Solar energy uses the power of the sun’s rays to produce electricity or heat. Electricity is the type of energy most often produced with the help of photovoltaic systems. Electrons begin to move when solar cells are exposed to sunlight, and flow through an electrical semiconductor. A power inverter then converts the direct current produced in this way into an alternating current and makes it available for use. An electric current is created during this process.

Solar thermal systems convert energy from the sun into heat. During a heat cycle, sunlight is absorbed via solar collectors for this purpose and guided into a heat reservoir. This thermal energy can then be used as warm water or to support heating systems. Despite its inexhaustible nature, solar energy requires flexible energy storage and considerably large surface areas due to the natural deviations in its daily and seasonal cycles. | Image: Adobe Stock / YouraPechki

Wind is available everywhere and is an inexhaustible energy supply. Wind power can be obtained both onshore and offshore. An uplift force is created when wind meets the wind turbine’s rotor blades. The rotor blades begin to turn, and the kinetic energy of the wind currents can thus be converted into rotational energy. The rotor gears forward this energy to the generator, which then finally converts it into electrical energy. The reliability of such a system’s energy production depends on the location, length of the rotor blades, and the turbine’s overall height. Offshore wind farms might be significantly more expensive than onshore plants, yet the energy they supply is more reliable because the wind speeds at sea are higher and more constant. Regardless of their location, the disadvantage of these systems is that wind is not reliable, and the construction and operation of wind farms always encroaches on the landscape and surrounding ecosystems. | Image: Adobe Stock / engel.ac

Bioenergy is the term used to describe energy generation from renewable raw materials such as corn and wood as well as waste products from private households or the agricultural and forestry industries. As its conversion possibilities are numerous, bioenergy can easily be used in essentially all energy-relevant sectors. Via fermentation processes, bioenergy can be used for energy production in the form of gas (biogas or biomethane) or used in liquid form (plant oil) as an organic fuel for heating, for example. It can be stored on a long-term basis and is thus always available. Pellets and industrial waste wood are the most important bioenergy carriers in Germany. The plethora of production methods and usage options makes biomass a high-yield energy carrier. Since fossil fuels have to be used during the cultivation of bioenergy plants and surface areas must compete with food crops, use of this bioenergy should be limited to leftover materials in future. | Image: Adobe Stock / Visions-AD

Hydropower has been around for centuries. Used in the past for mechanical purposes, the power of water is now primarily used to produce energy. The water’s kinetic energy (currents) or potential energy (height difference between the water’s source and outflow) is converted into electrical energy. This process occurs via the operation of turbines within a run-of-the-river power plant or a storage power plant. Run-of-the-river power plants use the natural currents of rivers and streams, while storage power plants use water from reservoirs. There are also “pumped storage plants” that are used to store potential electrical energy and pump water from valleys into reservoirs positioned higher up. The potential of water power in Germany is considered exhausted, not least due to the increasing resistance to extensive encroachments on landscapes. That said, increased energy production can be achieved by modernising and expanding existing plants. | Image: Adobe Stock / evgenii_v

Geothermal power can be directly stored and – at a sufficiently high temperature – be used to produce electrical power. Underground thermal conditions are especially decisive for the technical processes this requires. Near-surface geothermal energy up to a depth of 400 metres is obtained via thermal pumps, transferred to a heating system or warm water reservoir on the surface, and thus provides thermal power. Using deeper geothermal energy is more complicated. Heat reservoirs are opened up via bore holes up to 5,000 metres underground. These are then used for thermal heat or, at sufficiently high temperatures, are directly converted into electricity by steam turbines. Due to high costs and unreliability in regard to possible earthquakes and environmental or health hazards in the event of geothermal gas leaks, deep geothermal energy only makes up a small percentage of heat and energy production in Germany (0.03 percent). | Image: Adobe Stock / Andy Ilmberger

Ocean or sea power covers various technologies with which the wave and current powers of the world’s oceans can be harnessed. In theory, the available wave power is sufficient to meet all the world’s energy needs. However, the potential of this resource is nowhere near exhausted in practice. The few existing wave power plants are situated on shorelines or on the water’s surface. These plants use oscillating water columns; the back and forth of the waves transfers liquid to the inside of a water pendulum on the water’s surface in order to operate turbines or generators. In stationary power plants, inflowing water or the air pressed out by the inflowing water is used to propel the turbines. Providing energy during low wave movements and the plants’ low resistance to storms are two constant challenges. | Image: Adobe Stock / Regina

Damit Wasserstoff klimafreundlich (grün) produziert werden kann, muss dieser mit Strom aus erneuerbaren Energien gewonnen werden. Es ist jedoch nicht möglich, die hierfür erforderlichen Mengen in Deutschland zu gewinnen. Daher wird Deutschland große Mengen Wasserstoff aus Regionen oder Ländern importieren müssen, in denen Wind- oder Sonnenenergie ausreichend zur Verfügung steht, um den hiesigen Bedarf zu decken. Mit Wasserstoff kann man erneuerbare Energie weltweit transportieren und handeln und damit saisonale oder dauerhafte lokale Unterversorgung an Energie ebenso ausgleichen, wie das heute mit fossilen Energieträgern geschieht. Da die Herstellung von Wasserstoff an sehr vielen Orten der Erde effektiv möglich ist, kann ein Weltmarkt für erneuerbare Energie entstehen, der nicht die strategischen Abhängigkeiten wie die heutigen fossilen Energiemärkte aufweist. Die beim Transport entstehenden Verluste an Energie werden durch die oftmals bessere Effizienz der Herstellung in sonnen- und windreichen Gegenden zumindest ausgeglichen. Da viele dieser Orte im globalen Süden liegen, wird dadurch zusätzliche Wirtschaftstätigkeit in Ländern ermöglicht, die heute ökonomisch benachteiligt sind.