There are various types of solar: Passive, Daylighting, Solar Water Heating, Solar Thermal, Solar Photovoltaics, Solar Car Charging / Solar Buses and Concentrating Solar Energy.

Passive Solar

Screen Shot 2015-09-13 at 9.38.10 PMIn passive solar building design, structural elements (e.g., windows, insulation);  design features (e.g., building orientation and layout); and localized climate (e.g., natural shading) are used to heat and cool buildings. Unlike in active solar heating systems, these systems do not involve the use of mechanical or electrical devices.

Materials and design elements to be considered include window placement and size, and glazing type, insulation, thermal mass, and shading. Windows, walls, and floors are used to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer.

The Passive House is an ultra-low energy use design standard, originally developed in Europe and now in the United States, which requires little energy for space heating and cooling.


Daylighting is the practice of using natural light to provide a major proportion of lighting. Daylighting practices include placement of windows and other openings to maximize light gain, use of light colored paints and reflective surfaces to distribute light, and use of light tubes or skylights to transmit light where there are ceilings or floors. Light sensor and dimming switches can also reduce the need for artificial lighting in a process known as daylight harvesting.

Solar Water Heating

Solar hot water systems collect heat from the sun and transfer it to a heat transfer fluid which takes the heat from the collector for use or storage. A heat exchanger transfers the heat from the transfer fluid to the domestic or commercial hot water heater. Pumps move the fluid through the collector and exchanger.  Controllers run the pumps when there is collector heat available. Storage tanks may be added to the system.

A very basic approach to solar heating of water is to simply put a metal tank filled with water in the sun, but this approach would be inefficient because there would be a lot of heat loss from the tank. Adding an insulated box around the tank and glass above the top where sun comes in would do a lot to retain the heat. These basic principles are used in solar hot water system collectors.

Common uses for solar hot water systems are for showers and faucets, private swimming pools, and hot tubs/jacuzzis. Commercial applications include in schools, commercial laundries, car washes, public pools, restaurants, and dormitories.

Unlike solar PV systems, solar hot water systems involve mechanical parts and therefore are more difficult to install and maintain. With the rapid fall in the price of solar PV systems, more people are selecting to use PV to provide the electricity needed to power an electric hot water system.

Solar Thermal

Solar thermal systems use the sun’s energy, rather than fossil fuels, to generate low-cost, environmentally-friendly thermal (heat) energy. This energy is used to heat air or a fluid which is distributed to provide heating, and can also power solar cooling systems. Solar thermal differ from solar photovoltaic (PV) in that it generates heat rather than electricity.

The thermal energy can be used directly or to heat a fluid that produces steam which then drives a generator to produce electricity. The solar thermal system generally includes a means for heat collection, usually heat storage, and distribution within a structure or district heating network. Solar cooling can be achieved for a building or district cooling network by using a heat-driven absorption or adsorption chiller (heat pump).

 There are a great variety of solar thermal applications that make use of low-, medium-, or high-temperature collectors. To name only a few, applications include solar air heat collectors, solar hot water circulation heating, solar roof and evaporation ponds, solar drying (for construction and wood fuels, foods, and crops), solar cooking, solar distillation, and concentrated solar power (see below).

Solar Photovoltaics

Solar photovoltaic (PV) devices generate electricity directly from sunlight through an electronic process that occurs naturally in certain types of material, called semi-conductors. Electrons in these materials are freed by the solar energy and induced to flow in one direction to create a flow of electrical current which can be used to power electrical devices and send electricity to the grid. Solar panels may be roof or ground-mounted, and fixed or mounted with a single or dual-axis tracking device.

In addition to solar panels, another solar technology is thin film PV. Thin-film PV is a small part of the residential and commercial solar market that is still being researched and developed; it is generally less efficient but often cheaper than solar panels.  Other solar PV technologies in various stages of research and use include solar roadways; solar carports; solar windows, solar shingles, and solar paints.

Solar Car Charging / Solar Buses

A special application of solar PV Is electric vehicle (EV) charging stations used more commonly today for cars and buses, and in the future, for trucks and airplanes.  Typically, a solar PV array produces electricity that is then used to power an electric or plug-in hybrid car or electric bus.

EVs are projected to achieve an increasingly large market share yet barriers to their widespread adoption persist.  These include range before the vehicle must be recharged (currently around 80 miles), lack of a widespread EV charging station network, and the amount of time it takes to recharge a vehicle, which can be a few hours to overnight.  Wireless inductive charging stations now being developed and deployed reduce the charging time to minutes and require no more effort than parking over a unit and pressing a button.

Concentrating Solar Energy

imageConcentrating Solar Power (CSP) plants use lenses and mirrors to either reflect concentrated solar energy onto high-efficiency cells or convert the sun’s energy into high-temperature heat that then is used to drive a steam generator to produce electricity.

There are three types of CSP technologies: trough systems, dish/engine systems, and power towers. These systems are found in desert areas around the world and, in the U.S., primarily in the southwest. The largest CSP plant in the work, Ivanpah, is in the Mojave Desert in California and has the capacity to generate 392 MW of clean electricity–enough to power 94,000 average American homes. Spain has the greatest number of large CSP plants with a capacity of 100 MW or more.