Solar energy is the radiant light and heat from the sun. Solar radiations one of the most of the available renewable energy on earth.
There are tree main methods for utilization and transformation of the solar energy – solar thermal, photovoltaic (PV), photochemical.
The most energy efficiency technology.
Solar thermal technology is used for harnessing solar energy for thermal energy (heat).
We do this using solar thermal collectors. They trasform the sun light into heat for water heating.
Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.
The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.
Solar thermal collectors are designed to collect heat by absorbing sunlight. The term is applied to solar hot water panels, but may also be used to denote more complex installations such as solar parabolic, solar trough and solar towers or simpler installations such as solar air heat. The more complex collectors are generally used in solar power plants where solar heat is used to generate electricity by heating water to produce steam which drives a turbine connected to an electrical generator. The simpler collectors are typically used for supplemental space heating in residential and commercial buildings.
There are two main types of solar thermal collectors – flat plate and evacuated tube.
flat plate solar thermal collectors
Their main elements are: a dark flat-plate absorber of solar energy; a transparent cover that allows solar energy to pass through but reduces heat losses; a heat-transport fluid (air, antifreeze or water) to remove heat from the absorber, and a heat insulating backing. The absorber consists of a thin absorber sheet (polymers, aluminum, steel or copper) often backed by a grid or coil of fluid tubing placed in an insulated casing with a glass or polycarbonate cover. In water heat panels, fluid is usually circulated through tubing to transfer heat from the absorber to an insulated water tank.
Most vacuum tube collectors use heat pipes for their core instead of passing liquid directly through them. Evacuated heat pipe tubes are composed of multiple evacuated glass tubes each containing an absorber plate fused to a heat pipe. The heat from the hot end of the heat pipes is transferred to the transfer fluid (water or an antifreeze mix—typically propylene glycol) of a domestic hot water or hydronic space heating system in a heat exchanger. The vacuum that surrounds the outside of the tube greatly reduces heat loss.
Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect.
Solar PV pannels are constructed from materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light and release electrons. When these free electrons are captured, an electric current results that can be used as electricity.
A number of solar cells electrically connected to each other and mounted in a support structure or frame is called a photovoltaic module. Modules are designed to supply electricity at a certain voltage, such as a common 12 volts system.
Multiple modules can be wired together to form an array. In general, the larger the area of a module or array, the more electricity that will be produced. Photovoltaic modules and arrays produce direct-current (dc) electricity.
Photochemical reaction is any chemical reaction caused by absorption of light (including visible, ultraviolet, and infrared). The light excites atoms and molecules (shifts some of their electrons to a higher energy level) and thus makes them more reactive. In comparison to ordinary reactions using thermal energy alone, photochemical reactions can follow different routes and are more likely to produce free radicals, which can trigger and sustain chain reactions.
Photochemical solar technology uses photochemical solar cells to produce energy. That means the radiated energy from the sun in the form of light, is being transformed through a chemical process into electrical energy, which travels through the circuit to the motor, where electromagnets turn the electrical energy into movement (kinetic energy).
The workings of the solar panels we are most familiar with depend on the photovoltaic effect. It depends on a chemical called Titanium Dioxide, which is very cheap and available. Titanium Dioxide is great stuff when it comes to absorbing ultra violet light. It is used as a white pigment in paints, toothpaste and sun block.
solar systems for cooling
Main types of solar cooling systems are passive and active systems.
Typical example of passive solar system is a Trombe wall.
A Trombe wall consists of a vertical wall, built of a material such as stone, concrete, or adobe, that is covered on the outside with glazing. Sunlight passing through the glazing generates heat which conducts through the wall. Warm air between the glazing and the Trombe wall surface can also be channeled by natural convection into the building interior or to the outside, depending on the building’s heating or cooling needs.
During the day, sunlight shines through the glazing and hits the surface of the thermal mass, warming it by absorption. The air between the glazing and the thermal mass warms (via heat conduction) and rises, taking heat with it (convection). The warmer air moves through vents at the top of the wall and into the living area while cool air from the living area enters at vents near the bottom of the wall.
At night, a one-way flap on the bottom vent prevents backflow, which could act to cool the living area, and heat stored in the thermal mass radiates into the living area.
Active solar cooling systems
The two feasible types of active cooling systems are Rankine cycle and absorption.
Rankine cycle is a thermodynamic cycle used as an ideal standard for the comparative performance of heat-engine and heat-pump installations operating with a condensable vapor as the working fluid. This is an idealized thermodynamic cycle in which heat is converted to work or work to heat. In the Rankine cycle, the working fluid (water) is converted to steam in a boiler and then superheated at constant pressure in a superheater. The steam expands adiabatically in a steam turbine, thus performing work. The steam then is condensed at constant pressure in a condenser, and the condensate is first pumped to an economizer for preheating and then returned to the boiler for conversion into steam.
solar energy and environment
Solar power plants reduce the environmental impacts of combustion used in fossil fuel power generation such as green house gas and other air pollution emissions.
The large arrays of solar collectors may interfere with natural sunlight, rainfall, and drainage, which could have a variety of effects on plants and animals. Solar arrays may also create avian perching opportunities that could affect both bird and prey populations. Land disturbance could also affect archaeological resources.