Glossary O - Z
O
Optical losses
The percentage of the solar radiation that cannot be absorbed by the absorber. Losses occur through absorption by the plate and through reflection.
Optical efficiency
Indicates the percentage of incident sunlight that is transformed by the collector into heat.
Open circuit voltage
Voltage measured on the connection terminals of a solar module or solar cell, with current switched off.
Output
The amount of energy produced within a certain time frame. The unit is the watt (W).
P
Peak output
See Kilowatt peak.
Photovoltaics
Photovoltaics is the name for the solar technology that converts sunlight into electrical current. The term is derived from photon (Greek for light) and the name of the physicist Alessandro Volta (1745-1827).
Polycrystalline
Silicon with a partially ordered crystal structure. The base material of polycrystalline solar cells. The blue solar cells have the textured, crystalline appearance typical of PV modules. Polycrystalline cells differ from monocrystalline cells in that they are slightly less effective, but are a standard product in the PV industry due to special fabrication technology and high manufacturing capacities and represent good value for money.
PV
Abbreviation for photovoltaic.
PV module
Interconnected, encapsulated solar cells for obtaining particular key values and for their mechanical protection.
R
Reflection
The sunlight reflected by a surface.
Tube collector
See evacuated tube collector.
Rated output
Output of a solar module (solar cell) at the MPP
Rated current
Current generated by a solar module (solar cell) at the MPP.
S
Selective coating
Coating on the absorber which allows more energy to be absorbed whilst simultaneously reducing emissions by the absorber.
Silicon
After oxygen, the second most common chemical element on Earth. It is the base material for the semiconductor industry, and a raw material used in the manufacture of solar cells. Silicon is available mainly in combination with oxygen in the form of quartz sand (SiO2), not as an element.
Solar
(Solar, lat.: relating to the sun).
Solar system
Systems for transforming solar radiation into usable energy in the form of heat or electricity.
Solar coverage
See coverage.
Solar fluid
Fluid that absorbs the heat from the collector, transports this heat and transfers it to the water via the heat exchanger in the storage cylinder. A glycol-water mixture as heat transfer medium ensures protection against frost.
Solar generator
See generator.
Solar module
See PV module.
Solar storage cylinder
Because the energy supplied by the sun rarely coincides with the periods during which heating is required, the heat generated by solar power needs to be stored. Solar thermal systems store the heat in hot water storage cylinders.
Solar electricity
DC current generated directly in solar cells.
Solar thermal
Conversion of solar radiation into directly usable heat.
Solar cell
When solar cells come into contact with light or heat, positively and negatively charged particles are released (photo effect), generating direct current.
Standstill temperature
Temperature in the collector at the hottest point of the absorber when no energy is removed.
Standard Test Conditions (STC)
To enable objective comparison of different PV modules and solar cells, the following standard test conditions have been defined for determining their characteristics:
1. Incident radiation E of 1000 W/m²
2. A cell temperature T of 25°C with a tolerance of ± 2°C
3. A defined light spectrum AM = 1.5
Level of system utilisation
Ratio of solar yield to total incident radiation. This is a measure of the overall efficiency of the solar energy system.
T
Temperature difference control
Control of a solar thermal system according to the ratio of the collector temperature to the temperature in the bottom section of the storage tank.
Temperature layering
Stratification of temperatures within the solar storage cylinder. The temperature in the storage cylinder increases from bottom to top. Layering technology concentrates the heat at a high temperature that can be better used.
Solar thermal system
System for converting solar radiation into usable energy in the form of heat.
V
V
Abbreviation for volt. Unit of electrical charge.
Evacuated tube collector
In this type of design, the absorber is located in an evacuated glass tube to achieve useable temperatures of up to 150ºC that are useful in process heat applications. Where systems are used for hot water and heating, the key values of flat-plate collectors and evacuated tube collectors are more or less equal.
Shading
Shading of solar systems through protruding roofs or trees leads to reduced solar yield.
W
W
Abbreviation for watt. Unit of electrical output.
Heat exchanger
The energy absorbed by the collector is transferred via the heat transfer fluid from the primary or collector circuit to a secondary circuit (domestic water, heating).
Inverter
Device for transforming solar generated direct current into alternating current for use and feeding into the public grid.
Efficiency
Ratio of usable energy to energy used.