EU Energy Policy Blog

One of the reasons to support renewable energy resources in general, and wind the current front-runner in particular, is that they typically replace thermal generation and therefore reduce greenhouse gas emissions. But the question of “by how much” turns out to be complicated.

There have been a number of studies, some from reputable and non-biased sources, others not necessarily objective or non-biased. The studies typically examine what happens to GHG emissions in a country, state or region as the percentage of generation from wind – and other renewable resources – increases over time. Some examine actual historical data while others simulate the effect of alternative scenarios and project the impacts into the future.

The studies reach different conclusions, partly because they examine different systems with different fuel mix and different wind/renewable resources. In the case of wind, the critical factors include

- When does wind blow the most;
- How consistent and predictable it is; and
- What type of generation and fuel does it mostly replace.

Another critical factor is how does the grid operator maintain system reliability given the intermittency of wind. Not surprisingly, there are many nuances that enter the analysis – for example, the effect of hour-by-hour wind variability, which must be picked up from other resources. In systems with ample storage, say pumped hydro, the thermal units will be less adversely affected. Many models that focus on longer term effects of wind on a network miss these critical short-term, and hourly effects.

If, for example, wind blows mostly during the night – where system load tends to be low and mostly supplied by base load units such as nuclear or coal – its effect would be different than a case when wind patterns are strongly correlate with peak demand usage – when gas-fired peaking units may be replaced.

Since some types of units, for example nuclear, may not be able to accommodate cycling duty, they will continue to operate no matter what. Coal and natural gas units, on the other hand, may have to ramp up and down depending on how much wind and other intermittent resources are available. Moreover, some thermal units must remain on standby – usually at low levels of efficiency and high GHG emission rates – should wind suddenly die down or a cloud obscure the solar collectors.

Needless to say, the answer to what will be the net effect of an x% increase in wind generation on GHG emissions in a given system is not a simple y% – but is likely to depend on many variables, assumptions, modeling and number crunching. But the result is important, and hence a flurry of contradictory studies, confusing policymakers and the general public alike.

The National Renewable Energy Laboratory (NREL), for example, examined the impacts of integrating 20 to 30% wind power into the Eastern Interconnect in a major study titled Eastern Wind Integration & Transmission Study (EWITS). It concluded, among other things, that CO2 emissions would decrease by more than 25% under a 20%, and 37% under a 30% wind energy scenario, mostly due to significantly lower coal generation.

An earlier study by the US Department of Energy titled 20% wind by 2030, also covered in this newsletter, reached similar conclusions stating that achieving 20% wind generation would cut US electric sector CO2 emissions by 25%. Empirical evidence from a few European countries with significant wind penetration levels comes to similar conclusions. CO2 emissions in Denmark, for example, have reportedly been cut nearly in half since 1991, an outcome mostly attributed to the fact that roughly 20% of Danish electricity generation comes from wind. In the case of Denmark, which is interconnected with Germany, wind probably mostly replaces coal – yet the reported numbers appear to be exaggerated.

Lately, a few self-proclaimed experts have decided to join the debate, merely muddying the water and adding to the confusion. In an op-ed in The Wall Street Journal (24 Aug 2010) titled Wind Power Won’t Cool Down the Planet, Robert Bryce, quoting other studies, some of dubious quality, concludes that more wind generation does not do much to lower GHG emissions.

Mr. Bryce refers to a study commissioned by the Independent Petroleum Association of the Mountain States, a pro natural gas and oil lobby, and performed by Bentek Energy, a consultancy, that examined the effect of more wind generation in Colorado and Texas. Bentek concluded that increased wind-generation in Colorado “has had minimal, if any, impact on carbon dioxide” emissions, mostly attributed to the fact that, at least in Colorado, the increased cycling of coal-fired plants has wiped off the lower emissions associated with wind power generation in 2009.

In Texas, Bentek estimated that the increased wind generation resulted in a slight savings of CO2 emissions in 2008 and a slight increase in 2009, again due to the cycling of coal-fired plants. This newsletter is not in a position to verify the accuracy of these claims, but it appears that Mr. Bryce was looking for an exceptional case or two to support his prior beliefs and found them in the Bentek study. We suspect numerous other cases can be found with vastly different outcomes, but that would not be the answer that would satisfy Mr. Bryce.

University of Texas at Austin Professor Ross Baldick, who has studies the Texas market in far more detail, has also concluded that more wind generation in Texas has not had a commensurate effect on GHG emissions because of the many subtleties of when the wind blows – mostly during the off peak hours – and the detrimental effect that this has on the operational efficiency of the thermal units, which must pick up the variations. A summary of his paper may be found in the latest issue of the Dialogue with a more detailed version available from the author at baldick@ece.utexas.edu. You’d be much better off reading the results of a non-biased academic than someone like Mr. Bryce, whose motives may not be entirely altruistic.

The American Wind Energy Association (AWEA), of course, refuted the claims made by Mr. Bryce. It pointed out that wind energy generation in Colorado increased from 2.5% of electricity needs in 2007 to 6.1% in 2008 and CO2 emissions fell by 4.4% while coal decreased by 3% and natural gas by 14%. Similarly in Texas, DOE data show that wind and other renewables’ share increased from 1.3% in 2005 to 4.4% in 2008 while CO2 emissions from the electricity industry decreased by 3.3% even while overall electricity consumption increased by 2%, according to the AWEA.

Aside from making a name for himself, it is not entirely clear what Mr. Bryce’s motivations may be in beating on renewables. In his recent book, Power Hungry: The Myths of `Green’ Energy and the Real Fuels of the Future, he seems to be saying that we need to stick with the fossil fuels since renewables are simply not going to cut it, refuted by an earlier critique in this newsletter. His latest op-ed adds the GHG and subsidy issues to compound the controversy.

While one can certainly find exceptions, under most circumstances, more renewable generation can be expected to result in lower GHG emissions. And the subsidy issue is highly convoluted. For those who favor more renewables, it is money well-spent and an investment in a cleaner, greener future. Others see it as too much taxpayer funded pain for too little gain. But the nascent renewable industry would not be where it is today had it not been for the generous subsidies – and hopefully will be able to survive on its own once it reaches the elusive grid parity, always just around the corner.

F.P. Shioshansi

This post is extracted from EEnergy Informer, October 2010 issue.

This entry was posted on Sunday, October 3rd, 2010 at 6:45 pm and is filed under Climate Change, Electricity. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.