Solar Energy

Did you know that the amount of sunlight that strikes the earth’s surface in an hour is enough to power the entire planet for an entire year?

There are three primary types of solar technologies – photovoltaic (PV), concentrating solar power (CSP) for large scale power plants and solar thermal heating & cooling. When the sun shines onto a PV solar panel, photons from the sunlight are absorbed by the cells in the panel, which creates an electric field across the layes and causes electricity to flow.

When the sun shines onto thermal solar panels, heat from the sunlight is absorbed into water or a thermal fluid flowing through the panels. The heated fluid can be used for water & pool heating and space heating

In large scale power plants, mirrors and lenses concentrate heat from the sun onto a thermal fluid. The heated thermal fluid is passed through a heat exchanger to generate steam for large scale power plants typically known as CSP.

Watch Energy 101: Solar PV Watch Energy 101: Concentrating Solar Power

Solar Definitions

Angle of Incidence – The angle that a ray of sun makes with a line perpendicular to the surface. For example, a surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle of incidence is 90°.

Array – An interconnected system of PV modules that function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support our mounting. In smaller systems, an array can consist of a single module.

Antireflection Coating – A thin coating of a material applied to a solar cell surface that reduces the light reflection and increases light transmission. An antireflection coating is typically required near an airport.

Azimuth Angle – The angle between true south (180°) and the point on the horizon directly below the sun.

Balance of System – Represents all components and costs other than the photovoltaic modules/array. It includes design costs, land, site preparation, system installation, support structures, power conditioning, operation and maintenance costs, indirect storage and related costs.

Building Integrated Photovoltaics (BIPV) – A term for the design and integration of PV technology into the building envelope, typically replacing conventional building materials. This integration may be in vertical facades, replacing view glass, spandrel glass or other facade material; into semitransparent skylight systems; into roofing systems, replacing traditional roofing materials; into shading “eyebrows” over windows; or other building envelope systems.

Bypass Diode – A diode connected across one or more solar cells in a PV module such that the diode will conduct if the cell(s) become reverse biased. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.

Charge Controller – A component of a PV system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.

Combiner Box – Connect multiple fused input strings of PV modules to a common output.

Concentrating PV (CPV) – A solar technology that uses lenses or mirrors to concentrate sunlight onto high-efficiency solar cells.

Crystalling Silicon – A type of PV cell made from a slice of single-crystal silicon or polycrystalline silicon.

Fixed Tilt Array – A PV array set in a fixed angle with respect to horizontal.

Insolation – The solar power density incident on a surface of stated area and orientation, usually expressed as Watts per square meter or Btu per square foot per hour.

Inverter – A device that converts direct current electricity to alternating current either for stand-alone systems or to supply power to an electricity grid.

Irradiance – The direct, diffuse and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation.

Maximum Power Point (MPP) – The point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is about 0.45 volts.

Multicrystalline – A semiconductor (PV) material composed of variously oriented, small, individual crystals. Sometimes referred to as polycrystalline or semicrystalline.

Ohm – A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of 1 volt produces a current of 1 ampere.

Open-circut Voltage (Voc) – The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.

Orientation – Placement with respect to the cardinal directions, North, South, East and West.

PV Cell – The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (direct current voltage and current). Also called a solar cell.

Pyranometer – An instrument used for measuring global solar irradiance.

Pyrheliometer – An instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7° to transcribe the solar disc.

Solar Renewable Energy Credit (SREC) – A form of Renewable Energy Certificate produced by a solar system for 1,000 kilowatt-hours of electricity.

Thin-film PV – A layer of semiconductor material, such as copper indium diselenide or gallium arsenide, a few micros or less in thickness, used to make PV cells.

Tilt Angle – The angle at which a PV array is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.

Tracking Array – A PV array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are single axis where the array tracks the sun east to west and dual axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Dual axis tracking arrays capture the maximum possible daily energy.

Zenith Angle – The angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).

For more solar definitions, visit http://energy.gov/eere/sunshot/solar-energy-glossary.