The Math - Wind Energy is a False Solution
We're spending a lot of money to make the problem worse
He who refuses to do arithmetic is doomed to talk nonsense.
— John McCarthy
About a month ago I wrote Is Wind Energy a Chimera? followed shortly by Wind Energy is a Carbon Emitter (indirectly). These both got me a lot of responses disagreeing with me1. It made me realize that I needed to run these numbers with primary data.
So, here is how it works using the Siemens SGT-9000HL gas turbine. This is their most powerful 60Hz turbine and comes in both SCGT and CCGT models. These are the numbers from Siemens: 2 3
SCGT
Gas input - 81 US tons/hour
Efficiency - 43.2%
Power Output - 440MW
CO2 emissions - 1006 lb/MWh
CCGT
Gas input - 81 US tons/hour
Efficiency - 64%
Power Output - 655MW
CO2 emissions - 688 lb/MWh
Fundamental to this is you can run a CCGT 24/7, but it does not do well as a peaker on/off generator. So the backup for the wind generators is a SCGT4 5 which does do on/off pretty efficiently.
This backup SCGT emits CO2. And that emission is directly due to using wind as an intermittent provider. If instead of the wind+SCGT we instead had a CCGT, then we still have CO2 emissions, but we may have less. So let’s look at both.
Update: I initially screwed up in the below calculations. It should not multiply by 2.28 & 1.53 as the CO2 produced is per MWh and I’m calculating both for the same 1 GW power.
For a 1GW energy provider running 24/7 the entire year6, we get the following:
SCGT
Gas input - 2.28 * 81 * 87607 = 1.6 mega tons/year
CO2 emissions = 1006 * 1,000 * 8760 = 8.8 Giga lb/year
CCGT
Gas input - 1.53 * 81 * 8760 = 1.1 Mega tons/year
CO2 emissions = 688 * 1,000 * 8760 = 6.0 Giga lb/year
So now the question is, how often do the wind generators need to run so their backup CO2 emissions is less than the CCGT replacing the wind + SCGT? And that is super easy. First we get the time the SCGT needs to run for equal emissions: 6.0 / 8.8 = 0.68 or 68%. If the wind turbines are running with a capacity factor of 32% or more, then wind + SCGT emits less CO2 than CCGT.
In addition there is additional CO2 emissions from the rapid start-up and use of the SCGT. Once they’re running it’s the above numbers, but the initial time until it’s all heated up and running smoothly adds to the CO2 footprint of the wind backup.
Onshore wind turbines have, at best, a 35% capacity factor. So onshore wind + SCGT, for a 1GW wind farm, is emitting, at best, approximately the same amount of CO2 over the alternative of a CCGT. Offshore wind turbines claim a capacity factor of 60% and so those may8 make sense.
If I got the math wrong on this, please let me know. But I’ve run this by numerous people who know this a lot better than me - and they say I have it right9.
Conclusion
Why are we continuing with additional wind farms when their impact is negligible for CO2 emissions? Why not instead replace coal plants with CCGT? Is there a single valid argument for erecting even 1 more wind turbine?
In addition the wind + SCGT approach is ~ 2B while CCGT is ~ 800M. Spending 1.2B for 1 GW of ineffective greenwashing strikes me as a horrible misuse of funds.
Which leaves the giant question - why have the people in charge of our renewable energy efforts continued to push wind energy? Is there a valid argument for wind that I’m missing?
Colorado Example
From the eia, this is most of the densely populated parts of the state. Notice how gas, and a bit of coal10, go up when wind/solar go down. And a couple of days with almost no solar and others with little to no wind.
References
Big thank you to those who disagreed with me for arguing on facts and keeping the discussion professional. And these are people who strongly support wind energy. Things can be civil on the web. And those arguments lead to this post. So again, thanks.
Good article on the handwaving by wind proponents around the backup power. Which illustrates in practice the backup is almost always gas or coal (which is worse).
For the math this means we have 2.28 SCGTs and 1.53 CCGTs. Obviously we can’t have a partial turbine but this is a legit way to compare. In reality several wind farms would share a 3rd SCGT.
There are 8760 hours/year
I say “may” because every offshore wind farm I’ve read of has numerous turbines that are broken down, have lost a blade, etc. So their downtime may mean their actual capacity factor is well below 60%.
If anything is wrong, my fault, not theirs!
Which makes the numbers even worse for the effective CO2 emissions of wind + backup.
There's no reason wind backup generation (in this simple 3 bus model) needs to be a simple cycle CT.
Combined cycles can and do ramp up and down, a lot, and can ramp quickly to balance the variation in wind output.
In your simple example of 1 GW load being served, there's no plausible reason that it can't be served by a 35% capacity factor wind farm and a CCGT, rather than simple cycle.
Texas has bet big on wind and solar and people like Noah Smith @noahpinion are touting their wholesale production costs of $.003/KWh (clearly ignoring the backup). But does TX have a backup strategy other than brownouts, or do they just not care about total CO2 emissions?