SCHOTT solutions no. 1/2015 > Energy technologies

Multitalented glass
This BOROFLOAT® pane withstands more than 60,000 volts of power. SCHOTT is developing various types of specialty glasses that can be used to convert, transport, store or use energy. Photo: SCHOTT/A. Sell

Multitalented glass

Even though glass is usually not directly visible when used in energy technology, it is indispensable. And it holds immense potential for the energy landscape of the future. Glass experts at SCHOTT are already developing ”electrifying” solutions.

Thomas H. Loewe

Wind turbines rotate and solar modules capture the sun’s energy. The impact of the energy transition can be seen in many different places. Nonetheless, it is not obvious that a decentralized power supply using renewable energy requires innovation at many levels. ”Glass surprises us with its unexpected properties when electricity is generated, transported, stored or used,” explains SCHOTT Research Fellow Dr. Roland Langfeld.

To obtain power from the wall socket, energy must first be made available in electrical form. It can be produced in a much more environmentally friendly manner using stationary high-temperature solid oxide fuel cells (SOFC) (see solutions 1/14) instead of fossil fuels. The fuel cell uses hydrogen, natural gas or methane and oxygen and converts it into electricity and water. Power generation runs efficiently at temperatures of between 600 and 1000 degrees Celsius. ”This requires specially adapted materials, such as glass,” says Claire Buckwar, Director Strategic Marketing and Innovation at SCHOTT in Landshut, Germany. ”During the joining of the oxide ceramic electrolyte and the metal of the cell housing with glass solder, it forms a permanent hermetic seal. This ensures that no uncontrolled gas exchange takes place and that fuel cells have long lifespans,” she adds. If it is connected to stacks in series, the technology is quite impressive due to its high performance. High overall efficiency of up to 95 percent makes it the most efficient fuel cell type currently available and a potential cornerstone of decentralized energy production. Powered by methane from biogas, it can be seamlessly integrated into existing renewable energy networks.
High-voltage technology
High-temperature fuel cells convert hydrogen and oxygen into energy and water (left). Here, highly resistant sealing glasses (right) perform important sealing and insulation functions. Source left: SCHOTT/A. Schneiderwind, Photo right: SCHOTT/H.-J. Schulz

HVDC: Switch current flow on and off using fiber optics

Transporting energy is just as important as producing it. An extensive power grid ensures that energy can be distributed. Nevertheless, offshore wind parks produce only three-phase current, which is then converted into direct current. Voltages of up to 800,000 volts can be observed with high-voltage direct current (HVDC) transmission. ”The switches that turn current flow on and off are at a high potential and cannot be operated electrically with copper cables for insulation reasons,” explains Senior Product Manager for Industrial, Dr. Werner Sklarek, in pointing out the problem. ”For this reason, reliable switching is performed using light pulses that are guided through surge-resistant fiber optic cables,” adds Sklarek.
Fiber optic cable
Fiber optic cable (left) is used to transmit high-voltage direct current in converter stations (right) and to reliably turn electricity on and off with voltage differences of up to 800,000 volts. Photo left: SCHOTT/ C. Costard, Photo right: SIEMENS

More power in high-voltage technology

Capacitors are the universal performance providers of the energy landscape. These short-term energy storage devices are being used everywhere in electrical engineering applications: from high-­voltage components in supply networks to medical technology and consumer electronics. Their storage capacity is not solely dependent on their design, however. The insulating material, which experts commonly refer to as a ”dielectric” is also a decisive factor. SCHOTT has developed a new dielectric material especially for high-voltage capacitors called POWERAMIC®. Dr. Matthias Müller, Director of Glass-Ceramics for Electrical Applications, explains: ”The advantages that glass-ceramic offers are not only its high degree of homogeneity and lack of pores. These aspects allow for much higher energy storage density – roughly a factor of 10 – compared to the materials used today.” In addition, it is resistant to high temperatures, which can quickly lead to thermal overload of components. And additional cooling may no longer be necessary. “Capacitors that use POWERAMIC® glass-ceramic as a dielectric material are small and light and save space and weight,” Müller says. This also makes the material potentially attractive for use in mobile applications such as electric rail traffic and electric cars, for example. These types of high-voltage capacitors can potentially also be used directly at the energy source, for instance in wind turbines, where they can help to feed electricity directly into the grid as part of the electric components. As an instrument transformer, they contribute quite significantly to the stability of both today's and future power grids due to a high storage capacity and extreme robustness.
SCHOTT also developed POWERAMIC® for use in high-voltage technology. This innovative glass-ceramic (right) serves as a dielectric material and increases the ­performance of the capacitors. Photo left: Thinkstock, Photo right: SCHOTT/ T. Lohnes

Greater safety for electric mobility

The mobility of the future will require efficient energy storage and utilization and benefit from high-performance materials. Chemically highly stable special glasses for use in electric cars will help to seal lithium-ion batteries reliably and thus ensure stable and durable operation. In the event of a leak, there is a risk of a short circuit and the release of chemicals that can cause a fire or an explosion. To prevent this from happening, modern lithium-ion batteries are enclosed in aluminum housings. However, the sealing material used in the battery lid where the electrical contact between the inside of the battery and the outside takes place represents a weak point in the construction. The plastic insulators that are commonly used are sensitive to chemical corrosion and extreme temperature fluctuations. For this reason, SCHOTT has developed special battery feedthroughs under the SCHOTT GTAS® brand and complete cover systems. The result: a cell design that offers durable tightness.
Interview: Prof. Dr.-Ing. Volker Hinrichsen

”Glass is a hidden champion”

Prof. Dr.-Ing. Volker Hinrichsen from the Technical University of Darmstadt on glass for use in high-voltage technology

Future topic electric mobility
Future topic electric mobility: Glass-sealed penetrations increase the service lives and reliability of lithium-ion batteries (below). SCHOTT has developed ­ion-conducting glass-ceramics for innovative lithium-air batteries. To the right, test cells for increasing the range of electric cars inside a climate chamber. Photo left: SCHOTT, Photo right: Thinkstock, Photo below: SCHOTT/ C. Costard

Battery of the future for extended ranges

In order to advance electric mobility, SCHOTT operates along the entire battery roadmap. A glass innovation optimizes the reliability of high-power lithium-ion batteries. Today, so-called S-glass as glass powder in the form of a coating on the separator or as an additive to the electrolyte already allows for a longer lifespan, higher temperature resistance and improved safety in liquid electrolyte batteries because it makes conventional polymer film separators more resistant. SCHOTT is also a partner involved in projects aimed at developing more powerful ”next generation” battery technologies. The company is working with industry leaders on developing lithium-air batteries (see solutions 2/2012). ”The decisive factor for higher energy densities and more energy per unit of weight is the material that is located between the electrodes and replaces the previous liquid electrolyte as a solid ionic conductor,” says SCHOTT battery expert, Dr. Wolfgang Schmidbauer. In addition to offering good ionic conductivity, it must be absolutely impermeable to oxygen and water in ambient air. Dr. Schmidbauer explains: “SCHOTT has developed an innovative, ion-conducting glass-ceramic with high conductivity for lithium ions and excellent electrochemical stability.” The potential of lithium-air batteries is enormous: in commercial form, they promise to deliver three to five times higher storage capacity of approximately 1,000 watt hours per kilogram – and thus significantly longer ranges for electric cars.

Glass is already a contributor to the energy transition (see illustration Focus). ”The versatile material glass will definitely offer the flexibility and performance we need in the future as well,” says Research Fellow Dr. Langfeld. And SCHOTT experts are already developing new ideas on glass innovations that electrify.