Solar Glossary


Here is a list of some terms you may meet when browing our web site.
We have tried our best to make explanations easily understand. If you are still not quite clear about any parts, please feel free to contact us.
A - B - C - D - E - F - G - H - I - P
Aperture: The part of the collector through which light enters. In trems of 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.
(Eg. 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. In terms of solar tubes, this is defined as the cross-sectional area of the inner tube (selective coated) measured using the outside diameter. (Eg. 0.047 x 1.72m = 0.08m2) It is used to calculate efficiency values. For solar tube collectors with reflective panels, the entire circumferential surface area of the inner tube is often used to calculate absorber area, as the reflective panel is supposed to reflect light onto underside of the evacuated tube. The Sunflower AP solar collector does not use reflective panels, learn why by clicking here.
BTU - It stands for British Thermal Units. This is an imperial unit of measurement for heat. It is widely used in the US and UK. The conversion to the metric unit kWh is: 1 kWh = 3412Btu, and for surface area values, 1kWh/m2/day = 314Btu/ft2/day
Collector - A solar collector is different from a solar water heater. A solar water heater is a system which may include a water tank, pump, controller and solar collector panel,etc. A solar collector is one part of this system which absorbs the sun's energy and then converts it into heat. The Sunflower AP model is separate from the tank as so is a solar collector.
Celsius - The metric unit for temperature measurement. Convert as follows:
Fahrenheit = (oC x 1.8) + 32
Celsius = (oF - 32)/1.8
For Delta-T measurements the relative temperature difference is needed.
Eg. Delta-T = 7oC turn pump on, Delta-T 2oC turn pump off. How much is that in oF??
The conversion from Fahrenheit to Celsius is simple:
Fahrenheit = oC x 1.8
Celsius = oF / 1.8
Delta-T Controller: Delta-T refers to the difference in two temperatures. This term is often used together with solar controller. In such case, the Delta-T is the difference between the solar collector temperature and water temperature in the solar storage tank. A Delta-T controller can be configured to turn on the pump when the Delta-T difference surpasses a certain level (Eg.7oC / 12.7oF) and turn off it again when the Delta-T difference drops under another level (Eg. 2oC / 3.6oF). The controller turns on the pump once heat potential occurs 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 under 5oC.
Efficiency: Solar collector efficiency is usually expressed as a percentage value, or in a performance graph. When assessing a collector's performance, you should make sure it is based on the correct surface area values. Eg. If performance values are based on gross area, 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
Eg. (44oC - 20oC)/800Watts = 0.03
For more information about efficiency please click here.
Flow Rate: The volume of water flowing through plumbing in a given period of time. Usually measured in volume/minute or volume/hour. 1 Litre/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. Click here for more information.
Insolation: Don't confuse this term with insulation - one letter change makes a big difference. Insolation refers to the amount of sunlight irradiating on the earth. Click here to learn more
Insulation: The ability to protect against transfer of heat/cold. Sunflower solar collectors use compressed glass wool to insulate the header from heat loss. Glass wool has excellent insulation properties, which is very light and can bear high temperatures, making it an ideal choice for a solar collector. It is made from at least 80% old glass bottles and can be recycled, so it is very environmentally friendly.
Irridance, Irridation: Basically the same as Insolation -as explained above.
Incidence Angle Modifier (IAM): It refers to the change in performance as the sun's angle changes in relation to the collector surface. 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 (0o), however Sunflower solar tubes provide peak efficiency in mid morning and mid afternoon, at around 40o from perpendicular. This results in stable heat output for the most of the day.
Pressure: It refers to the water pressure in the water heating system. The conversions for the most commonly used units are: 1 bar = 1.02kg/cm2 = 14.5psi = 100kPa = 0.1Mpa = 10m water head
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