Ch 8: Energy from the Sun Flashcards
What are the components on a solar thermal system?
A solar collector, an energy transfer system and a storage tank.
What are the 2 types of solar collectors?
Flat plate solar collectors and evacuated tubes.
What are the benefits of a passive solar heating system?
- Where high solar radiation occurs the heat transfer fluid receives energy more quickly and its temperature rises rapidly.
- No pumps are required reducing initial costs and running costs.
- The system tends to have less maintenance requirements. But to ensure this the storage tank must be placed above the collector.
What are the benefits of an active thermal heating system?
- Storage tanks isn’t placed on the solar collector so it reduces the visual impact.
- Can be better insulated.
What does solar PV stand for?
Solar PhotoVoltaic
Where can solar PV systems be used?
- Remote homes where connection to the grid may not be possible or expensive.
- Communications satellites in space.
- Communications and remote monitoring of infrastructure on earth.
What is a single axis tracking system?
Allows the solar collectors to turn towards the east or west to track the sun’s positioning during the course of the day. It is positioned on the north west axis.
What are the advantages of single axis tracking system?
- Energy output is higher by as much as 25%.
- The repayment period is reduced.
What are the disadvantages of single axis tracking system?
- Expensive as there are complex mechanical and electrical equipment required.
- Some of the electricity produced from the system is used for the tracking system.
- Restricted to higher solar radiation regions.
- When the front panel faces the sun, the back panel will have a shadow.
What is a dual axis tracking system?
It is built onto the single axis tracking system. This tracking system has an additional degree of rotation which lies on the east west plane, which allows the system to be rotated on the north south plane which more closely aligns the collectors with the sun.
What are the advantages of a dual axis tracking system?
- The energy output will be higher by as much as 35% in warmer climates.
- The repayment periods are reduced.
What are the disadvantages of a dual axis tracking system?
- Expensive as there are complex mechanical and electrical equipment required.
- Some of the electricity produced from the system is used for the tracking system. The quantity of energy required is greater than single axis tracking system.
- Restricted to higher solar radiation regions, which makes it unfeasible in NI.
- When the front panel faces the sun, the back panel will have a shadow. This happens in the EW plane and the NS plane so less panels can be installed per unit area.
How can an automated solar tracking system maximise the energy output from the solar collectors?
- 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.
- It can track the annual variations in the sun’s position during years.
- It can adjust according to location in northern or southern hemispheres.
What is the operation of a flat plate collector?
The sun’s energy is captured by the absorber plate and transferred to the water which heats up a tank in a house.
What is the use of a glazing sheet on a flat plate collector?
- Increase the solar radiation transmitted through it to the absorber plate.
- Reduce as far as possible the heat losses back through conduction and convection.
- Protect the system from rain and weather conditions.
What are the advantages of a flat plate collector?
- Cheapest collector.
- Suited to colder environments.
- The efficiency of converting solar energy into thermal energy is good at around 80%.
What are the disadvantages of a flat plate collector?
- Heat losses even with insulation.
- Efficiency drops in warmer weather (above 30 C).
- Requires 2 people to install.
- Will only be directly facing the sun once per day as the collector is flat.
- The weight of the panel and the heat transfer fluid can impose loads on the roof.
What are the advantages of an evacuated tube solar collector system?
- The tubes are circular so they face the sun for most of the day.
- Heat losses through conduction and convection are almost 0.
- Less load on the roof as the system is not fully filled with the heat transfer fluid.
- Higher efficiencies at almost 90%.
- One person needs to install.
- Can be stored vertically, so transportation costs are low.
What are the disadvantages of an evacuated tube solar collector system?
- Higher cost than a flat plate collector.
- Not able to melt snow hue to lower heat losses through conduction and convection.
What are the comparisons of the 2 types of solar collectors?
- Both solar collectors transfer solar energy to water in a storage tank via a pipe network containing a fluid, often water.
- In a flat plate collector, the absorber plate is in direct contact with the pipe network. In evacuated tube collector, the absorber plate is contained in a vacuum tune and is not in direct contact with the pipe network.
- Evacuated tube solar collectors are more efficient that flat plate collectors. A smaller area of evacuated tube solar collectors is required to deliver the same heat energy as flat plate solar collectors.
What are the factors which should be considered when calculating the roof area required to install solar collectors?
- Solar radiation levels
- Shading
- Collector type
- Family size
- Lifestyle of users
What are the benefits to households of installing a flat plate solar collector?
- Reducing environmental impact
- Reduced costs
- Energy security
What is the main benefit to a household of installing a flat plate collector?
The primary advantage of the flat plate collector compared to the evacuated tube is cost. While it is less efficient, it costs less.
What is the role of the glass on a PV cell?
Offers a protective coating for the top layer of the PV cell, keeping out water and dirt to ensure the transmission of the incident radiation into the glass to reach the n-type layer.
What is the role of the anti-reflective coating on a PV cell?
Maximises the quantity of photons absorbed by the PV cell and therefore minimises the amount of reflection back off the panel. This ensures maximum efficiency of the PV cell.
