Solar Thermal Glossary

AAV
Automatic Air Vent. This is an air valve that automatically releases air from the system without any manual intervention.

Absorber
The blackened surface in a collector that absorbs the solar radiation and converts it to heat energy.

Aperture
Area on the solar panel that collects energy. When solar collectors are tested the energy collected is measured against the aperture area. When comparing collectors a reference area is important - that is, the surface area from whish the collectors characteristic values are drawn. In the collector test methods according to EN 12975 the reference area is equal to either the aperture area or the absorber area.

Active System
A solar heating or cooling system that requires external mechanical power to move the collected heat.

Ambient Temperature
The temperature of the surrounding air.

Auxiliary Heat
The extra heat provided by a conventional heating system for periods of
cloudiness or intense cold when a solar heating system cannot provide enough.

Azimuth
The angular distance between true south and the point on the horizon directly below the sun.

British Thermal Unit - BTU
The quantity of heat needed to raise the temperature of one pound of water one degree Fahrenheit.

Calorie
The quantity of heat needed to raise the temperature of one gram of water one degree Celsius.

Collector
The collector or panel usually is positioned on the roof of you house. When solar radiation falls on the collector it is absorbed by the selective coating on the absorber plate. This turns solar radiation or light into heat.

Collector Efficiency
The ratio of usable heat energy extracted from a collector to the solar energy striking the cover.

Concentrating Collector
A device which concentrates the sun's rays on an absorber surface which is significantly smaller than the overall collector area.

Controller
This is the brain of the system. The controller monitors the temperature in the collectors and in the bottom and top of the storage cylinder. When it is warmer in the collectors than the bottom of the storage cylinder the controller turns on the solar pump and pumps the heat round from the collectors to your storage cylinder, where it is stored ready for you to use.

Diffuse Radiation
Indirect sunlight that is scattered from air molecules, dust and water vapor.

Direct Radiation
Solar radiation that comes straight from the sun, casting shadows on a clear day.

Evacuated Tube
See Vacuum Tube.

Expansion Vessel
A large steel drum with a rubber balloon inside. This rubber balloon inflates and deflates with Tyfocor GLS as the solar system warms up and cools down. The expansion vessel is designed to take and thermal expansion and contraction that happens in the solar circuit.

Flat Plate Collector
A solar collection device in which sunlight is converted into heat on a plane surface without the aid of reflecting surfaces to concentrate the rays.

Heat Exchanger
A device, such as a coiled copper tube immersed in a tank of water, that is used to transfer heat from one fluid to another through a separating wall.

Indirect System
The solar circuit is called an indirect system and refers to the heat exchanger inside your storage cylinder. It is the most common form of solar water heating system. The storage cylinder is manufactured with two heat exchangers inside. The highest one is what the hot water from the boiler flows through (the boiler will heat 70% of the cylinder) and the lower heat exchanger is what the solar systems Tyfocor flows through (the solar system will heat 100% of the cylinder). The heat exchanger allows water from the boiler and Tyfocor from the solar circuit to pass through, but not mix with the water in the storage cylinder itself. Thus, in effect, it really consists of three systems that appear to join at the storage cylinder.

Insolation
The total amount of solar radiation direct, diffused and reflected-striking a surface exposed to the sky.

Night Time Cooling
The cooling of a building or heat storage device by the radiation of excess heat into the night sky.

Pressure Gauge
Informs the user about the current pressure in ‘bar’ in the solar circuit. The black hand will point to the systems pressure. This gauge will normally read 1-1.5 bar. It can read as high as 6 bar. It should never read 0. If it does turn off the solar system and call Green Systems UK.

PRV
Pressure Relief Valve. This is a safety valve that will only open up and release liquid if the pressure in the system becomes to great and reaches 6 bar.

Pump
The solar pump is usually located in your airing cupboard or in the loft space. It is a different pump to your central heating pump. The solar pump will only work when there is heat to be transferred from the collectors to the cylinder.

Radiation
The flow of energy through open space via electromagnetic waves, such as visible light.

Reflected Radiation
Sunlight that is reflected from surrounding trees, terrain or buildings onto a surface exposed to the sky.

Retrofitting
The application of a solar heating or cooling system to an existing building.

Scale Inhibitor
Fitted inline to the storage cylinder. This inhibits scale formation in the cylinder increasing life expectancy and efficiency of the product.

Selective Coating or Surface
This is where the science is in new solar collectors and makes them much more efficient than solar collectors of years gone by. The selective coating is a special paint that absorbs solar radiation and doesn’t let much reflect out again. It absorbs radiation of one wavelength (for example, sunlight) but emits little radiation of another wavelength (for example, infrared). This way most of the radiation that falls onto the collector is turned into heat.

Solar Radiation (Solar Energy)
Electromagnetic radiation emitted by the sun.

Standby Heat Loss
Heat lost though storage tank and piping walls.

Storage Cylinder
This is where all the heat collected during the day is kept. The storage cylinder is usually sited where your old cylinder was. Warm water is stored here for you to use when washing or bathing.

Tilt Angle
The angle that a flat plate collector surface forms with the horizontal plane.

TMV
Thermostatic Mixing Valve. This valve located in you airing cupboard near the storage cylinder will mix cold water with the hot water coming out of the cylinder. This will reduce the risk of scalding and allow the solar to store temperatures of 85 degrees C in the cylinder. You can change the temperature of the hot water coming out of you cylinder by rotating the knob on top of the TMV.

Tyfocor GLS
Tyfocor GLS is a solar anti-freeze that flows through the pipes on the solar circuit. It is designed to protect down to –28 degrees C. It can also withstand very high temperatures that occur in solar thermal systems without degrading. Tyfocor GLS is not a harmful product.

Vacuum Tube
Vaccum tubes are solar collectors with the absorber surface coating sealed inside a vacuum. Collectors that are produced like this have better insulation and can produce more energy per m2 of aperture area compared to flat plate collectors. This does vary on the brand used, some vacuum tubes do not produce as much energy as flat plates.

"Only after the last tree has been cut down, the last river poisoned, the last fish caught. You will find that money cannot be eaten." Cree Prophecy