SIEMENS

Who says that far-reaching technologies can’t be based on simple processes? Take two electrodes, for instance, connect them to the positive and negative poles of a voltage source and put them in water, and presto, bubbles appear when electricity flows through the liquid. The bubbles on the positive pole are filled with oxygen, while those on the negative pole contain hydrogen. This process of splitting water into its constituent elements is called electrolysis.

Although this may not seem earth shaking at first glance, electrolysis nevertheless has the potential to become a key part of the energy supply networks of the future. “The larger the share of electricity production accounted for by renewable sources such as the wind and sun, the greater will be the fluctuations in the amount of energy available,” says Dr. Manfred Waidhas from the new Hydrogen Electrolyzer Division at Siemens’ Industry Sector. “The problem is that supply and demand must always be caprecisely balanced in the electricity grid if overload is to be avoided. That’s why we need electrical energy storage units that absorb energy surpluses and then return the energy to the grid when it is needed.”

This is where electrolysis comes in. The process uses surplus electricity from renewable sources to produce hydrogen that can then be stored as an energy carrier in subterranean caverns in salt domes, for example — the kinds of locations that energy companies typically use for stockpiling huge amounts of natural gas.

But doesn’t proven storage technology already exist in the form of pumped-storage hydroelectric power plants? Such plants use surplus electricity to pump water into a basin at a higher level. Then, when extra power is needed, the water is allowed to flow downwards to drive turbines that generate electricity. “Pumped-storage plants are in fact the ideal solution,” says Waidhas. “They have efficiencies as high as 80 percent and their technology has been used for decades.” Unfortunately, however, the best locations for such installations have already been tapped. What’s more, plans to build new facilities invariably lead to massive protests.

Alternatives are therefore needed. One possibility is to use batteries from electric vehicles (see Pictures of the Future, Fall 2010, Get a Charge!). However, the cost of batteries, and the amount of space they need, generally prohibit the construction of centralized storage facilities. The largest such facility is in Japan. Despite being as big as a soccer field, it can supply only 30 megawatts of electricity for seven hours. In the future, it will be necessary to deliver several hundred megawatts — and when the wind drops, this output will have to be available for several days.

Storing Energy in Hydrogen. Waidhas believes hydrogen offers the best energy storage solution. “You could set up an electrolyzer at a location where electricity from an offshore wind park reaches land, for example,” he says. “If the wind park were to produce too much electricity, you could use it to produce hydrogen, which could then be stored in a cavern.” If demand for power rises, the energy-rich gas could then drive a turbine to supply CO2-neutral electricity to the grid. If you combine the efficiency of the electrolysis (approx. 75 percent) with that of a gas turbine (around 60 percent in combined cycle operation with a steam turbine), the resulting “energy-recirculation” process would still exploit up to 45 percent of the original energy. “That’s not as good as a pumped-storage plant, but it’s better than shutting down windmills when demand isn’t there,” says Waidhas.

But there’s a hitch. Flames resulting from the combustion of hydrogen gas would have a temperature of around 3,000 degrees Celsius. And that would cause today’s turbine blades to melt. “In view of this, what’s technically feasible at the moment is a hydrogen component of 40 to 50 percent, which could be mixed with conventional natural gas,” says Waidhas. “You could then circulate part of the steam back into the combustion chamber in order to keep the temperature below the critical level.”

Siemens researchers in Moscow are working to make the dream of an efficient hydrogen turbine a reality (see Pictures of the Future, Fall 2009, Red Hot Ideas).

Today’s turbines can be operated smoothly using methane, which can be produced from hydrogen and carbon dioxide with the help of a catalyst. Researchers working at the Center for Solar Energy and Hydrogen Research Baden-Württemberg in Stuttgart, Germany, and the Fraunhofer Institute for Wind Energy and Energy System Technology in Kassel, Germany, have teamed up with Austrian energy company Solar Fuel Technology to build a pilot facility in which hydrogen is “methanized” with an efficiency of around 80 percent. As soon as this methanization process can be reproduced on an industrial scale, producers could begin pumping the resulting synthetic natural gas into storage facilities in Germany.

