-BEVs and coal-CCS-BEVs

10. coal-CCS-BEVs (tied with nuclear-BEVs)

11. corn-E85 (ethanol)

12. cellulosic-E85 (ethanol)

Source: Jacobson, M.Z. (2009). Review of solutions to global warming, air pollution, and energy security. Energy and Environmental Science. DOI: 10.1039/b809990c. Contact: jacobson@stanford.edu �Theme(s): Climate change and energy, Environmental technologies