Solar Glossary
Aperture
The part of the collector through which light enters. For evacuated tubes this refers to the cross-sectional surface area of the outer clear glass tube measured using the internal diameter, not the outside diameter.
(Ex. 0.0548m x 1.72m = 0.094m2). 1.72m is the exposed length of the evacuated tube.
Absorber
The part of the collector that actively absorbs the light rays. For solar tubes this is defined as the cross-sectional area of the inner tube (selective coated) measured using the outside diameter. (Ex. 0.047 x 1.72m = 0.08m2) This value is used when calculating efficiency values. For solar tube collectors with reflective panels, the entire circumferential surface area of the inner tube is often used when calculating absorber area, as the reflective panel is supposed to reflect light onto underside of the evacuated tube.
Collector
A solar collector is not really a solar water heater. A solar water heater is a system which may include a tank, pump, controller and solar collector panel. A solar collector is that part of the system which absorbs the sun's energy and converts it into heat.
Delta-T Controller
Delta-T refers to the difference in two temperatures. This term is often use in relation to a solar controller. In such case the Delta-T is the difference between the solar collector temperature and the temperature of the water in the solar storage tank. A Delta-T controller can be configured to turn on the pump when the Delta-T difference exceeds a certain level (Eg.7oC / 12.7oF) and off again when the temperature difference drops below another setting (Ex. 2oC / 3.6oF). The controller turns on the pump when there is heat potential in the manifold. A Delta-T controller can also be used to provide freeze protection by circulating warm water from the tank through the manifold when the manifold temperature drops below 5oC.
Efficiency

Solar collector efficiency is usually expressed as a percentage value, or in a performance graph. When assessing a collector's performance make sure it is based on the correct surface area values. Ex. If performance values are based on gross area, then the gross area must be used when determining total heat output. IAM values have a significant influence on actual heat output throughout the day, and should be considered. Looking at just the percentage efficiency value will not give a true indication of daily heat output.

Efficiency testing is usually completed by testing bodies such as SPF, SRCC and other government approved testing bodies.

Tm* is the x axis value on performance graphs for solar collectors.
Tm* is calculated as:
(water temp - ambient temp)/Insolation
Ex. (44oC - 20oC)/800Watts = 0.03 

Flow Rate
The volume of water flowing through plumbing in a given period of time. Usually measured in volume/minute or volume/hour. 1 Liter/min = 0.264 US Gallon/min
Gross Area
The total surface area of the collector including the frame, manifold and absorber. This area is often used when comparing collectors, but a better comparison to use is value for money. Roof size is not usually a limiting factor for domestic solar water heating installations, so the size of the collector is not really that important.
Heat Pipe
An evacuated rod or pipe used for heat transfer.
Insolation
Don't confuse this with insulation - the one letter change makes a big difference. Insolation refers to the amount of sunlight falling on the earth.
Incidence Angle Modifier (IAM)
Refers to the change in performance as the sun's angle in relation to the collector surface changes. Perpendicular to the collector (usually midday) is expressed as 0o, with negative and positive angles in the morning and afternoon respectively. Collectors with a flat absorber surface, which includes some types of evacuated tubes, only have 100% efficiency at midday, whereas solar tubes provide peak efficiency mid morning and mid afternoon, at around 40o from perpendicular. This results in good stable heat output for most of the day.
Pressure
Refers to the water pressure in the system. The conversions for the most commonly used units are: 1 bar = 1.02kg/cm2 = 14.5psi = 100kPa = 0.1Mpa = 10m water head

Insulation

 

Evacuated Glass Tubes Specs.
Evacuated tubes are the absorber of the solar water heater. They absorb solar energy, converting it into heat for use in water heating. Evacuated tubes have already been used for years in Germany, Canada, China and the UK. There are several types of evacuated tubes in use in the solar industry. This type of tube is chosen for its reliability, performance and low manufacturing cost.

Each evacuated tube consists of two glass tubes made from extremely strong borosilicate glass. The outer tube is transparent allowing light rays to pass through with minimal reflection. The inner tube is coated with a special selective coating (Al-N/Al) which features excellent solar radiation absorption and minimal reflection properties. The top of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures. This "evacuation" of the gasses forms a vacuum, which is an important factor in the performance of the evacuated tubes.

Evacuated Tube Basic Specifications

Heat pipes might seem like a new concept, but you are probably using them everyday and don't even know it. Laptop computers often using small heat pipes to conduct heat away from the CPU, and air-conditioning system commonly use heat pipes for heat conduction. The principle behind heat pipe's operation is actually very simple. 

 

Glass wool is a very popular insulation material, used throughout the world in many high temperature insulation applications. Glass wool is also non-flammable, and so an excellent choice for a high temperature solar thermal solar collector. One key advantage of glass wool is that it can be molded into any shape. Via a process similar to baking a cake, the glass wool is "cooked" at high temperatures matching perfectly the shape of the header and the evacuated tubes.

Glass wool is:
  
 - An excellent insulator K = 0.043W/mK
   
- Non-flammable (can withstand temperatures up to 300oC / 572oF)
   
- Made from 90% recycled glass
   
- Very Lightweight (~70kg/m3 density - 4.36p/ft3)

 

The manifold casing serves two main purposes, protecting the header and Puf / glass wool insulation from the elements, and making the collector attractive and neat. The casing is made from corrosion resistant grade aluminum and is available industry standard design and finish.

 

  Single Target Vacuum Tube Specs. Three High Tube Three Cavity Tube Heat Pipe Tube
Length 1800mm 1800mm 1800mm 1000/ 2000mm
Outer Tube Diameter 58mm 58mm 58mm 58mm
Glass Thickness 1.6mm 1.6mm 1.6mm 1.6mm
Thermal Expansion     3.3 x 10-6 0C 3.3 x 10-6 0C
Material High Borosilicate 3.3 glass High Borosilicate 3.3 glass Borosilicate Glass 3.3 Borosilicate Glass 3.3
Absorption Coating AL/AL-ALN(H) / AL-ALN(L)ALN Cu/SS-ALN(H) / SS-ALN(L)ALN Graded AI-CU-SS Graded AI-CU-SS
Absorptance as=0.90 ~ 0.93(AM1.5) as=0.93 ~ 0.96(AM1.5) >94% (AM 1.5) >92%-94% (AM 1.5)
Emittance 0.05~0.075(800C + 50C) 0.04~0.06(800C + 50C) <6% (800C) <6% (800C)
Vacuum P<5.0x10-3Pa P<5.0x10-3Pa P<5x10-3 Pa P<5x10-2 Pa
Stagnation Temperature     >200 0C >200 0C
Heat Loss Ult=0.6~0.7W / (m2 0C) Ult=0.4~0.6W / (m2 0C) <0.6W/ (m20C) Ult=0.6~0.7W / (m2 0C)
Maximum Strength     0.8MPa 0.8MPa

 

Manifold Casing

The SunGold Solar Collector can be installed on most roof surfaces, and a full range of roof angles. A standard frame is provided with all collectors, and additional frame kits are available to suit most common installations. The various frame components can also be used to install on most other non-standard surfaces.

The frames are designed to withstand high speed winds; the tubes provide minimal resistance due to the round shape. Attachment points must also be strong enough to withstand significant pull forces that will occur during strong winds.

 

 

 

Mounting Frame