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What types of power inverters are there?

There are stand-alone (off-grid) inverters and grid interactive (grid tie) inverters. Among the stand-alone inverters, there are square wave inverters, modified sine (square) wave inverters and pure sine wave inverters.

What can be run on an inverter?

Inverters can run typical AC appliances like blenders, hair dryers, microwave ovens, computers, even washing machines.

Are there any appliances that cannot be run on an inverter?

As a general principle you can connect almost any appliance to a power inverter, assuming it has been properly sized.  But because of the high capital cost of renewable energy products like solar panels, appliances that use a very large amount of power, such as electric stoves and ovens, air conditioners and electric clothes dryers, are usually excluded from off-the grid systems.  (No items need to be excluded if you are on a grid-tie system.)  If such items are required on an off-grid system, then a back-up system such as a propane generator is usually suggested.  But solar power is cost effective for running most other appliances in an off-grid house.  Lighting, TV, computer, washing machine, VCR, efficient refrigerators, ceiling fans, FAX, bread oven, microwave oven, coffee maker, toaster, blender, sewing machine etc. are often run off a solar system.

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Choosing a Power Inverter

Selecting an inverter to meet your needs is a major decision.  We tend to become very dependent on our power sources. In many cases, an entire home or business, including lights, refrigerator, TV, computer and other expensive equipment may be powered from it.  In selecting an inverter to meet your needs, it is important to look at the type of loads you have - their wattage, power factor, continuous and surge power requirements. From there you can determine whether or not a less-expensive modified sine wave inverter will do the job.  In all but a few cases, Fire Mountain Solar will recommend the installation of a true (also knows as a pure) sine wave inverter (see Modified Sine Wave Vs. True Sine Wave),  Once this determination is made, a specific model inverter can be chosen.

Some of the things to consider:

WATTAGE: This is usually the first and often the only thing that an uninformed person may look at.  Power inverters are usually given a continuous, intermittent (30 minute), and surge rating.  Be wary of inverter specifications that don't give you such ratings.  Some manufacturers list the surge rating in huge print and the continuous rating in the fine print, which is very misleading.  Large power inverters will be less efficient on very small loads than smaller inverters.  Lightweight inverters with no transformer generally do not have much surge ability.

OUTPUT WAVE SHAPE: A true sine wave inverter is best. Cheaper inverters don't mention it, or are termed modified square or sine wave. Many appliances including fans, washing machines, stereos, digital clocks and timers, will not work satisfactorily on this type of inverter.  Many items will run slower, or hotter or noisier on square wave type inverters.  (see Modified Sine Wave Vs. True Sine Wave)

FREQUENCY AND DISTORTION: Good inverters typically hold their frequency to within .01% and have less than 4% harmonic distortion.

AUTOSTART:  Does the inverter have a standby/autostart mode?  This typically reduces the DC load to about 0.05 Amps when then is no load on.  Some cheaper inverters will draw 2 amps continuously with no load on!   Is the demand start sensitivity adjustable in case you want it to start up with a small load such as only one fluorescent light?

MINIMUM INPUT CURRENT: How much power does the inverter use if it is on 'run' mode to run or detect a very small load?  A good inverter might only use 0.6 Amps.

INPUT VOLTAGE: A battery on a solar system may typically vary from as low as perhaps 10 volts up to 15.5 volts when the solar is 'equalizing'. A good inverter will generally operate between 10 to 16 volts.

OUTPUT VOLTAGE: Will it maintain its AC voltage to 3-5%?

EFFICIENCY: How efficient is the inverter?  Does the specification just give you one 'peak efficiency' or does it show you a graph with small 50-100 watt loads up to its rated power?

SAFETY: Does the inverter meet all relevant safety standards?

DISPLAYS: Does the inverter identify common faults such as low and high battery, overload, over temperature, etc?

WARRANTY: How long is the warranty? Good inverters come with a 5-year warranty, some even 10!

Modified Sine Wave vs. True Sine Wave
There are two types of waveforms available from a high-quality power inverter. These are the so-called "modified sine wave" and the "true sine wave". The "modified sine wave" is not really a sine wave at all, but rather a stepped wave. It achieves voltage regulation by varying in width according to the battery voltage and the load. Thus, the wave is not as smooth as a sine wave.

Conclusion
The choice of an appropriate inverter is an important and complex choice. Fire Mountain Solar can help you determine not only which power inverter is right for your application, but also which one is the best overall value.