Photovoltaic Terms 2

Load - Electrical power being consumed at any given moment. The load that an electric generating system supplies varies greatly with time of day and to some extent season of year. Also, in an electrical circuit, the load is any device or appliance that is using power.

Parallel connected - A method of connection in which positive terminals are connected together and negative terminals are connected together. Current output increases and voltage remains the same. (See also series connected.)

Photovoltaic cell - The semiconductor device that converts light into dc electricity. The building block of photovoltaic modules.

Series connected - A method of connection in which the positive terminal of one device is connected to the negative terminal of another. The voltages add and the current is limited to the least of any device in the string. (See also parallel connected.)

Solar constant - The rate at which energy is received from the sun just outside the earth's atmosphere on a surface perpendicular to the sun's rays. Approximately equal to 1.36 kW/m2.

Thick cells - Conventional cells, such as crystalline silicon cells, which are typically from 4 to 17 mils thick. In contrast, thin-film cells are several microns thick.

Thin-film cells - Photovoltaic cells made from a number of layers of photo-sensitive materials. These layers are typically applied using a chemical vapor deposition process in the presence of an electric field.

Voltage regulator - A device that controls the operating voltage of a photovoltaic array.

Photovoltaic Terms 1

Cell efficiency - The ratio of the electrical energy produced by a photovoltaic cell (under full sun conditions or 1 kW/m2) to the energy from sunlight falling upon the cell.

Charge controller - A component that controls the flow of current to and from the battery subsystem to protect the batteries from overcharge and over discharge. The charge controller may also monitor system performance and provide system protection.

Diffuse radiation - Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust or other substances in the atmosphere.

Direct radiation - Light that has traveled in a straight path from the sun (also referred to as beam radiation). An object in the path of direct radiation casts a shadow on a clear day.

Flat-plate array - A photovoltaic array in which the incident solar radiation strikes a flat surface and no concentration of sunlight is involved.

Fresnel Lens - A concentrating lens, positioned above and concave to a PV material to concentrate light on the material.

Grid-connected - An energy producing system connected to the utility transmission grid. (Also called utility interactive.)

Hybrid system - A power system consisting of two or more power generating subsystems (e.g., the combination of a wind turbine and a photovoltaic system).

Insolation - The amount of sunlight reaching an area, usually expressed in watts per square meter per day.

How does solar energy work?

Solar Electric or Photovoltaic Systems convert some of the energy in sunlight directly into electricity. Photovoltaic (PV) cells are made primarily of silicon, the second most abundant element in the earth's crust, and the same semiconductor material used for computers. When the silicon is combined with one or more other materials, it exhibits unique electrical properties in the presence of sunlight. Electrons are excited by the light and move through the silicon. This is known as the photovoltaic effect and results in direct current (DC) electricity. PV modules have no moving parts, are virtually maintenance-free, and have a working life of 20 - 30 years.

Solar energy is a major contributor to the overall growth of renewable energy resources, and global output is expecting to be 26GWH by 2025.