Chapter 8

Question 1

What is the equation to calculate solar energy available in the uk per year

Answer 1

Total energy = solar energy received per m2 per year x total area in m2
This equation can be expressed in symbol form:
ET = S x A

Question 2

Explain solar thermals purpose

Answer 2

This solar technology involves the absorption of energy from the Sun for the purposes of heating a heat transfer fluid which can then be used in a number of different ways.

Question 3

State the three ways in which heat transfer fluid can be used in solar thermal.

Answer 3

Active solar heating
Passive solar heating
Solar thermal engines

Question 4

Describe active solar heating

Answer 4

This technique involves the use of a solar collector to absorb the Sun’s energy which is then typically used to heat domestic hot water (DHW); uses of DHW include heating homes, hot water for washing dishes, showers and bathing.

Question 5

Describe passive solar heating.

Answer 5

This technique involves the direct absorption of the Sun’s energy into a building which can then circulate this energy naturally (or aided by electrical fans and ventilation systems) around the building environment.

Question 6

Describe how solar thermal engines work

Answer 6

This technique involves use of a solar collector to heat a fluid much like the active solar heating technique described above. They differ however in that they are implemented in higher temperature environments where steam is produced, either directly from the heated transfer fluid or via use of a heat exchanger, which can then be used to drive a generator to produce electricity.

Question 7

Name the three components in a solar thermal system

Answer 7

1. Solar collector
2. An energy transfer system (via a heat transfer fluid)
3. Storage tank

Question 8

What is a direct loop solar thermal system and what is the difference from an indirect loop

Answer 8

The water gets heated directly from the sun in the solar collector in a direct loop but in an indirect loop heat exchange fluid gets heated which then goes to the storage tank and heats the water.

Question 9

Describe how photovoltaic works.

Answer 9

Unlike solar thermal, solar photovoltaic (PV) takes the energy from the Sun and produces electricity directly.

Question 10

What are the three ways sunlight strikes the earth

Answer 10

1.Direct sunlight
2.Diffused sunlight
3.Reflected sunlight

Question 11

Describe what direct sunlight is

Answer 11

This is when sunlight travels from the sun in a straight line and hits the earth directly

Question 12

Describe what diffused sunlight is

Answer 12

Some sunlight that hits the atmosphere scatters in different directions as it hits the earths atmosphere.

Question 13

Describe what reflected sunlight is

Answer 13

This is when sunlight strikes the earth and is reflected

Question 14

What is the ideal orientation for solar collectors

Answer 14

In both cases the solar collectors should be directed towards the equator. Consequently, the ideal orientations for each hemisphere is as follows:

Southern Hemisphere: System should be north facing.
Northern Hemisphere: System should be south facing.

Question 15

Describe how a single axis tracker maximizes output

Answer 15

The angle of incidence on solar collectors is minimised to absorb the maximum amount of direct radiation from the Sun. To do this a single axis tracking system can be utilised. Here the solar collectors turn the collectors towards the east or west to track the Sun’s positioning during the course of the day.

Question 16

4 disadvantages of single axis tracking

Answer 16

1. Complex electrical and mechanical equipment which raises price of the system
2. A motor is required to rotated the panel which requires electricity.
3. The locations where single axis tracking can be utilized in minimum as it only works with direct sunlight
4. When one panel rotates towards a sun a shadow will be left e behind it meaning other panels will have to be placed further away

Question 17

2 advantages of single axis tracking

Answer 17

1. The energy output from the system will be higher; it can be higher by as much as 25%. In warmer climates this justifies the higher initial costs.
2. The higher output obtained means that the repayment period is reduced which makes them better long-term investments in warmer climates.

Question 18

Describe how a dual axis differs from a single axis tracking system

Answer 18

The dual axis tracking system has an additional degree of rotation, the additional axis of rotation lies in the east west plane. This allows the collectors to be rotated in the north south plane which more closely aligns the collectors with the Sun throughout all seasons.

Question 19

4 disadvantages of dual axis tracking

Answer 19

1. Complex mechanical equipment needed which raises price
2. Motors need electricity to operate
3. Location where these can be installed are restricted
4. Overshadowing from panels can be caused

Question 20

2 advantages of dual axis tracking

Answer 20

1. Energy output from system will be as much as 35% higher than a fixed system.
   2.With outputs much higher the repayment periods are reduced which makes them better long-term investments in warmer climates.

Question 21

How does a flat plate operate

Answer 21

Cold water is pumped into the collector at low level. Here it enters and travels up heat absorbing riser tubes.The heat absorbing riser tubes are connected to an absorber plate, sometimes on top of it, sometimes under it; it has a special black paint applied which maximizes the system’s absorption of solar radiation. Under this absorber plate is insulation which reduces the heat losses from the system through conduction and convection.

