PHYSICS S.S ONE 3RD TERM , WEEK 5

 

Topic:              SOLAR COLLECTOR               

Sub topic:

Reference materials:

(1) ESSENTIAL PHYSICS, TONALD PUBLISHERS, EWELUKWA (2017)

(2) NEW SCHOOL PHYSICS, AFRICAN FIRST PUBLISHERS, ANYAKOHA M.W (2011)

(3) INTERNET

Instructional materials:

Entry behavior: The students have been familiar with solar panel

Behavioural objective: At the end of the lesson the students should be able to:

i.                     Explain energy from sun is harvested

ii.                   State the devices used to intercept solar radiation

iii.                  Mention some of the components of flat plat collector

iv.                 List  the application of solar panel

CONTENT

SOLAR COLLECTOR

The Sun is an enormous energy source. This energy released from the sun is known as Solar Energy. The sun being a high temperature body emits energy in form of heat. The energy is plentiful, it is however thinly distributed over a large area and must be harvested or collected using Solar collectors.

Production of Solar Energy

The sun is a vast ball of hot glowing gas. The temperature at the core of the Sun is a high as about 15 million degrees centigrade ( 15 X 106 oC ), but at the surface, the temperature is about 6000 oC .

In most areas of the world, solar energy is collected by large concave mirrors and concentrated on water to produce steam that drives steam turbines; some are also collected by solar panels on roofs of houses for domestic heating purposes.

SOLAR COLLECTORS OR SOLAR PANELS

Two kinds of devices are used to intercept solar radiation and convert it to thermal energy. They are the

I.                     Flat plate collector.                       II. Focusing collector.

Construction of flat plate solar collector

A flat plate collector is a large shallow metal box – typically mounted on a roof or high stand – that heats water using solar energy. It is designed to operate in the low temperature of about 65oC or temperature of about 100oC. the designed is to delivered heat at low cost for long periods.

Typical Flat Plate Collector

 

 The flat plate collector consist of:

(a)    A metal flat plate- it absorb solar radiation, usually made of copper or aluminium.

(b)    Tubes or channel or passage- attached with the metal plate which aid to circulate the   liquid (water)that remove the thermal energy from the plates.

(c)    A thermal insulator- it minimizes the heat losses

(d)    A transparent cover (called glazing) on top- a cover made of transparent glass or Perspex or transparent plastic. Its purpose is to:

i.                     Reduce the heat loss in the upward direction, usually associated with the absorber plate

ii.                   To allow for maximum solar energy transmission to the metal plate

iii.                 To shield absorber plate from direct exposure to weathering.

(e)    Metal box casing- other components of flat plate collector are encased in the box, with a dark coloured absorber plate on the bottom. The sides and bottom of the collector are usually insulated to minimize heat loss.

Principle of operation

The metal sheet is exposed to solar radiation. Sunlight passes through the glazed cover and strikes the absorber metal plate(painting with selective coating). The plate heats up changing the absorbed solar energy into heat or thermal energy. The temperature of the absorber plate rises until at the equilibrium temperature, the rate at which energy received from the sun equal the rate at which heat is lost from the plate. The heat in the metal collector is then transferred to the liquid passing through the pipes attached to the absorber plates. The heated liquid is transferred to a tank for storage and use.

FOCUSING COLLECTOR

This type of collector uses a concave reflector (mirror or lens) to concentrate the solar beam. In this way the intensity of the beam is raised from 2 to 10000 times. This high intensity radiation is focused on the black absorbing surface receiver which is insulated to reduce thermal losses. Because of this high concentration of solar energy, the temperature of the absorber is raised up to 100-2800 oC. The focusing collector must be movable so that it can always be oriented to gather the sunlight.

Application of solar panels

i.                     To provide hot water supply in homes for domestic purposes, for commercial purposes.

ii.                   To heat swimming pools during cold weather and for space heating

iii.                 Used for evaporation of salt water to produce salt and distillation of salt

iv.                 For electricity supply

Advantages of solar energy over other energy from fossil fuel

I.                     A cleaner source of energy

II.                   It is an inexhaustible form of energy

Disadvantage of solar energy over other energy from fossil fuel

I.                     More expensive to installed

PRESENTATION

Step I: The teacher explains production of solar energy

Step II: The teacher explains solar collector

Step III: The students chorus the components of flat plate collector

Step IV: The students state the application of solar panel

Step V: The teacher states the advantages and disadvantages of solar energy.

EVALUATION

The teacher evaluates the lessons by asking the following questions:

i.                     Explain energy from sun is harvested

ii.                   State the devices used to intercept solar radiation

iii.                  Mention some of the components of flat plat collector

iv.                 List  the application of solar panel

ASSIGNMENT

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