“Solar heat storage costs half those of PV”

That’s right. Given our sunlight hours, it would be impossible to operate a solar thermal power plant profitably here, but they are more than sufficient to conduct research into the technology. Thanks in part to public subsidies, DLR has been exploring the use of solar energy for 40 years. Experience of this nature provides an advantage that should not be underestimated in such investment-heavy areas. Furthermore, we feel our mission is to be of service to the German economy. German companies contribute up to 40 percent of the value created when building solar farms. However, we also have a site in Andalusia.

They cover a wide spectrum. We cooperate with major manufacturers like MAN, which is developing a molten salt receiver with us, and Siemens, the hidden champion of steam turbines for solar farms. Also included are established component producers such as Schlaich Bergermann Partner, whose heilostats we test here, as well as young, innovative companies such as Lufthansa partner Synhelion, which we support in engineering solar-based fuel. Moreover, our research work often culminates in spinoffs, which continue to collaborate with us. Five of these startups have become fairly well established, with a sixth being founded in Spain.

What we’re testing in two of the three chambers is heat transfer media, which absorb the bundled solar heat and generate steam with it. We’re exploring molten salts, which are already the de-facto standard in solar towers, but we also want to use in parabolic trough power stations. In another chamber, we’re working with black bauxite particles which can be pumped similarly to a liquid, but can store heat at higher temperatures. Going forward, we also want to explore whether liquid metal like sodium can serve this purpose, but we’re just at the theoretical stage right now.

The third test chamber is being used to look into solar hydrogen production processes as a thermal alternative to electrolysis. Although this method isn’t competitive yet, we expect that it will clearly best the efficiency of PV-powered electrolysis. In theory, it could outperform PV two to three-fold.

Exactly. All told, we are active in five major fields of research: thermodynamic systems, heat transfer fluids and receivers. Our Solar Chemistry Unit is dedicated to producing chemical energy sources, i.e. predominantly hydrogen. Some of our experts develop new methods and techniques for validating and measuring wear, efficiency, etc. The fourth major field of research is energy meteorology, which involves predicting solar radiation. And in my department, we are working on engineering autonomous solar thermal power stations with a degree of digitisation and automation sufficient for them to be operated nearly entirely or completely without onsite personnel.

Actually, the electricity generation costs of these two technologies don’t differ that much from one another. Financing costs are more problematic as investors still don’t trust the technology enough.

But costs aren’t everything. Quality is also important. Solar thermal power stations don’t stop generating electricity when the sun goes down. When equipped with appropriately dimensioned and capable storage systems, solar thermal power plants at good locations can run for up to 7,000 hours a year. Even at the most favourable of sites in the Sahara, PV arrays rarely achieve more than 2,500 operating hours.

However, the biggest advantage of solar heat technology is that it can supply electricity on tap, making it largely suitable for covering base load needs. PV and wind energy need electricity stores to do this – and they’re much more expensive than heat storage systems.

Elon Musk has announced a battery capable of storing a kilowatt hour of electricity for 100 dollars. By comparison, a kilowatt hour of heat storage roughly costs a mere 20 dollars. If we assume that thermal energy is converted to electricity with an efficiency of 40 percent, its kilowatt hour costs are about half as high.

Plus, there’s the issue of lifetime. We will only be able to draw empirical comparisons several years from now, but it is safe to assume that the service life of a solar thermal power station matched with a heat storage system is longer than that of a PV system mated to a lithium-ion battery.

PPAs (power purchase agreements) and invitations to tender saw CSP (concentrated solar power) plants record a drop in price to five to seven dollar cents last year. And I believe they harbour further potential, especially owing to economies of scale. Moreover, there is substantial potential for innovation. This is also reflected in interest shown in our research. The recently inaugurated multifocal tower has already been completely booked for the next few years by collaborative projects of various industrial partners.