Question 22

State the 3 operations the glazing plate is designed to carry out.

Answer 22

1. Increase the solar radiation transmitted through it to the absorber plate.
2. Reduce as far as possible the heat losses back through the glazing sheet cover through conduction and convection.
3. Protect the system from rain and weather conditions.

Question 23

State the operations of a evacuated tube

Answer 23

1. A double walled glass circular cylinder containing an absorbing plate provides a vacuum so minimal heat loss takes place.
2. The absorber plate is attached to the copper heat pipe as solar radiations strikes the absorber plate energy is transferred to the copper heat pipe.
3. The copper heat pipe has an enclosed cavity which is partially filled with a heat transfer fluid in liquid form. This fluid in ní is a mixture of water and glycerol to reduce freezing point
4. When the absorber plate transfers energy to the heat pipe this heat transfer fluid is heated

Question 24

State the 6 advantages of an evacuated tube

Answer 24

1. It’s circular geometry results in the tube facing perpendicular to the sun for most of the day.
2. Heat losses through conduction and convection are almost zero
3. There is less loading onto the roof and support structure as the system is not filled entirely with a heat transfer fluid
4. 90% efficiency
5. They can typically be installed by one person
6. As they can be stored vertically, transportation cost can be minimised

Question 25

State 2 disadvantages of evacuated tubes

Answer 25

1. It has a higher cost compared to a flat plate collector 2. Where snow fall is possible because of almost 0 thermal losses snow cannot he melted

Question 26

State the equation for area required for roof space.

Answer 26

A= RE/ energy per m2 A= area of solar collector required in m2 Re= renewable energy in kWh

Question 27

State the equation for energy required

Answer 27

Re= Ereq x % from renewables in decimal form

Question 28

Give 2 factors installing a flat plate solar thermal collector would benefit

Answer 28

1- reduced costs - as hot water can be retained from the flat plate collector domestic hot water (dhw). Therefore reducing costs on an annual basis 2- energy security- protects the house hold owner from fluctuating fuel prices. As the price of energy overtime will rise steadily having to not rely on fuel will be beneficial to consumers. Hint - make sure to compare to evacuated tube when answering this question

Question 29

What is the role of an anti-reflective coating on a solar pv cell

Answer 29

It maximizes the quantity of photons absorbed by the PV cell minimizing the reflection of the PV cell. Maximizing efficiency

Question 30

What is the role of the n-type layer on a solar PV cell

Answer 30

A silicon wafer with excess electrons to provide a negative charge

Question 31

What is the role of the depletion zone in a solar PV cell

Answer 31

A region over with potential difference therefore an electric field exists, this acts as a driving force to push the electrons around the circuit

Question 32

What is the role of the p-type layer in the solar PV cell

Answer 32

A silicon wafer with a shortage of electrons therefore has a positive charge

Question 33

What is the role of the rear metal contact in a solar PV cell

Answer 33

The underside of the p-type layer has a metal contact which is required to provide a complete conductive path around the circuit

Question 34

What is the 3 roles of the silicon wafer producing electricity

Answer 34

1. when solar radiation falls on the p-n junction some of the photons can create electron hole pairs through the photoelectric effect. 2. As the electrons move this creates a potential difference with net positive and negative charge at either side of the p-n junction. This region is called the depletion zone. 3. Contact on either side of the PV cell connects to an external load and permit the electrons to travel around a loop back to neutralize the valency hole at the opposite side of the depletion zone.

Question 35

What are the 4 material types of solar PV modules

Answer 35

Monocrystalline, polycrystalline, thick-film and thin-film. Note: mono and polycrystalline fall under the thick modules

Question 36

How can a monocrystalline cell be identified

Answer 36

Monocrystalline cells exibit a dark blue or black colour which is uniform throughout the cell

Question 37

How can a polycrystalline cell be identified

Answer 37

polycrystalline cells has almost a purplish colour and you can see the individual crystals

Question 38

What are he three types of thin solar cells

Answer 38

1.amorphous silicon 2.copper indium gallium diselenide 3.cadmium telluride

Question 39

Advantages and disadvantages of monocrystalline ( cost, longevity and efficiency

Answer 39

1.The crystalline structure is one whole one with no bounderies therefore lower resistance and higher efficiency 2.with the need of high skilled personnel, complex equipment and it being time consuming makes monocrystalline the highest costing domestic use 3. with a warrenty of 25 years monocrystalline is seen to have a long life

Question 40

Advantages and disadvantages of polycrystalline ( cost, longevity and efficiency

Answer 40

1.Polycrystalline cells are made from multiple grain boundaries which increases resistance lowering efficiency 2.with less energy intensive manufacturing and less time consuming polycrystalline is cheaper than monocrytalline 3.With a 25 year warranty its longevity is long

