How Much Emissions Does a Solar Power System Prevent?
01 October 2020
Solar panels not only reduce energy bills in companies, but also their environmental impact. Each megawatt-hour produced by a solar array displaces grid electricity, which could come from coal or natural gas. Considering that solar panels can last for over 25 years, the avoided emissions are significant.
It would be incorrect to say that solar power has zero emissions, since PV modules and other components are made of materials that are mined and processed. There is also an environmental footprint when equipment is delivered to the project site, and during the construction stage. However, even when all these factors are considered, the lifetime emissions from solar power are much less than those produced by fossil fuels.
The US-based National Renewable Energy Laboratory (NREL) estimated that solar power produces lifetime emissions of 40g CO2 equivalent per kilowatt-hour. A study published by Nature Energy was more optimistic, with estimated emissions below 21 g CO2 eq / kWh.
For comparison, many coal power plants produce over 1,000 g CO2 eq / kWh, and even the “cleanest” coal power is generally above 700 g CO2 eq / kWh. Natural gas generation is less polluting, with emissions above 400 g CO2 eq / kWh, but still 10 times higher than the NREL estimate for solar power.
Estimating the Total Emissions of a Solar Array
The emissions avoided by solar power depend on the project size and the energy source that is being displaced. This article will calculate a very rough estimate, based on a 2-MW solar power system replacing coal and natural gas. We will assume the following conditions:
- The solar array has a service life of 25 years.
- The electricity output decreases gradually over time, and solar panels still have 80% of their original output after 25 years.
In a site with favorable sunshine, each megawatt of solar panels can produce over 1,500 MWh per year. With a capacity of 2 MW, the solar array produces around 3,000 MWh in its first year of operation. By year 25 the annual production will have reduced to 2,400 MWh, and the accumulated generation will be 67,500 MWh.
Based on the 40g CO2 eq / kWh value from NREL, this project will accumulate 2,700 tonnes of emissions. While this may seem high, it pales in comparison to the emissions released with 67,500 MWh of fossil fuel generation.
Avoided Emissions When Solar Power Replaces Coal
Assuming 1,000 g CO2 eq / kWh, a coal power plant will release 67,500 tonnes of emissions when producing 67,500 MWh. This is 25 times more than the total emissions produced by the 2-MW solar array described above. Even if we consider a less polluting coal power plant that releases 700 g per kWh, an output of 67,500 MWh results in 47,250 tonnes of emissions.
Carbon capture and storage (CCS) is often presented as a solution to make coal power clean. Assuming that CCS technology reaches 90% effectiveness, coal power could reach emissions of around 100 g CO2 eq / kWh. The emissions for 67,500 MWh would be 6,750 tonnes, which is still 2.5 times higher than the estimated solar power emissions. Also consider that this example uses a very optimistic scenario for coal, and a conservative estimate for solar power.
Avoided Emissions When Solar Power Replaces Natural Gas
Natural gas is less polluting than coal, with typical emissions above 400 g CO2 eq / kWh. To generate 67,500 MWh, a natural gas power plant must produce 27,000 tonnes of emissions, which is 10 times the solar power value. With CCS technology and being optimistic, the emissions from gas-fired generation could be reduced to around 80g CO2 eq / kWh. For an output of 67,500 MWh, this results in 5,400 tonnes – still 200% of the estimated value for solar power.
There is a common misconception that solar panels produce zero emissions, but this only applies for the power generation process. When manufacturing, construction, maintenance and decommissioning are considered, it is possible to calculate emissions for solar arrays and wind turbines. However, the emissions produced by coal and gas generation are considerably higher, which means that a large solar farm keeps thousands of tonnes of emissions away from the atmosphere.