You might have got an idea of the working of the inverter after reading the article "What is the functioning of the solar inverter?". But you cannot purchase inverter without having the answer to the following questions:
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Your inverter should be able to provide 2 types of power to the electrical appliances: one is Starting Power and another is Running Power.
For example, when a ceiling fan with power rating of 80 watts is switched ON will withdraw around 130 watts for first few seconds and after that it will settle down to 80 watts. We can say, 130 watts is the Starting Power and 80 watts is the Running or Continuous Power of the fan. When I switch ON the fan, my Inverter should take enough D.C. power from the battery and convert it into 130 watts A.C. power and after few seconds it should settle down to 80 watts. In short, the Inverter should have 2 types of rating:
Let us understand more about these terms with another example. Suppose, I want to run the following electrical appliances on solar power:
So, we need to consider this before choosing an inverter for our solar power system. Let us consider the following table: 
(*I am assuming that you start one appliance at a time that is you switch on the electrical appliances one by one not all in one time. Otherwise the sizing of the inverter will increase and hence its cost) Therefore, I should look for an Inverter with Peak Power Rating of 674 watts and Continuous Power Rating of 360 watts. The rating of the inverter generally comes in VA (Volt-Ampere). Watt vs. VA
In the market, the rating of Inverter is generally specified in VA (Volt-Ampere) not in Watts.
But we calculated our Inverter Rating in Watts. Dose this mean that our calculations are good for nothing? Cheer up Guys! We have a relation between VA and Watts It is true that both are the units of power but the former (VA) is the Apparent Power and the latter (Watts) is the Real Power. The relation between the two is as follows:
Assuming, you buy an Inverter having Power Factor of 0.9 (90% Efficient). We sized the Peak Rating of Inverter as 674 Watts and the Continuous rating is 360 watts. We can easily calculate its VA rating using this formula: Watts = Power Factor x VA Or VA = Watts/Power Factor Calculating Peak Power Rating in VA:
Calculating Continuous Power Rating in VA:
Finally, I should look for Inverter with Peak Power Rating of 749 VA or above and Continuous Power Rating of 400 Watts or above.
Our electrical appliances are designed to run on pure sine wave that we get from the grid.
In other words, the performance of these appliances is dependent on the shape of the input wave form. A change in shape of input waveform can affect the performance of these electrical appliances. Let us suppose you run your television on the inverter and you find some noise or the flicker on the television screen, this is due the fact that the output from your inverter is not the pure sine waveform, it is distorted. The prolong operation or running of the electrical appliances on the distorted waveform can considerably affect the life of these devices. The types of Inverter
There are basically two types of inverters which are available in the market,
Pure sine wave inverter:
The output voltage of this type of inverter is sine wave just like a wave form which we get from grid supply or mains. The voltage rises and falls smoothly and it instantly changes the polarity when it crosses the zero volts. The phase angle also changes smoothly. 
Modified sine wave inverter:
Pure sine wave inverter vs. Modified sine wave inverter
Advantages of pure sine wave inverter:
If you are not using above mentioned devices then you can go for Modified sine wave inverter to trade off between price and the performance otherwise it is advisable to go for Pure sine wave inverter for better performance and the safety of the electrical appliances. By now, we have calculated the desired rating of the inverter based on our requirement as mentioned in the above example. Now, we have to decide whether to Modified sine wave inverter or Pure sine wave inverter. It is true that initial cost with Modified sine wave inverter is less, but if we look at the reduction in the performance, increase in the maintenance cost of the devices and negative impact on their operational life, it is concluded that one should go for Pure sine wave inverter. Online Solar Course: "A complete Solar Course for Newbie Solar Entrepreneurs, Students, and Home-owners interested in installing Solar at the roof-top" Conclusion
I am concluding the topic in the following points:
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