The growing proportion of renewable energies in worldwide power generation is playing a key role in the reduction of global CO2 emissions. However, this development poses huge challenges to power grids, which will have to become much more flexible in the future in order to accommodate these fluctuating energy sources. Technologies such as electrolysis can help to meet this challenge. Electrolysis uses electrical energy to split water into oxygen and hydrogen, which can serve as a storage medium, energy carrier, CO2-neutral fuel or feedstock for many industrial applications. As a result, hydrogen is driving the decarbonization process and paving the way for a new age — one of affordable renewable electricity.
Almost half of the world’s population has mobile access to the Internet through smartphones — a situation that was unimaginable just a few years ago, but which is now part of our daily lives. Another development that hardly anyone would have thought possible until recently, but which is now starting to look like a distinct possibility is a dramatic reduction in the cost of “green” electricity. In 2014 the record-setting lowest price for solar energy was seven US cents per kilowatt-hour. Three years later, the lowest price had fallen to approximately two US cents. If this trend in prices continues, the generation of electricity from wind and sunlight could soon become almost free of charge.
Renewables Require Flexible Power Grids
Although the declining cost of renewable energy is a positive development, it nevertheless involves some challenges. For example, in Germany there are already periods when more energy is generated than the power grid can accommodate. This phenomenon will intensify, mainly in countries where the cost of generating electricity from wind and photovoltaic sources continues to decrease. Power grids will therefore need to respond flexibly to the fluctuating generation of renewable energy —the only way to ensure system stability and security of supply.
Energy storage systems are one solution that can be used to increase the flexibility of power grids. By capturing energy during periods when there’s lots of wind and sunlight and feeding this power into the grid during periods of no wind or gray skies, energy storage systems can create a balance between generation and demand— and decouple the times when these two processes occur. That is why experts are increasingly turning to energy storage systems as the key ingredient in ensuring a stable supply of electricity generated from renewable energy sources. Various analyses, including the “Energiespeicher” (Energy Storage) study conducted by the UMSICHT and IWES Fraunhofer Institutes, predict that Germany will require as much as 50 gigawatts (GW) of energy storage capacity by 2030.
Hydrogen Electrolysis — Wide-ranging Applications
“In the future, the technologies we have today, such as batteries, capacitors, and flywheel and compressed air energy storage, will not be sufficient,” explains Gabriele Schmiedel, who heads Hydrogen Solutions at Siemens Corporate Technology. “We will need solutions with a storage capacity that has not yet been achieved — namely, in the realm of terawatt-hours.” Hydrogen, she says, is ideally suited for this purpose.
How can an electrolyzer help to cover the growing need for storage capacity? Put simply, an electrolyzer splits water into hydrogen and oxygen with the help of electricity — ideally, “green” electricity. “Hydrogen is impressively versatile,” says Schmiedel. It can store between a few kilowatts and a gigawatt of electricity over a period of several weeks. Subsequently it can be used as a process gas in industry or as a fuel for zero-emission fuel cells in the mobility mix. In addition, it can be processed further to form raw materials such as ammonia for fertilizer production or methanol as a base chemical or fuel. If electricity prices are low, it would even be worthwhile to store hydrogen and subsequently reconvert it into electricity in combined cycle power plants that guarantee security of supply. This multifunctionality illustrates how important hydrogen electrolysis could be for worldwide decarbonization. Such large-scale storage systems would make it practical to generate increasing quantities of renewably-produced electricity. This would set the stage for a steady decline in CO2 emissions and an end to the era of fossil fuels.
Second Generation PEM Electrolysis
Although electrolysis, which was discovered at the beginning of the 19th century, is far from new, it is the focus of a great deal of innovation. For instance, Schmiedel’s team is concentrating on proton exchange membrane (PEM) electrolysis, which is the basis of Siemens’ second generation SILYZER electrolysis technology. PEM’s special property is that it is permeable to protons but not to gases such as hydrogen or oxygen. As a result, in an electrolytic process the membrane takes on, among other things, the function of a separator that prevents the product gases from mixing. On the front and back of the membrane are noble metals electrodes that are connected to the positive and negative poles of the voltage source. This is where water molecules are split. By contrast to traditional alkaline electrolysis, PEM technology is ideally suited to harvesting energy generated from wind and solar power, which are irregularly generated, because it can be quickly switched on and off without any need for preheating.
Record-setting Facilities in Operation
Siemens operates several PEM electrolysis facilities for customers in Europe. Indeed, one of these, which has a capacity of five megawatts (MW) and is located in an oil refinery in Hamburg, is the world’s largest such facility. In Austria, Siemens is working with several partners to build the first facility to be based on its new SILYZER 300 product generation. Its planned output will be six MW. And that’s just the beginning, because the larger the amounts of transformable energy, the larger the capacities of potential facilities. As a result, customers from regions that have plenty of wind and sunshine are particularly interesting for Siemens. Solar farms in the Middle East and Australia, which are much larger than those in Europe, could eventually make use of electrolyzers of unprecedented dimensions. “We are talking to interested parties who are thinking in dimensions of up to 400 MW,” says Schmiedel. She is convinced that scenarios of this kind, which still seem distant, could soon become reality. And the example of mobile networking via smartphones justifies her optimism.