Solar Inverter Specs

Grid-Tied

• Grid-tied inverters connect to the utility electrical grid common to most residential and commercial buildings. Sometimes referred to as grid-interactive inverters, this component also powers other renewable energy sources like wind turbines. Grid-tied systems should have anti-islanding protection, which disconnects the solar-energy system from the main grid when a fault occurs within the utility's system. Many municipal regulations allow home and business owners to sell excess energy generated by their solar-power systems to the utility company -- a process called net metering.

Stand-Alone and Battery-Operated

• Stand-alone inverters operate completely off grid. Remote cottage locations, rural farms, monitoring stations, RVs or boats benefit from this type of solar-energy system. Stand-alone inverters with a pure sine wave feature, which allows a smoother current flow, works best for large appliances and power tools. Battery-powered inverters can also tie into the grid. A fully-charged battery routes excess power to the electrical grid. During power failures, the system provides power for important appliances and is available 24 hours a day. Most have a power-saving mode that prevents the system from charging during the night.

Voltage and Wattage

• Most inverters in the U.S. and North America vary between 110 to 120 volts, with 117 as the standard. Typical household appliances operate off 120 volts. Appliances such as hot water heaters and electric clothes dryers typically require 240 volts, but most solar-powered homes tend to use natural gas to fuel these appliances. Some manufacturers provide inverters that supply both 120- and 240-volt capacity in a unit. Select an inverter that has the capacity for meeting the total AC load for your different appliances. Add the wattage rating for each appliance, such as refrigerator, computer and television, that will operate off the system. This calculation determines the total AC load, or the wattage, the inverter must have the capacity to power.

Inverter Chargers

• Inverters types include optional battery chargers. The chargers come in handy for charging alternating current batteries like the ones used for recreational vehicles. In addition, property owners who desire an uninterruptable power supply need inverters with battery chargers. Most inverter chargers always remain on and have three-stages. This feature charges the battery at a constant rate, until the battery reaches a higher level, and maintains the voltage. The inverter eventually switches to a float voltage to maintain the voltage indefinitely. A mechanism called a transfer relay allows running appliances off AC or grid power and directs some of the energy to the battery. The system switches automatically to battery power if the power goes out. Inverters with less than 1,000 watts do not usually have battery chargers.

Efficiency

• The efficiency of an inverter depends on its capacity for converting DC current to AC voltage without waste. Most inverters have an efficiency range of 85 to 95 percent and an average efficiency rating of 90 percent. One inverter product currently on the market has a 98.5 percent efficiency rating. Some battery-operated inverters have a standard DC to AC conversion efficiency of about 91 percent.