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A-F of solar technology terms.

10/8/2008

A-F of solar technology terms

A

Air Mass
A measure of how far light travels through the Earth's atmosphere. One air mass, or AM1, is the thickness of the Earth's atmosphere. Air mass zero (AM0) describes solar irradiance in space, where it is unaffected by the atmosphere. The power density of AM1.5 light is about 1,000 W/m"; the power density of AM0 light about 1,360 W/m".

Ampere
A unit of electrical current. A potential of one volt across a resistance of one ohm causes a current of one ampere (6.25 X 1018 electrons per second) to flow.

Ampere-hour
A unit of energy, typically referring to battery capacity. One ampere of current flowing for one hour.

Angle of incidence
The angle between a ray of sunlight striking a surface and a line perpendicular to that surface. Rays perpendicular to a surface have a zero angle of incidence.

Array
A number of solar modules electrically connected to produce a single electrical output.

Azimuth
The angular measure between due south and the point on the horizon directly below the sun.

B

Balance-of-Systems (BOS) components
All the components in a power system other than the photovoltaic array.

Battery
Two or more electrochemical cells connected to provide energy storage. Also commonly used to designate one cell.

Blocking diode
A diode which prevents reverse current flow in a circuit, commonly used to prevent a battery from discharging through the array at night.

C

Charge controller
The PV system component which controls the battery's state of charge. It may also provide other system control functions.

Charge rate
The current applied to a battery to restore its energy capacity. The rate is typically normalized with respect to the battery's full capacity and a designated time period. Thus, the current necessary to nominally charge a 100-ampere-hour battery from zero to full charge in five hours (20 amperes) is referred to as the battery's C/5 rate. The term is also applied to discharge rate.

Concentrator array
A photovoltaic (PV) array which uses concentrating devices (reflectors, lenses) to increase the intensity of the sunlight striking the array.

Czochralsky (CZ) method
The method used to make monocrystalline silicon.

D

DC – direct current
The type of current provided by a battery or solar cell, which flows in one direction.

Depth of discharge
A measure of how much energy has been withdrawn from a battery, expressed as a percentage of full capacity. A 100 Ah battery from which 30 Ah has been withdrawn has undergone a 30% depth of discharge (DOD). This term is the inverse of state of charge (SOC); the example battery would be at 70% SOC.

Diffuse radiation
The sunlight received indirectly, as a result of scattering due to clouds, fog, dust, moisture vapour or other substances in the atmosphere.

Diffusion
The wafers are given a negative characteristic by exposure to a phosphorus source at high temperature.

Direct radiation
Sunlight received directly, which has travelled in a straight path from the sun, also referred to as beam radiation.

E

Efficiency
With respect to solar cells, the percentage of light energy that is converted to electricity by the cell. Depending on cell technology and production technique, this ranges from as low as 5% to as high as 30%.

Elevation (solar)
The sun's angle above the horizon.

Equalizing charge
A controlled overcharge of a battery bank for the purpose of restoring equality of charge in all cells.

F

Finishing charge
That part of the charging process which restores the final segment of a battery's charge, roughly between 90% and 100% SOC.

Flat-plate array
A photovoltaic (PV) array which does not use concentration.

Frequency
The rate at which a periodic event occurs. In electricity, the rate at which current reverses direction in an alternating current system. In the US and some other countries, alternating current systems use a frequency of 60 cycles per second (60 Hz); in Europe and remaining countries, the standard is 50 Hz.