Setting the Foundation for Gigawatt-Scale Renewable Energy

From the 2007 Research Review.

A composite of seven photos illustrates the workings of the Wind2H2 facility. A caption under the photos says 'Wind energy or solar energy is converted to the appropriate current to electrolyze water to hydrogen, which is compressed and stored for subsequent electrical generation.' The photos are of a wind turbine; an array of solar panels; a man wearing a hard hat and safety glasses and peering into a rectangular upright box in which are mounted about eight electrical components with wires running between them; the same man reaching into a similarly shaped box and touching an electrolyzer, a device with a cylindrical base with about a dozen inch-thick cylinders protruding from its top in a circular pattern, which is surrounded by a complex jumble of tubes and hoses; the same man adjusting something on a hydrogen compressor, which is a complex jumble of pipes and valves including several large pressure gauges; hydrogen storage tanks, which are long metal cylinders about two feet in diameter and labeled 'hydrogen, flammable gas, no smoking, no open flame,' with wind turbines in the background; and the same man examining a generator, a box about three feet high filled with a complex tangle of pipes and wires.

Sitting on an exposed, wind-blown plateau along the front range of Colorado's Rocky Mountains, a 40-foot by 40-foot concrete pad may hold a key to our energy future. This is the home of the "wind to hydrogen" project, a unique facility that uses electricity from wind turbines and solar panels to produce hydrogen from water.

In chemical nomenclature, hydrogen is "H₂," and researchers at the "Wind2H2" facility are working to solve some of the biggest problems facing the world today: how to generate electricity and produce transportation fuels without accelerating climate change.

"The ultimate goal is to get more wind power onto the grid and provide cost-effective hydrogen for vehicles in an environmentally conscious manner, although economical and robust fuel-cell-powered cars are still years away," says project leader Kevin Harrison.

Producing electricity from renewable resources like the wind and the sun is an environmentally friendly way to meet our future needs for power. But there's a major drawback: these resources don't produce electricity when the wind isn't blowing and the sun isn't shining, and this variability has hampered their development and wide-scale adoption. So, the major goal of Wind2H2 is to improve the reliability, dispatchability, and economics of renewable energy by storing it as hydrogen, opening the door for gigawatt-scale renewable energy deployment. The hydrogen could then be converted to electricity when it's needed or used as a vehicle fuel.

Hydrogen is a flexible energy carrier that can be generated from coal, natural gas, biomass, water, and other hydrogen-rich materials. Using renewable energy to produce hydrogen from water allows inherently clean energy to be stored for later uses. Hydrogen can be stored and converted back to electricity or used to run vehicles while producing little or no greenhouse gases. That's why hydrogen is often regarded as the fuel of the future. There are, however, quite a few technical challenges to be overcome before that vision becomes a reality.

The Wind2H2 facility at NREL's National Wind Technology Center is a joint venture between NREL and Xcel Energy, the largest provider of wind energy in the country. Xcel provided most of the capital equipment, while NREL, designed, built, and now operates the facility, which had to comply with stringent safety codes and standards governing sites that produce and store hydrogen.

The hydrogen is produced by electrolysis, which is the process of splitting water into hydrogen and oxygen using electricity. The electricity needed for this process comes from utility-supplied power and three renewable sources:

A 10-kilowatt wind turbine that produces alternating current (AC) that varies in magnitude and frequency as the wind speed changes
A 100-kilowatt wind turbine, from which some direct current (DC) electricity is directed toward electrolysis before the remaining energy is inverted back to regulated AC for the grid
An array of solar electric photovoltaic panels capable of producing 10 kilowatts of DC electricity.

The electricity from these sources is run through power converters—designed and built by NREL—that provide the electrolyzers with the DC power they need to operate efficiently. Two polymer electrolyte membrane (PEM) electrolyzers and one alkaline electrolyzer produce hydrogen and oxygen from an onsite water supply. The PEM electrolyzers each produce approximately 2.3 kilograms of hydrogen per day, and the alkaline electrolyzer produces 12 kilograms per day, for a total of 16.6 kilograms of hydrogen, equal in energy content to about 16.6 gallons of gasoline.

After the hydrogen is compressed, it's stored in tanks at 3,500 psi (pounds per square inch) for later use. When the demand for electricity is at its peak, the stored hydrogen is fed to an internal combustion engine connected to a generator, producing AC electricity that is fed into the utility grid. Future plans for the facility include adding the equipment necessary to compress and store hydrogen at the 5,000 psi or more needed for vehicle refueling. Another option would be a fuel cell, which could be used to convert the hydrogen back to electricity at nearly twice the efficiency of the internal combustion engine.

Today, the research focus is on developing the power electronics and control systems required to integrate all these different components into a single, smoothly functioning entity. The ability to do this is one of NREL's great strengths and the primary reason that Xcel chose the lab as a partner. NREL has a strong track record in integrating multiple generators and battery storage systems for village power grids in both the United States and the developing world.

Wind2H2 project partners hope to reduce the complexity of an integrated renewable hydrogen system and improve its overall efficiency. The first challenge is to convert the variable energy output from the wind turbines and photovoltaic array into a form that can be used by two different kinds of commercially available electrolyzers. Additional challenges involve creating a control system for integrating multiple electrolyzers of both PEM and alkaline technologies, which produce hydrogen at different pressures. If Wind2H2 facilities are to operate cost-effectively and propagate throughout the country, it is essential that they operate safely and smoothly without needing onsite monitoring.

"One of our major challenges is designing a fully autonomous system that does not require human input," says Harrison.

The design concept of the Wind2H2 facility is exquisitely simple, but the real-world challenges associated with operating it are legion. Despite those challenges, the pressing need for clean, autonomous energy systems has placed this project on a fast track. At the facility's inauguration in December 2006, NREL director Dan Arvizu emphasized a key advantage of joint ventures like this.

"Our growing strategic partnership with Xcel Energy helps us reduce the time and effort between research discoveries and sharing the benefits of what we learn with energy consumers," Arvizu said.

And according to Harrison, we won't have long to wait for the results of NREL's research on the optimal ways to integrate and control wind, solar, and hydrogen systems. "Expect answers by late 2008," he says. Now that's the power of partnership in action.

Illustration that shows the five steps of the R&D process: Innovation, Technology Development, Product Development, Commercial Demonstration, and Large-Scale Deployment. Commercial Demonstration is highlighted.

This technology is in the Commercial Demonstration phase of the R&D process. Learn more in "From Research Discoveries to Market: Five Steps to Commercialization."

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