Wednesday, October 30, 2013

U.S. CO₂ emissions for electricity from coal have risen over past 10 years

A report from Spain and a news release from the U.S. Environmental Protection Agency have recently touted a decline in CO₂ emissions from electricity generation. Both, however, actually cite only a reduction of electricity generated by fossil fuels. A much more meaningful measure, considering the complexity of the grid, would be the amount of fossil fuels burned per unit of electricity generated. But that seems to be precisely what is studiously never reported (outside of this space, e.g., here, here, and here).

It requires a bit of digging into many different sources of data at the U.S. Department of Energy’s Energy Information Administrations. To be as up to date as possible, the following has used the latest Electric Power Monthly, release Oct. 24, 2013, to include data from 2012. First, instead of looking at power plant heat rates of fossil fuels, we need to look at their simple heat contents, i.e., not how much electricity they generate but how much energy they contain. This is because not all burning of fossil fuels at power plants goes to generating electricity. The heat content is expressed as Btu/unit of fuel: The present analysis used the values of 9,530,000 Btu/ton of coal, 1,021,000 Btu/1,000 cubic feet of natural gas, and 5,871,390 Btu/barrel of petroleum liquids.

Second, instead of electricity generated by fossil fuels, we need to look at the amount of fossil fuels burned at power plants.

Finally, assigning amounts of CO₂ per unit of fuel, we can calculate the actual CO₂ emitted by each fossil fuel. Here we assume 210 lb. CO₂/million Btu coal, 117 lb. CO₂/million Btu natural gas, and 170 lb. CO₂/million Btu petroleum liquids.

Then we can total them up and express those emissions as a ratio to total electricity generated. If, e.g., wind power is causing a reduction of, say, coal-generated electricity and thus a reduction of CO₂ emissions, then that ratio of CO₂ per unit of electricity will be lower.

Overall, the CO₂ emitted per GWh in total has indeed gone down, from 1,288,801 pounds in 2003 to 1,120,663 in 2013 — a 13% decrease. This is due mostly to the increasing share of natural gas over coal, because natural gas releases almost half the amount of CO₂ as coal. Furthermore, the amount of CO₂ emitted per unit of electricity generated by natural gas has also decreased, from 1,032,279 CO₂/GWh in 2003 to 918,727 in 2013 — an 11% decrease.

The picture is further complicated by the fact that over the past 10 years, the amount of CO₂ emitted per unit of electricity from coal has actually steadily risen, from 2,107,148 pounds CO₂/GWh in 2003 to 2,234,734 in 2012 — an increase of 6%. At the same time, wind energy rose from 11,187 GWh in 2003 to 140,089 GWh in 2012. This suggests that wind does indeed cut into the efficiency of using coal for electricity, because coal plants need to “stay warm” even when not generating electricity so that they are able to kick in when the wind conditions change.

Assuming that wind is the primary reason for coal’s decreasing efficiency, what if the 140,089 GWh generated from wind power in 2013 were generated by coal operating at its heat rate from 2003? Then the overall CO₂/GWh would have been 11.5% instead of 13% lower than in 2003, suggesting that wind power has been responsible for only a 1.5% decrease in CO₂/GWh and a 1.6% decrease in total CO₂ emissions. Considering that wind’s share of U.S. electricity generation increased from 0.3% in 2003 to 3.5% in 2013, it is clear that its effect on CO₂ emissions is very far from — less than half of — what its proponents claim.

In the scale of the graph below, the decrease in CO₂ emissions with wind (blue, mostly hidden - not the teal line for coal generation) or without wind (green) are nearly identical, whereas other changes, including the addition of wind energy, are quite obvious. Also note the exactly parallel lines of coal CO₂/GWh (orange) and wind generation (red).

And that clearly suggests that the costs and impacts of wind energy — the necessary consequence of trying to harness such a diffuse and variable source — well outweigh its benefits. Compared with the very modest conservation that would achieve the same emissions results, wind appears to be a very wasteful and destructive alternative indeed.

wind power, wind energy, environment, environmentalism