Solar water heating

Presented by :

• Shehryar Ahmad• Hamza Saleem• Aqib Jah Temuri• Sidra Salahuddin• Mariam Gul• Sana Masood

D-14-CH-39D-14-CH-57D-14-CH-33D-14-CH-117D-14-CH-73D-14-CH-53

DEPARTMENT OF CHEMICAL ENGINEERING

UTILISATION OF SOLAR ENERGY FOR HEATING

WATER

INTRODUCTION : Solar water heating is a well established, highly

effective and pollution free process for heating water that can be used through out the country for various applications.

It also minimizes the consumption of fossil fuels for heating water.

Reduces the emission of unwanted gases.

Why Solar Energy is better than Fossil Fuels?Fossil fuels = Pollution. That is a fact that we are all

aware of.Unlike solar powered energy, fossil fuels are non-

renewable resources. Not only do they take years to form, but the rate of use is far greater than the rate of formation.

In addition to being non-renewable, fossil fuels also produce around 21.3 billion tons of CO2 each year. According to scientists and environmentalists, CO2 is our global warming contributor that causes the average surface temperature of the Earth to rise.

SOLAR COLLECTOR: A solar collector is a device, used to capture or

concentrate sun thermal energy and transfers this heat energy to the water or other fluid which can be used for various purposes as follows;

Industrial Purposes.Domestic Purposes.Residential Purposes.

PROCESS OF THE SOLAR WATER HEATING:

The process of solar water heating is carried out in the

solar water heaters.

There are mainly two processes for water heating

through solar energy;

1. Passive water heating

2. Active solar water heating.

PASSIVE WATER HEATING:

Passive water heating system involves no moving parts (no any external source required to circulate the water). Passive solar water heaters work on the principle of convection, in which hot water rises and cold water sinks within the tank in a continual process as long as there is sunlight available the process is also called Thermosiphon solar water heating.

ACTIVE WATER HEATINGsolar water heating in this system the water is circulated forcedly through external source (pumps are used for circulation). The water is circulated through pump in the solar collector and then stored in the hot water storage tank.

DIRECT V.S. INDIRECT HEATING SYSTEM

Direct solar water heating systems pass potable water through the thermal collector that eventually flows directly to the desired application (No heat exchanger is required).

Indirect Heating System works similarly to direct models but rather than ‘directly’ heating the water in the solar collectors, a special fluid with anti-freeze properties is heated. This fluid transfers the heat to the water by heat exchanger when it drains back into the tank.

TYPES OF SOLAR COLLECTORS:There are mainly two types of solar collectors

classified on the basis of the nature of materials and their geometrical shapes.

1. Non-concentrating Collectors.2. Concentrating Collectors.

NON-CONCENTRATING COLLECTORS: The stationary or non-concentrating collectors are

permanently fixed in position and do not track the sun and can be further subdivided into two types.

Flat-plate collectors Evacuated tube collectors

They are used to achieve low to medium temperatures.

FLAT-PLATE COLLECTOR:Flat plate collectors

easily attain temperatures of 60 to 100ºC.

Highly transparent polymer films insulation can be used to attain temperature up to 125ºC.

Double glazed flat plate collectors filled with inert gas also increases its efficiency.

COMPONENTS OF SOLAR COLLECTOR:1. Absorber Plate : Made of any material, which will rapidly absorb

heat from sun’s rays and quickly transfer that heat to the tubes or fins attached in some manner, which produces a good thermal bond.

2. Tubes or Fin : For conducting or directing the heat transfer fluid from the inlet header or duct to the outlet.

3. Glazing : This may be one or more sheets of glass or a diathermanous (radiation transmitting) plastic film or sheet.

4. Thermal Insulation : This minimizes downward heat losses from the plate.

5. Cover Strip : To hold the other components in position and make it all Water tight.

6. Container or Casing : This surrounds the foregoing components and keeps them free from dust, moisture, etc.

EVACUATED TUBE COLLECTOR:ETC use rows of glass tube, each

of which contains a heat pipe collector with a heat transfer fluid surrounded by a vacuum which greatly reduces heat losses.

It provides temperatures up to 120°c

More suitable for use in cold climates.

With the use of inert gas or ultra-high vacuum, temperature can be increased up to 150°c.

PARTS OF EVACUATED TUBE COLLECTOR:The ETC solar collector is comprised of four main parts:Evacuated Tube (ET): Absorbs solar energy and converts it to

usable heat. A vacuum between the two glass layers insulates against heat loss. The Heat Transfer Fin helps to transfer heat to the Heat Pipe.

Heat Pipe (HP): Copper vacuum pipe that transfers the heat from within the ET up to the manifold. 

Manifold: Insulated box containing the copper header pipe. The header is a pair of contoured copper pipes with dry connect sockets that the heat pipes plug into.

Mounting Frame.

CONCENTRATING COLLECTORS:Concentrating collectors use mirrored surfaces to concentrate the sun's

energy on an absorber called a receiver.Concentrators perform best when pointed directly at the sun. To do this,

these systems use tracking mechanisms to move the collectors during the day to keep them focused on the sun. Single-axis trackers move east to west; dual-axis trackers move east and west and north and south.

They can achieve temperatures up to 400°C.

They can be further divided into three types.

1. Parabolic Dish Collectors.2. Linear Parabolic Trough Collectors.3. Linear Fresnel Collectors.

PARABOLIC DISH COLLECTOR:The collector collects the solar energy

coming directly from the sun and concentrates or focuses it on a small area. The resultant solar beam has all of the power of the sunlight hitting the dish but is concentrated in a small area so that it can be more efficiently used.

Glass mirrors reflect ~92% of the sunlight that hits them.

The dish structure must track the sun continuously to reflect the beam into the thermal receiver.

PARABOLIC TROUGH COLLECTOR:Because of their parabolic shape,

troughs can focus the sun at 30 to 60 times its normal intensity on a receiver pipe located along the focal line of the trough.

Synthetic oil captures this heat as the oil circulates through the pipe, reaching temperatures as high as 390°C (735ºF).

The hot oil then goes through a heat exchanger to produce steam.

Linear Fresnel Collector:Linear Fresnel reflector approximate

the parabolic shape of trough system but using long rows of curved mirrors to reflect the sun´s rays onto a downward-facing linear, fixed receiver.

The main advantage is that their simple design of flexibly bent mirrors and fixed receivers requires lower investment costs and facilitates direct steam generation, eliminating the need for heat transfer fluids and heat exchangers.