By Teresa Hansen, Senior Editor
The American Wind Energy Association reports that more than 11,600 MW of wind capacity was operating in the United States in 2006 and it expects that number to increase substantially by the end of this year. Wind generated electricity is gaining a foothold in the U.S. electricity generating mix; however, the amount of installed capacity can be somewhat misleading, especially to people who are not familiar with electricity generation.
In the United States, wind power installations are generating electricity at full capacity only about 10 percent of the time. The average capacity factor for all wind power installations in the country is somewhere between 30 percent and 35 percent. This low capacity factor coupled with wind power’s unpredictability (it’s hard to predict when and how fast the wind will blow) create some unique challenges for the wind industry.
Xcel Energy and the National Renewable Energy Laboratory (NREL) have launched a demonstration project at the National Wind Technology Center in Golden, Colo., aimed at mitigating the challenges and limitations associated with generating electricity with wind. The Wind-to-Hydrogen (Wind2H2) demonstration project links wind turbines to electrolyzers, which pass the wind generated electricity through water to split the liquid into hydrogen and oxygen. Researchers plan to store the hydrogen and use it to generate electricity from an internal combustion engine or a fuel cell. According to NREL’s website, the project’s goal is to “improve the system efficiency of producing hydrogen from renewable resources in quantities large enough, and at costs low enough, to compete with traditional energy sources such as coal, oil and natural gas.”
Although hydrogen is the most commonly found element in the universe, it isn’t found in its pure form on the Earth. It either must be electrolyzed from water or stripped out of natural gas. Both of these processes use large amounts of energy that, when obtained through traditional generation technologies, create greenhouse gases and other harmful emissions. For this reason, using wind energy to create hydrogen that can be stored and used when needed could transform hydrogen into “the perfect fuel,” said Richard Kelly, Xcel Energy’s chairman, president and CEO, during the project facility’s unveiling this past April.
The Wind2H2 project links two variable speed wind turbines, a Northern Power Systems 100 kW turbine and a Bergey 10 kW turbine, to the electrolyzers. The electrolyzers, devices that compress the hydrogen for storage, four large hydrogen storage tanks, a generator with a hydrogen-burning engine and a control room where the process can be monitored are housed in a new building constructed especially for this project.
The energy from the 10 kW wind turbine will be converted from “wild AC” current (current that varies in magnitude and frequency) to DC current. This DC current will then be used by the electrolyzer to produce hydrogen from water. The 100 kW wind turbine’s energy will be taken from its existing controller, which produces between 750 V and 800 V DC bus power. This voltage is too high for the electrolyzer, so researchers will design the electronics necessary to make a DC-to-DC conversion, creating a current that the electrolyzer can use.
According to an NREL press release, the Wind2H2 project has two main goals. First, it aims to help researchers achieve efficiency gains through unique, integrated AC-to-DC and DC-to-DC power electronics-based connections between the wind turbines and the electrolyzers. These should reduce duplicated components in the wind turbine and the electrolyzers to decrease cost and increase overall system efficiency.
Second, to allow researchers to compare multiple electrolyzer technologies, including alkaline and proton exchange membrane electrolyzers, to gauge their efficiencies and abilities to be brought on- and off-line quickly.
“By marrying wind turbines to hydrogen production, we create a synergy that systematically reduces the drawbacks of each,” Kelly told those attending the facility’s unveiling. “Intermittent wind power is converted to a stored fuel that can be used anytime, while at the same time offering a totally climate-friendly way to retrieve hydrogen, to power our homes and possibly cars in the future.”
In 2005, Xcel Energy and NREL conducted a study to determine if hydrogen for transportation fuel could be economically produced by wind power. Two cases were studied; one where hydrogen was produced at the wind site and delivered to the point of use. The second study looked at an approach where hydrogen was produced at the point of use using wind energy transported through the electric grid from several wind farms. In both studies, low-temperature electrolyzers were used to convert the wind energy to hydrogen.
More information about both of these Xcel Energy and NREL wind-to-hydrogen programs is available at NREL’s Web site: www.nrel.gov/wind.
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