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Environmental Tech > Chapter 8 > Flashcards

Chapter 8 Flashcards

1
Q

Equation for power

A

Power=energy/time
Energy=power x time

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2
Q

Equation for total energy

A

Total energy= solar energy received per m2 per year x total area in m2

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3
Q

What are the 3 types of solar thermal

A

Active solar heating
Passive solar heating
Solar thermal engines

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4
Q

What are the 3 components in a solar thermal system

A

Solar collector
An energy transfer system
Storage tank

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5
Q

Where are passive solar thermal systems used

A

Hotter climates and active is not used here in the Uk as it is not a hot climate

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6
Q

What is solar PV

A

Solar PV takes energy from the sun and produces electricity directly it is often used in rural areas as well as space and waste water treatment works

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7
Q

What is solar thermal

A

It takes energy from the sun and heats a transfer fluid which is then used in a number of different ways

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8
Q

What 3 ways does solar radiation hit the earth

A

Direct radiation
Diffuse radiation
Reflected radiation

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9
Q

Advantages of single axis tracking

A

Higher energy output
Higher output means the repayment period is reduced

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10
Q

Disadvantages of single axis tracking

A

Expensive
Can only be installed in high solar radiation areas
Panel beside needs to be spaced further away to avoid shadow

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11
Q

What are the advantages of dual axis tracking in solar systems

A

The energy output will be much higher
Higher output means reduced repayment periods

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12
Q

What are the disadvantages of dual axis tracking systems

A

Complex electrical and mechanical equipment is required this increases the price
The quantity of energy required for its operation is larger than in single axis tracking system

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13
Q

Advantages of solar flat plate collector

A

Cheapest collector available
It is suited to colder environments where snowfall is likely, this is because the snow can be melted due to conduction and convection heat losses from the panel
Efficiency of converting solar energy into thermal energy is 80%

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14
Q

Disadvantages of flat plate collector

A

Heat losses
At higher temperatures the efficiency of the collector drops especially over 30 degrees
Installation requires at least 2 ppl
As the surface is flat it will will only be facing the sun once per day
Can impose considerable loads onto a roof

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15
Q

Explain the operation of a flat plate solar collector

A

Cold water is pumped into the collector at a low level, it then travels up heat absorbing riser tubes.
The heat absorbed tubes are connected to an absorber plate which has a special black paint to maximise the systems absorption of solar radiation.
Under the absorber plate is insulation which reduces heat losses through conduction and convection.
The water then rises up the heat absorbing pipe and absorbs energy from the sun and absorber plate, this increases the temperature of the heat transfer fluid.
When this fluid reaches the top it leaves the panel to be pumped to the hot water tank within the house.

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16
Q

What are the 3 roles of the glazing sheet on top of flat plate solar collectors

A

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

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17
Q

Explain how the evacuated tube solar collector works

A

A double walled glass circular cylinder called the evacuated tube contains an absorber plate connected to a copper heat pipe.
The evacuated tube contains a vacuum between the two glass walls which reduces heat losses via conduction and convection to almost zero
Solar radiation strikes the absorber plate and energy is transferred to the copper heat pipe
The copper pipe contains an enclosed cavity which is partly filled heat transfer fluid in liquid form.
When the absorber plate transfers energy to the copper heat pipe the heat transfer fluid is heated. At the lower end of the copper heat pipe the heat transfer fluid increases in temp evaporating into a gas which rises up the tube because of convection.
Once the gas reaches the top of the copper heat pipe which is embedded in the copper manifold heat exchanger which has water circulating through it.
The high temperature vapour loses energy to the colder water in the copper manifold heat exchanger. The vapour condenses back into a liquid when sufficient energy is transferred to the water
The heat transfer fluid now in liquid form travels back to the bottom of the tube due to gravity
This cycle will repeat itself if there is continued solar radiation

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18
Q

Advantages of an evacuated tube

A

It’s circular geometry result in the tube facing the sun most of the day
Heat losses through conduction and convection are almost zero
There is less weight put on the roof
It has a very high efficiency at 90% when the temperatures are high
Can be installed by one person

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19
Q

Disadvantages of evacuated tube

A

Higher cost than flat plate
Not able to melt snow as easy due to the lower heat losses

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20
Q

5 factors that affect area of solar collectors required

A

Solar radiation levels
Shading
Collector type
Family size
Lifestyle of users

21
Q

Benefits of households installing flat plate solar collectors

A

Reduced costs as you don’t have to pay for fossil fuels to power ur house
Energy security- protected from fluctuations in energy price

