State the merits and demerits of Solar energy conversion and

State the merits and demerits of Solar energy conversion and utilization. State various types of solar thermal collectors along with their advantages and disadvantages. 12 marks

Solution

Solar energy is the conversion of the energy from sun to usable electricity .The most common source of solar energy utilizes photovoltaic cells to convert sunlight into electicity and again these cells use a semiconductor to absorb the radiation from sun .

Merits of Solar energy conversion and utiliation :

Solar energy is the source that is not only sustainable for energy consumption ,it is definitely renewable .It can be used to generate electricity ,also used in relativelt simple technology to heat water .The use of skylights in home construction can greatly reduce energy consumption required to light rooms in a home interior during the day .

Solar panels also require lessmaintanance .After installing and optimizing they are very reliable due to fact that they create electricity in just a few millimeters and do not require any type of mechnical parts that can fail .Also these panels are a silent producer of energy .The federal government introduced generous tax credits for individuals companies that invest in solar and other clean energy systems .

Demerits of Solar energy conversion and utilization :

The primary demerit of solsr energy is that it cannot be created during the night .The energy generated is also reduced during times of cloud cover .Solar panel is maximised when panel is directly facing the sun .This means that panels in a fixed location ,such as above the building ,not at an optimal angle .Many largescale solar farms face this problem as the panels on the towers that can track the sun tokeep the panel at optimal angles along the whole day .

Even todays most efficient solar cells convert only over 20% of suns rays to electicity.With increased advance in solar cell technology this number may increase .Besides their low conversion efficiency ,solar panels can be substantial initial investment .However ,the cost of solar panels incurred is only the initial cost ,after buying and installing they create free energy .

Various types of solar thermal collectors along with their advantages and disadvantages :

Solar thermal collectors heating liquid :

Solar thermal collectors are either non concentrating or concentrating . In the non concentrating type ,the collector area is same as the absorber area .Concentrating collectors have a bigger interceptor than absorber . These are of 1)Flat plte collectors ,2)Evacuated tube collectors ,and 3)Bowl

Flat plate collectors : They consists of 1)a dark flat plate absorber 2)a transparent cover that reduces heat losses 3)a heat transport fluid to remove heat from the absorber and 4)a heat insulating backing .The absorber consists of a thin absorber sheet often backed by a grid of fluid tubing placed in an insulated casing with a glass cover .In water heat panels ,fluid is usually circulated through tubing to transfer heat from absorber to a insulatred water tank.This may be achieved by a heat exchanger. The main use of this technology is in residential buildings where demand for hot water has large impac on energy bills.It can also be used for space heating if building is located off grid or if utility power is subject to frequent outages.

Evacuated tube collectors : Evacuated heat pipe tubes are composed of multiple evacuated glass tubes each containing an absorber plate fused to a heat pipe.The heat is transferred to the transfer fluid of a domestic hot water or the hydronic space heating systems in a heat exchanger called manifold.The manifold is wrapped in insulation and covered by a protective sheet metal or plastic case.The reflected coating for design is encapsulated in the vaccum inside of tube,which wioll not degrade untril the vaccum is lost. The gaps between the tubes allow for snow to fall through the collector minimizing the loss of production in in some snowy conditions through the lack of radiated heat from tubes can also prevent effecting shedding of accumalated snow.

Flat-plate collectors usually lose more heat to the environment than evacuated tubes, as an increasing function of temperature. They are inappropriate for high temperature applications such as process steam production. Evacuated tube collectors have a lower absorber plate area to gross area ratio compared to flat plates. Based on absorber plate area, most evacuated tube systems are more efficient per square meter than equivalent flat plate systems.

Bowl :A solar bowl is a type of solar thermal collector that operates similarly to a parabolic dish, but instead of using a tracking parabolic mirror with a fixed receiver, it has a fixed spherical mirror with a tracking receiver. This reduces efficiency, but makes it cheaper to build and operate. Designers call it a fixed mirror distributed focus solar power system. The main reason for its development was to eliminate the cost of moving a large mirror to track the sun as with parabolic dish systems.

Proponents of the solar bowl design claim the reduction in overall power output compared with tracking parabolic mirrors is offset by lower system costs. the use of the solar bowl is in the production of steam for cooking.

Solar-thermal collectors heating air ;

A simple solar air collector consists of an absorber material, sometimes having a selective surface, to capture radiation from the sun and transfers this thermal energy to air via conduction heat transfer. This heated air is then ducted to the building space or to the process area where the heated air is used for space heating or process heating needs. Simple and effective collectors can be made for a variety of air conditioning and process applications.

A variety of applications can utilize solar air heat technologies to reduce the carbon footprint from use of conventional heat sources, such as fossil fuels, to create a sustainable means to produce thermal energy. Applications such as space heating, greenhouse season extension, pre-heating ventilation makeup air, or process heat can be addressed by solar air heat devices.