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There are various parameters that affect the Performance of a flat plate Solar collector. Many parameters have a great influence on the performance of a liquid flat plate collector. These parameters can be classified as operational parameters, design parameters, meteorological parameters, and environmental parameters. Some of the parameters are as given below.

Selective Surfaces

Absorber plate surfaces that exhibit the characteristics of a high value of absorptivity for incoming solar radiation and low-value emissivity for outgoing of re-radiation are called selective surfaces.

These type of surfaces are preferred because of the net energy collection. Some examples of these selective surface layers are nickel black, copper oxide, and black chrome. Also, see the applications of copper wires in these plates.

The Number Of Covers

More the number of covers, less is the heat loss from the absorber plates. In other words, if there are a significantly large number of covers, the amount of heat loss from the absorber plate reduces. However, the amount of decrease may not be the same in both cases. Maximum efficiency is obtained with either one or two covers.

Spacing

The amount of heat loss varies with spacing between two covers and also the space between the absorber plate and the first cover. The occurrence of minimum loss varies with temperature as well as the tilt. Since collectors are designed to be flexible to be able to operate at different locations with varying tilts (angles) and under varying service conditions, it is difficult to specify an optimum value of spacing. The spacing range of 4 to 8 cm is widely used as well as suggested. Additionally, large spacing reduces the requirements of the collector area.

Effect Of Shading

The main problem that arises by using larger spacings is that shading of the absorber plate that is placed by the side walls of the collector casing increases. Some amount of shading always occurs in each collector and needs to be corrected. Further, in some collectors, the inside of the side walls is lined or coated with a reflecting surface to alleviate the shading effect.

Collector Tilt

Flat plate solar collectors are generally used in a fixed position and do not track the sun. Hence, the tilt angle at which they are fixed is essential. The maximum tilt depends on the application of the panel.

Fluid Inlet Temperature

The efficiency of the flat plate collector decreases almost linearly with the increasing value of the fluid inlet temperature. This decrease is due to the higher temperature level at which the collector as a whole operates when the fluid inlet temperature increases.

Dust On The Top Of The Cover

Dust gets accumulated on a collector when it is deployed in a practical system and reduces the flux that gets transmitted through the cover. This process requires continuous cleaning of the cover, which is not practically possible. It is usually cleaned once in a few days. Therefore, it is recommended that the incident flux is multiplied by a correction factor that accounts for the reduction in the intensity due to the accumulation of dust.

Cover Transmissivity

The transmissivity of the cover has a significant effect on the performance of a collector. In other words, higher the transmissivity, better is the performance of the collector.

Some Applications of Solar Flat Plate Collectors:

  • Water heating
  • Space heating and cooling
  • Low-temperature cycles for power generation

Alternatives to The Conventional Flat Plate Solar Collector:

Evacuated Tube Collectors:

They are used to reduce heat loss by convection from the top. The process is done by placing a vacuum above the absorber plate. As a consequence, it becomes necessary to use a glass tube as a cover as only a tubular surface can withstand the stresses that are introduced by the pressure difference.

The Concrete Collector:

A huge amount of metal (aluminum, copper, galvanized iron, etc.) is used in conventional FPC (Flat Plate Collector) systems. But the energy input required for their production is high in comparison to traditional FPC.

The BNL (Brookhaven National Laboratory) Collector:

It is a light flat plate collector whose construction is simple and can be cost-effective because of the use of new engineering plastics like films, polymer coatings, and rigid foams.

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