What is the role of the front metal contacts on 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.
What is the role of the N-type layer on a PV cell?
A silicon wafer doped such that is has an excess of electrons and so can be considered a negative charge provider.
What is the role of the depletion zone on a PV cell?
A region over which a potential difference and hence electric field exists. This zone acts as the driving force to push electrons around the circuit.
What is the role of the P-type layer on a PV cell?
A silicon wafer doped such that it has a shortage of electrons and so can be considered a positive charge provider.
What is the role of the rear metal contacts on a PV cell?
The underside of the p-type layer has a metal contact which is required to provide a complete conductive path around the circuit.
What is the operation of a PV cell?
1.When solar radiation falls on the silicon 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. 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, i.e. the depletion zone.
What are the 4 material types of PV modules?
- Thick film
- Thin film
- Monocrystalline
- Polycrystalline
What are the advantages of monocrystalline PV systems?
- Longevity: long lasting as they last up to 25 years.
- Efficiency: has the highest efficiency of 22%
What are the disadvantages of monocrystalline PV systems?
Cost: the most expensive solar cells.
What are the advantages of polycrystalline PV systems?
- Cost: lower cost than monocrystalline cells.
- Longevity: long lasting as they last up to 25 years.
What are the disadvantages of polycrystalline PV systems?
Efficiency: lower efficiency than monocrystalline which is 18-20%
What are the advantages of thin film PV systems?
Cost: falls between monocrystalline and polycrystalline cells.
What are the disadvantages of thin film PV systems?
- Longevity: lower longevity than mono and poly.
- Efficiency: lowest efficiency of 7-13%.
How can planning permission affect the installation of solar panels?
- No part of the solar panel much protrude beyond the edge of the roof.
- The solar panel must not exceed the highest part of the roof.
- The solar panel must not be visible from the road if the house is situated within a conservation area or world heritage site.
- Must not exceed 1.5m above the plane of the roof.
What are the range of financial incentives available to homeowners installing solar panels?
- Green deal
- Feed in tariff / NI renewable obligations certificate
- NI renewable heat incentives
What is green deal as a financial incentive for solar panel installation?
Financial assistance towards cost of installing solar panels.
What is feed in tariff as a financial incentive for solar panel installation?
Where homeowners are paid for the amount of electricity they generate and feed back into the grid.
What is NI renewable heat incentives as a financial incentive for solar panel installation?
Where homeowners are paid for the amount of heat they generate using their own solar thermal panels.
What are the passive solar design techniques that can be applied to new and existing buildings?
- Window placement and orientation
- Size and glazing type
- Thermal mass
- Thermal insulation
How can window placement and orientation be applied to new and existing buildings?
Larger windows should be placed in rooms that are used a lot during the day, preferably if these rooms are due south. This will maximise solar gains during the day. Smaller windows should be placed in bedrooms and these should face due north which will reduce thermal losses at night.
How can size and type of glazing be applied to new and existing buildings?
The use of low emissivity glass is critical as it reduces heat losses through the windows. This can also be the use of thin solar cells which produce a small amount of electricity while also being transparent to let solar radiation through.
How can thermal mass be applied to new and existing buildings?
If high thermal mass materials such as marble are used above the fireplace or the oven, during the day they will absorb thermal energy and at night they will distribute heat throughout the room.
How can thermal insulation be applied to new and existing buildings?
Important to maximise thermal insulation in the house as it will reduce heat losses through the walls, windows and roof of the house.
What does CSP stand for?
Concentrating Solar Power
What is the operation of CSP systems?
- Reflect solar radiation to a specific point where a heat transfer fluid absorbs the energy. If it is water it will turn to steam but if it is an antifreeze it will transfer energy to water via a heat exchanger.
- This steam is then used to drive a steam turbine as per a conventional power plant. this steam turbine is connected to a generator. This generator turn and inside electromagnetic induction takes place to produce electricity.
What are the types of CSP systems?
- Parabolic troughs
- Fresnel reflectors
- Parabolic / solar dish
What is a parabolic trough?
A parabolic shaped mirror tracks the Sun’s motion during the day. This system must track the Sun as it relies upon the direct radiation from the Sun. When the Sun’s radiation strikes the mirror, it is reflected.
What are fresnel reflectors?
The Fresnel reflectors work along the same principles as the parabolic trough. They reflect the Sun’s radiation towards a fixed receiver tube, which has a heat transfer fluid circulated through it. The reflectors in this case are much more simplistic in design and are a flat plate. As these reflectors reflect the Sun’s direct radiation, they must also track the Sun during the course of the day.
What is a parabolic / solar dish?
Another approach is to locate the generator itself at the focal point of the mirror. This method is utilised in a parabolic dish (also called solar dish). In this method the Sun’s radiation, again direct radiation, strikes the surface of the mirror and is reflected to the focal point. At this focal point an engine is located which absorbs the Sun’s radiation. This energy heats a fluid inside the engine and under repeated expansion and contraction, a piston is forced to move backwards and forwards repeatedly. This motion is used to turn a generator which produces electricity.
