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InvertersThe inverter is a basic component which converts low voltage DC power from the batteries into high voltage (typically 120 or 240) AC power as needed. Why do I need an inverter? Alternating current (AC) is easier to transport over long distances and is the modern electrical standard. Most common appliances and loads are designed to operate on alternating current. Solar panels and wind turbines only produce and batteries only store direct current power. Alternating current and direct current are essentially incompatible. Inverters change Direct Current (DC) to Alternating Current (AC). Inverters of the past were inefficient and unreliable. Today’s generation of inverters are very efficient (85% - 94%) and very reliable. Today, the majority, if not all of the loads in a typical remote home operate at 120 VAC from the inverter. The only reason to operate select loads at low voltage DC is to maximize efficiency. Most inverters produce only 120 VAC, not 120/240 VAC as in typical utility-connected homes. The reason being, once electrical heating appliances are replaced with gas appliances, there is little need for 240 VAC power. Exceptions include large submersible pumps and shop tools which can either be powered be the generator, step-up transformer, or possibly justify the cost of a larger or second inverter - Grid-Connected Inverters
Synchronous or line-tied inverters are connected to, and operate in parallel with the electric utility grid. Most commonly connected to photovoltaic systems, these grid-connected inverters interface generated DC power to the utility grid. Regularly used in net-metering States, these inverters allow power produced by the PV system to power on-site electrical loads or to back-feed power into the grid when PV production exceeds load demands. As load demands become greater than the PV system output, such as at night, the balance of power is received by the grid.
- Stand-Alone Inverters
Stand-alone or static inverters are designed off-grid power systems. These inverters are connected to a battery bank and operate independently of renewable energy DC inputs such as wind or solar. Inverter performance is affected by the electrical load connected to the AC output, rather than the DC power source. The inverter must be sized appropriately to accommodate the total AC load and surge-load potentials for the system to function properly. Stand-alone inverters are available with three basic power output waveforms: square wave, modified sine wave and pure sine wave.
- Multi-function Inverters
Some inverters have features from both grid-connected and stand-alone types to facilitate future grid-connection options. A multi-function inverter is connected to a battery bank, grid power, standby generator and the house load center. This interactive inverter automatically provides uninterrupted power to household loads in the event of a grid shut-down. If the batteries become discharged, the inverter supplies the house loads from the utility lines, and charges the batteries in the process. If the batteries become fully charged by another power source, such as photovoltaic modules, wind or hydroelectric generator, excess power may be sold back to the utility. If utility power fails, the inverter can still operate and supply critical AC loads to the house from the batteries. If a standby generator is started, it can also supply power to loads and or recharge the battery bank. The inverter will synchronize with the generator and allow loads to be powered that are too large for either the generator or inverter to supply alone.
Two types of inverter wave forms predominate the market - modified sine and sine wave inverters. Modified sine wave units are less expensive per watt of power and do a good job of operating all but the most delicate appliances. Sine wave units produce power which is almost identical to the utility grid, will operate any appliance within their power range, but cost more per watt of output. |
