Basically, an inverter can supply three types of power. They are as follows:
Usual or typical power: An inverter has to supply usual or typical power on a steady basis which is continuous rating. It is comparatively lower than the surge power. For example, after the first few seconds, a refrigerator pulls this power to start up the motor.
Surge or peak power: Supplying maximum power by an inverter for short time period is called surge or peak power. Typically, it ranges from few seconds up to 15 minutes or so. For example, we can say about electric motors like pumps which require higher startup surge while running.
Average power: This power is comparatively lower than typical or surge power. Typically, it is not any factor while choosing an inverter. While estimating required battery capacity, average power is only useful factor. Inverters need to be sized for the typical continuous and maximum peak load. For example, running a small television or a pump for 20 minutes during a one hour period, the average should be approximately 300 watts only, even though the pump requires 2000.
There are various types of inverters are available in the market. Usually, the size of inverters are rated in the range from 50 watts up to 50,000 watts, although, sometimes units larger than 10,000 watts are used in solar photovoltaic systems or in household. Various types of inverters are as follows:
Square Wave Inverters: These types of inverters are not desirable at all. They produce inefficient square wave which is horrendous for running appliances. They are comparatively very cheap and the size of these inverteres are typically 500 Watt or less. These types of inverters should not be considered for a home or solar photovoltaic system.
Modified Sine Wave Inverters: These are most economical and popular inverter. Usually, they produce an AC waveform in between a square wave and a pure sine wave. Modified Sine Wave Inverters are also called Quasi-Sine Wave inverters. They are not too expensive and perform well in almost all household appliances. Most computers perform well with a Modified Sine Wave inverter. But, it is not good for appliances which use timer or motor speed controls.
True Sine Wave Inverters: Among all inverters, a True Sine Wave inverter produces considerably a pure sine wave. These type of inverteres are comparatively very expensive. Practically, it can run all kind of AC equipment perfectly. Most of True Sine Wave power inverters are controlled by computer. They can automatically turn on and off as per requirement of AC loads. If you need to supply automatic power to a normal home using a wide variety of electrical devices, it is recommended to use a True Sine Wave inverter. It has been observed that most appliances operates more efficiently and smoothly with a True Sine Wave inverter consuming less power.
Grid Tie Inverters: Grid Tie Inverters are suitable for the system which is connected to grid power supplied by utility company. Whatever electricity your solar panels produce, by using a grid power inverter, you can expect reduced electricity bill from your utility company. You can also sell back your excess power produced by solar panels to tour utility company. In this system, a much smaller battery bank should be installed in order to cover short term outages from a few minutes to an hour or so. If there is no frequent long term power outages and back-up power requirement, no batteries are required indeed.
Installing two inverters in a system is known as stacking which can provide more power or higher voltage. You can increase the output voltage by stacking two compatible inverters in series. This would be the technique to use to provide 120/240 volts AC. On the other hand, if you want to increase the power, you should configure them in parallel. For example, if two 2000 watt inverters are connected in parallel, then it will provide 4000 watts (4KW) of power.