Renewable sources of energy are those that are available in virtually inexhaustible amounts or can be regenerated fairly quickly. By contrast, fossil energy sources are finite. Or it takes millions of years to replenish them. Fossil fuels such as coal, oil and natural gas are responsible for a large portion of the planet’s greenhouse emissions and thus for global warming. That means expanding the use of renewables is a way to protect the climate.
On the bright side: The solar energy beaming down on the earth would cover humanity’s energy needs several thousand times over. An inventive, innovative spirit can help us find the technological path to this inexhaustible store of energy. Another reason for optimism: In late 2022, the United States announced a breakthrough in nuclear fusion, a potential energy source for the future. For the first time, more energy was gained than consumed during the fusion of atomic nuclei.
Earth
Biomass can be exploited as energy in various ways. Early humans were already using wood to fuel fi res. Biofuels can be produced from crops such as sugarcane, sugar beets, wheat, rye, maize and rapeseed, but then they are no longer available as foodstuff s. Green clippings, compostable waste, manure and sewage sludge can be used to produce biogas, which can be directly used to generate electricity.
Geothermal energy utilizes the heat stored beneath the earth’s surface: The planet itself is the heating mechanism. In the case of near-surface geothermal systems, the heat extracted from the earth generally does not reach the temperature that people require. It takes auxiliary electric heat pumps to raise it to the right level. That extra help is unnecessary with deep geothermal systems, which descend several kilometers below the ground. They generate electricity as well as heat. The process works in reverse for geo-cooling, which provides comparatively cool temperatures from near-surface layers. The earth becomes an air conditioner.
Wind
Since antiquity, windmills have exploited the wind’s kinetic energy to drive machines for milling, sawing and conveying materials. In wind turbines today, the kinetic energy is transmitted to a rotating axle. It, in turn, drives a generator that produces electrical energy. The systems are mostly built on land (onshore) but increasingly at sea (off shore).
The sun
Photovoltaics directly transform light into electrical energy, that is, electric current, using solar modules. By contrast, thermal solar collectors transform sunlight into heat. One example would be a system that draws hot water from beneath the roof of a home. Solar thermal power plants are another example. They use either a parabolic mirror or innumerable adjustable mirrors that capture sunlight hitting a large surface and then reflect it onto a single point (“burning glass effect”). In the case of nuclear fusion, atomic nuclei are fused into new, larger nuclei at extreme temperatures using lasers. A similar process occurs inside the sun. Enormous quantities of energy are released – without the radioactive waste created during nuclear fission.
Water
Until the turn of the 20th century, hydropower was mainly used in mills. Today it almost always generates electricity using turbines and generators. There are various types of hydropower plants, including run-of-river power stations with dams obstructing the flow of water, and tidal power plants that use tidal forces to generate electricity. In pumped storage plants, water is temporarily pumped into basins or reservoirs. Once released, the fl owing water is used to drive turbines to generate power.
