Chapter 8 Flashcards
Equation for power
Power=energy/time
Energy=power x time
Equation for total energy
Total energy= solar energy received per m2 per year x total area in m2
What are the 3 types of solar thermal
Active solar heating
Passive solar heating
Solar thermal engines
What are the 3 components in a solar thermal system
Solar collector
An energy transfer system
Storage tank
Where are passive solar thermal systems used
Hotter climates and active is not used here in the Uk as it is not a hot climate
What is solar PV
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
What is solar thermal
It takes energy from the sun and heats a transfer fluid which is then used in a number of different ways
What 3 ways does solar radiation hit the earth
Direct radiation
Diffuse radiation
Reflected radiation
Advantages of single axis tracking
Higher energy output
Higher output means the repayment period is reduced
Disadvantages of single axis tracking
Expensive
Can only be installed in high solar radiation areas
Panel beside needs to be spaced further away to avoid shadow
What are the advantages of dual axis tracking in solar systems
The energy output will be much higher
Higher output means reduced repayment periods
What are the disadvantages of dual axis tracking systems
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
Advantages of solar flat plate collector
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%
Disadvantages of flat plate collector
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
Explain the operation of a flat plate solar collector
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.
What are the 3 roles of the glazing sheet on top of flat plate solar collectors
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
Explain how the evacuated tube solar collector works
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
Advantages of an evacuated tube
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
Disadvantages of evacuated tube
Higher cost than flat plate
Not able to melt snow as easy due to the lower heat losses
5 factors that affect area of solar collectors required
Solar radiation levels
Shading
Collector type
Family size
Lifestyle of users
Benefits of households installing flat plate solar collectors
Reduced costs as you don’t have to pay for fossil fuels to power ur house
Energy security- protected from fluctuations in energy price
Role of glass in a PV cell
Offers protective coating for top layer of PV cell and allows light through due to it being transparent
Role of anti reflective coating in a PV cell
Maximises the quantity of photons absorbed by the PV cell and therefore minimises the amount of reflection of the cell, this maximises efficiency
Role of front metal contacts in a PV cell
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
Role of N-type layer in PV cell
A silicon wafer is doped such that it has an excess of electrons making it negatively charge provider
Role of depletion zone in PV cell
This zone acts as a driving force to push electrons around the circuit
P-type layer role in PV cell
Provides a positive charge as it has and excess in protons
Role of rear metal contact in a PV cell
Provides a complete conductive path around the circuit
PV cell operation key principles
- When solar radiation falls on the silicon p-n junction some of the photons can create electron-hole pairs through photoelectric effect
- 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
- 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
What are the four material types of PV modules
Monocrystalline
Polycrystalline
Thick film
Thin film
What are the three types of thin solar PV cells
Amorphous silicon
Copper indium gallium diselenide
Cadmium telluride
What is the difference between thin modules and thick modules
Thick modules silicon wafers are a few hundred microns thick whereas thin modules have wafers as thin as one micron
Advantages of monocrystalline
Higher efficiency compared to other forms
Good longevity- up to 25years
Disadvantages of monocrystalline
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
Polycrystalline advantages
Cheaper than monocrystalline
Good longevity
Easier manufacturing process than monocrystalline
Polycrystalline disadvantages
Reduced efficiency due to higher resistance
Thin cells advantages
Cheaper than monocrystalline
Efficiency does not drop at higher temperatures like monocrystalline and polycrystalline
Thin cell disadvantages
Don’t have as long a warranty
Lower overall efficiency
More expensive than polycrystalline
What is the reason for differing efficiencies in monocrystalline and polycrystalline
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.
What are the bonuses for households installing solar panels
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
What is the best way to position windows in order to have passive solar gain
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
What is the best type of glass for windows
Low emissivity glass as it reduces heat losses the best
Why are high thermal mass materials better in passive solar design
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
Name the two CSP systems
Parabolic trough
Fresnel reflector
Explain the operation of CSP systems
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
What is active solar heating
This takes energy from the sun and is used to heat domestic hot water
What is passive solar heating
This involves taking energy from the sun and circulating the energy naturally around the building environment
What is solar thermal engines
This involves taking energy from the sun and using it to heat a fluid however this form is used in warmer environments
