What is an inverter?
An inverter changes DC voltage from batteries or solar panels, into standard
household AC voltage so that it can be used by common tools and appliances
Essentially, it does the opposite of what a battery charger or "converter"
does. DC is usable for some small appliances, lights, and pumps, but not
much else. Most systems should include an inverter of some type, even
if it is just an el-cheapo $29 Walmart thing to run the TV occasionally.
Some DC appliances are available, with the exception of lights, fans and
pumps there is not a wide selection. Most other 12 volt items we have
seen are expensive and/or poorly made compared to their AC cousins. The
most common battery voltage inputs for inverters are 12, 24, and 48 volts
DC - a few models also available in other voltages.
There is also a special line of inverters called a utility intertie or
grid tie, which does not usually use batteries - the solar panels or wind
generator feeds directly into the inverter and the inverter output is
tied to the grid power. The power produced is either sold back to the
power company or (more commonly) offsets a portion of the power used.
These inverters usually require a fairly high input voltage - 48 volts
or more. Some, like the Sunny Boy, go up to 600 volts DC input.
A few grid tie inverters can also be used with batteries, but there will
be some loss in overall efficiency for feeding the grid. How much loss
can vary considerably, depending on the inverter and the size and type
of batteries. If you need battery backup power for a grid tie system,
we recommend the Outback Power inverters, as they have the best efficiency
with batteries - you will get about a 5-10% loss. With some older inverters,
such as the Xantrex SW series, that can sell back excess power to the
grid overall losses can be as high as 50
How does an inverter work?
An inverter takes the DC input and runs it into a pair (or more) of power
switching transistors. By rapidly turning these transistors on and off,
and feeding opposite sides of a transformer, it makes the transformer
think it is getting AC. The transformer changes this "alternating
DC" into AC at the output. Depending on the quality and complexity
of the inverter, it may put out a square wave, a "quasi-sine"
(sometimes called modified sine) wave, or a true sine wave.