(Disclaimer: the below article is a thought experiment. I'm not suggesting it as a real solution, but rather a way to analyze two different carbon mitigating strategies. Enjoy!)
You might have seen the environmental articles recently related to Carbon Capture and Storage (CCS). Basically, all CCS does is take the CO2 that coal plants produce, collect it, and pump it underground. Sounds like a good idea right? Well, on the surface it does, but let's dig down into the actual numbers a little bit.
In order to better understand the proposed function of CCS, let's walk through a comparison of a power generation plant with and without CCS. I'm going to look at two options:
- Option 1: 500 MW (capacity before CCS) IGCC (type of coal plant) with Carbon Capture and Storage
- Option 2: 500 MW IGCC plant with the money that would be used on CCS to be spent on a wind farm
In comparing our two options, pretend you're the President of Power Generation Company for planet Earth (this is a made up company. The point is you base your decisions on what is best for the planet and the people buying your power. You don't base your decisions on politics). In both options the 500 MW IGCC plant is already installed, you are just comparing whether to spend money on carbon capture and storage, or take the equivalent amount of money and use it for another purpose that would help the environment, in this case a wind farm.
You may ask: Why do I want to install a wind farm if my goal is to reduce CO2 (even though your real goal is to do what's best for Earth)? Because you are all powerful, you are going to figure out how much energy the wind farm produces, then find an old dirty coal plant that produces the same amount of energy, and take that coal plant off line. Therefore, reducing the amount of CO2 that enters the atmosphere by enabling the old coal plant to be taken off line, and also helping wind power reach economies of scale.
Installing CCS or a Wind Farm that replaces old Coal:
A recent paper by David and Herzog at MIT estimated the future cost of CCS at $1,145/kw (estimated cost in 2012) of installed power. So, for the 500 MW IGCC plant, it would cost $572.5 million dollars to install CCS technology. Now, you have the option of taking this money and using it to buy a Wind Farm instead. The American Wind Energy Association states that it costs about $ 1 million to install 1 MW of generating capacity for a wind farm. Therefore, $572.5 million will enable you to install 572 MW of installed wind energy (with $500 k left over)!
In order to analyze how much CO2 will be kept out of the atmosphere by taking the old coal plant off line, we have to calculate the yearly power output of the wind farm. To do this, you need what is called a Capacity Factor. Basically, this is just the percentage of time during the year that a power producing facility produces power at its rated capacity. The organization National Wind Watch states that in 2003, the average capacity factor for US wind farms was 26.9%. Therefore, to calculate how much energy the wind farm produces (MWh) during the year:
Yearly Output (MWh) = (installed capacity)*(capacity factor)*(hours in a day)*(days in a year) =
(572 MW)(.269)(24 hours/day)(365 days/year) = 1,347,884 MWh/year
Now we have to use this value to decide how big a coal plant this would replace. Using the wind farm yearly output and the average capacity factor for Coal plants in the US, which is 73.6%, we can use the above Yearly Energy Output equation to back-solve for the "installed capacity" the wind farm would replace:
Installed Capacity (MW) = (yearly output) ÷ (Capacity factor * hours in a day * days in a year) =
(1,347,884) ÷ (.736*24*365) = 209 MW
Therefore, if you use the $527.5 million dollars it would cost to install CCS on a 500 MW IGCC coal plant for a wind farm, the energy the wind farm produces is equivalent to a 209 MW pulverized coal plant!
According to the EIA, the average coal plant in the US outputs 2.095 lbs. of CO2 for every kWh it produces. If we look at the option where the wind farm would replace the old coal plant, the coal plant in question would be rated at 209 MW. So, taking into account the aforementioned capacity factor to find the annual energy(MWh/year) and the rate that CO2 enters the atmosphere (lbs/kWh), this coal plant would output 1,412,000 tons of CO2 per year. If the coal plant is de-commissioned once the wind farm comes online, that is equivalent to removing 1,412,000 tons of CO2 out of the atmosphere each year!
If you did decide to go through with Carbon Capture/Storage you would need to calculate how much CO2 would be captured. According to American Progress, CCS will have a carbon capture rate of 85%. Our IGCC plant is estimated to have a capacity factor of 85% (it is just a coincidence that this number is the same as carbon capture rate of CCS), which thankfully is better than the old pulverized coal plants! Using the yearly output formula for our 500 MW IGCC plant, we get an annual energy production of 3,504,000 MWh.
Next, we have to calculate how much CO2 is released by this annual energy production. I dont have the official numbers, but I'm assuming the IGCC won't ouput as much CO2/kWh as old coal power generation, so we'll say the number is closer to what natural gas plants output, which is 1.314 lbs/kWh. We'll use 1.5 lbs/kWh. Multiplying the annual energy output by the lbs of CO2 it produces per kWh, we get an annual amount of 2,628,000 tons of CO2 that enter into the atmoshphere as a result of our IGCC without CCS. Once we add CCS at 85% efficiency, we are preventing 2,233,800 tons of CO2 from entering the atmosphere. If you remember, our wind farm option that shut down an old coal plant kept 1,412,000 tons of CO2 from entering the atmosphere, which is about 63% of the CCS option.
How much energy does it take to operate the CCS for the IGCC plant you ask? Wonderful question. According to the Institute of Science in Society (which also thinks CCS is dumb), the CCS portion of the power plant would consume 10 to 40 percent of the power the IGCC plant produces! According to this VERY detailed paper by House, Aziz, and Schrag of Harvard and Harvey of MIT they say it is unlikely that the energy required to run the CCS side would be below 25%. Therefore, we will assume that it takes 25% of the power plants output to operate the CCS operation!
What does this mean? Well, if it takes 25% of the plant's power output to operate our CCS, our 500 MW plant that would normally put all that power (taking into account capacity factor) onto the power lines is only putting the equivalent of a 375 MW plant's power onto the lines! Therefore, the CCS is taking 125 MW to operate! Since this 125 MW is prevented from being used on the grid (because the CCS is consuming it), this power has to be made up somehow! What do you think is going to make it up? My guess is old coal!
Think about it! Not only could the wind farm replace a 209 MW old coal plant, it would also enable the 500 MW IGCC plant to use all of its power on the grid!!! The wind farm wouldnt require an extra 125 MW to power it (it uses the wind!) like the CCS operation does. If we assume that the 125 MW that the CCS consumes from the IGCC plant has to be made up for on the grid by old coal, we also have to include the amount of CO2 that this 125 MW adds to the atmosphere to our "wind farm" case!
We originally just thought the wind farm prevented 1,412,000 tons of CO2 from entering the atmosphere (because of the removal of the 209 MW plant) but now we should add in this extra amount from the 125 MW plant. This amount comes out to be 844,201 tons. Therefore, the wind farm would effectively remove 2,256,109 tons of CO2/year. WHICH IS MORE THAN THE CCS REMOVES!!!!!! So in this example, it looks like the wind farm is a better option for spending the money on instead of CCS in regards to removing CO2 from the atmosphere.
And I'm still not done, read part 2 for an analysis of the two scenarios of the environmental impacts that aren't related to CO2!