Does wind power reduce carbon emissions?

Update: Peter Lang, author of the wind study referred to below, responds here.

If renewable or nuclear energy is going to be successful in decarbonising our electricity supply (and, ultimately, all energy use), it needs to hit a couple of fundamental benchmarks:

(i) its life cycle energy inputs must be low compared to its ‘clean energy’ output; and

(ii) it must be able to displace fossil fuels — with elimination of carbon emissions from stationary energy being the first major objective.

Regarding life cycle emissions from nuclear power, I’ve already touched on the issue, but will be exploring this in more detail in the future. But this post is about wind.

To tackle this topic, I profile a recent analysis circulated by retired engineer Peter Lang, called “Cost and Quantity of Greenhouse Gas Emissions Avoided by Wind Generation“. Peter has 40 years experience on a wide range of energy projects throughout the world, including managing energy R&D and providing policy advice for government and opposition. His experience includes: coal, oil, gas, hydro, geothermal, nuclear power plants and nuclear waste disposal (6.5 years managing a component of the Canadian Nuclear Fuel Waste Management Program). Click on the title of the paper to download the 14 page PDF.

Okay, so what does he say? Let’s start with the bottom line and then work back:

1. Wind power does not avoid significant amounts of greenhouse gas emissions.

2. Wind power is a very high cost way to avoid greenhouse gas emissions.

3. Wind power, even with high capacity penetration, can not make a significant contribution to reducing greenhouse gas emissions.

Strong statements, to be sure. Here’s the justification.

Peter looks at the issues of variability and back-up generation. Energy storage in the form of batteries is dismissed as uneconomic for the amount of energy required. For hydro, he says:

“We have insufficient hydro resources to provide peak power let alone provide back-up for wind power. Hydro energy has high value for providing peak power and for providing rapid and controllable responses to changes in electricity demand across the network. So our very limited hydro resource is used to generate this high value power.”

Pumped hydro is obviously an alternative route, if you are willing to accept the energy conversion losses in going from electricity from wind turbines to mechanical energy (pumps) to potential energy (water stored in the dam) to kinetic energy (falling water to turn the turbines) and back to electrical energy. But let’s focus for now on the most touted (and widely used) form of back up for wind: natural gas (that is, fossil methane) using open cycle gas turbines (OCGT).

To calculate the true cost of wind back up, one must include the following sort of items (an incomplete list): cost of maintaining back-up plants, costs of holding large amounts of spinning reserve, costs of rapid power-ups and power-downs, use of high value hydro for balancing,  costs imposed on utilities in managing variable supply and meeting government mandated purchases, etc. In capturing some of these, Lang concludes that the total cost for wind with OCGT back up at a capacity factor of 45% is $121 per MWh (versus $60/MWh if back-up costs are ignored). See Option 2 on page 7 of his analysis.**

He then looks at the critical issue of emissions of CO2e avoided by installing wind with back up. The baseline comparison is made against combined cycle gas turbines (CCGT), for which the emissions intensity (EI) is 577 kg CO2e/MWh (for reference, it’s 750 to 1400 kg for various coal grades and non-CCS technologies).

The conclusion he reaches is rather startling (see pg 8-9). For wind power without back up, the EI is a mere 18 kg CO2e/MWh (mostly coming from materials and energy used to construct the steel and concrete turbines). Yet for wind with adequate OCGT back up, the EI is 519 kg CO2e/MWh.

Thus, the emissions avoided by wind amount to a grand total of 5.8 kg CO2e/MWe. This estimate seems ludicrious at first pass, but it turns out to be similar to one derived independently by the UK Royal Academy of Engineering, which put the figure of emissions avoided at an ever so slightly less trifling 9 kg CO2e/MWe.

From there, it’s straightforward to do the sums on the cost per tonne of CO2e avoided by installing wind power. It’s a whopping $830 to $1,149…

On the basis of the above, Lang concludes with the following:

“These calculations suggest that wind generation saves little greenhouse gas emissions when the emissions from the back-up are taken into account.

Wind power, with emissions and cost of back-up generation properly attributed, avoids 0.058 to 0.09 t CO2-e/MWh compared with about 0.88 t CO2-e/MWh avoided by nuclear. The cost to avoid 1 tonne of CO2-e per MWh is $830 to $1149 with wind power compared with $22 with nuclear power. If the emissions and cost of back up generation are ignored then wind power avoids about 0.5 t CO2-e/MWh at a cost of about $134/t CO2-e avoided. Even if the costs of and emissions from back up generation are ignored, wind is still over six times more costly that nuclear as a way to avoid emissions.

A single 1000 MW nuclear plant (normally we would have four to eight reactors together in a single power station) would avoid 6.9 million tonnes of CO2 equivalent per year. Five hundred 2 MW wind turbines (total 1000 MW) would avoid 0.15 to 1.3 million tonnes per year – just 2 to 20% as much as the same amount of nuclear capacity. When we take into account that we could have up to 80% of our electricity supplied by nuclear (as France has), but only a few percent can be supplied by wind, we can see that nuclear can make a major contribution to cutting greenhouse emissions, but wind a negligible contribution and at much higher cost.“

So, do you believe that this analysis is all a load of old cobblers? Can you point to the obvious (or subtle) flaws in this assessment? I’ve tried, and I can’t fault the logic, but perhaps a savvier analyst than me is up for it. I look forward to the feedback in the comments.

** I had one question for Peter, which I asked him by email:

“In the wind study, on p7 you present a table under option 2. I’m having trouble following how the top 3 rows contribute to the bottom line. Could you explain this to me in a little more detail, as I think it’s critical for understanding, and indeed for interpreting the emissions table on the following page. Basically, why is the wind cost not just row 2+3 (and then how do you derive the 45% CF)? I know I’m probably being thick, but it just doesn’t click, despite re-reading this a dozen times.”

… to which Peter replied:

“The table you referred to is not well explained in the text. Here is the explanation.

First, the reason for the 45% capacity factor is that, that is the average capacity factor given in the ESAA paper for intermediate load (CCGT). I wanted to stay consistent with the ESAA figures so I could continue to include to use them for comparison with the other studies. Refer: Figure 2, p12 in

http://www.esaa.com.au/images/stories//energyandemissionsstudystage2.pdf

Let me know if you need more explanation in answer to this part of the question.

Second, what is the Option 2 about. We want 45% capacity factor for intermediate load. The output must be provided on demand, not just when the wind is blowing. Assuming the capacity factor for wind is 30%, we will get 2/3 of the required 45% of the energy from Wind with OCGT back up, and the other 1/3 of the required 45% of the energy from OCGT.

Row 1 – OCGT at 15%/45% CF x $105/MWh = $35/MWh

Row 2 – Wind at 30%/45% CF x $90/MWh = $60/MWh

Row 3 – OCGT operating in back up mode for wind at 30%/45% CF x $39/MWh = $26/MWh

I do need to find a better way to explain this in the paper. Any suggestions greatly appreciated.”

If you wish to ask Peter any questions yourself, perhaps he’ll be happy to reply in this thread — I’ll certainly alert him to the fact that it’s now posted.