How to Select the Perfect Inverter for Your Photovoltaic System

Electricity flows in two ways: AC (alternating current) and DC (direct current). DC current flows steadily in a forward direction while AC current finds the electrons switching directions, backwards and forwards. The power you use in your home every time you plug an appliance in is AC electricity. While it would seem a direct current would be more efficient, AC power can travel further without losing energy and is also able to transfer different amounts of power. Another advantage of AC power is that it can be easily bumped up or down in strength be way of a transformer, which is located on electric poles and allows electricity to be changed into the lower voltage necessary for appliances such as refrigerators, lamps, toasters and microwaves.

An inverter is a necessary part of your PV system as it takes the DC power produced from your solar panels or stored in your battery bank and converts it to the AC power necessary to run household items. A good quality inverter for an off-grid system will cost approximately 25% of the cost of the entire system, while an on-grid inverter runs about 10% of the total cost.

12-Volt, 24-Volt or 48-Volt System

Although a 48-Volt inverter will likely require a larger initial investment, it has advantages such as more voltage, less voltage loss, the ability to use a smaller wire gauge and to run longer distances of wire without the level of voltage drop seen in a 12 or 24-Volt system. If you are simply adding enough solar power to run only a few items in your home, you can get by with a 12 or 24-Volt system, however if you are serious about switching your entire home over to solar power, spend the extra money and buy a 48-Volt inverter. Outback, Xantrex, Sunny Boy and Magnum all have high-quality 48-Volt inverters available.

Sine Wave vs. Modified Sine Wave

AC current has a constantly varying voltage which swings from positive to negative-a hertz (Hz) indicates the number of times the AC alternates in a second. Most United States inverters convert 120 volts at 60 Hz while other countries prefer AC output of 220 volts at 50 Hz. Most appliances in the average home can run on AC from a quasi- or modified sine wave inverter, and the modified sine-wave inverter is definitely less expensive. However, the current trend for PV systems is the pure sine wave inverter; while most electrical appliances can run on modified sine waves, they don't like to. Modified sine waves cause fan motors and refrigerator compressors to run louder and hotter, and high-end electronics such as televisions, computers and printers may not be able to filter out the dirtier wave form. What this means to you is that if you choose to use a modified sine wave inverter your television screen could have lines in it, your stereo could hum annoyingly and your washer may not be able to properly complete a cycle. Pure sine wave inverters are the better choice unless you live in a situation where you use very few electrical appliances on a daily basis.

Continuous or Surge Output Power

Finally, check your chosen inverter specs carefully to see whether the power output is continuous or surge. The answer to this question is really important because the electrical motors in your home in appliances such as ceiling fans, blowers, blenders or refrigerators-all appliances which go on and off throughout the day-need as much as six times the normal operating power to start up. Your inverter must be rated to handle the extra load, or a good portion of your appliances might not be able to start.