At NREL's National Wind Technology Center, researchers are evaluating a system that converts electricity from wind and solar energy to produce hydrogen, which could be used to to fuel vehicles.
Wind to Hydrogen
February / March 2009
Volume 7 Number 1
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 overcome before that vision becomes a reality.
The Wind2H2 facility at the National Renewable Energy Laboratory'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 that varies in magnitude and frequency as the wind speed changes
—€ A 100-kilowatt wind turbine, from which some direct current 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 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.
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 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.
Erik Ness is a senior communicator at NREL.
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