Solar Power (Thermal) Part 1

Question 1

What is passive solar energy?

Answer 1

Passive solar energy refers to the use of incident solar energy without the direct use of mechanical of electrical devices.

Question 2

What are the 3 types of passive design?

Answer 2

Direct gain, indirect gain and isolated gain

Question 3

What is indirect gain?

Answer 3

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

Question 4

What is isolated gain?

Answer 4

These designs are usually built as an add-on structure but may be embedded in the initial design. e.g. courtyards, conservatories & atria

Question 5

What are some features of direct gain?

Answer 5

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

Question 6

What are some features of indirect gain?

Answer 6

Transparent

Thin air gap

Inner wall with high specific heat capacity

Isolated from ground and any metal framework

One way ventilation slots

Question 7

What are some features of isolated gain?

Answer 7

Glazed roof, used in commercial buildings, protected from the weather

Question 8

What are the 5 main components of passive energy design?

Answer 8

Apertures – windows

Absorbent materials – dark surfaces

Heat store – bricks, concrete

Distribution system - ventilation, reflective surfaces

Control mechanisms – sun shades, opening windows, shutters

Question 9

What are the properties of glass?

Answer 9

glass is transparent to visible light and opaque to the IR radiation

Question 10

What is the daylight factor?

Answer 10

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

Question 11

What contributes to the daylight factor?

Answer 11

direct sunlight, externally reflected light and internally reflected light

Question 12

What are the advantages of passive systems?

Answer 12

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

Question 13

What are the disadvantages of passive systems?

Answer 13

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

Question 14

What are 3 basic components of a solar water heater?

Answer 14

solar collection panel
circulating/pumping system
storage tank

Question 15

What are the advantages of solar water heaters?

Answer 15

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.

Question 16

What are disadvantages of solar water heaters?

Answer 16

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.

Question 17

What features are in a flat plate solar water heater?

Answer 17

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

Question 18

What features are in a flat plate solar air heater?

Answer 18

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

Question 19

What features are in an evacuated tube solar water heater? (E.T.S.W.H)

Answer 19

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

Question 20

Describe a electrically pumped E.T.S.W.H

Answer 20

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

Question 21

Describe a thermosyphon system?

Answer 21

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

Question 22

Describe with the aid of diagrams the main features of a glazed flat plate solar concentrator as a commonly used for heating water.

Answer 22

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.