Renewable Energy From the Sun

 Energy from the sun is renewable, meaning it never runs out. Unlike fossil fuels, it does not create pollution that harms the environment and human health.

Humans have been using solar energy for more than two millennia, beginning with the use of glass lenses to focus sunlight and make fire. In 1839, a French physicist named Alexandre-Edmond Becquerel discovered the photovoltaic effect at the age of 19.

Photovoltaic cells

Solar cells convert sunlight into electricity by using semiconductor material to absorb photons of light and release electrons. The absorbed electrons then flow through the cell and out of its conductive metal contacts, generating an electric current that can be used to power equipment.

Silicon is the most common semiconductor material for PV cells, but other materials like amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS) can also be used. The cells can be either brittle crystalline structures, or flexible thin-film cells.

The top layer of a PV cell is typically made of a transparent conductive material like indium tin oxide (ITO), which allows light to pass through to the active layers beneath. Beneath this is the emitter layer, which is a thin layer of heavily doped (high concentration of impurities) n-type silicon that facilitates the flow of electrons generated by the absorbed sunlight. In some solar cells, multiple layers of semiconductor material are stacked to create multijunction cells. These have the potential to achieve record-breaking efficiency levels by absorbing portions of the solar spectrum that are not absorbed by the first semiconductor layer.

Concentrated solar power

Concentrated solar power (CSP) is a form of renewable energy that uses mirrors to focus sunlight onto a receiver tube to produce electricity. The concentrated sunlight is used to heat a thermal fluid, which drives a steam turbine and generates electricity. The heat can also be stored for later use, which makes CSP a reliable source of energy.

There are several ways to produce CSP, including parabolic troughs, heliostat field collectors, and solar power towers. The most efficient and productive CSP plants are solar power towers. These plants have a central solar heat receiver and are surrounded by mirrors.

The largest CSP plant is Ivanpah in California, which produces 392 megawatts of electricity. This is enough to power 140,000 homes and avoids 400,000 metric tons of carbon dioxide emissions a year that would otherwise be produced by fossil fuels. In addition to reducing greenhouse gas emissions, CSP technology can provide heat for industries that rely on high-temperature processes, such as cement manufacturing.

Solar furnaces

Solar furnaces use mirrors to concentrate sunlight on a small area, increasing the temperature of that area. They are used in a variety of applications, including melting metals, testing materials, and conducting research.

The first practical solar furnace was built by Professor Felix Trombe in 1949 in France. The Odeillo solar furnace in the Pyrenees Mountains is still in operation today, and it serves as a giant symbol of solar technology.

NREL’s High-Flux Solar Furnace (HFSF) is a unique 10-kW optical furnace that harnesses concentrated sunlight to test high-temperature processes and applications. It is located on NREL’s South Table Mountain campus and includes tracking heliostats and 25 hexagonal concave mirrors that deliver 10 kW of thermal power to a focal point.

The HFSF can produce peak solar fluxes of up to 2,500 suns and achieve temperatures up to 3,300 degC in seconds. It can also be modified to change the focal point and tailor flux levels and distributions for a variety of research activities.

Solar power towers

Solar power towers, also known as central receiver systems (CRS), use hundreds of two-axis sun tracking mirrors to concentrate the sun’s rays on a large receiver atop a fixed tower. The thermal energy of the concentrated sunlight is used to heat a fluid to produce steam which drives a turbine generator to produce electricity. The thermal energy is stored in a molten salt storage system which allows solar power to continue producing energy even after the sun goes down.

To operate properly, solar power towers require flat open spaces with a good amount of direct sunlight and minimal cloud cover. Moreover, the size of the solar power tower and its surrounding heliostat field takes up a significant amount of land. It can also have a negative impact on local wildlife and the environment. Several solar power tower projects have been canceled or abandoned because of the difficulty to find suitable locations and high costs. However, new developments allow for smaller solar power plants to be built and operated at lower cost.