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April 19, 2014  |  Login
Buying an Inverter for Your Solar Electric System
By Dan Chiras
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Buying a Solar Electric System: Panels and Inverters

Inverters are a key component of virtually all residential solar electric systems. They come in many shapes, sizes, and prices. When purchasing an inverter from a local supplier who’s also going to install the system, your choices may be relatively limited. They typically have inverters they like and therefore will probably make a recommendation that fits your needs. Even though a local supplier/ installer will do the thinking for you, you should still understand something about inverters, so they don’t supply you with a model that doesn’t work for you.

First and foremost, you need to determine whether you need an inverter for a grid-connected or stand-alone system.

Second, when selecting an inverter, be sure that its voltage corresponds to the voltage of your system. As noted earlier, solar electric systems are either 12-, 24-, or 48-volts (the most common are 24- and 48-volt systems; 12-volt systems are common in small applications such as cabins or summer cottages). This means that the panels produce 12-, 24-, or 48-volt electricity; the inverter boosts the voltage to 120 standard household current. So remember, the inverter you buy must fit your system voltage. A 12-volt inverter won’t work in a 24-volt system.

The next selection criterion is the wave output form. Here, you will find two basic options: modified sine wave or pure sine wave model. Basically, output wave form tells you how pure the electricity is. Sine wave is purer than modified sine wave. It is equivalent to the electricity you buy from the electrical grid, without the hassles of blackouts, brownouts, and dangerous power surges!

Sine wave is also more expensive.

Unless money is a problem, I strongly recommend that you purchase a sine wave inverter, not a modified sine wave inverter. Sine wave inverters produce “cleaner” AC electricity, so they tend to work much better with modern electronic equipment. In fact, some of the newest electronic equipment — like most of the energy- and water-efficient frontloading washing machines — won’t operate on modified sine wave electricity. The sensitive computers that run these washing machine just plain won’t work! Some laser printers apparently also have a problem with modified sine wave electricity, as do some cheaper battery tool chargers. Furthermore, and here’s an important thing, I found that electronic equipment like TVs and stereos give off a rather annoying high-pitched buzz when they’re operating on modified sine wave electricity.

When selecting an inverter, you will also need to check out three additional factors: output power, surge rating, and efficiency. Let’s start with output power.

Output power is a measure that tells you how many watts the unit can produce on a continuous basis. The Xantrex RS3000 inverter, for instance, produces 3,000 watts of continuous power, which means it will be able to power a microwave using 1,200 watts, an electric hair dryer using 1,200 watts, and many other smaller loads simultaneously without problem. The Sunny Boy 2500U, made in Germany but available in the US, produces 2,500 watts of continuous power, still quite a lot for most households (that’s the size inverter I have in my house and we rarely, if ever, reach this level).

Surge rating is the wattage an inverter can put out over a short period, usually around five seconds. The Xantrex RS3000 inverter has a 7,500-watt surge power rating (60 amps).That means it can produce a surge of power up to 7,500 watts. Why is this important?

Many appliances like washing machines, refrigerators, and power tools like table saws require a surge of power when first turned on. more



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