Renewable energy sources are: solar PV, bio-power projects (40g of CO2 per kWh) and concentrated solar power (27g CO2 per kWh).

Cradle-to-grave greenhouse gas emissions from solar photovoltaics are about 5 percent of those from coal; wind power and solar energy are about equal in emissions; and nuclear energy is on a par with renewable energy, according to a new study by the National Renewable Energy Laboratory, which claims to use a more precise method for calculating life cycle emissions of such technologies.

In Meta-Analysis of Life Cycle Assessment, published in the Journal of Industrial Ecology, NREL analysts looked at more than 2,000 studies across several energy technologies, and “harmonized” the results by applying quality controls and narrowing the range of estimates for GHG emissions.

NREL says its new approach to assessing GHG emissions from energy technologies is more accurate than previous method that relied heavily on estimates. It hopes the study will give stakeholders a clearer view of the likely environmental impacts of various projects.

According to the harmonized results, the median solar photovoltaic project produced 40 grams of CO2 equivalent for every kWh of energy produced, compared to the 43 grams per kWh estimated by the same results before the quality controls were applied.

Median life-cycle emissions from those coal power projects harmonized stood at 979g of CO2 per kWh, slightly less than the 1,001g of CO2 per kWh from the results pre-harmonized. Emissions from natural gas after harmonization averaged out at 467g of CO2 per kWh.

Nuclear power had median emissions of 12g of CO2 per kWh, lower than that for renewable energy sources solar PV, bio-power projects (40g of CO2 per kWh) and concentrated solar power (27g CO2 per kWh).

Wind power (11g of CO2 per kWh) is the only renewable energy with a lower harmonized median life-cycle emissions total than nuclear power, according to the results.

In April, NREL and the EPA released a tool to determine the feasibility of on-site renewable energy projects on vacant and contaminated land. The alternative energy “decision trees” aim to give landowners, communities and elected officials ways to evaluate sites for solar and wind energy potential from a logistical and economic standpoint, without the need for technical expertise.