Solar Glossary

The following is a list of terms you may encounter as you explore our website. If you have any questions after reading this document please feel free to contact us.

A-B-C-D-E-F-G-H-I-P

A

Aperature: 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.
(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. For 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) 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. The Apricus AP solar collector does not use reflective panels.

B

BTU - Stands for British Thermal Units. This is an imperial unit of measurement for heat widely used in the US and also in the UK. The conversion to the metric unit kWh is: 1 kWh = 3412Btu, and for surface area values, 1kWh/m²/day = 317.1Btu/ft²/day

Boosting - Solar radiation levels (the collected energy from the sun) depend on climate, season and daily weather, so solar may not provide all of the energy required of your system year round. In order to accommodate this, solar hot water systems incorporate a backup water heater, usually an existing one, in order to boost the system with electricity or gas to ensure appropriate levels of hot water when solar energy is not enough

C

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.

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 = 7^oC turn pump on, Delta-T 2^oC 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

D

Differntial Controller: This is the main control of a solar water heating system. The controller measures two temperatures and based on the settings decides whether or not it is appropriate to activate a system component, usually a pump. In most cases the controller will be monitoring the temperature at the collector and the bottom of the storage tank. When the temperature exceeds a certain level (Ex. 15oF) the pump will run until it drops below the second setting (Ex. 5oF).

E

Efficiency:  The efficiency of a solar collector is determined by how much energy it can convert based on it's size. Solar collector efficiency is usually expressed as a percentage value, or in a performance graph. There are many factors that contribute to a collector efficiency and many times efficiency numbers can be misleading.

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

For more information on efficiency please click here.

F

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

G

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.

H

Heat Pipe: An evacuated rod or pipe used for heat transfer. Click here for more information.

I

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. Click here to learn more

Insulation: The ability to protect against transfer of heat/cold. Apricus solar collectors use compressed glass wool to insulate the header from heat loss. Glass wool has excellent insulation properties, is very light and can withstand high temperatures, making it an ideal choice for a solar collector. It is made from a least 80% old glass bottles and can be recycled so is very environmentally friendly.

Irridance, Irridation: Basically the same as Insolation - explained above.

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 0^o, 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 a maximum IAM value of 1 at midday (0^o), whereas Apricus solar tubes can exceed 1 throughout both the morning and afternoon, peaking at around 40^o from perpendicular.  This results in good stable heat output for most of the day.

P

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

If there is anything you think we should add to this glossary, please let us know.