Glossary

 

 

Glossary of Common Solar Terms

 

 

Apricus

Apricus is a latin word meaning “loving or attracting the sun”.

 

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. For plate plate collectors it is the area of the glass panel through which light can pass.

 

Absorber

 

The part of the collector that actively absorbs the light rays. The absorber is normally a dark blue or black colour, and may be a coating on glass, aluminum or copper, depending on the collector design.

 

Collector

A solar collector is is not really the same as 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

 

Delta-T refers to the difference in two temperatures. This is often the name used for solar controllers, as they work on comparing the difference between two temperatures to control the operation of the pump. Delta-T is also used when looking at collector performance, the value being collector temp minus ambient temp.

 

Efficiency

 

Also referred to as performance, 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. Eg. 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 as part of product certification to meet SRCC, Solarkeymark and other country specific solar certificates.

 

Evacuated Tube

 

An evacuated tube is a glass tube that has been evacuated to form a vacuum. The vacuum helps to protect against heat loss, thus providing excellent performance even in cold conditions. There are many types of evacuated tubes. Apricus uses “twin-glass” evacuated tubes which have a glass-glass seal and are chosen for reasons of reliability and low cost.

 

Flow Rate

 

The volume of water flowing through plumbing in a given period of time.

 

Usually measured in: volume/minute or volume/hour.

 

1 L/min = 0.264 US gpm

 

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. Apricus solar collector use heat pipes to transfer heat from within the evacuated tube to the heat transfer manifold. Heat pipes are commonly used in computers to transfer heat from the CPU to cooling vent.

 

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 / 33′ water head

 

Incidence Angle Modifier (IAM)

 

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 zero degrees, 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 when the sun is overhead, whereas Apricus’ evacuated tubes passively track the sun, providing peak efficiency mid morning and mid afternoon, at around 40º from perpendicular. This results in good stable heat output for most of the day.

 

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 (solar radiation). This is normally measured in kWh/m²/day or Btu/ft²/day.

 

Insulation is material used to reduce heat transfer, such as the glass wool used in the manifold of the Apricus solar collector.

 

Insulation

 

A material that protects against heat loss. Apricus solar collectors use compressed glass wool to insulate the header from heat loss. The piping running to and from the solar collector should be well insulated to prevent heat loss.

 

Irridation

 

Irridation is the exposure of something to radiation. This terms is sometimes when talking about sunlight. See Insolation, which is the more widely used term for solar radiation.

 

Solar

Relating to the energy derived from the suns rays. Sunlight can be converted into heat or electricity.

 

Stainless Steel

 

Stainless steel is a generic terms for steel alloys that have anti-corrosive properties. There are many types of stainless steel, with different properties of strength and corrosion resistance. It is a common myth that real stainless steel does not attract a magnet. Only certain grades (300 series – austenitic) of stainless steel fail to attract a magnet. Many grades such as 439, used for Apricus solar collector mounting frames, do in fact attract magnets. 439 is widely used for automotive exhaust pipes, and provide excellent strength and corrosion resistance (similar to 304).

 

Stainless steel corrosion resistance is a result of Chromium and other trace metals that form an oxidised layer of protection on the surface of the metal. Unlike painted metal, when scratched, most types of stainless steel with quickly “reform” the protective layer if exposed to oxygen.

 

Stainless steels are not “stainless” in all conditions. Each grade has certain environments it performs well in, and certain conditions that will still result in corrosion.