Question 41

Advantages and disadvantages of thin cell ( cost, longevity and efficiency

Answer 41

1. The cost lies between polycrystalline and monocrystalline 2. Long warranty's aren't offered therefore not as long longevity 3.amorphous silicon has lowest efficiency's and cadmium has highest

Question 42

Explain the Planning permission for roof mounted panels on pitched roof

Answer 42

1. no part off the panel exceeds the highest part of the roof 2.No part of the panel protrudes more than 20 cm over the plane of a roof slope facing onto and visible from a road 3.Panels do not exceed the boundaries of roof 4.House within conservation area must not have panels visible to the road

Question 43

Explain the Planning permission for roof mounted panels on a flat roof

Answer 43

1.panels do not exceed 1.5 metres above the plane of the roof 2.panels do not exceed boundaries of existing roof 3..House within conservation area must not have panels visible to the road

Question 44

Explain the planning permission for wall mounted panels

Answer 44

1.Panels do not exceed boundaries of the wall 2.No part of the panel is higher than the highest point on the roof

Question 45

Explain financial incentives like the green deal

Answer 45

Home owners can get a loan to install solar panels this loan can then be paid off by the energy created by the solar panel as you can send it back to the grid

Question 46

Explain financial incentives like the feed in tariff

Answer 46

This is where the home owner can sell electricity to the national grid for a fixed price that changes yearly to match inflation this contract lasts for 20 years.

Question 47

What are the three incentives to use renewable energy

Answer 47

1.feed in tarrif 2.green deal 3.Renewable heat incentive

Question 48

What are the 4 passive solar design techniques

Answer 48

1.Window placement and orientation 2.Size and type of glazing 3.Thermal mass 4.Thermal insulation

Question 49

explain how window placement and orientation works in passive solar design

Answer 49

Large windows should be placed in commonly used rooms like the kitchen if possible these rooms should be south facing (as NI is in the northern hemisphere). Rooms such as bedrooms are to have smaller windows to reduce heat loss.

Question 50

Explain how Size and type of glazing works in terms of passive solar design techniques

Answer 50

Bigger windows let in more heat and light and smaller windows reduce more heat loss. Also low emmisivity glazing is needed as this reduces heat loss to the outside environment.

Question 51

Explain how thermal mass is used in terms of solar design techniques

Answer 51

Materials like marble that absorb large amounts of energy but do not heat up quickly is perfect as: During the day the marble can absorb alot of thermal energy which will prevent the room from getting to hot 2. during the night as the house cools down this marble transfers this energy into the living room reducing the heating requiremens of the house

Question 52

Explain how thermal insulation is used in terms of design techniques in passive solar design

Answer 52

Thermal insulation in walls windows and the room and doors will prevent heat losses and reduce the energy requirments of the household

Question 53

what are the operations of a parabolic trough and fresnal reflectors

Answer 53

1.Reflects solar radiation to a specific point to heat transfer fluid absorbs the energy and turn into steam 2.This steam is then used to turn a turbine which turns a generator and electrcity is produced

Question 54

How does a parabolic trough work

Answer 54

A parabolic trough tracks the sun during the day as it relys on direct solar radiation to strike the parabolic shaped mirror and hit the focal point which has a tube circulating heat exchanged fluid

Question 55

How does a fresnal reflector work

Answer 55

Much like the trough the fresnal uses a focal point with a tube to absorb energy however the fresnal is a flat plate that reflects the suns direct solar radiation

Question 56

How does a dish work

Answer 56

Direct solar radiation is directed to a focsal point but at thus focal point the generator is located to make it much more efficient

Question 57

What are the three Concentrating solar power systems

Answer 57

1. Solar dish 2.Fresnal reflector 3.parabolic trough

Question 58

What is the definition of reliability

Answer 58

consistently good in quaility or performance; can be trusted

Question 59

What is the definition of intermittent

Answer 59

occuring at irregular intervals not continues or steady

Question 60

Are wind and solar intermittent or reliable

Answer 60

Wind and solar is intermittent as throughout the year wind speeds and solar radiation is forever changing one way that wind and solar can be used more effectively is to place multiple wind farms around one region.

Question 61

When will energy storages need to be used and why

Answer 61

As wind and solar is interrmittent storage can be used when demands exceeds supply.

Question 62

State 4 advantages of energy storage

Answer 62

1.Decrease the reliance on expensive and sometimes volatile fossil fuel prices. 2.Decrease fossil fuel usage therefore help mitigate the effects on climate change

Question 63

What is CSP

Answer 63

Concentrated solar power