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Environmental technology > Chapter 8 > Flashcards

Chapter 8 Flashcards

1
Q

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

A

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

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2
Q

Explain solar thermals purpose

A

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.

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3
Q

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

A

Active solar heating
Passive solar heating
Solar thermal engines

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4
Q

Describe active solar heating

A

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.

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5
Q

Describe passive solar heating.

A

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.

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6
Q

Describe how solar thermal engines work

A

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.

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7
Q

Name the three components in a solar thermal system

A
  1. Solar collector
  2. An energy transfer system (via a heat transfer fluid)
  3. Storage tank
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8
Q

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

A

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.

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9
Q

Describe how photovoltaic works.

A

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

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10
Q

What are the three ways sunlight strikes the earth

A

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

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11
Q

Describe what direct sunlight is

A

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

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12
Q

Describe what diffused sunlight is

A

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

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13
Q

Describe what reflected sunlight is

A

This is when sunlight strikes the earth and is reflected

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14
Q

What is the ideal orientation for solar collectors

A

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.

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15
Q

Describe how a single axis tracker maximizes output

A

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.

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16
Q

4 disadvantages of single axis tracking

A
  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
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17
Q

2 advantages of single axis tracking

A
  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.
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18
Q

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

A

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.

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19
Q

4 disadvantages of dual axis tracking

A
  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
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20
Q

2 advantages of dual axis tracking

A
  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.
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21
Q

How does a flat plate operate

A

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.

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22
Q

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

A
  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.
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23
Q

State the operations of a evacuated tube

A
  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
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24
Q

State the 6 advantages of an evacuated tube

A
  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
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25
Q

State 2 disadvantages of evacuated tubes

A
  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
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26
Q

State the equation for area required for roof space.

A

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

27
Q

State the equation for energy required

A

Re= Ereq x % from renewables in decimal form

28
Q

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

A

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

29
Q

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

A

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

30
Q

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

A

A silicon wafer with excess electrons to provide a negative charge

31
Q

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

A

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

32
Q

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

A

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

33
Q

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

A

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

34
Q

What is the 3 roles of the silicon wafer producing electricity

A
  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.
35
Q

What are the 4 material types of solar PV modules

A

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

36
Q

How can a monocrystalline cell be identified

A

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

37
Q

How can a polycrystalline cell be identified

A

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

38
Q

What are he three types of thin solar cells

A

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

39
Q

Advantages and disadvantages of monocrystalline ( cost, longevity and efficiency

A

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

40
Q

Advantages and disadvantages of polycrystalline ( cost, longevity and efficiency

A

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

41
Q

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

A
  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
42
Q

Explain the Planning permission for roof mounted panels on pitched roof

A
  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
43
Q

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

A

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

44
Q

Explain the planning permission for wall mounted panels

A

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

45
Q

Explain financial incentives like the green deal

A

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

46
Q

Explain financial incentives like the feed in tariff

A

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.

47
Q

What are the three incentives to use renewable energy

A

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

48
Q

What are the 4 passive solar design techniques

A

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

49
Q

explain how window placement and orientation works in passive solar design

A

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.

50
Q

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

A

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.

51
Q

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

A

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

52
Q

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

A

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

53
Q

what are the operations of a parabolic trough and fresnal reflectors

A

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

54
Q

How does a parabolic trough work

A

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

55
Q

How does a fresnal reflector work

A

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

56
Q

How does a dish work

A

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

57
Q

What are the three Concentrating solar power systems

A
  1. Solar dish
    2.Fresnal reflector
    3.parabolic trough
58
Q

What is the definition of reliability

A

consistently good in quaility or performance; can be trusted

59
Q

What is the definition of intermittent

A

occuring at irregular intervals not continues or steady

60
Q

Are wind and solar intermittent or reliable

A

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.

61
Q

When will energy storages need to be used and why

A

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

62
Q

State 4 advantages of energy storage

A

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

63
Q

What is CSP

A

Concentrated solar power

Environmental technology (9 decks)

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