Inverter Terminology

Terminology:

  1. “Grid” (a.k.a. “the grid”, “commercial power grid”, power lines, and others)
  2. Grid tie inverter
  3. Hybrid (“intentional island”) inverter system
  4. Inverter
  5. Island
  6. Stand-alone inverter
  7. String inverter
  8. PV module (a.k.a. PV Panel, solar panel, photovoltaic panel, etc.)
  9. PV AC Module
  10. Maximum Power Point Tracking (“MPPT”)

Grid” (a.k.a. “the grid”, “commercial power grid”, power lines, and others)

Power distribution lines energized by utility companies for delivery of electric power to utility company customers. Power sources used commonly include coal, nuclear, hydroelectric, natural gas, and others.

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Grid tie inverter

An inverter designed to connect to the commercial power grid and feed power back into the grid. A grid-tie inverter must be connected to the grid in order to function. Safety regulations require a grid-tie inverter to cease operating in the event of a power failure on the commercial power grid. The most common energy source for a residential grid-tie inverter are “solar modules” that make electricity from sunlight (see also “PV” ).

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Hybrid (“intentional island”) inverter system

A hybrid inverter combines features of the stand-alone inverter and the grid-tie inverter. Hybrid systems use batteries for storage, and are able to provide power for critical loads in the event of a grid power failure. Hybrid systems achieve this intentional islanding by first disconnecting from the commercial power grid (by use of a heavy-duty mechanical relay), then continuing to operate as a stand-alone inverter until the utility power is restored, at which time the hybrid inverter returns to grid-tie mode.

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Inverter

An electronic device that converts direct current (“DC”) into alternating current (“AC”). In this context, an inverter produces 60Hz sine-wave electricity identical to what is produced by US domestic power companies.

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Island

An “island” condition exists when an inverter continues to provide power to one or more residences or other structures. If this occurs in a grid-tie inverter, the inverter is malfunctioning. Sometimes, systems are designed to intentionally island (see “Hybrid system”).

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Stand-alone inverter

An inverter designed to operate independently of the commercial power grid. A stand-alone inverter creates its own 60Hz reference (50 Hz for international models), and is not designed to connect to or feed power back into the commercial power grid. Mechanical relays may be used in conjunction with stand-alone inverters to allow a load to be powered from either the grid or the inverter, and have the relay change position to use the respective other power source as needed, but at no time are the stand-alone inverter and the power grid connected to each other.

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String inverter

An inverter designed to connect to a high-voltage input such as provided by a series string of photovoltaic (“PV”) modules. Typical string inverter systems require 250 to 600 volts input. String inverters do not have batteries, thus are unable to provide backup power in the event of a power failure.

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PV module (a.k.a. PV Panel, solar panel, photovoltaic panel, etc.)

PV is an abbreviation for “photovoltaic”, meaning “from light”. A PV module (note the lower-case ‘m’) is a large, flat device comprised of many “solar cells” that generate direct current (“DC”) electricity from sunlight. It uses silicon and combinations of other special metals in the solar cells, that when exposed to the sun, generate an electrical current. Common PV module voltages are 12V and 24V, although other voltages are also available.

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PV AC Module

A PV AC module is a special version of grid-tie inverter. Unlike conventional grid-tie inverters, which require many PV panels in series or parallel connection, PV AC modules are permanently attached to a PV panel and produce grid-ready electricity directly. DC wiring becomes an integral part of the PV AC module and is thus no longer required to be designed into the system, nor be connected through other circuits to protective or other devices. PV AC modules reduce wiring requirements in grid-tie inverter systems by up to 50% or more.

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Maximum Power Point Tracking (“MPPT”)

The maximum power available from a PV module varies with temperature and sunlight level. PV modules produce more power at cold temperatures than hot. Sunlight energy is greatest during mid-day. The Exeltech PV AC Module, using an internal microprocessor, adjusts its operating conditions to use as much of the available power as possible. As an example, think of a transmission in a car. It changes gear ratios according to the speed of travel. The maximum power point tracking feature (“MPPT”) incorporated into the Exeltech PV AC Module accomplishes the same task, but does so electronically. In this manner, the Exeltech PVAC Module won’t try to produce more power than is available from the PV module.

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