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Solar Inverter
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A Solar inverter
or PV inverter is a type of electrical inverter that is made to
change the direct current (DC) electricity from a photovoltaic array
into alternating current (AC) for use with home appliances and
possibly a utility grid.
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Solar inverters may
be classified into three broad types:
* Stand-alone inverters, used in isolated systems where the inverter draws
its DC energy from batteries charged by photovoltaic arrays and/or other
sources, such as wind turbines, hydro turbines, or engine generators. Many
stand-alone inverters also incorporate integral battery chargers to
replenish the battery from an AC source, when available. Normally these do
not interface in any way with the utility grid, and as such, are not
required to have anti-islanding protection.
* Grid tie inverters, which match phase with a utility-supplied sine wave.
Grid-tie inverters are designed to shut down automatically upon loss of
utility supply, for safety reasons. They do not provide backup power during
utility outages.
* Battery backup
inverters. These are special inverters which are designed to draw energy
from a battery, manage the battery charge via an onboard charger, and export
excess energy to the utility grid. These inverters are capable of supplying
AC energy to selected loads during a utility outage, and are required to
have anti-islanding protection
Solar inverters use special procedures to deal with the PV array, including
maximum power point tracking and anti-islanding protection.
Anti Islanding Proctection
Normally, grid-tied inverters will shut off if
they do not detect the presence of the utility grid. If, however, there are
load circuits in the electrical system that happen to resonate at the
frequency of the utility grid, the inverter may be fooled into thinking that
the grid is still active even after it had been shut down. This is called
islanding.
An inverter designed for grid-tie operation will have anti-islanding
protection built in; it will inject small pulses that are slightly out of
phase with the AC electrical system in order to cancel any stray resonances
that may be present when the grid shuts down.
Since 1999, the standard for anti-islanding protection in the United States
has been UL 1741, harmonized with IEEE 1547. Any inverter which is listed to
the UL 1741 standard may be connected to a utility grid without the need for
additional anti-islanding equipment, anywhere in the United States or other
countries where UL standards are accepted.
Charge Controllers
Stand-alone inverters – that is, solar inverters that are
designed to be used without the presence of the electrical utility grid –
can be run from PV panels and batteries using a charge controller. The
charge controller regulates the input from the PV and the batteries,
regulates the battery output, and handles charging the batteries.
Resouce:
http://en.wikipedia.org/wiki/Solar_inverter
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