Inverters

The inverter is the heart of all but the smallest power systems. It is an electronic device the converts direct current DC power from batteries or solar modules into alternating current AC power to operate lights, appliances or anything that normally operates on power supplied by the utility grid. Inverters come in many varieties, sizes and qualities and offer various features that specialize them for particular applications.

Off-Grid Inverters

Off-grid, or standalone, inverters convert DC power stored in batteries to AC power that can be used as needed. Select an inverter for your power system based on the maximum load you will be powering, the maximum surge required, AC output voltage required, input battery voltage and optional features needed. High quality standalone inverters are available in sizes from 100 watts, for powering notebook computers and fax machines from your car, to 60 kilowatts, for powering a commercial operation. 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.

Grid-Tie Inverters

Grid-tie, or utility intertie, inverters convert DC power from PV modules into AC power to be fed into the utility grid. There are two major types of grid-tie inverters; string inverters and low voltage input inverters. The SMA Sunny Boy, Fronius and Xantrex GT-3 inverters are string inverters. The name “string” comes from the way the PV modules are wired together, in series to achieve a higher voltage. These inverters are designed to run at voltages up to 600 VDC. String wiring is faster to install, more efficient and allows the use of smaller gauge wire. DC voltage this high can be very dangerous and life-threatening, so string inverters should be installed and serviced by qualified electricians. A grid-tie PV system uses the utility company, in effect, as its storage battery. When the sun is shining, your electricity comes from the PV array, via the inverter. If the PV array is generating more power than you are using, the excess is sold to the power utility company through your electric meter, by making the meter run backward. When you need more power than the PV array can supply, the utility makes up the difference. This type of system makes the most sense in most cases where you have utility power, because there are no batteries to maintain or replace. Unfortunately, if the utility power goes down, this type of inverter will go off, too, regardless of whether or not the sun is shining.

Dual-Function Inverters

Using a dual-function inverter allows you to sell excess power to the utility, and also maintain a battery bank for standby power in the event of a utility power failure. In a typical installation, the inverter is connected to a battery bank, a sub panel for critical loads that will be powered during a power outage, and the house load center. If the utility is available, the inverter will supply the house loads from the utility. If the utility fails, the inverter will supply power to the loads from the battery. When the utility is available again, the inverter will switch the loads back to the utility, and recharge the batteries. If the batteries become fully charged by another power source, such as photovoltaic modules or a wind or hydroelectric generator, excess power may be sold back to the utility in locations where net metering is allowed.

Sunny Boy, the String Inverter for Photovoltaic Power Plants

The Sunny Boy is the most successful solar inverter for grid connected PV-plants. There are plenty of good reasons for this. SMA has successfully been developing and manufacturing systems for energy conversion in railway applications and for industry for over two decades. This outstanding know-how is the basis for the Sunny Boy inverter. The Sunny Boy is an essential component of your PV-plant and the basis for long term yields. More than 200,000 are in the field by now. They are reliably doing their work and you can rely on this.

 

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