Non-metallic materials such as brick, stone and brick are good absorbers of solar energy, especially if they have dark colors. Plastics and wood can be good energy absorbers, but many types are not suitable for solar applications because most plastics have relatively low melting points and wood can catch fire. Spirulina, an algae found in open sources of fresh and warm water, absorbs energy from the sun. Called solar food, spirulina contains phycocyanin, which helps the plant absorb the entire spectrum of light, allowing it to absorb more solar energy than other plants.
It is often used as a dietary supplement, as it stimulates the production of red blood cells and can also protect cells against aging. This is called diffuse solar radiation. Solar radiation that reaches the Earth's surface without diffusing is called direct beam solar radiation. The sum of direct and diffuse solar radiation is called global solar radiation.
Atmospheric conditions can reduce direct beam radiation by 10% on clear and dry days and by 100% on cloudy days and. You are probably more familiar with photovoltaics, which is used in solar panels. When the sun shines on a solar panel, the energy of sunlight is absorbed by the photovoltaic cells of the panel. This energy creates electrical charges that move in response to an internal electric field in the cell, causing electricity to flow.
The Sun provides the Earth with most of its energy. Today, about 71% of the sunlight that reaches Earth is absorbed by its surface and atmosphere. The absorption of sunlight causes the molecules of the object or surface they hit to vibrate faster, increasing their temperature. This energy is then re-radiated by Earth as long-wave infrared radiation, also known as heat.
The more sunlight a surface absorbs, the more it heats up and the more energy it radiates again as heat. This reradiated heat is absorbed and reradiated by greenhouse gases and clouds, and heats the atmosphere through the greenhouse effect. Most of the atmosphere is relatively transparent to solar radiation, with the most notable exception being clouds. The Department of Energy's Office of Solar Energy Technologies is driving innovative research and development in these areas.
The annual mean absorbed solar radiation (ASR) and the outgoing long-wave radiation (OLR) are shown in Fig. These new solar energy systems are of practical interest for many applications, as they can effectively contribute to covering electrical and thermal loads. Cities like Denver, Colorado (about 40° latitude) receive nearly three times more solar energy in June than in December. The reflectance d used in this equation is the reflectance of the roof valid for diffuse radiation scattered by the absorbing surface and incident on the inner side of the roof.
However, the technical feasibility and economic operation of these technologies in a specific location depend on the available solar resource. At the media interface (covering air), the radiation is partially reflected and returns to the absorbing surface, where its part is absorbed and the rest is reflected over and over again reaches the cover. However, the relative contribution of atmosphere and surface to each process (absorption of sunlight versus radiant heat) is asymmetrical. The main function of the tower of a HAWT is to allow the capture of wind energy at a sufficient height above the ground, to safely absorb and discharge the static and dynamic stress exerted on the rotor, power train and nacelle on the ground.
Note that the Sahara desert has a high OLR, consistent with dry, cloudless and warm conditions, but it is also bright and reflects solar radiation, and stands out as a region of net radiation deficit. This parameter (σα) is slightly higher than the product of the transmittance of the cover and the absorbance of the absorber. The model of the Earth system shown below includes some of the ways in which human activities directly affect the amount of sunlight that is absorbed and reflected by the Earth's surface. The Earth system model shown below shows how human pollutants and debris affect the ozone layer and the amount of ultraviolet sunlight that is absorbed by the Earth's upper atmosphere (the stratosphere).
Maximum solar-to-electric conversion efficiencies are just over 20% for feeders, 23% for power towers and 29% for dishes, but annual rates are much lower, i.e. 10 to 18% for feeders, 8 to 19% for towers and 16 to 28% for trays. The effective value takes into account the fact that the energy absorbed in the glass increases its temperature, thus decreasing the temperature difference between the absorber and the cover and, therefore, also reducing the heat losses of the absorbing surface. .