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Inverters supply reactive power

Photovoltaic systems require an inverter. This converts the direct current generated by solar modules into alternating current. The power can then be fed into the public grid. If inverters also supply reactive power in addition to active power, they can stabilise the power grid by compensating for minor voltage fluctuations in the grid. This function is increasingly demanded by network operators. Active power describes the proportion of electrical power that can be converted into other forms of power, such as mechanical power.

Digital twin

This is the core component of a self-learning factory. This promising technology creates a bridge between the physical and digital worlds. Digital twins represent for instance virtual counterparts of physical plants, materials and products. They can store and process exact data and actions of their analogue twins in real time and optimise processes. An example is the digital twin of a solar cell, which analyses the cells during the various process steps. This increases the quality of the cells and reduces costs.

Offshore servicing

Wind turbines at sea are exposed to waves and saltwater. Algae, mussels and rust affect offshore plants considerably. Coatings therefore protect the support structures of wind turbines both above and below the water surface. In addition, operators must regularly check the condition of the structures. Divers have been taking over the tasks so far. The assignments are expensive and dangerous. For this reason, remote-controlled mini-submarines will in future document the condition of the plants in a time- and cost-saving manner with the help of cameras and other innovative technology.

Solar foil greenhouses

Producing plants and generating power at the same time: In the future, fruits and vegetables may thrive in greenhouse tunnels made of transparent solar foils. These offer the same protection against pests, cold and evaporation as greenhouses covered with plastic sheeting. This is made possible by organic solar cells printed on foils. The transparent and flexible photovoltaic layer allows the radiation needed for growth to reach the plants unobstructed. Current projects aim to optimise solar foils for greenhouses in technical and economic terms.

Alkali elements for solar cells

They are the "salt in the soup": Alkali elements such as sodium, potassium and rubidium. Even the smallest amounts of sodium, around 0.3 per mille, significantly improve the efficiency of CIGS thin-film solar cells. The Centre for Solar Energy and Hydrogen Research ZSW achieved the current efficiency records of up to 22.6 per cent with the heavy alkali element rubidium. What does this element do? New measurement methods have shown that rubidium in the absorber is distributed along the so-called grain boundaries (crystallites), thereby improving the electronic properties of the solar...

Energy for satellites

Satellites generally have to be supplied with energy for many years. This task was initially performed by silicon solar cells. Since 2004, they have been almost completely replaced by triple-junction solar cells consisting of various stacked semiconductor materials, such as InGaP/InGaAs/Ge. In contrast to silicon solar cells, these have a very high stability against cosmic radiation. They also use sunlight more efficiently. This is also demonstrated by a new quadruple solar cell by AZUR SPACE with an efficiency of 32 per cent.

Submersible centrifugal pumps

These pumps are used in geothermal plants to convey hot water to the earth's surface. The water is accelerated and pumped up by a rotating wheel. Submersible centrifugal pumps pump up to 150 litres of water per second. Depending on the head of the deep water, they are suspended at a depth of several hundred metres. One pump unit is up to 35 metres long, costing several hundred thousand euros. BakerHughes is currently the market leader for these special feed pumps. In development projects they strive for a service life of 3 years per pump.

Powerful laser

One of the most powerful lasers is used in geothermal energy. It has an output power of 30,000 watts. Laser beams used in industry are more than ten times less powerful with output powers ranging between 2,000 and 3,000 watts. These lasers are used to weld and liquefy steel. In geothermal drilling, the laser beams loosen the crystals in the stone. This creates cracks in the rock. The porous material can then be broken more easily and quickly with a mechanical drill.

CIGS solar cells

CIGS solar cells consist of a layer of copper, indium, gallium and selenium (abbreviated to CIS or CIGS) that is only a few micrometres thick. During production, this absorber layer and other contact and intermediate layers are deposited on glass sheets in integrated processes. A second glass plate is then added and the solar module is complete.

Maintenance costs

Experts estimate that servicing and maintenance account for up to a quarter of the costs of offshore wind farms, while the turbines themselves account for around a third. By way of comparison: On land the costs of the turbines account for two thirds of the total costs, while the proportion of costs due to servicing and maintenance is in the low, single-digit percentage range.

Calculating the yield

Operators can use a simulation programme to calculate the possible yield of a renewable power plant project at a specific location. The tool plans how the plant must be constructed and designed to feed the targeted amount of electricity into the grid. Plant constructors can check whether a power plant powered exclusively by wind or solar energy or a hybrid power plant makes sense.

Deep geothermal

In Germany, deep geothermal refers to the borehole extraction of geothermal at depths greater than 400 metres and temperatures over 20 degrees Celsius. Deep geothermal uses either natural hot water resources or heat stored in the rock. Both can be used to generate heat and electricity. Germany’s deep geothermal sector currently has eight power plants for electricity production and five combined heat and power plants for heat and electricity production. (Figures from the German Geothermal Association)

Heat transfer fluid

"Molten salt" power plants use molten salt, which can be heated to 565 degrees Celsius, as a heat transfer fluid. However, the melt can solidify if its temperature falls below about 245 degrees Celsius. Intelligent operating strategies are necessary to prevent this. In an emergency, the solar array heating ensures the necessary operational reliability, and the liquid salt can also be emptied into well-insulated containers and stored temporarily.

Power plant safety

Frequent starts and transitions to partial-load operation place loads on conventional coal-fired and natural gas-fired power plants. The components are exposed to frequent temperature changes of several hundred degrees. The technical regulations for power plants evaluate the fatigue loads on components purely mathematically. If a power plant component exceeds the allowable value of 100 per cent for fatigue, the test conditions are intensified. The regulations are now being adapted. They allow for differentiated, operation-accompanying investigation methods.

Funding programme

Since 2017, 15 research projects have been investigating bioenergy plants that work flexibly and across sectors. The German Federal Ministry for Economic Affairs and Energy made 6 million euros available for this purpose as part of the Biomass Energy Use funding programme. One focus of the research projects is on the combined generation of electricity and heat in small-scale CHP systems (useful heat around 100 kilowatt thermal). It is intended that energy from biomass shall play a balancing role in the transformation of the energy system and link different sectors such as...

Water flow power

Ocean current power plants work according to a similar principle to wind turbines. Turbines with a free flow around them use sufficiently strong water currents to generate electricity. There are nevertheless significant differences: because water has a higher density, the power produced by water flow at a given speed is a thousand times higher than power produced by air flow. That’s why rather gently flowing tidal currents are sufficient for producing electricity. By comparison, underwater rotors have to be able to absorb enormous bending moments.

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