The energy of tomorrow is renewable, but fluctuating supply underscores the need for new ways to store wind and solar power. Researchers in Germany say transforming excess clean power into gas could be one way forward.
How can we tap renewable energy when the wind isn't blowing?
The solar and wind energy sectors are booming. In 2010, new solar panels installed on rooftops in Germany generated a combined 8 gigawatts of energy. That exceeds the production capacity of the seven nuclear power plants most recently taken offline in the country.
Wind power has even more potential. According to German government's energy policy roadmap, coastal wind parks should start feeding at least 25 gigawatts of power into the grid by 2030.
If the weather were breezy and sunny every Sunday in Germany, the country wouldn't need any other power sources to meet its energy needs for the day.
Of course, not every day is a breezy, sunny Sunday. Changing weather patterns keep the supply of wind and solar power inconsistent.
That raises some key questions. What if the wind isn't blowing and the sun isn't shining? What happens to the energy supply overnight or during rainy months, like November?
Nature's energy reserves aren't always reliable, and that makes viable power storage options all the more important. So far, researchers have struggled to develop economical technologies that facilitate long-term storage of large amounts of power.
The capacity of pumped-storage hydroelectricity, which preserves power through pumping water from lower reservoirs to higher elevations, is still largely inefficient in Germany and abroad. For other forms of energy storage, such as batteries, the costs are still too high.
Yet some see a promising solution in gas.
A hybrid power plant stores hydrogen from wind power in these tanks
Storing renewables as gas
"Which storage technologies can be implemented and how can they be integrated into the current infrastructure?" asks Ulrich Zuberbühler, a researcher at the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW).
Zuberbühler has teamed up with the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) and the company Solarfuel to find new solutions.
The new concept involves effectively turning wind and solar power into gas, and then storing it.
Germany has tremendous gas storage capacity: at 200 terawatt hours, the reserves are capable of meeting Germany's gas needs for several months.
Thanks to natural gas "caverns" underground, the country has the largest storage capacity of any European Union member state.
Scientists developed this procedure to produce methane gas
60-percent efficient, and counting
Scientists used a small, 25-kilowatt facility in Stuttgart to perform their initial tests.
For the first time, they combined two tried-and-tested procedures: electrolysis and methanation, which was first explored in 1906 by Paul Sabatier.
Electrolysis uses an electric current to split water into hydrogen gas and oxygen. Through methanation, that hydrogen is transformed into methane with the help of carbon dioxide.
About 60 percent of the source power – the electricity needed for the procedure – can be successfully converted into methane. The rest is released as heat. If that heat is harnessed during the procedure, it becomes even more efficient.
Zuberbühler says the scientists' next test will involve 10 times the kilowatts compared to the initial experiment and is due to be completed in 2012. ZSW sees big potential in the technology.
Audi looks to wind energy
The team's methane can be stored and used to power heaters, industrial furnaces, other power plants and even cars.
In initial experiments, it took just three minutes to fill a test car's gas tank with the methane "e-gas," and the vehicle was able to run for 450 kilometers.
Audi is due to release a climate-neutral, natural gas-powered car by 2013, and the company has already bought wind farms in the North Sea to provide the power. A 3.6-megawatt wind turbine produces enough energy in a single minute to provide drivers with 300 kilometers of climate-neutral mobility.
Meanwhile, plans are already in the works to build a methanation station in Werlte, northern Germany. Construction is estimated to cost about 20 million euros.
The 6-megawatt facility is due to be completed by May 2013, something that will aid the commercialization process.
Methane e-gas was tested as a fuel for automobiles
An affordable transformation?
Building methanation facilities is still an expensive proposition. But Gregor Waldstein, managing director of Solarfuel, said that could soon change.
Serial production stands to cut costs considerably. Moreover, he said, the energy market is undergoing major changes, and that has increased demand for new power storage technologies.
With more solar and wind facilities, there will be an even bigger surplus of energy on sunny, windy days. With methanation facilities in place, that excess can be harnessed to produce e-gas.
Waldstein said the procedure will help reduce the strain on existing power grids. It will also make wind and solar power facilities more profitable.
The German government aims to build new gas-fueled power plants with a combined capacity of 6 gigawatts in the years to come. As the renewable energy sector continues to grow, these plants could run on methane e-gas, instead of imported natural gas.
Author: Elsa Wimmel / arp
Editor: Nathan Witkop