Thursday, July 26, 2007

Worldwatch makes erroneous carbon savings claims for wind

A July 25 press release from the Worldwatch Institute claims that "2006 Wind installations offset more than 40 million tons of CO2":
Calculations are based on U.S. data: average capacity factor for new wind power capacity (34%, from American Wind Energy Association); average capacity factor for coal-fired power plants (72%, from North American Electric Reliability Council - NAERC); average CO2 emissions from U.S. coal-fired power plants (0.95 kg/kWh, from U.S. Energy Information Administration); and average coal-fired power plant capacity (318 megawatts, from NAERC).
There are two big flaws in Worldwatch's calculation.

First, a more objective source than the industry itself for the average capacity factor for wind energy facilities in the U.S. is the U.S. Energy Information Administration. According to their Annual Energy Outlook 2007, the capacity factor for wind was 21% in 2005. The AWEA's figures of 34% is promotional spiel and not based on actual data.

Second, there are other sources of electricity on the grid besides coal, including relatively cleaner-burning natural gas and carbon-free nuclear and hydro. At the least, the relative contributions of these sources must be considered. The renewable energy certifier Green-E, has recently proposed to value renewable energy output in terms of actual greenhouse gas emissions from the equivalent output by the rest of the grid.

By Green-E's calculations, the total greenhouse gas (not just CO2) emissions for different grid regions range from about 1,000 lbs/MWh generated to almost 2,200 lbs/MWh, or 0.47 kg/kWh for new (since 2000) facilities in the Southwest to 0.99 kg/kWh for all non-baseload facilities in the Midwest. The average among all regions in the U.S. for wind's theoretical equivalence according to Green-E is 0.66 kg/kWh.

Then there is the complication of how a highly variable and significantly unpredictable source such as wind actually affects the grid. Obviously, it can't replace any building of new capacity, because the grid still needs to be able to supply power when the wind isn't blowing. Its ability to reduce emissions from those other sources, particularly fossil fuel–fired sources, is also problematic for several reasons.

First, extra ramping and startups cause more fuel to be burned, with more emissions, cutting into whatever savings might have been achieved by using them less. Second, plants that can't ramp quickly may be switched to "spinning standby", in which they don't generate electricity but continue to burn fuel and create steam to be ready to switch back to generation when the wind dies. And third, all sources on the grid are not equally involved in the balancing of wind's variability. Hydro is the first choice to be ramped down, with no carbon savings, and natural gas plants are the second, with much less carbon savings than if coal were reduced.

In addition, the high cost per installed megawatt of wind reflects the energy required in its manufacture, transport, and construction. It may take several years before the theoretical carbon savings from a facility's output allows it to break even.

But now look again at what Worldwatch, with its very flawed formula, claims for wind: "Already, the 43 million tons of carbon dioxide displaced by the new wind plants installed last year equaled more than 5 percent of the year’s growth in global emissions. If the wind market quadruples over the next nine years -- a highly plausible scenario -- wind power could be reducing global emissions growth by 20 percent in 2015."

Global carbon emissions will continue to grow substantially, but not quite so much as they might without 300,000 MW (requiring 23,000 square miles) of new industrial wind energy facilities. That's pathetic even before considering the flaws in their calculation.

With the likes of Worldwatch watching out for it, the world indeed needs to watch out.

wind power, wind energy, environment, environmentalism