M.RAJASEKAR

CB.EN.U4MEE11243

Introduction: The present world energy exhibits that most of the

energy requirements are met from fossil fuels which cannot be rate therefore, the present stocks are finite.

Also these fossil fuels are not environmental friendly and emits significant amount of pollutants causing serious environmental issues such as, global warming, ozone layer depletion and climate change.

The renewable energy sources are clean and freely available in the nature, however, the efficient utilization is still a cause of concern among the scientific and business communities.

Renewable energy sources, with advantages of being environment friendly and abundant in availability are the promising option to meet the increasing demand of energy world wide.

In a "close-coupled"

SWH system the storage

tank is horizontally mounted immediately

above the solar collectors on the roof.

No pumping is required as the hot water naturally rises into the tank through thermosiphon flow.

In a "pump-circulated" system the storage tank is ground- or floor-mounted and is below the level of the collectors.

SWH systems are generally very simple using only sunlight to heat water.

A working fluid is brought into contact with a dark surface exposed to sunlight which causes the temperature of the fluid to rise.

This fluid may be the water being heated directly, also called a direct system, or it may be a heat transfer fluid such as a glycol/water mixture that is passed through some form of heat exchanger called an indirect system.

Direct or open loop systems circulate potable

water through the collectors.

They are relatively cheap but can have the following drawbacks:

They offer little or no overheat protection unless they have a heat export pump.

They offer little or no freeze protection, unless the collectors are freeze-tolerant.

Collectors accumulate scale in hard water areas, unless an ion-exchange softener is used.

Until the advent of freeze-tolerant solar collectors, they were not considered suitable for cold climates since, in the event of the collector being damaged by a freeze, pressurized water lines will force water to gush from the freeze-damaged collector until the problem is noticed and rectified.

(A)Passive (B)Active

Indirect or closed loop systems use a

heat exchanger that separates the potable water from the fluid, known as the "heat-transfer fluid" (HTF), that circulates through the collector.

The two most common HTFs are water and an antifreeze/water mix that typically uses non-toxic propylene glycol.

After being heated in the panels, the HTF travels to the heat exchanger, where its heat is transferred to the potable water.

Though slightly more expensive, indirect systems offer freeze protection and typically offer overheat protection as well.

Passive and active systems:

Passive systems rely on heat pipes to circulate water heating fluid in the system. Passive solar water heating systems cost less and have extremely low or no maintenance, but the efficiency of a passive system is significantly lower than that of an active system. Overheating and freezing are major concerns.

Active systems use one or more pumps to circulate water and/or heating fluid in the system.

Use of solar energy depends on the type of application, one of the most common application of solar energy at low temperatures is heating of water for useful purposes.

The most common types of collector used in solar water heating systems are flat plate collectors (FPCs), evacuated tube collectors (ETCs), and integrated collector storage(ICS).

An integrated collector storage (ICS or Batch Collector) system uses a tank that acts as both storage and solar collector.

Batch Collector are basically thin rectilinear tanks with a glass side facing the position of the sun .

ICS or batch collectors reduce heat loss by placing the water tank in a thermally insulated box.

This is achieved by encasing the water tank in a glass-topped box that allows heat from the sun to reach the water tank.

Using a box does not eliminate heat loss from the tank to the environment, but it largely reduces this loss.

There are many variations on this basic design, with some ICS collectors comprising several smaller water containers and even including evacuated glass tube technology, a type of ICS system known as an Evacuated Tube Batch (ETB) collector.

The evacuated tube collector and copper tubes have been used of the same dimensions .

In this system copper tubes are inserted inside the ETC tubes due to which temperature at the outlet doesn’t drop suddenly, it takes time and hence we got better efficiency even if solar radiation decreases.

The glass wool was used to cover the copper tubes exposed into the open air viz. outside the ETC tubes for insulation purpose to reduce/minimize the heat loss to the ambient air.

Flat plate collectors are an extension of the basic idea to place a collector in an 'oven'-like box with glass in the direction of the Sun.

They are used extensively for domestic water heating applications.

The variation in solar radiation and efficiencies with respect to time for 15 LPH volume flow rate it can be seen that experiment starts at 11:30 AM when irradiation is quite good about 660 W/m2.

Time(hrs) Intensity(W/m2)

11.30 660

12.10 670

12.40 690

12.55 720

13.00 740

13.15 720

13.55 715

14.15 705

14.35 690

14.45 530

15.00 460

15.30 280

From this it is also observed that solar radiation first increases with time then remains almost constant for some time then again decreases which is an obvious case in practice.

The efficiencies are low which is due to the fact that initially solar radiation is also low and also temperature difference is less initially because it takes some time to warm the water.

Flat plate collector is simplicity in construction reduces initial cost and maintenance of the system.

Flat-plate collectors are used extensively for domestic water heating applications.

In higher latitudes, there are often additional design requirements for cold weather, which add to system complexity.

Evacuated-Tube Collectors are used in industrial applications, where high water temperatures or steam need to be generated where they become more cost effective.