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Inverters

Inverters are used to change Direct Current (DC) from the battery into Alternating Current (AC) from the grid:

• In grid connected systems to adapt the solar electricity from the solar panel so that it can be fed into the grid. Most solar panels produce DC. Some solar panels have a inverter integrated in the back of the panel (so called AC modules).
• In stand-alone solar electric systems to adapt electricity from the solar panel and the battery for electric appliances that cannot run directly from the battery.
• In backup systems to provide AC for appliances that are normally using electricity from the grid.
  

Inverters are available in many sizes and types. Some inverters have very high efficiencies, which is to be preferred. If you plan to have the inverter on stand-by most of the time, make sure that you buy one with low stand by power consumption. If you plan to have the inverter operational most of the time, choose one with a high efficiency (ask your supplier).

PV cells generate direct current (DC), and batteries store electricity as DC, but most common appliances require alternating current (AC). In cases where you need AC power, an inverter is used to change low-voltage DC (12, 24, 32, 36, 48, 96, 120) to higher voltage AC (120 or 240). Some power is lost in the conversion as inverters are, on average, about 80- to 95-percent efficient. AC wiring, components and appliances are more available and generally less expensive than similar DC products. Consequently, inverters are convenient for many systems.

Inverters cover a wide range of power capacity, and the type needed depends on the application. Light-duty inverters (100-1000 W) are suitable for small systems (e.g. power for lights). They are available with 12- or 24-volt direct current (VDC) input voltages and 120-volt alternating current (VAC) output. Larger inverters (1000-4000 W) are available, mainly with 12, 24 and 48 VDC input and 120 or 240 VAC output. For high-start power surges (e.g. from large electric motors), heavy-duty inverters are needed.

Low-cost inverters produce a modified square wave, which is not as good as utility power. Roughly a dozen electrical loads do not run well on this type of inverter. Your dealer can help you overcome most of these load problems by choosing proper appliances, tools, etc. Sine-wave inverters generally produce power that is similar to the quality of utility power.

So-called AC modules have an inverter on the back of the solar panel

Some PV modules even come with built-in inverters. Such modules are called AC modules. You can build up a complete AC system, AC module by AC module, increasing the capacity with each addition. (These inverters are used only for grid-connected systems.)

Many of today's inverters also come equipped with the following features:

1. Metering: a display to provide volts input/output, frequency output, voltage and frequency of a fuel-fired generator.
2. Fuel-fired generator start capability: Extra relays are provided to auto-start a generator if the batteries reach a programmed state of low capacity. Some can even be programmed to keep the generator from starting during the night (to avoid the noise), unless the batteries reach a second programmed low, in which case the generator will start regardless.
3. Grid-connected capability: The inverter can convert the DC output from the array to AC power that can be synchronized with the grid (utility). This feature makes it possible to reduce or even eliminate monthly utility bills.
4. Charging capability: Inverters can draw power from either the grid or a fuel-fired generator to charge the battery bank while, at the same time, continuing to pass that power through to the electrical loads in your house. Some inverters vary the charge rate and voltage to certain types of batteries and their current temperature.
5. Stacking: Some inverters can be linked together, either to produce twice the output or to produce power that is out of phase from inverter to inverter in order to produce 240-VAC power.

Information from http://www.mysolar.com and other sources were used, hardly edited by our engineers.

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