Clean Electricity
Clean energy is a concept that’s getting more attention from the public, industry and policymakers. But clean is a subjective and qualitative metric that does not measure anything unless specified. For most people, due to the increased popularity of climate change, clean energy means energy that does not have greenhouse gas emissions. When it comes to energizing technology and our modern way of life, there is no cleaner and more efficient source than electricity.
Electricity must come from a source, and it’s then that we have to evaluate the source of this power to determine whether the electricity was generated cleanly or not. For most, electricity generated from wind or solar is the only source of clean energy, but there are other sources that are low in greenhouse gas emissions over their entire lifecycle: nuclear, hydro, geothermal, hydrogen, or biomass. A very common misconception is that any of these are completely greenhouse gas free, but they require the input of energy to process the materials and manage the waste in order to produce electricity. Smelting of metals, mining for minerals and refining petrochemicals are energy-intensive processes that are mostly technologically feasible with hydrocarbons.
As such, it’s important to note that not only greenhouse gases are emitted across the lifecycle of the different electricity sources. Due to either the burning of hydrocarbons, microbial activity in hydropower reservoirs, or chemical processes, many other harmful substances are emitted along the way. CO2, CH4,N2O,HFC-134a,BC,SO2, CO, OC, NOx, NH3 may be emitted to the air to name just a few. Their impact is different, for example, CO2 is harmless but it induces warming, while SO2 leads to cooling but is toxic and leads to acid rain. It is thus essential to measure all of the atmospheric emissions associated with sources of electricity to be able to measure what is truly clean. On this case, we will focus on those that have the biggest impact due to a mix of both their volume and their associated harm: carbon dioxide (CO2), sulfur dioxide (SO2) and nitrogen oxides (NOx).
Based on Turconi, R., Boldrin, A., & Astrup, T. (2013), we can compare different generators of electricity and compare them to fossil-fuel based power plants to measure their impact on atmospheric emissions of CO2 eq. (here onwards simply CO2),SO2 and NOx. The level of emissions depends on the conditions and processes of the different technologies, for instance, solar photovoltaics (PV) from countries with stringent environmental regulations could have much lower emissions than countries with no regulations, while the location and energy source of the supply chain might cancel the previous effect. Image below shows the lower and upper bound estimates for the emissions released per unit of electricity generated for different electricity sources, including fossil fuels.
As shown above, different energy sources have varied impacts based on what you measure. In order to determine which one is more clean, we need to have a way to compare the different pollutants. A straightforward way to do is by valuing the damage associated to a unit of emissions released to the atmosphere in monetary terms. While this is far from a perfect measurement and relies on several assumptions, it is a useful glimpse. Using Shindell (2015) The social cost of atmospheric release, we can associate the cost of a ton of the pollutants of interest. Assessments of social damages rely on the physical-sciences-based risks, their economic value, and the value of present versus future risk.
These assessments are therefore highly uncertain, but Shindell’s is useful as a baseline. The author estimates the social damage of several pollutants based on their air quality impact on health, and the climate impacts. Since it omits other important factors such as acidification, biodiversity loss, or nitrogen deposition, it can be considered a conservative estimate. We are doing two comparisons: comparing the best case and worst cases scenarios. We are using a 3% discount rate (i.e., the value of future vs present).
There might be cases where fossil fuels can be cleaner than some sources usually considered as clean energy. Context is key, thus it depends on the supply chain and energy fuel of the processes that ultimately lead to electricity generation by source. Except in the case of coal and oil, NOx emissions are the largest impact for each electricity source, irrespective of whether they are low carbon or not. Interestingly, carbon is the highest impact of all fossil fuels only in their lower bound. For this reason, the concept of clean electricity as no carbon emissions at the power plant is fuzzy and misleading, a more comprehensive analysis is needed in order to assess at least a low impact on emissions vented to the atmosphere.
Based on previous assumptions, and using the definition of clean as the lowest economic damage from lifecycle emissions of CO2, SO2 and NOx, the cleanest sources of electricity are hydroelectric power and nuclear power. Though it is important to mention that the data from Turconi, R., Boldrin, A., & Astrup, T. (2013) omits hydroelectric powers at tropical areas, where CO2 eq. emissions are higher due to methane released from the reservoir. We are also only measuring three pollutants emitted to the atmosphere, and neglecting the impact on land use, soil pollution and water pollution. And while different sources have different externalities, other benefits such as reliability, affordability and availability might offset the damages. A systematic approach and holistic study of energy use and conversation is of the utmost importance to assess the lowest polluting sources of electricity.
