Types of Solar Energy Systems!

Types of Solar Energy systems: 

Active Systems

Active solar energy systems are used to provide heat for thermal comfort in buildings (space heating) and water heating. Most space heating applications are in residences, but commercial buildings are heated with active solar systems as well. Residential water heating is the most common application for active systems, but they are also effective for heating larger volumes of water for commercial purposes, such as for car washes, beauty salons, public health facilities, and even swimming pools. Several of the rest areas along the interstate highways in North Carolina use active solar systems to provide both space and water heating.

Active systems use mechanical equipment such as pumps and fans to regulate and distribute the energy collected from the sun. A typical system consists of one or more flat plate collectors connected to a storage and distribution system. The flat plate collector is essentially a well insulated box with a dark metal absorber plate underneath a transparent cover. A heat transfer fluid, either air or a liquid, is moved through the collector, where it picks up heat from the absorber plate. The fluid is then directed to a storage area (typically a rock bin for air systems, a water tank or some type of phase change material for liquid systems) where it is available for use in the space or water heating system.

Passive Systems 

Like active systems, passive solar systems are used to provide space and water heating for buildings. Unlike active systems, they do not use pumps or fans to store or distribute heat. Instead, they rely on the natural heat transfer forces of conduction, convection, and radiation to distribute the heat collected.

Passive space heating systems consist of south-facing glass to collect heat, and massive building materials within the structure (such as brick, concrete, stucco, tile, or containers of water) to store the heat. These massive materials have the ability to absorb heat, and then release it slowly to the surrounding, cooler areas.

Solar Ponds

A solar pond is a body of water which is used to collect and store solar energy. The pond, either natural or man-made, contains salt water, which acts differently than fresh water. In a fresh water pond, sunlight entering the pond would heat the water, and, by natural convection, the heated water would rise to the top, while the heavier cool water would sink to the bottom. Salt water, however, is heavier than fresh water, and will not rise or mix by natural convection. This creates a larger temperature gradient within the pond. Fresh water forms a thin insulating surface layer at the top, and underneath it is the salt water, which becomes hotter with depth - as hot as 200 degrees Fat the bottom.

Although it can provide heat for other applications, the most common use for solar salt gradient ponds is the generation of electricity. Heated brine is drawn from the bottom of the pond and piped into a heat exchanger, where its heat converts a liquid refrigerant into a pressurized vapor which spins a turbine, generating electricity. Since the US Department of Energy's solar pond program was terminated, most solar pond progress has been made in other countries, principally Israel and Australia. An Israeli project covering nearly 62 acres near the Dead Sea produces up to 5 MW of electricity during peak demand periods.

Photovoltaics is the process of converting sunlight into electricity by means of a photovoltaic cell. The photovoltaic cell is a solid-state device composed of thin layers of semiconductor materials which produce an electric current when exposed to light. Single cells are connected in groups to form a module, and modules are grouped to form an array. The voltage and the current output from the array depend upon how the system is configured.

Photovoltaic cells produce direct current (DC) electricity, the type of electricity in batteries. Most appliances, however, are designed to use alternating current (AC) electricity, the type available from a standard wall socket. When AC current is required, an invert is added to the photovoltaic system to change the current from DC to AC, but this will incur some loss of power output.

Photovoltaic-generated electricity has many applications. It has already become a permanent fixture in the consumer products market by providing energy for products with small power requirements, such as solar calculators and watches. Other applications include water pumping, navigational signals, lighting, electric fence charging, vehicle battery charging, radio relay stations, and utility-scale electricity generation. The latter, while feasible, is not commonplace due to the current low costs of producing electricity from coal or nuclear energy.

Photovoltaics shows its true worth in the ease with which it can be used to provide power to remote locations. "Remote" can take on different meanings. Remote can refer to villages in Third World nations that use photovoltaics to provide power for irrigation of crops and the refrigeration of medicines - power that had previously come from a balky diesel generator, or had not existed, because they were hundreds of miles from an electricity generating station. Remote can refer to a mountain cabin a mile or so from utility lines that uses photovoltaics to provide lighting and refrigeration. Remote can also refer to a photovoltaic yard light installed because it was cheaper to install a photovoltaic system than to pay the cost of running a utility line that short distance.

Systems may be either "stand-alone", meaning that they are not connected to an electric utility, or "utility-interactive". Utility-interactive systems require the use of an inverter, but inverters are not required for stand-alone systems if only DC appliances are to be used. Stand-alone systems may also include a backup system such as a diesel generator.