Flat plate collectors
Flat-plate collectors are the most common solar thermal technology in Europe.They consist of an (1) enclosure containing (2) a dark colored absorber plate with fluid circulation passageways, and a transparent cover to allow transmission of solar energy into the enclosure. The sides and back of the enclosure are typically insulated to reduce heat loss to the ambient. A heat transfer fluid is circulated through the absorber's fluid passageways to remove heat from the solar collector. The circulation fluid in tropical and sub-tropical climates is typically water. In climates where freezing is likely, a heat transfer fluid similar to an automotive antifreeze solution may be used instead of water, or in a mixture with water. If a heat transfer fluid is used, a heat exchanger is typically employed to transfer heat from the solar collector fluid to a hot water storage tank. The most common absorber design consists of copper tubing joined to a high conductivity metal sheet (copper or aluminum). A dark coating is applied to the sun-facing side of the absorber assembly to increase it absorption of solar energy. A common absorber coating is black enamel paint.
In higher performance solar collector designs, the transparent cover is tempered soda-lime glass having reduced iron oxide content same as for photovoltaic solar panels. The glass may also have a stippling pattern and one or two anti-reflective coating to further enhance transparency. The absorber coating is typically a selective coating, where selective stands for having the special optical property to combine high absorption in the visible part of the electromagnetic spectrum coupled to low emittance in the infrared one. This creates a selective surface, which reduces black body energy emission from the absorber and improves performance. Piping can be laser or ultrasound welded to the absorber sheet to reduce damage to the selective coating, which is typically applied prior to joining to large coils in a roll-to-roll process.
Absorber piping configurations include:
harp: traditional design with bottom pipe risers and top
collection pipe, used in low pressure thermosyphon and pumped
systems;
serpentine: one continuous s-shaped pipe that maximises temperature
but not total energy yield in variable flow systems, used in
compact solar domestic hot water only systems (no space heating
role);
flooded: consisting of two sheets of metal molded to produce a wide
circulation zone that improves heat transfer;
boundary layer: consisting of several layers of transparent and
opaque sheets that enable absorption in a boundary layer. Because
the energy is absorbed in the boundary layer, heat conversion may
be more efficient than for collectors where absorbed heat is
conducted through a material before being accumulated in the
circulating liquid.[citation needed]
A flat plate collector making use of a honeycomb structure to
reduce heat loss also at the glass side too has also been made
available commercially.[7] Most flat plate collectors have a life
expectancy of over 25 years.
Low-temperature solar thermal installations are considered those installations of solar thermal energy that provide useful heat at temperatures below 65 ° C through solar energy.
A low-temperature solar thermal installation consists of solar collectors, two water circuits (primary and secondary), heat exchanger, accumulator expansion vessel and pipes.
The circulation of water inside the circuits can be obtained by thermosiphon, taking advantage of the density difference of the water at different temperatures or by means of a circulation pump. Although with a circulation pump an external contribution of electrical energy is needed.
Applications of solar thermal energy
Low-temperature solar thermal energy is a form of renewable energy
that can be applied in many areas in order to reduce dependence on
other sources of non-renewable energy such as natural gas or coal
combustion.
Solar thermal systems at low temperature are useful in applications such as heating swimming pools, for domestic use (hot water and heating), for industrial uses that require hot water but not at a higher temperature of 65ºC.
Solar hot water heaters can reduce your household carbon emissions by more than 20%, besides cutting your energy bills drastically. Choosing a style of solar hot water heater can be quite tricky, and it's a great idea to get a solar professional to work through your options. However, here's an explanation about close-coupled thermosiphon (mains pressure) systems.
This is the type that you'll see most commonly - you'll see roof mounted collectors with a horizontal tank about the panels. Usually, no pump is needed because heated water naturally rises through the collectors and into the storage tank. When the heated water enters the tank, cold water in the tank is forced into the collectors and is then heated. This cycle happens over and over throughout the day while the sun shines.
Solar heating systems are classified as “active” or “passive” solar heating systems, or a combination of both. We will first look at active systems.
Active solar heating systems are comprised of collectors, a distribution system, and a storage device.
Active solar heating systems operate as follows:
Flat plate collectors are usually placed on the roof or ground
in the sunlight. The top or sunny side has a glass or plastic cover
to let the solar energy in. The inside space is a black (absorbing)
material to maximize the absorption of the solar energy.
Cold water is drawn from the storage tank by pump #1 and is pumped
through the flat plate collector mounted on the roof of the
house.
The water absorbs the solar energy and is returned back to the
tank.
Warm water from the tank is pumped by pump #2 though the heating
coil.
The fan blows air (from the room) over the heated coil, and the
heated air then passes into the room and heats the room.
Cold air sinks to the bottom and is recirculated over the heating
coil.
Describe the structure and principle of operation of flat plate and evacuated tube solar collectors (both water heatin...
The equation for the useful energy prođuced by a solar thermal collector can be written as: ) Qu Ac FR(a)IT-FRUL (T; - Ta) From this derive an cquation for the efficiency of a solar thermal collector. The results of a standard collector test for such a collector are shown below. Efficiency of a Flat Plate Collector 1 0,8 0.6 0.4 0.2 0 0.03 0.02 0.04 0.05 0.01 (T-T What important information do the slope and intercept of this curve provide?...
The equation for the useful energy produced by a solar thermal collector can be written as: ) QuAc FR(a)T-FRUL (T; - Ta) From this derive an equation for the efficiency of a solar thermal collector. The results of a standard collector test for such a collector are shown below. Efficiency of a Flat Plate Collector 1 0.8 0.6 0.4 0.2 0 0.04 0.05 0.01 0.02 0.03 (Т-т.ул. What important information do the slope and intercept of this curve provide? If...
QUESTION 2 a) Define solar thermal energy and explain the working principle of Active water heating system with neat sketch. (5 marks) b) Explain how hot water is produced in Evacuated Tube Collector (5 marks) c) Explain the working principle of Photo Voltaic cells in generating electrical energy. (5 marks) d) To obtain high amount of solar energy from PV panel, what are the key factors to be considered (5 marks)
Question 2 [Total Marks 25 High Temperature Solar Thermal Systems a) Describe the principle of operation of a central receiver concentrating solar thermal system Include a discussion of the method of collecting sunlight, working fluid, generating electricity and storage. Include appropriate diagram(s) in your description 10 Marks Describe the key differences between solar trough and parabolic dish solar thermal b) collectors. Why is the receiver for a parabolic dish located a long way above the rim of the collector, while...
Both please 13.3 Estimate the amount of solar heating that is lost as a result of using one or two tempered 1/8 in thick glass plates covering a flat-plate absorber. The transmission coefficient for radiation is 2% for wavelengths greater than 3 m and 80% for wavelengths ranging from 0.2 to 3 um. 13.4 The amount of solar energy captured in a given application is expressed in terms of how much thermal energy is delivered relative to the total demand...
summatize the following info and break them into differeng key points. write them in yojr own words apartus 6.1 Introduction—The design of a successful hot box appa- ratus is influenced by many factors. Before beginning the design of an apparatus meeting this standard, the designer shall review the discussion on the limitations and accuracy, Section 13, discussions of the energy flows in a hot box, Annex A2, the metering box wall loss flow, Annex A3, and flanking loss, Annex...
summarizr the followung info and write them in your own words and break them into different key points. 6.5 Metering Chamber: 6.5.1 The minimum size of the metering box is governed by the metering area required to obtain a representative test area for the specimen (see 7.2) and for maintenance of reasonable test accuracy. For example, for specimens incorporating air spaces or stud spaces, the metering area shall span an integral number of spaces (see 5.5). The depth of...