Meta Solar Glossary
Azimuth angle
The angle between true south and the point on the horizon directly below the sun.
Battery available capacity
The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions including discharge rate, temperature, initial state of charge, age, and cut-off voltage.
Battery life
The period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. Life may be measured in cycles and/or years, depending on the type of service for which the cell or battery is intended.
Bypass diode
A diode connected across one or more solar cells in a photovoltaic 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.
Cell
A solar cell is the basic component of solar modules. Cells are manufactured from wafers.
CO2
An abbreviation for carbon dioxide. CO2 is well-known as a “green-house gas.” When people talk about “Carbon Footprint,” they are usually referring to CO2 emissions.
Conversion efficiency
This measure gauges the percentage of solar (light) power reaching a module that is converted into electrical power. Conventional cells now range in the high percentage teens. Theoretical and laboratory conversion rates typically are much higher than rates from mass production.
Direct current (DC)
A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. To be used for typical 120 volt or 220 volt household appliances, DC must be converted to alternating current, its opposite.
Energy Payback
The amount of time required for a solar panel to generate the amount of energy it took to manufacture it. Modern PV panels have an energy payback of 1 to 3 years depending on where they’re installed; over a 30+ year life, a PV system will return 10 to 30 times the energy that went into making them.
Grid Connected
A grid-connected solar electric system generates its own electricity and feeds its excess power into the utility grid for later use. Grid-connected solar electric systems are eligible for many incentives and rebates.
Inverter
The inverter electronically converts Direct Current (DC) power into Alternating Current (AC) power and is required for grid-connected solar power systems.
Micro inverters can be installed on each solar module. The cost is typically higher, but they provide certain advantages for very small or geometrically complex PV systems.
String inverters are the most common type of inverter for residential and small commercial PV systems.
Central inverters are used for very large PV systems.
Insolation
Sunlight varies by region. Insolation is a measure of the solar radiation energy in a given region. It is usually expressed as the intensity of light energy per unit of land area. As a whole, the U.S., especially the sunny Southwest and Southeast, offers strong insolation. By comparison, Germany, the PV industry’s leader, gets little better sun than Alaska.
Kilowatt (kW)
A standard unit of electrical power equal to 1000 watts. This usually refers to the size of a solar panel system e.g. 20 300w panels = a 6000w or 6kw solar system. Keep in mind a 6kw system in California will produce much more than 6000kwhs in a year.
kWh
The abbreviation for kilowatt-hours, a unit of energy. One kWh represents a 1,000 watt load operated over a period of one hour—that's the amount of energy an average plasma TV uses. Electricity rates are most commonly expressed in cents per kilowatt hour.
Module
Commonly called a “solar panel,” a PV module is composed of multiple solar cells that are electrically connected to increase the total power output and are encapsulated in tempered glass for weather protection and ease of handling.
Monocrystalline
Silicon is a metal and, therefore, its atoms are organized into a crystalline structure. Monocrystalline refers to silicon that is pulled as a single, completely homogenous crystal. Monocrystalline PV cells are generally the most efficient and reliable available.
National Electrical Code (NEC)
Contains guidelines for all types of electrical installations. The 1984 and later editions of the NEC contain Article 690, "Solar Photovoltaic Systems" which should be followed when installing a PV system.
Net-Metering
Net-metering allows the solar electric system to send excess electricity back through the electric meter to the utility. The meter actually runs backwards! Your utility will bill you for the net (kWh used – kWh generated). While most utilities will not pay you cash if you generate more than you use, many will carry forward a credit toward your next bill.
Photon
A photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. Solar radiation arrives on the surface of photovoltaic cells in the form of photons, providing the main energy that activates cells to produce electricity.
Photovoltaics (PV)
Photo = light; Volt = electrical potential — Literally: electricity from light. Einstein won the Nobel Prize for discovering that when light shines on certain materials (like silicon), an electrical current is generated. Learn how a PV module (solar panel) works.
Polycrystalline
Officially called “multicrystalline,” this refers to cast silicon where several crystals form in a mold. Some manufacturers use this casting process as it is less expensive than pulling single crystals, but the resulting cells generally have lower efficiency due to internal resistance along the grain boundaries. Polycrystalline cells can be recognized by a visible grain, a “metal flake effect.”
Silicon
The basic material used to make solar cells. It is the second most abundant element in the earth’s crust, after oxygen.
Stand-alone system
Energy generated by these systems is stored in batteries and then subsequently used. Also known as “off-grid,” these systems are not connected to the utility grid.
Wafer
A sawn silicon disc, used as the starting point for manufacturing a solar cell.