Inverters make up roughly 25 percent of the cost of an off-grid and 10 percent of a grid-tie system. Power losses are inherent, but advances in technology allow 85-90+ percent efficiency, and are continuing to improve efficiency and reliability.
Choosing an inverter is critical to your solar system. Poorly designed inverters can lower energy output dramatically. High temperatures can shut down an entire system, and because all of the panels are linked to one inverter in traditional systems, if one panel has problems, the output of the entire system is decreased. Micro inverters are now being developed that are installed in each solar panel so the entire system is not affected.
When choosing an inverter, make sure that it can handle all the electrical devices and appliances you currently use, and plan for future additions. This is referred to as "loads".
Note that electric motors such as those that power the compressor of a refrigerator, that go on and off throughout the day need considerably more operating power to get started, so the inverter must be rated to handle this extra load. Therefore, look for an inverter with a high surge power rating.Inverters are grouped into three types; Square-wave inverters, which do no exist in the market any longer. Under certain conditions a modified sine wave inverter will suffice; however, for solar applications a pure-sine wave inverter is required. It is important to have disconnect and overcurrent protection on the system. Most local building codes will require this. When comparing inverters, the major factors to be considered are the wattage rating, the surge power, and the efficiency.
Electronic inverters are available as high frequency switching units or transformer based units. The switching units are lighter and less expensive, but have a shorter life expectancy because of their limited surge capacity. Transformer-based units accommodate surges more readily, but the initial cost is significantly more.
Intertie, or grid-tie inverters, are connected to the utility grid and synchronize power between the utility and what is produced by the home system. When they are generating excess power, it is sent to the utility grid.
Battery backup systems manage the flow of electricity, and are also capable of supplying energy during utility outages. These units manage the flow of electricity not only between the utility and energy produced by the home system, but also the electric charge stored in the batteries. If the system can't keep the batteries charged, it uses the utility to charge them. Understandably, the cost for these units generally exceeds that of non-battery systems.
Inverter Technology Continues to Improve