Classifications of solar power technology

Solar power technologies can be classified in a number of ways.

Photovoltaic cells produce electricity directly from sunlight

Direct or Indirect

In general, direct solar power involves a single transformation of sunlight which results in a usable form of energy.
Sunlight hits a photovoltaic cell creating electricity.
Sunlight warms a thermal mass.
Sunlight strikes a solar sail on a space craft and is converted directly into a force on the sail which causes motion of the craft.
Sunlight strikes a light mill and causes the vanes to rotate as mechanical energy (little practical application has yet been found for this effect).

In a direct solar water heater the water heated in the collector is used in the domestic water system.

In general, indirect solar power involves multiple transformations of sunlight which result in a usable form of energy.

Vegetation uses photosynthesis to convert solar energy to chemical energy. The resulting biomass may be burned directly to produce heat and electricity or processed into ethanol, methane, hydrogen and other biofuels.
Hydroelectric dams and wind turbines are powered by solar energy through its interaction with the Earth's atmosphere and the resulting weather phenomena.
Ocean thermal energy production uses the thermal gradients present across ocean depths to generate power. These temperature differences are produced by sunlight.[33]
Fossil fuels are ultimately derived from solar energy captured by vegetation in the geological past.

In an indirect solar water heater the fluid heated in the collector transfers its heat through a heat exchanger to a separate domestic water system.


Passive or active

This distinction is made in the context of building construction and building services engineering.
Passive solar systems use non-mechanical techniques of capturing, converting and distributing sunlight into usable outputs such as heating, lighting or ventilation. These techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air and referencing the position of a building to the sun.
Passive solar water heaters use a thermosiphon to circulate fluid.
A Trombe wall circulates air by natural circulation and acts as a thermal mass which absorbs heat during the day and radiates heat at night.
Clerestory windows, light shelves, skylights and light tubes can be used among other daylighting techniques to illuminate a building's interior.
Passive solar water distillers may use capillary action to pump water.
Active solar systems use electrical and mechanical components such as photovoltaic panels, pumps and fans to process sunlight into usable outputs.

Concentrating or non-concentrating

A large parabolic reflector solar furnace is located in the Pyrenees at Odeillo, French Cerdagne. It is used for various research purposes.[34]
Concentrating solar power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam capable of producing high temperatures and correspondingly high thermodynamic efficiencies. Concentrating solar is generally associated with solar thermal applications but concentrating photovoltaic (CPV) applications exist as well and these technologies also exhibit improved efficiencies. CSP systems require direct insolation to operate properly.[35]

Concentrating solar power systems vary in the way they track the sun and focus light.

Line focus/Single-axis
A solar trough consists of a linear parabolic reflector which concentrates light on a receiver positioned along the reflector's focal line. These systems use single-axis tracking to follow the sun. A working fluid (oil, water) flows through the receiver and is heated up to 400 °C before transferring its heat to a distillation or power generation system.[36][37] Trough systems are the most developed CSP technology. The Solar Electric Generating System (SEGS) plants in California and Plataforma Solar de Almería's SSPS-DCS plant in Spain are representatives of this technology.[38]

Point focus/Dual-axis
A power tower consists of an array of flat reflectors (heliostats) which concentrate light on a central receiver located on a tower. These systems use dual-axis tracking to follow the sun. A working fluid (air, water, molten salt) flows through the receiver where it is heated up to 1000 °C before transferring its heat to a power generation or energy storage system. Power towers are less advanced than trough systems but they offer higher efficiency and energy storage capability.[39] The Solar Two in Daggett, California and the Planta Solar 10 (PS10) in Sanlucar la Mayor, Spain are representatives of this technology.
A parabolic dish or dish/engine system consists of a stand-alone parabolic reflector which concentrates light on a receiver positioned at the reflector's focal point. These systems use dual-axis tracking to follow the sun. A working fluid (hydrogen, helium, air, water) flows through the receiver where it is heated up to 1500 °C before transferring its heat to a sterling engine for power generation.[40][39] Parabolic dish systems display the highest solar-to-electric efficiency among CSP technologies and their modular nature offers scalability. The Stirling Energy Systems (SES) and Science Applications International Corporation (SAIC) dishes at UNLV and the Big Dish in Canberra, Australia are representatives of this technology.
Non-concentrating photovoltaic and solar thermal systems do not concentrate sunlight. While the maximum attainable temperatures (200 °C) and thermodynamic efficiencies are lower, these systems offer simplicity of design and have the ability to effectively utilize diffuse insolation.[39] Flat-plate thermal and photovoltaic panels are representatives of this technology.

From wikipedia