Solar Flashcards
Define the solar declination angle.
The angle between the Sun’s rays and the equatorial plane.
Define the solar azimuth angle.
The azimuth angle is the compass direction from which the sunlight is coming.
Define the solar altitude angle.
The angular height of the sun in the sky measured from the horizontal.
Define solar time.
Reckoning of the passage of time based on the sun’s position in the sky. Units - Day.
Define solar spectrum.
Solar radiation is all of the light and energy that comes from the sun, and there are many different forms. The electromagnetic spectrum explains the different types of light waves that are emitted from the sun.
Describe the components of a concentrating solar power plant.
The key features of a concentrating solar power plant are the heliostats and the solar receiver. The heliostats are devices, normally featuring a control system, which focus the sun’s direct beam irradiance onto a common point. This common point is known as the solar receiver. Depending on the system, the solar receiver is either a boiler system itself, or it contains a working fluid which can be heated, circulated and stored to produce a constant electrical output, using heat exchange and a steam cycle.
As well as these components, the system will always have a boiler/steam generator, a turbine and an electrical generator. The system also requires a storage unit for the working fluid of the steam cycle.
Feedwater heating may also be applied to give a further rise to efficiency levels.
Differentiate between isotropic and anisotropic sky conditions in the context of inclined surface solar irradiance prediction and state why the latter case gives rise to modelling complexity.
Isotropic: Uniform brightness
Anistropic: Non-uniform brightness
Difficulty in calculating the diffuse component of solar heat gains.
Give one means by which the efficiency of the PV panels could be improved, also briefly explaining why the efficiency improves.
Making the surface inclination to between 30 and 45 degrees dependant on location. This is the optimal angle in which a non-tilting solar panel south facing can maximise the sun within the northern hemisphere.
Explain how concentrating solar power plant, making use of an intermittent resource, could be reconfigured
to provide a steady supply of electrical power over 24 hours.
Reconfigure by changing from water system to use silica sand or salt as thermal storage and heat transfer medium for concentrated solar power (CSP).
● Opposed to concentrating the heat directly to a boiler system, the furnace will heat a salt solution to be circulated and stored.
● Energy can be gathered during the day, when maximum generation occurs, then the use of storage permits continuous generation at a reduced output level day and night.
State whether a solar concentrating power plant would be viable in a climate such as Glasgow’s and explain your answer.
Radiation from the sun reaches the earth’s surface in two forms: Beam Radiation and Diffuse Radiation.
● Only beam radiation can be focused, which means that this is the vital radiation needed for the operation of a solar power plant.
● Glasgow rarely has clear skies, which means that the there is more diffuse radiation than beam radiation.
● Thus a concentrating solar power plant is not viable in a climate such as Glasgow.
● Additionally, large scale derelict land is required to collect the energy.
In solar irradiance calculations, which solar energy quantities are normally available as input and which are normally calculated?
Known:
- Direct horizontal
- Direct normal
- Diffuse horizontal
- Global horizontal
- Ground reflectivity
Unknown:
- Direct radiation
- Diffuse radiation
- Ground reflected radiation
Describe the fundamental efficiency limitation affecting single juntion PV cells.
The Shockley-Queisser Limit refers to the maximum theoretical efficiency of a solar cell using a single p-n junction to collect power from the cell. Efficiency is limited by the band gap of the solar cell material. Maximum efficiency reached so far is around 34%. Most energy is lost through heat and as the temperature of the cell increases the band gap decreases.
How does ocean thermal energy conversion work?
- Extracts energy from the difference in temperature between the surface of the sea and deep water (typically 5, can be up to 29 degrees in the tropics)
- this powers a heat engine by which a temperature difference creates electricity
- Not a proven technology, could prove costly
- A 250 MW plant could produce 300 million litres of drinking water a day
