The expansion of renewable energies in Germany is booming. However, it is not yet enough for a complete energy transition. New concepts for existing technologies and innovations are needed to enable the global energy transition. In Part 1 of our series, we present new approaches to the use of solar energy.
Climate change is increasingly manifested in local weather events, some of which are extreme: Forest fires, floods, droughts and heat records increase the pressure on global politics to act. The primary goal is to reduce climate-damaging CO2 emissions by decarbonising many areas of life.
This sounds easier than it is. For a successful transformation, politics, science and the population must pull together, because time is pressing. The search for suitable locations for wind and solar energy can become a real challenge. Innovative solutions that use existing infrastructures, for example, can help here.
We know solar modules from the roofs of single-family homes and industrial buildings, but not every roof is suitable for the heavy modules. Conventional PV modules weigh between 18 and 40 kilograms, depending on size and output. In order to be able to bear this weight, a good structural design of the supporting roof is essential. The weight is also a relevant value for transport and installation, which is sometimes carried out with lifting platforms or larger cranes, and this clouds the CO2 balance.
The situation is different with solar foils. In contrast to conventional modules, a semiconductor material is vapour-deposited onto a light and flexible carrier film. This already saves a lot of energy during production and makes frame constructions made of light metals such as aluminium superfluous. This is not unimportant for the globally conceived energy transition, because the aluminium reserves for conventional modules would not be sufficient for a worldwide switch to solar energy. Silicon, lead and other heavy metals are also no longer needed for the ultra-light foils.
However, the advantages of solar foils are not only in their production, but also in their wide range of applications. Their lightness and flexibility make them interesting for new areas of application: lightweight roofs, building facades and even the surfaces of wind power towers can be covered with the film.
The disadvantage: so far, the electricity yield is significantly lower than with conventional solar cells. But the efficiency could still improve through further research. On the other hand, the potentially usable surfaces are much larger, which may compensate for the lower efficiency. With only seven to nine grams of CO2 equivalent per kilowatt hour, the film already performs much better than solar modules (about 50 grams of CO2e).
Solar films could achieve a significantly higher efficiency if they converted the sunlight into electricity not only on one side, but on both sides. According to recent research, these bifacial thin-film solar cells could enable up to 30 percent higher solar yields on the same surface area.
An innovative idea does not always have to result in a completely new product; sometimes a new form of use is enough. A cycle path with a solar roof in Freiburg is a good example of this in several respects. A roof made of 912 translucent photovoltaic modules was installed here over a distance of 300 metres, keeping cyclists dry even when it rains. This not only makes cycling more attractive as a sustainable mobility solution, but also generates around 280 megawatt hours of electricity per year.
This could supply around 200 households. The largest customer, however, is the Fraunhofer Institute for Solar Energy Systems (ISE) located in the neighbourhood, which can use it to supply its laboratories with electricity. At the same time, the ISE researchers want to evaluate the data from the test track for the further development of such plants.
The facility also includes a modern lighting concept. It consists of permanent basic lighting that increases comfort and safety. In the dark hours of the day, an additional intelligent light strip provides bright light as soon as motion detectors register people. Inadequately lit bicycles can thus be largely excluded as a cause of accidents on the route.
Solar energy is available to us in almost unlimited quantities. This makes this natural resource an important building block of the energy transition. However, there are two interrelated problems in generating electricity with solar cells: Firstly, electricity can so far only be stored at great expense, and secondly, solar cells only produce electricity when the sun shines sufficiently. But we also need a lot of electricity in the dark half of the day, so solar energy alone is not enough.
This could change in the future, because an Australian company has developed a technology that bypasses the interruption of solar energy during the dark part of the day. With a "solar-plus-storage system", RayGen combines photovoltaics and solar thermal energy in one system: the electricity generated during the day is fed into the grid, and the heat generated at the same time is fed into an underground water storage tank. The water temperature generated in this way is sufficient to drive a turbine after sunset, which in turn generates electricity.
A new plant is currently being built in Australia using this technology, which will have a storage capacity of 3.6 GWh. This would make it one of the largest storage facilities in the world.
Text: Falk Hedemann
In part 2 of our series on innovations in renewable energies, we look at the use of wind.
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