6. Energy From The 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

Answer to make reference to the fact that a solar tracking device must be able to track the relative motion between the Earth and the Sun and make reference to at least three of the following design parameters;
• 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

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

Answer 2

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

Question 3

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 3

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 4

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}

(Assume 1m2 of a flat plate collector provides 450 kWh of useful heat per year)

Answer 4

65% of hot water requirement=0.65 x 6500 kWh= 4225 kWh
1m2 flat plate collector provides 450kWh
4225/450 =9.38m2
Cannot buy fractions of panels, to meet the ‘at least’ requirement must install 10m2

Question 5

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

Answer 5

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

Question 6

The figure below shows the typical arrangement of a PV cell.
Explain the following;
Question (I);The purpose of the antireflective coating.
Question (II); The role of the metal contacts. {1}
Question (III); The operation of the PV cell. {3}

Answer 6

Answer (I); Maximises the efficiency of the cell by reducing the reflection of light (photons) from the surface. {1}
Answer (II); Necessary to allow for circuitry necessary to facilitate the flow of electrons in the circuit from the p to the n layer of the cell. {1}
Answer III
When light falls on a silicon p-n junction some of the photons can create electron hole pairs through the photoelectric effect. {1}
As the electrons move, this creates a potential difference with net positive and negative charge at each side of the junction (pn junction). {1}
Contacts on either side of the cell connect the cell to an external load and permit the electrons to travel around the circuit loop back to neutralise the valency hole on the opposite side of the potential barrier

Question 7

.Describe one advantage and one disadvantage of monocrystalline PV modules

Answer 7

Advantage; most efficient type of PV module

Disadvantage; Cost – Expensive manufacturing techniques required to ensure efficiency

Question 8

Name two other material types of PV modules.

Answer 8

Answer to include any two of the following; • Polycrystalline.
• Thick-film
• Thin-film

Question 9

Name and briefly describe any two financial incentives that are available to homeowners considering the installation of solar panels. {4}

Answer 9

Any two from;
• Green deal {1}; Financial assistance towards cost of installing solar panels {1}.
Feed-in-Tariff for Solar PV {1} Where homeowners are paid for the amount of electricity they generate and feed back into the grid {1}.
• Renewable heat incentive {1}; Where homeowners are paid for the amount of heat they generate using their own solar thermal panels {1}.

Question 10

Explain briefly any two passive solar design techniques that can be applied to new and existing buildings. {4}

Answer 10

Orientation {1}; Main glazed ‘dayrooms’ orientated South (or within 15 degrees of South) Non-habitable rooms towards north {1}.
• Windows to be appropriately sized {1}; To provide good day-lighting and prevent excessive heat loss / heat gain {1}.
• Use low emissivity glazing {1}; To reduce heat loss through windows {1}.

•high levels of thermal insulation will reduce the nets loss of the building

Question 11

Name two types of concentrating Solar Power (CSP) systems; {2} Answer;

Answer 11

Parabolic troughs.
• Fresnel Reflectors.
• Solar Dishes.

Question 12

Explain how Concentrating Solar Power (CSP) systems may be used in power plants. {2}

Answer 12

CSP plants produce electricity by converting the suns energy into high-temperature
heat (steam) using various mirror configurations. {1} The steam is then sent through a generator to produce electricity. {1}

Question 13

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

Answer 13

Solar radiation levels of the site/roof. [1]
• Shading. [1]
• Proposed collector type and performance specification. [1]
• Family size and hot water requirements. [1]
• Lifestyle of users and hot water requirements. [1]

Question 14

State one benefit to households of installing a flat plate solar collector.

Answer 14

• Reducing environmental impact. [1]
• Financial benefit – reducing energy costs. [1]
• Improved energy security. [1]

Question 15

A family uses 6800 kWh of hot water per year. If they wish to install a
solar thermal hot water system to meet at least 70% of their annual
hot water needs, what area of flat plate solar panel would provide a
practical solution?
(Assume 1 m2 of flat plate collector provides 550 kWh of useful heat
per year and that solar panels are supplied in 1 m2 modules). Show
your working out in the space below.

Answer 15

70% of hot water needs = 0.7 × 6800 kWh = 4760kWh. [1]
1m2 of collector provides 550 kWh.
4760
550 = 8.65 [1]
Must be a whole number of panels.
Therefore family must install 9m2 of panels.

Question 16

Fig. 2 below shows a section through a flat plate solar collector.
(a) Identify the components which have been labelled A and B in the
diagram.
A:
B:

Answer 16

Protective glass cover [1];

B: Absorber plate [1].

Question 17

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

Answer 17

The Sun’s energy is captured by the absorber plate [1] and transferred
to the water which heats up a tank in the house. [1]

Question 18

Name one other type of solar thermal collector.

Answer 18

Evacuated tube solar collector.

Question 19

Identify the type of Concentrating Solar Power (CSP) system shown
in Fig. 3.

Answer 19

Parabolic Trough.

Question 20

Outline how Concentrating Solar Power (CSP) systems may be used
in power plants to convert the Sun’s energy into electricity.

Answer 20

Concentrating Solar Power (CSP) plants use mirrors to focus the
Sun’s energy for conversion into high grade heat (steam) [1]; the steam
drives a turbine which turns a generator creating electricity.

Question 21

Describe any two passive solar design techniques that could be
applied to the design of a new house.

Answer 21

two from:
• Main glazed ‘dayrooms’ to be oriented towards South (or within
15 degrees of south) [1]; Non-habitable rooms (bathrooms, stores etc.)
oriented towards North [1];
• Windows to be appropriately sized to provide good day-lighting [1]
and also prevent excessive heat loss/heat gain [1];
• Use low emissivity/double/triple glazing [1] to reduce heat loss
through windows [1];
• Provide eaves overhangs/bris-soleil [1] to reduce summer heat gain
through windows [1];
• Heavy construction/high thermal mass [1]; will absorb heat in winter to
even out temperature fluctuations [1];
• High levels of thermal insulation [1]; will reduce the heat loss of
the building [1].
Award [2] for a detailed description and [1] for a limited description

Question 22

Explain the purpose of the anti-reflection coating.

Answer 22

State one advantage and one disadvantage of monocrystalline PV
modules.
Advantage:
[1]
Disadvantage:

Question 23

Explain the operation of the PV cell.

Answer 23

When light falls on the silicon p–n junction some of the photons can
create electron–hole pairs through the photoelectric effect [1]; As the
electrons move this creates a potential difference with net positive and
negative charge at each side of the p–n junction [1]; Contacts on either
side of the cell connect to an external load and permit the electrons to
travel around a loop back to neutralise the valency hole at the opposite
side of the potential barrier. [1]

Question 24

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

Answer 24

It can tilt and rotate on its own axes to achieve optimum tracking. [1]
• It can track the variations in the sun’s position during daylight hours
(earth spinning on its axis). [1]
• It can track the annual variations in the sun’s position during
year/seasons (earth orbiting the sun). [1]
• It can adjust according to location in northern or southern
hemispheres. [1]

Question 25

State one advantage and one disadvantage of monocrystalline PV
modules.
Advantage:
[1]
Disadvantage:

Answer 25

Advantage: it is more efficient than other PV cells. [1]
Disadvantage: It is more expensive. [