Tuesday, February 20, 2007

Wind Energy and the East Coast

Among U.S. states, California and Texas currently generate the most wind energy. It is also well-known that the Dakotas have enormous wind potential. I was pleasantly surprised to come across a recent paper highlighting wind energy available off the Northeastern seaboard. The study covers states (MA to NC, plus D.C.) adjacent to the Middle-Atlantic Bight (MAB):

(To enlarge a particular image, click on it.) The paper concludes that if one takes the total electricity and fuels consumed by the states, the total energy translates to just 64% of the wind energy available in the MAB. The 330 GW estimate is based on installing "... 166,720 wind turbines, each generating up to 5 megawatts of power." As we explain below, for added efficiency, the authors assumed the wind turbines were about half a mile apart.

Light vehicle fuels (gasoline) and, low-grade heat and building fuels (distillate fuel oil and natural gas), currently come from fossil fuels. The goal is to generate clean wind energy and move users to technologies that can harvest the energy through the power grid. Light vehicle fleet would be replaced by plug-in hybrids, heaters get replaced with electric space heaters, stoves with electric stoves, etc. Simply supplying more of the electricity and heating needs of these states, with wind would be a huge achievement. As I pointed out last week, 50% of electricity in the U.S. comes from coal. The authors estimate that replacing current energy sources with wind, would reduce CO2 emissions by 68%.

The paper also presents ideas on how to better match the supply of wind energy with "24 x 7" demand. A common criticism of wind energy is that it is unpredictable and not available when demand is highest. The authors point out that wind cross-correlations drops with distance: as the distance between two locations increase, the likelihood that wind occurs simultaneously at both sites, decreases. One way to increase wind availability, is to increase the number of sites, and connect them by electric transmission lines. Using models first presented in a previous paper, the authors demonstrate the power of "site diversification" on the availability of wind power. In the graph below, we present the amount of power generated by 1, 3, and 6 MAB wind sites. For convenience we normalized the hourly power outputs, of the 1, 3, or 6 sites, into a single 3.6 megawatt turbine:

The above graph is my attempt to replicate the original graph in the paper. A point on the horizontal axis represents the percentage of time (as measured by hours in a year) that wind power production is AT LEAST the value found on the vertical axis. The area under a curve, represents the amount of MWH produced in a year, by the given configuration of sites.

Using the curve for 1 Site, we note that 15% of the time no power is produced, and 13% of the time the site is generating the maximum amount of power. In the case of 6 sites (respectively 3 sites) power is off only 0.2% (respectively 3%) of the hours in a year. As the authors point out:
... Because wind speed cross-correlation drops with distance, distributed wind resources, connected by electrical transmission lines, produce more level power than their individual constituent sites. ... Since the off-time for all multi-site combinations is well under the 6% forced outage time for baseload fossil generators [North American Electric Reliability Council, 2005], it is incorrect to call power from these interconnected offshore wind sites ‘‘intermittent.’’ Rather, the problem is that the fluctuations in the wind resource are not matched to fluctuations in load, whereas fossil plants are scheduled to match load.
Distributed wind resources, connected by electric transmission lines, have off-times less than the 6% that fossil fuel generators typically have. To match wind power properly with fluctuations in demand, the authors give the following example:
... A light vehicle fleet of battery, plug-in hybrid and/or hydrogen fuel cell vehicles would have substantial energy storage, which could be controlled by the electric grid operator when the vehicle is idle and plugged-in. Assume 2/3 of the 29M registered automobiles in the MAB region [ U.S. Census Bureau, 2006] were electrified with 30 kWh storage, and assume that at any one time when needed, only half of these electrified vehicles could respond, each providing half their storage. This is a 145 GWh storage resource, capable of carrying the average 73 GW electrical load for 2 hours. Prior analysis of one such large-scale example showed that electrified vehicles would be sufficient for wind backup all but 5 times/year. For the occasions when vehicle storage is inadequate, today’s fossil fuel plants could be retained in standby mode and tapped several times per year. The inverse problem, excess wind power, would first supply any deferred demand for heat and vehicle battery charging; any subsequent remaining excess wind power would be sold on regional markets, or spilled.
In the absence of adequate storage, wind energy can still be used to lessen the use of fossil fuels. While the authors are not claiming that wind alone can displace all the fossil fuels used in the given states, clearly, the MAB region can supply enough wind to substantially reduce the amount of fossil fuels currently used. Given that progress and innovation will most likely accelerate over the next several years, solid state storage technologies are bound to improve and load matching will become more realistic.

Hopefully, the current crop of Presidential candidates will take the results of this research on the Middle-Atlantic Bight and use it to educate the American public about the enormous potential energy source sitting right off the East Coast. All it takes is one of the top-tier candidates to champion it!

Digg It! , Bookmark to del.icio.us , My Yahoo! , ATOM Feed

No comments: