Kareem Hammoud
11th April 2017, 19:15
Hi everyone (first post),
I need some help checking my calculations based on some information in this WSJ article https://www.wsj.com/articles/investors-are-building-their-own-green-power-lines-1491471009.
I thought it was worth seeing how long it would take to offset the carbon emissions to construct a 4000 MW wind farm and multi-state transmission line, since the thousands of tons of steel and concrete needed to build these systems seemed like a lot. I did some quick research and estimates to figure it out for the Oklahoma-to-Tennessee power line and wind farm, linking the sources for my metrics as relevant:
The steel
The proposed power line and wind farm requires 500,000 tons of steel. Depending on the method used to produce steel, the emissions intensity is 0.6- 2.8 tons CO2/ton steel. Since the US produces a greater mix of its steel through the lower emission method, I assumed it’s something like 1.5 ton CO2/ton steel. So just the steel in the line and turbines will create 750000 tons CO2.
http://climate.columbia.edu/files/2012/04/GNCS-Iron-Steel.pdf
The wind farm
The proposed wind farm is 4,000 MW, which using the EPA’s average capacity of wind turbines in the US (2014) of 1.92 MW/turbine, comes out to roughly 2,083 turbines.
The National Renewable Energy Lab (NREL) estimates that the lifecycle emissions of a wind turbine are about 11 grams CO2/kWh, or 0.000011 tons CO2/kWh. Converting 4,000 MW to kW and multiplying by 8760 hours (the hours in a year) and a capacity factor of 0.34 I got 11913600000 kWh, which multiplied by 0.000011 tons CO2/kWh comes out to 131050 tons CO2 for the whole wind farm.
https://www.epa.gov/energy/greenhouse-gases-equivalencies-calculator-calculations-and-references
http://www.nrel.gov/analysis/sustain_lca_wind.html
Total
Adding the totals for the steel and wind farm, we get 881050 tons CO2 (I realize the emissions for the steel in the turbines is double-counted, but that just makes my estimate more conservative)
The EPA also estimates that each 1.92 MW turbine offsets 3,960 tons CO2/year. Multiplying this by 2083 turbines we get 8248680 tons CO2 offset/year, or 687390 tons CO2 offset/month.
Dividing 881050 tons CO2 by 687390 tons CO2/month we get 1.3 months, which means the whole project will offset its construction emissions within just over 1 month of power generation.
I know that this doesn’t account for other production emissions related to the transmission line, as I’m sure there will be a lot of concrete and other materials I’m not considering. However, modern wind turbines have higher nameplate MW, and generating capacities closer to 50%. So, this is likely to be an overestimate anyway! However, I am no energy expert, and this offset period seems really fast, so I figured this might be a good forum to find out.
TL;DR: I calculated that a 4,000 MW wind farm and its neighboring transmission line would generate 881050 tons CO2 to build. However, these emissions would be offset within 1.3 months of the wind farm being in operation. Am I approaching this problem and calculating it properly, or am I missing something?
Thanks in advance!
I need some help checking my calculations based on some information in this WSJ article https://www.wsj.com/articles/investors-are-building-their-own-green-power-lines-1491471009.
I thought it was worth seeing how long it would take to offset the carbon emissions to construct a 4000 MW wind farm and multi-state transmission line, since the thousands of tons of steel and concrete needed to build these systems seemed like a lot. I did some quick research and estimates to figure it out for the Oklahoma-to-Tennessee power line and wind farm, linking the sources for my metrics as relevant:
The steel
The proposed power line and wind farm requires 500,000 tons of steel. Depending on the method used to produce steel, the emissions intensity is 0.6- 2.8 tons CO2/ton steel. Since the US produces a greater mix of its steel through the lower emission method, I assumed it’s something like 1.5 ton CO2/ton steel. So just the steel in the line and turbines will create 750000 tons CO2.
http://climate.columbia.edu/files/2012/04/GNCS-Iron-Steel.pdf
The wind farm
The proposed wind farm is 4,000 MW, which using the EPA’s average capacity of wind turbines in the US (2014) of 1.92 MW/turbine, comes out to roughly 2,083 turbines.
The National Renewable Energy Lab (NREL) estimates that the lifecycle emissions of a wind turbine are about 11 grams CO2/kWh, or 0.000011 tons CO2/kWh. Converting 4,000 MW to kW and multiplying by 8760 hours (the hours in a year) and a capacity factor of 0.34 I got 11913600000 kWh, which multiplied by 0.000011 tons CO2/kWh comes out to 131050 tons CO2 for the whole wind farm.
https://www.epa.gov/energy/greenhouse-gases-equivalencies-calculator-calculations-and-references
http://www.nrel.gov/analysis/sustain_lca_wind.html
Total
Adding the totals for the steel and wind farm, we get 881050 tons CO2 (I realize the emissions for the steel in the turbines is double-counted, but that just makes my estimate more conservative)
The EPA also estimates that each 1.92 MW turbine offsets 3,960 tons CO2/year. Multiplying this by 2083 turbines we get 8248680 tons CO2 offset/year, or 687390 tons CO2 offset/month.
Dividing 881050 tons CO2 by 687390 tons CO2/month we get 1.3 months, which means the whole project will offset its construction emissions within just over 1 month of power generation.
I know that this doesn’t account for other production emissions related to the transmission line, as I’m sure there will be a lot of concrete and other materials I’m not considering. However, modern wind turbines have higher nameplate MW, and generating capacities closer to 50%. So, this is likely to be an overestimate anyway! However, I am no energy expert, and this offset period seems really fast, so I figured this might be a good forum to find out.
TL;DR: I calculated that a 4,000 MW wind farm and its neighboring transmission line would generate 881050 tons CO2 to build. However, these emissions would be offset within 1.3 months of the wind farm being in operation. Am I approaching this problem and calculating it properly, or am I missing something?
Thanks in advance!