How green is Solar Energy compared to fossil fuels?

No energy source is a zero-emission solution. Criticism is sometimes made of renewable energy by claiming that they are not in fact ‘green’ solutions, and contribute to greenhouse gas (GHG) emissions in different ways. It is true, that whilst solar photovoltaic (PV) installations have minimal impact once installed, they can require high energy input during manufacturing.

A unit that is worthwhile understanding in relation to this is ‘gCO2eq/KWh’. This denotes the grams of carbon dioxide equivalent that are emitted per KWh of energy generated. Whilst carbon dioxide is the most significant GHG produced, other gases such as methane are included in this unit by calculating the global warming potential equivalent in grams of CO2 emissions, as calculated over a certain period of time.  

The gCO2eq/kwh of solar PV can vary depending on a number of factors, the primary one being where the PV cells are produced. In China, where many of the world’s cells are today manufactured, the majority of the energy used is still predominantly produced from coal plants. Whereas in France, the main bulk of that energy would come from nuclear. The gCO2eq/KWh for a Chinese produced cell would therefore be higher than one produced in France, and the carbon debt owed by the cell would take longer to pay off.

Regardless of this, the National Renewable Energy Laboratory (NREL) estimated that solar PV generates 40g CO2/KWh over its lifetime.[1] The main bulk of this contribution comes from the manufacturing phase. Depending on the rate of energy it produces, which is dependent on where in the world it is, it can in fact pay off its carbon debt (the amount of carbon emitted during its manufacture) within a number of years.[2] Considering that solar PV can last for up to 25 years, it proves that it is an attractive alternative to fossil fuels that continue to emit high levels of GHG over their lifetimes.

Comparing the 40g CO2eq/KWh of solar PV with coal power plants reveals the great difference between the two, with NREL estimating that coal plants produce over 1000g CO2/KWh over their lifetime. Natural Gas is lower than this, at 400g CO2/KWh, but this remains significantly above the emissions produced by using solar.

There are Carbon Capture Solutions (CCS) that are available, and there are claims that these can be up to 90% effective.[3] Even bearing this in mind, coal power plants would still emit 100g CO2eq/KWh – 2.5 times higher than solar PV.

We can see from this that whilst solar PV is not a zero emissions solution, the amount of GHG emissions that can be avoided by switching to solar are significant.  

[1] NREL, ‘Life Cycle Greenhouse Gas Emissions from Solar Photovoltaics’, National Renewable Energy Laboratory (2012) <https://www.nrel.gov/docs/fy13osti/56487.pdf> Accessed on 4 September 2021

[2] The Renewable Energy Hub UK, ‘Solar Photovoltaics- Cradle to Grave Analysis and Environmental Cost’ The Renewable Energy Hub UK (2020) <https://www.renewableenergyhub.co.uk/main/solar-panels/solar-panels-carbon-analysis/> Accessed on 4 September 2021

[3] C2ES, ‘Carbon Capture’ Centre for Climate and Energy Solutions (2021) <https://www.c2es.org/content/carbon-capture/> Accessed on 4 September 2021