Exploded View Of A Flat Plate Collector And Absorbed Details

www.meteonorm.com

Copyright: METEOTEST Bern, Switzerland

FIGURE 2.30 Annual total solar irradiation on horizontal surface for Europe. Source: Meteonorm database of Meteotest (www.Meteonorm.com).

www.meteonorm.com

Copyright: METEOTEST Bern, Switzerland

FIGURE 2.30 Annual total solar irradiation on horizontal surface for Europe. Source: Meteonorm database of Meteotest (www.Meteonorm.com).

kWh/m2 >1850

Global radiation, annual mean 1981-2000

1750-1850

Solar Radiation North America

www.meteonorm.com Copyright: METEOTEST Bern, Switzerland

FIGURE 2.31 Annual total solar irradiation on horizontal surface for North America. Source: Meteonorm database of Meteotest (www.Meteonorm.com).

1650-1750 1550-1650 1450-1550 1350-1450 1250-1350 1150-1250 1050-1150 950-1050 850-950 <850

www.meteonorm.com Copyright: METEOTEST Bern, Switzerland

FIGURE 2.31 Annual total solar irradiation on horizontal surface for North America. Source: Meteonorm database of Meteotest (www.Meteonorm.com).

Table 3.1 Solar Energy Collectors

Motion

Collector type

Absorber type

Concentration ratio

Indicative temperature range (°C)

Stationary

Flat-plate collector (FPC)

Flat

1

30-80

Evacuated tube collector (ETC)

Flat

1

50-200

Compound parabolic collector (CPC)

Tubular

1-5

60-240

Single-axis tracking

5-15

60-300

Linear Fresnel reflector (LFR)

Tubular

10-40

60-250

Cylindrical trough collector (CTC)

Tubular

15-50

60-300

Parabolic trough collector (PTC)

Tubular

10-85

60-400

Two-axis tracking

Parabolic dish reflector (PDR)

Point

600-2000

100-1500

Heliostat field collector (HFC)

Point

300-1500

150-2000

Note: Concentration ratio is defined as the aperture area divided by the receiver/absorber area of the collector.

permanently fixed in position and do not track the sun. Three main types of collectors fall into this category:

1. Flat-plate collectors (FPCs).

2. Stationary compound parabolic collectors (CPCs).

3. Evacuated tube collectors (ETCs).

3.1.1 Flat-Plate Collectors (FPCs)

A typical flat-plate solar collector is shown in Figure 3.1. When solar radiation passes through a transparent cover and impinges on the blackened absorber surface of high absorptivity, a large portion of this energy is absorbed by the plate and transferred to the transport medium in the fluid tubes, to be carried away for storage or use. The underside of the absorber plate and the two sides are well insulated to reduce conduction losses. The liquid tubes can be welded to the absorbing plate or they can be an integral part of the plate. The liquid tubes are connected at both ends by large-diameter header tubes. The header

Pictorial View Flat Plate Collector
FIGURE 3.1 Typical flat-plate collector. (a) Pictorial view of a flat-plate collector. (b) Photograph of a cut header and riser flat-plate collector.

and riser collector is the typical design for flat-plate collectors. An alternative is the serpentine design shown on the right-hand side of Figure 3.1a. This collector does not present the potential problem of uneven flow distribution in the various riser tubes of the header and riser design, but serpentine collectors cannot work effectively in thermosiphon mode (natural circulation) and need a pump to circulate the heat transfer fluid (see Chapter 5). The absorber plate can be a single sheet on which all risers are fixed, or each riser can be fixed on a separate fin, as shown in Figure 3.1b.

The transparent cover is used to reduce convection losses from the absorber plate through the restraint of the stagnant air layer between the absorber plate and the glass. It also reduces radiation losses from the collector because the glass is transparent to the shortwave radiation received by the sun, but it is nearly opaque to longwave thermal radiation emitted by the absorber plate (greenhouse effect).

The advantages of flat-plate collectors are that they are inexpensive to manufacture, they collect both beam and diffuse radiation, and they are permanently fixed in position, so no tracking of the sun is required. The collectors should be oriented directly toward the equator, facing south in the Northern Hemisphere and north in the Southern Hemisphere. The optimum tilt angle of the collector is equal to the latitude of the location, with angle variations of 10° to 15° more or less, depending on the application (Kalogirou, 2003). If the application is solar cooling, then the optimum angle is latitude -10° so that the sun will be perpendicular to the collector during summertime, when the energy will be mostly required. If the application is space heating, then the optimal angle is latitude + 10°; whereas for annual hot water production, it is latitude +5°, to have relatively better performance during wintertime, when hot water is mostly required.

The main components of a flat-plate collector, as shown in Figure 3.2, are the following:

• Cover. One or more sheets of glass or other radiation-transmitting material.

• Heat removal fluid passageways. Tubes, fins, or passages that conduct or direct the heat transfer fluid from the inlet to the outlet.

• Absorber plate. Flat, corrugated, or grooved plates, to which the tubes, fins, or passages are attached. A typical attachment method is the embedded fixing shown in the detail of Figure 3.2. The plate is usually coated with a high-absorptance, low-emittance layer.

• Headers or manifolds. Pipes and ducts to admit and discharge the fluid.

• Insulation. Used to minimize the heat loss from the back and sides of the collector.

• Container. The casing surrounds the aforementioned components and protects them from dust, moisture, and any other material.

Flat-plate collectors have been built in a wide variety of designs and from many different materials. They have been used to heat fluids such as water, water plus antifreeze additive, or air. Their major purpose is to collect as much

Exploded View Flat Solar Collector

FIGURE 3.2 Exploded view of a flat-

:-plate collector and absorber details.

FIGURE 3.2 Exploded view of a flat-

:-plate collector and absorber details.

solar energy as possible at the lowest possible total cost. The collector should also have a long effective life, despite the adverse effects of the sun's ultraviolet radiation and corrosion and clogging because of acidity, alkalinity, or hardness of the heat transfer fluid, freezing of water, or deposition of dust or moisture on the glazing and breakage of the glazing from thermal expansion, hail, vandalism, or other causes. These causes can be minimized by the use of tempered glass.

In the following two sections, more details are given about the glazing and absorber plate materials. Most of these details also apply to other types of collectors. A third section refers to the collector construction and types of absorber configurations used.

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment