Basics Equipment Inverters
Inverters
Inverters change the direct current (DC) from solar arrays or batteries to the alternating current (AC) used by the utility company and most household appliances. The two basic types of inverters are grid-connected and stand-alone.
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Grid-connected inverters have a special safety feature that shuts off the inverter in case there is a power outage. They will not run without the utility company being online. Grid-connected inverters are sometimes called grid-tied or intertied. They produce very "clean" electricity, without voltage spikes or distorted wave forms. The electricity is often cleaner than the utility company.
Grid-connected inverters are connected directly to the solar array. They usually have something called maximum peak power tracking (MPPT) that keeps the array operating at the maximum power point. This can save money by not having to buy as many modules.
Stand-alone inverters are made to run autonomously, without utility grid power. They use the battery bank for their power source. They cannot be hooked to the utility grid because they will not shut off automatically in case the utility grid goes down. Some stand-alone inverters have square-wave or modified square-wave voltage wave forms that should not be used with certain types of equipment.
Hybrid inverters are made to operate as a grid-connected inverter, but disconnect from the utility company when the power goes out and operate as a stand-alone inverter. This type of inverter is used in a grid-connected system with battery backup for critical loads, such as a refrigerator, computer, or security system. Battery backup systems are used where the utility has frequent or sustained blackouts.
Inverters come with many features. Some have a ground fault protection device to keep the array from catching fire if there is a ground fault. There is usually a display to show the system status. Others have a method to disconnect the battery bank if the voltage gets low.
More about inverters is in the Solar Basics book and how to size inverters is in the Solar Design book.