Glossary of Solar Terms
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California Energy Commission (CEC) The state agency responsible for energy policy in California. Efficiency The ratio of output power (or energy) to input power (or energy). Expressed in percent. Grid Term used to describe a utility's electricity distribution network. Inverter Device that converts DC electricity into AC electricity. Irradiance: The direct, diffuse, and reflected solar radiation that strikes a surface. kilowatt (kW) 1000 watts. kilowatt-hour (kWh) One thousand watts acting over a period of 1 hour. Minimum Operating DC Voltage: The minimum DC input voltage required for the inverter to operate. If the DC input voltage drops below the minimum operating voltage, the inverter will stop producing power. Maximum Operating DC Voltage: The maximum DC input voltage that can be supplied to the inverter without damaging the inverter. Before connecting the PV array to the inverter you must confirm that the open circuit voltage is at or below the maximum DC input voltage for your inverter. Maximum Input DC Current: The maximum input DC current that can be connected to the inverter. Maximum DC Power: The maximum DC input power that should be connected to the inverter. This number is derived from the nominal output rating of the PV panels. Maximum Continuous AC Power: The maximum continuous output power that an inverter can deliver. Minimum AC Power The minimum output power rating of the inverter. Maximum Power Voltage (Vmp) The maximum rated voltage output of a Photovoltaic module. Maximum Power Point Tracker (MPPT) Means of a power conditioning unit that automatically operates the PV-generator at its MPP under all conditions. Open-circuit voltage (Voc) A PV cell or module's voltage potential in sunlight when there is no current flowing. Parallel connection Electrical connection where the positive terminals of a number of devices (ie PV modules) are connected together as well as their negative terminals. The resulting output voltage of the devices is equal to the average of the devices and the total current is equal to the sum of the current of all the devices connected in parallel. Power (watts) A unit of electricity in DC circuits equal to the product of current and voltage. Series connection An electrical connection where the positive terminal of one device is attached to the negative terminal of the next in a series string. In a series connection, the string voltage is the sum of the device voltages and the string current is the current of the least productive device in the string. Short-Circuit Current (Isc) The current flowing through an external circuit that has no load. Standard test conditions (STC) A set of reference conditions used for PV device measurement. They consist of irradiance of 1 kW/m2, AM 1.5, and 25ºC cell temperature. Temperature Coefficient of Isc: Coefficient used to determine effect of temperature on PV panels output current. This coefficient is important when sizing a PV array for an inverter to ensure that the PV array is within the minimum and maximum DC input current limits. Temperature Coefficient of Voc: Coefficient used to determine effect of temperature on a PV panels output voltage. This coefficient is important when sizing a PV array for an inverter to ensure that the PV array is within the minimum and maximum DC input voltage limits. Temperature Coefficient of Pmax: Coefficient used to determine effect of temperature on a PV panel's power output. Utility-interactive Inverter Also referred to as a grid-tied inverter. An inverter which interacts with the utility grid, taking power from the grid to satisfy its loads as necessary, and sending power to the grid when not required by the loads. Vac Volts ac Vdc Volts dc |