1.8 Energy From Sun Flashcards by Matt McEvoy

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

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.

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

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

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

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}

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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.

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

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

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

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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; ____________________________________________________________

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

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

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

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

Evacuated tube solar collector. {1}

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

Flat plate solar collector

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(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}

(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}

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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 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.

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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}

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}

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

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.

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

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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}

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}

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}

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

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

shading {1}
roof orientation {1}

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

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

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

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

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

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

Explain the following;
(i); The purpose of the antireflective coating. {1}

(ii); The role of the metal contacts. {1}

(iii); The operation of the PV cell. {3}

(i) Maximizes the efficiency of the cell by reducing the reflection of light (photons)
from the surface. {1}

(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}

(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. {1}

(i); Explain the purpose of the anti-reflection coating. {2}

(ii); Explain he operation of the PV cell. {3

(I) Anti-reflection coating maximises the efficiency of the cell {1} by reducing
the reflection of light (photons) from the surface {1}.

(II) 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 either 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}

Name A and B in Fig. 3 below. {2}

A: Anti-Reflection coating – must be named correctly
B: Junction Layer – must be named correctly

Explain the operation of the Solar PV cell in Fig. 3. {4}

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] and thus they create an electric current [1]

Explain the purpose of the anti-reflective coating on a PV cell. {2}

The anti-reflective coating maximises the efficiency of the cell and hence the panel by reducing the reflection of light from the surface of the cell. {2}

Name two of the main material types of PV module. {2}

Any two types from: Monocrystalline [1] Polycrystalline [1] Thin-Film [1] Thick-Film [1]

Solar power can also be used for microgeneration of electricity in PV panels. List the four material types of PV panels. 1: ______________ {1} 2: ______________ {1} 3: _______________ {1} 4: ________________ {1}

Monocrystalline {1} Polycrystalline {1} Thick-film {1} Thin film {1}

Describe one advantage and one disadvantage of monocrystalline PV modules. {2}

Advantage; Most efficient type of PV module. {1} Disadvantage; Cost – Expensive manufacturing techniques required to ensure efficiency. {1}

Name two other material types of PV modules. {1}

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

State one advantage and one disadvantage of monocrystalline PV modules. {2}

Advantage: It is more efficient than other PV cells. Disadvantage: It is more expensive. {1} {1}

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

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}.

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

Any two descriptions from the following; • 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}. • 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 and even out temperature fluctuations {1}. • High levels of thermal insulation {1}; Will reduce the heat loss of the building {1}.

Describe any two passive solar design techniques that could be applied to the design of a new house. {4}

Any two from; * Main glazed ‘dayrooms’ to be orientated towards South (or within 15 degrees of south) {1}; Non-habitable rooms (bathrooms, stores etc) orientated 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} tp reduce heat loss through windows. * 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 level of thermal insulation {1}; will reduce the heat loss of the building {1}.

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

Any two from; • Parabolic troughs. • Fresnel Reflectors. • Solar Dishes.

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

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}

Identify the type of Concentrating Solar Power (CSP) system shown in Fig. 3. {1}

Parabolic trough. {1}

Outline how Concentrating Solar Power (CSP) systems may be used in power plants to convert the Sun’s energy into electricity. {2}

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 {1}.

Concentrating solar power (CSP) is a renewable technology used to assist in electricity generation on a large scale. Explain how CSP systems assist in electricity generation. {3}

Concentrating Solar Power plants produce electricity by converting the sun’s energy into high-temperature heat (steam) using various mirror configurations. [1] The steam is then sent through a generator to produce electricity. [1] The steam can be heated directly or indirectly using a working fluid such as salt. [1]