22
Q

Role of glass in a PV cell

A

Offers protective coating for top layer of PV cell and allows light through due to it being transparent

23
Q

Role of anti reflective coating in a PV cell

A

Maximises the quantity of photons absorbed by the PV cell and therefore minimises the amount of reflection of the cell, this maximises efficiency

24
Q

Role of front metal contacts in a PV cell

A

Provide a highly conductive path for the electrons to travel from the top of the PV cell through the external load to the rear metal contact

25
Q

Role of N-type layer in PV cell

A

A silicon wafer is doped such that it has an excess of electrons making it negatively charge provider

26
Q

Role of depletion zone in PV cell

A

This zone acts as a driving force to push electrons around the circuit

27
Q

P-type layer role in PV cell

A

Provides a positive charge as it has and excess in protons

28
Q

Role of rear metal contact in a PV cell

A

Provides a complete conductive path around the circuit

29
Q

PV cell operation key principles

A
  1. When solar radiation falls on the silicon p-n junction some of the photons can create electron-hole pairs through 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. Contacts on either side of the PV 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 ie the depletion zone
30
Q

What are the four material types of PV modules

A

Monocrystalline
Polycrystalline
Thick film
Thin film

31
Q

What are the three types of thin solar PV cells

A

Amorphous silicon
Copper indium gallium diselenide
Cadmium telluride

32
Q

What is the difference between thin modules and thick modules

A

Thick modules silicon wafers are a few hundred microns thick whereas thin modules have wafers as thin as one micron

33
Q

Advantages of monocrystalline

A

Higher efficiency compared to other forms
Good longevity- up to 25years

34
Q

Disadvantages of monocrystalline

A

Expensive compared to other forms
Involves specialised equipment and personnel to install
Time consuming to make sure there are no impurities which would reduce efficiency
Takes a lot of energy to install which increases cost

35
Q

Polycrystalline advantages

A

Cheaper than monocrystalline
Good longevity
Easier manufacturing process than monocrystalline

36
Q

Polycrystalline disadvantages

A

Reduced efficiency due to higher resistance

37
Q

Thin cells advantages

A

Cheaper than monocrystalline
Efficiency does not drop at higher temperatures like monocrystalline and polycrystalline

38
Q

Thin cell disadvantages

A

Don’t have as long a warranty
Lower overall efficiency
More expensive than polycrystalline

39
Q

What is the reason for differing efficiencies in monocrystalline and polycrystalline

A

Monocrystalline has a single silicon cell meaning their is less resistance for electricity so their is a higher efficiency. Polycrystalline is made up of multiple grains between each grain is a grain boundary which increases resistance which decreases efficiency.

40
Q

What are the bonuses for households installing solar panels

A

The green deal- this gives households loans to install the solar system this is paid back by fuel savings from installing the panels
Feed in tariff- this allows owners of solar systems to sell electricity back to the grid which can make them more money
NI renewable heat incentive- this scheme gave money to ppl who heated there homes using renewable energy

41
Q

What is the best way to position windows in order to have passive solar gain

A

Large windows should be put in rooms used a lot and they should be facing south or within 15 degrees of south this will maximise solar gain
Smaller windows should be placed in bedrooms or other rooms this will minimise heat losses at night

42
Q

What is the best type of glass for windows

A

Low emissivity glass as it reduces heat losses the best

43
Q

Why are high thermal mass materials better in passive solar design

A

During the day these materials absorb the suns energy and can stop the room from becoming to hot
At night the material will transfer the energy into different rooms this helps keep the house warm and reduces the need for heating

44
Q

Name the two CSP systems

A

Parabolic trough
Fresnel reflector

45
Q

Explain the operation of CSP systems

A

They reflect solar radiation to a specific point where a heat transfer fluid absorbs energy. The heat transfer fluid if water will convert directly into steam. If it is antifreeze it transfers the energy to water via a heat exchanger so the water turns into steam.
This steam will then be used to drive a steam turbine as per a conventional power plant. The steam turbine is connected to a generator. The generator turns and inside the electromagnetic induction takes place to produce electricity

46
Q

What is active solar heating

A

This takes energy from the sun and is used to heat domestic hot water

47
Q

What is passive solar heating

A

This involves taking energy from the sun and circulating the energy naturally around the building environment

48
Q

What is solar thermal engines

A

This involves taking energy from the sun and using it to heat a fluid however this form is used in warmer environments

Environmental Tech (11 decks)

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