The synchronous inverter has one function, which is to change DC power to AC power that will be fed into the utility grid. The power output from this type of inverter is sold to the utility company. Synchronous inverters require utility power to operate and cannot be used in a remote site, away from utility lines.

If you are planning to sell power to a utility company, choose a synchronous inverter with a wattage rating that matches the size of the photovoltaic array you plan to use. Check with your local utility company or PV dealer to decide which synchronous inverter best meets your need and fits the utility requirements for safety and compatibility.



Static inverters convert DC power stored in batteries to AC power that can be used as needed. Selecting the static power inverter required for a stand-alone solar electric power system will depend on the maximum total load at any given time, the maximum surge required, output voltage required, input voltage available and optional features needed.

The size of an inverter is measured by its maximum continuous 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. The size of an inverter can be kept to a minimum if the number of AC loads run at any given time is kept under control. Wattage of AC loads can usually be determined from a tag or label on the appliance, usually located near the power cord, or from the owners manual.



In the last few years, several inverters have become available which while able to feed power back into the utility grid, can also run in a stand-alone mode with batteries. Most popular in this category is the Trace SW series. This type of inverter is truly "the best of both worlds, " as it can operate without utility connection, but is also able to sell excess power generated by your system to the power company and provide power even if the utility grid is temporarily disabled.



If the inverter is expected to run induction motors, like the ones found in automatic washers, refrigerators, dishwashers, and large power tools, it must be designed to surge, or deliver extra power for short periods of time when these motors start. "Surge capacity", the wattage that the inverter can deliver in short bursts, should be 6 to 10 times the wattage rating of the largest motor that will be used. For example, a washing machine will usually be labeled as requiring 700 watts but it is unlikely to run reliably on an inverter with a surge rating of less that 6000 watts.



Another factor in inverter choice is the type of wave form required by the loads that will be used. Utility power is delivered as a pure sine wave. Inverters deliver power in one of three basic wave forms; a square wave, a modified sine wave or an actual sine wave.

Low cost inverters deliver a square wave, which has approximately 40% harmonic distortion. This type of inverter will not run induction motors or fluorescent lights and is rarely used any more. It will function well on universal AC/DC motors, found in small kitchen appliances, small hand power tools and vacuum cleaners.
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Many of the better quality power inverters designed for the home market have a modified or quasi sine wave output. These inverters generally perform better than a square wave inverter, but their cost is considerably higher per watt. In the past pure sine wave inverters had a prohibitively high cost, but lower cost models are now becoming the standard. For many applications, they may be the proper choice. See the Outback FX, Trace SW series and the Exeltech inverters in the section following. It is a good idea to discuss your application with us before ordering an inverter.



1. Has a wattage rating greater than the sum of all wattage that will be run at one time.
2. Has a surge rating greater than 6 times the wattage of your largest induction motor.
3. Has frequency regulation if any appliances have synchronous motors. (Some stereo turntables, tape decks, clocks)
4. Has appropriate AC output voltage. (120 or 120/240 volts).



These days it is rare to find a PV system of more than a few modules that does not have an inverter. An inverter is the magic "black box" that changes to DC power stored in batteries to 110 volt AC 60 Hz power, used by most lighting and appliances found in today's grid-connected home. While DC lighting and appliances are available (some can be found in this catalog), smaller selection, less features and considerably higher prices for these items are the norm. During the last decade inverter quality has taken a quantum leap forward, while price per watt has dropped dramatically. Running a mostly AC system allows you to wire your house with low-cost Romex wiring familiar to any electrician. By saving the cost of heavier, more expensive DC wiring as well as lower priced appliances, you will almost certainly have paid for your inverter.