by Tim Storer
Renewable energy sources, such as wind power generation, are often touted as preferable alternatives to fossil fuels because they produce electricity in an “emissions-free” manner. In actuality, some emissions are created during the production, distribution, and disposal of these technologies, making them not a truly “emissions-free” means of energy production. In order to determine the real relative advantages of various energy sources (in respect to carbon emissions), the full life cycle must be considered. Daniel Nugent and Benjamin Sovacool conducted a literature review of 153 lifecycle studies examining total carbon emissions associated with energy from wind and solar plants and determined estimates of industry averages. Of the 41 studies deemed “best,” an average of 34.1 g CO2/kWh was seen for wind energy and 49.9 g CO2/kWh for solar. Among these cases, substantial variability was observed, with wind emissions varying between 0.4–364.8 g CO2/kWh and solar emitting 1–218 g CO2/kWh.
When conducting the literature review, 153 peer-reviewed papers were initially found that discussed the issue of lifecycle emissions from renewable energy. Of those studies, some were excluded for poor relevance, old dates, unoriginality, and inability to consider all sources of emissions. Studies published before 2003 were not considered. Once narrowed down to a more accurately representative sample, the remaining 41 studies were considered for analysis.
For both solar and wind energy, 71% of the total emissions came from cultivation and fabrication, which consist of multiple stages. This percentage includes resource extraction necessary for the final products and processing the materials —two stages that often involve the use of petroleum. Construction yields another 20% of emissions and the remainder come from operation. Decommissioning actually yields a net loss in emissions because the materials are often recycled, especially in the case of wind energy, where “–19.4%” of its emissions arise.
The final average emission values for wind are only part of the story. Most values tend to be much lower, but the averages were brought up by two studies that predicted drastically higher emissions of 138–220 and 364.83 g CO2/kWh. In the second and highest case, the extra-high emissions came from the storage batteries needed for that system. Several factors were found to reduce emissions in wind energy systems, such as longer lifespan, excluding battery backup, increased height, and building offshore. Storage systems for wind energy are often proposed to help combat intermittent power supply, but the higher emissions from these systems adds complication, especially considering that one main advantage of wind power is its low-carbon status.
Nugent and Sovacool list three main conclusions: first, more scrutiny is needed in the research of emissions from renewable energy systems. Only a small fraction of the existing literature was usable for their study due to various methodological issues. Second, the specific configurations of a wind or solar project can drastically change GHG emissions, and such consequences should be considered. Third, even when including the outlier examples, the average value of 34.1 g CO2/kWh for wind energy is drastically lower than coal or natural gas, which have emissions of 960–1050 and 443–611 g CO2/kWh respectively. So while wind power is by no means “emissions-free,” it is still a significantly more climate-friendly option than fossil fuels. It should also be noted that these studies assume energy changes are done in isolation, and that the materials are being produced in a society that still generates power from fossil fuel sources. Emissions would likely be lower if, for example, wind turbines were constructed using energy from other wind turbines.
Daniel Nugent and Benjamin K. Sovacool, 2014. Assessing the lifecycle greenhouse gas emissions from solar PV and wind energy: A critical meta-survey. Energy Policy, Vol. 65: 229–244.