The country’s pipelines and caverns can accommodate enough gas to store a total energy content of more than 200 terawatt hours (TWh). This is substantially more than the current capacity of all pumped-storage facilities in Germany (0.04 TWh). It also represents roughly one-third of the country’s annual gross electricity consumption. Alongside recirculation to turbines, methanization would also make it possible to use the new fuel in natural gas vehicles and heating systems.

Hydrogen is a very attractive alternative because it can also serve as a feed stock for many chemical industry processes — from semiconductor production to margarine hardening. “Today, more than 95 percent of the annual global hydrogen requirement is obtained from natural gas,” says Waidhas, who is a chemist. “With steam reforming, hydrocarbons react at high temperatures and pressure with water, producing carbon monoxide and hydrogen in the process.”

Electrolysis enables another alternative here — one in which hydrogen produced from renewable sources could be sent via pipelines to chemical industry centers for use as a feedstock. Valuable natural gas would thus be conserved, and hydrogen produced from excess renewable energy would not produce any CO2 emissions.

Electrolysis in the Lab. Waidhas and his colleagues will first have to make electrolyzers capable of working on an industrial scale. The current state of technology in this area is on display at the Siemens Corporate Technology lab in Erlangen. Here, the latest generation of Siemens electrolyzers operate completely silently in a metal housing. The two cube-shaped devices are made of stainless steel and held together by sturdy bolts. Black high-pressure pipes protrude from the silver blocks on the right and left. Their job is to transport the hydrogen and oxygen gas produced by the units to tanks at pressures up to 50 bars. Internal temperature measurements are transmitted to the neighboring control units via vertical cables connected to the devices.

“The new unit has been operating without interruption for several months; its predecessor unit has been running since 2006,” says Waidhas. “Right now, we’re optimizing operational parameters such as current density, and upgrading membranes and other components.” That’s because unlike a school lab experiment involving nothing more than two wires in a glass of water, an industrial electrolyzer is an extremely complex device whose components must have very special properties. The front and back consist of two stainless steel plates that ensure no gas escapes and that transport electricity into the interior. Sandwiched between these plates are the cells in which water is broken down.

A Teflon-like membrane in the middle of each cell separates the sections in which hydrogen and oxygen form. On the front and back of the membrane are precious-metal electrodes that are connected to the positive and negative poles of the voltage source. “This is where the water is split,” Waidhas explains. “The electrodes need to have as large a surface area as possible, as this guarantees a high yield.” It’s also important that large amounts of both electricity and water reach the electrodes. This is ensured by current collectors made of porous sintered metal. The collectors not only surround the electrodes but also collect the gas and transport it upwards.

The new membrane electrolyzers from Siemens offer several advantages over their established counterparts that use potash lye to separate the electrodes. “Existing state-of-theart electrodes take several minutes to react to changes in the amount of available electricity,” says Waidhas. “Our membrane version, on the other hand, reacts in just milliseconds.” The new electrolyzers can be temporarily overloaded with a maximum of three times the level of their rated output. They can also operate at hydrogen pressures of 50 to 100 bars — which lowers costs and improves yield.

Coveted Gas. Waidhas and his colleagues plan to build a demonstration unit by 2012 that will fit into a container and be able to operate on site at a potential customer location. “All we’ll need then is a water and electricity connection,” he explains. “The new electrolyzer will be able to utilize a maximum of 300 kilowatts of power — as opposed to our current test unit, which runs at 30 kilowatts maximum.”

The electrolyzer, which produces around two kilograms of hydrogen per 100 kilowatts and hour, is already attracting interest. Siemens is working with Bayer, RWE, and ten other partners in a project called “CO2RRECT,” which is exploring methods for using carbon dioxide to produce everything from chemical feedstocks to plastics. Here, hydrogen obtained from renewable sources is used as a raw material.

Waidhas expects the first commercial electrolyzer to be ready by 2014. “That unit will be able to operate in the single-digit megawatt range and could be used, for example, by a regional power supplier to collect surplus electricity from one or two windmills or photovoltaic facilities,” he says.

Waidhas also believes the market for the technology will be enormous in the future. “Converting only ten percent of globally-generated wind energy into hydrogen using electrolysis would result in the storage of several terawatt- hours of energy each year — that’s a huge amount,” he points out. In this scenario, large electrolyzers with a capacity of 100 megawatts would be built in close proximity to wind parks whose excess electricity would be used to produce a universal energy carrier in the form of hydrogen.