Owner`s manual

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INVERTERS
68
System Design
to start large motors while their high efciency makes them eco-
nomical with power when running small loads like a stereo or a
small light. They can power most lighting, televisions, appliances
and computers very well. Unfortunately, this type of inverter may
destroy some rechargeable tools and ashlights, and laser printers
and copiers. They may not allow many laser printers, copiers,
light dimmers and some variable speed tools to operate. Equip-
ment with silicon controlled rectiers (SCRs) will not operate.
Some audio equipment will have a background buzz that may
be annoying to music connoisseurs.
Grid-Tie Inverters
Grid-tie, or utility intertie, inverters convert DC power from PV
modules into AC power to be fed into the utility grid. There are
two major types of grid-tie inverters; string inverters and low
voltage input inverters.
The SMA Sunny Boy, Fronius and Xantrex GT-3 inverters are
string inverters. The name “string” comes from the way the PV
modules are wired together, in series to achieve a higher voltage.
These inverters are designed to run at voltages up to 600 VDC.
String wiring is faster to install, more efcient and allows the use
of smaller gauge wire. DC voltage this high can be very danger-
ous and life-threatening, so string inverters should be installed
and serviced by qualied electricians.
A grid-tie PV system uses the utility company, in effect, as
its storage battery. When the sun is shining, your electricity
comes from the PV array, via the
inverter. If the PV array is gen-
erating more power than you are
using, the excess is sold to the
power utility company through
your electric meter, by making
the meter run backward. When
you need more power than the
PV array can supply, the utility
makes up the difference. This
type of system makes the most
sense in most cases where you
have utility power, because there
are no batteries to maintain or
replace. Unfortunately, if the util-
ity power goes down, this type of
inverter will go off, too, regard-
less of whether or not the sun is
shining.
Off-Grid Inverters
Off-grid, or standalone, inverters convert DC power stored in bat-
teries to AC power that can be used as needed. Select an inverter for
your power system based on the maximum load you will be pow-
ering, the maximum surge required, AC output voltage required,
input battery voltage and optional features needed. High quality
standalone inverters are available in sizes from 100 watts, for
powering notebook
computers and fax
machines from
your car, to 60
kilowatts, for pow-
ering a commercial
operation. The size
of an inverter is
measured by its
maximum continu-
ous output in watts.
This rating must be
larger than the total
wattage of all of the
AC loads you plan
to run at one time. Wattage of most AC loads can be determined
from a tag or label on the appliance, usually located near where
the power cord enters, or from the owner’s manual. If the inverter
is expected to run induction motors, like the ones found in top
loading washers, dryers, dishwashers and large power tools, it
must be designed to surge, or deliver power many times its rat-
ing for short periods of time while these motors start. Standalone
inverters are available with two basic power output waveforms:
sine wave, and modied sine wave (the proper term is actually
modied square wave, but since modied sine wave is much more
commonly used, we use that term in this catalog).
Grid-tie inverters, dual-function inverters and utility companies
deliver a sine wave. Exeltech, Xantrex XW Series, SMA Sunny
Island, Magnum MS and OutBack FX inverters are sine wave
off-grid inverters. Sine wave inverters have a higher cost, but
they can operate almost anything that can be operated on utility
power. Exeltech sine wave inverters are an excellent choice for
power systems running audio or telecommunications equipment
and other electronics that are waveform-sensitive. The OutBack
and Xantrex XW series inverters can be ganged together for up
to 36 kW of output and can operate off-grid or grid-tie. We now
carry Samlex sine wave PST inverters for a lower cost, a small-
system sine wave alternative.
Xantrex TR series, Magnum, and Samlex PSE inverters have
modied sine wave output with harmonic distortion of around
40%. They are an economical choice in power systems where
waveform is not critical. Their high surge capacity allows them
Inverters
The inverter is the heart of all but the smallest power systems.
It is an electronic device that converts direct current DC power
from batteries or solar modules into alternating current AC
power to operate lights, appliances or anything that normally
operates on power supplied by the utility grid. Inverters come
in many varieties, sizes and qualities and offer various features
that specialize them for particular applications.