Solar Power (Thermal) Part 1 Flashcards
What is passive solar energy?
Passive solar energy refers to the use of incident solar energy without the direct use of mechanical of electrical devices.
What are the 3 types of passive design?
Direct gain, indirect gain and isolated gain
What is indirect gain?
If large fluctuations in heat and light by direct gain will make the building uncomfortable it may be better to use indirect gain. eg trombe wall
What is isolated gain?
These designs are usually built as an add-on structure but may be embedded in the initial design. e.g. courtyards, conservatories & atria
What are some features of direct gain?
Devices like overhanging skirts on the roof shade the sun in summer and allow light in the winter
Shutters on windows keep sunlight out and can prevent overheating
What are some features of indirect gain?
Transparent
Thin air gap
Inner wall with high specific heat capacity
Isolated from ground and any metal framework
One way ventilation slots
What are some features of isolated gain?
Glazed roof, used in commercial buildings, protected from the weather
What are the 5 main components of passive energy design?
Apertures – windows
Absorbent materials – dark surfaces
Heat store – bricks, concrete
Distribution system - ventilation, reflective surfaces
Control mechanisms – sun shades, opening windows, shutters
What are the properties of glass?
glass is transparent to visible light and opaque to the IR radiation
What is the daylight factor?
The daylight factor (DF) is used to express how much of the externally available sunlight enters a building.
DF% = (internal light present / external light available ) x 100
What contributes to the daylight factor?
direct sunlight, externally reflected light and internally reflected light
What are the advantages of passive systems?
Good designs result in reduced electricity/heating bills
Simple in their design
Little or no maintenance required
Usually inexpensive if incorporated into initial building design
Pay-back periods are short to moderate.
Reduces emissions in comparison to conventional systems.
Reduces dependence on fossil fuels by a large amount
What are the disadvantages of passive systems?
Can be expensive if retrofitted to an existing dwelling.
Reduced efficiency if dwelling is not south facing.
Nearby obstructions such as trees and buildings may reduce the passive heat and light gains.
Dependant upon the local climate
What are 3 basic components of a solar water heater?
solar collection panel
circulating/pumping system
storage tank
What are the advantages of solar water heaters?
Applicable to most buildings
Thermosyphon systems are low/moderate cost
Life span relatively long term for both pumped and thermosyphon systems.
Grants and subsidies available often available
It is possible to make your own system.
Zero emissions for the thermosyphon system and very low emissions for the pumped systems
Negates the need to burn a large amount of fossil fuels therefore reducing carbon emissions, saving resources and money.
What are disadvantages of solar water heaters?
Erosion/fouling may take place.
Installed systems may be intrusive.
Pumped systems are moderate/high cost
Pumped systems may require more maintenance.
Low to moderate efficiency.
Potential hazard to the environment or people if a toxic transfer fluid is used.
What features are in a flat plate solar water heater?
Heat loss is greatly reduced by the insulation provided by glazing
Glazing protects system from weather
Can be used to heat the domestic water supply for space heating in homes
What features are in a flat plate solar air heater?
Similar to flat plate water heaters but heats air as opposed to water, so it has a similar design to a trombe wall
Less efficient than flat plate water heaters
Warm air heats a building or water supply
What features are in an evacuated tube solar water heater? (E.T.S.W.H)
Transfer fluid flows down copper pipes inside a pair of concentric glass tubes. There is a sealed vacuum between two glass tubes.
The surface of the inner glass tube is coated with a dark absorbing material
Describe a electrically pumped E.T.S.W.H
Sensors are used on the solar collector when pipes are hot
The fluid is pumped to a hex where i the transfer fluid cools by heating water for domestic water supply
Electric immersion coil maintains tank temperature
Describe a thermosyphon system?
Water flows from the tank down into the pipes at the bottom of the collection panel where its heated by the sun. The warmer water rises by convection exiting from the top of the collection panel back into the storage tank.
Top up immersion heaters can also be used o these systems
Describe with the aid of diagrams the main features of a glazed flat plate solar concentrator as a commonly used for heating water.
Glazed flat plate solar concentrators consist of a series of tubes enclosed inside a glazed frame. The surfaces inside the frame are usually dark in colour to maximise the absorption of solar radiation. The glazing on the top prevents heat loss, as does the insulation underneath the frame.
