1.8 Energy From Sun

Question 1

With reference to the figure below, explain how an
automated tracking system can maximise energy output from solar devices.
{3}

Answer 1

Daily variations of the position of the sun during day light hours (earth
spinning on its own axis).
• Annual variations in the position of the sun in the sky depending on the
season / time of the year (Earths elliptical orbit around the Sun).
• Variations in positioning in the Northern and Southern hemisphere (Earths tilt
on its own axis is 23.45 degrees and elliptical orbit).
• Tracking device must be able to change tilting angle and rotate on its own
axis to achieve optimum tracking.

Question 2

Outline two ways in which automated solar tracking can
maximise the energy output from solar collectors. {2}

Answer 2

Any two from;
• It can tilt and rotate on its own axis to achieve optimum tracking.
• It can track the variations in the sun’s position during daylight hours (earth
spinning on its axis).
• It can track the annual variations in the sun’s position during years/seasons
(earth orbiting the sun).
• It can adjust according to location in northern or southern hemispheres.

Question 3

Outline two ways in which automated solar tracking can
maximise the energy output from solar collectors. {2}

Answer 3

Any two from;
• It can tilt and rotate on its own axis to achieve optimum tracking.
• It can track the variations in the sun’s position during daylight hours (earth
spinning on its axis).
• It can track the annual variations in the sun’s position during years/seasons
(earth orbiting the sun).
• It can adjust according to location in northern or southern hemispheres.

Question 4

Outline two methods by which automatic solar tracking maximises the energy
output from solar collectors. {2}

Answer 4

Any two methods from:
• Tilts and rotates on its own axis to achieve optimum tracking
• Tracks the variations in the Sun’s position during daylight hours (Earth
spinning on its axis)
• Tracks the annual variations in the Sun’s position during year/seasons
(Earth orbiting the sun)
• Adjusts according to location in northern or southern hemispheres {2}

Question 5

In the space below sketch a diagram of a typical flat plate
thermal solar panel and clearly label the following; {4}
• Inlet and outlet connections.
• Flow tubes
• Absorber plate.
• Insulation.

Answer 5

Inlet and outlet connections. {1}
• Flow tubes. {1}
• Absorber plate. {1}
• Insulation. {1}

Question 6

State one advantage provided by an evacuated tube
solar collector compared to a flat plate solar collector. {1}

Answer 6

Answer should make reference to the fact that evacuated design eliminates;
• Conduction losses. {1}

Question 7

Fig. 2 below shows a section through a flat plate solar
collector.
Identify the components which have been labelled A and B in the diagram. {2}
A; ____________________________________________________________
B; ____________________________________________________________

Answer 7

A – Protective glass cover. {1}
B – Absorber plate. {1}

Question 8

With reference to the diagram, explain the operation of
a flat plate solar collector. {2}

Answer 8

The suns energy is captured by the absorber plate {1} and transferred to the
water which heats up a tank in a house {1}.

Question 9

Name one other type of solar thermal collector. {1}

Answer 9

Evacuated tube solar collector. {1}

Question 10

(a) Name the type of solar thermal collector in Fig. 1. {1}

Answer 10

Flat plate solar collector

Question 11

(b) Fig. 2 shows an image of an evacuated tube solar thermal collector.

Compare the operation of the solar thermal collector shown in Fig. 1 with an
evacuated tube solar thermal collector shown in Fig. 2.
1. ________________ {2}
2. _______________ {2}
3. ________________ {2}

Answer 11

(b) Any three comparisons from:
• Both solar collectors transfer solar energy to water in a storage tank
via a pipe network containing a fluid, often water. {2}

In a flat plate collector, the absorber plate is in direct contact with the
pipe network. In an evacuated tube collector, the absorber plate is contained
in a vacuum tube and is not in direct contact with the pipe network. {2}

In a flat plate collector, the absorber plate absorbs solar energy as heat,
which is transferred to the pipe network. In an evacuated tube collector, a
thermal fluid is heated by the absorber plate and evaporates inside the vacuum
tube. Its heat energy is transferred to the pipe network via a heat exchanger. {2}

Question 12

State three factors which should be considered when
calculating the roof area required to install flat plate thermal solar panels on a
house. {3}

Answer 12

Answer to include any three of the following;
• Solar radiation levels of site / roof.
• Shading.
• Proposed collector type and performance specifications.
• Family size and hot water requirements.
• Lifestyle of users and hot water requirements.

Question 13

A household uses 6,500 kWh of hot water per year. If the
owners wish to install a solar thermal hot water system to meet at least 65% of
their annual hot water demand, what area of solar panel (flat plate) would
provide a practical solution? {3}

Answer 13

65% hot water requirement = 0.65 x 6500 = 4225 kWh {1}
1m2 flat plate = 450 kWh
4225 / 450 = 9.38m2 {1}
Cannot buy fractions of panels hence must install 10m2 {1}

Question 14

State three issues which should be considered when
calculating the amount of roof space required for a flat plate thermal collector.
{3}

Answer 14

Any three issues from;
• Solar radiation levels of the site / roof
• Shading
• Proposed collector type and performance specification.
• Family size and hot water requirements.
• Lifestyle of users and hot water requirements.

Question 15

State three issues which should be considered when
calculating the amount of roof space required for a flat plate thermal collector.
{3}

Answer 15

Any three issues from;
• Solar radiation levels of the site / roof
• Shading
• Proposed collector type and performance specification.
• Family size and hot water requirements.
• Lifestyle of users and hot water requirements.

Question 16

A household uses 6,800 kWh of hot water per year. If the
owners wish to install a solar thermal hot water system to meet at least 70% of
their annual hot water demand, what area of solar panel (flat plate) would
provide a practical solution? {3}

Answer 16

70% of hot water needs = 0.7 x 6800kWh = 4760kWh {1}
1m^2 of collector provides 550kWh
4760/550 = 8.65 {1}
Must install 9 panels {1}

Question 17

The occupants of the house in Fig. 2 wish to install a solar thermal hot water
system to meet part of their annual hot water needs of 7200 kWh per year. If
they only have enough roof space for 7 flat plate panels, what percentage of
their annual hot water needs would be met by the installation? {3}

Answer 17

7 x 650kWh = 4,550 kWh {1}
4550/7200 {1} x 100 = 63% {1}

Question 18

Identify two factors, other than cost, that should be taken into consideration by
the occupants when deciding whether to install the solar collector. {2}

Answer 18

shading {1}
roof orientation {1}

Question 19

Explain the main benefit to households of installing a flat
plate solar collector. {1}

Answer 19

Economic reasons. Cost more important in the application than efficiency. {1}

Question 20

State one benefit to households of installing a flat plate
collector. {1}

Answer 20

One from;
• Reducing environmental impact.
• Financial benefit – reducing energy costs.
• Improved energy security.

Question 21

State one benefit that the occupants would get from installing the flat plate solar
collector. {1}

Answer 21

Any one benefit from:
Reducing environmental impact
Financial benefit – reducing energy costs
Improved energy security {1}