Types of solar inverters
A solar inverter is a device that converts direct current (DC) produced by solar panels into alternating current (AC) for consumers or injection into the power grid. In a photovoltaic solar system, inverters act as the heart of the system and convert the generated DC electricity into AC. In the following, we will examine the types of solar inverters, including connected to the grid (ongrid) and disconnected or separated from the grid (offgrid). We also explain how solar inverters work.
In general, solar inverters are classified as follows:
Classification of inverters in terms of output waveform
Classification of inverters in terms of connection to the grid
Classification of inverters in terms of panel connections
Review of inverters in terms of output waveform:
Square wave inverters
Modified sine wave inverters
pure sine wave inverter
Square wave inverters
This inverter is the cheapest and at the same time the worst type of inverters. A square wave is an inappropriate and unpleasant wave for most electrical devices. These inverters are usually cheap, powers less than 500 watts and more are used for car cigarette lighters. So these inverters do not work at all for home and industrial use.
Modified sine wave inverters
It can be said that the most economical and common inverter is this type. This type of inverter produces an alternating wave whose shape is between a square wave and a perfect sine wave. In many cases, these types of inverters are also called quasi-sine wave inverters. The advantage of these types of inverters is their low price and overall good performance, and most electrical devices such as lighting devices, radios, many televisions and computers, etc., can be started with these inverters, but some electrical devices, such as most motors, are capable of They do not work with these inverters. So we conclude that this inverter is used for small purposes.
Pure sine wave inverter
As it is clear from the name of this inverter, it produces a complete or pure sine wave to the extent that in some inverters it even produces a better sine wave than city electricity. This inverter is able to run all electrical appliances at its capacity, but the price of this inverter is expensive. So it can be said that this model is the best type of inverter and it can be used for all purposes.
As mentioned, the best type of inverter is the pure sinusoidal type, but because it is expensive, it cannot be used in many small applications. But among the other two inverters, the pseudo-sine type is better than the square one. Because with a pseudo-sine inverter, it is possible to start electrical appliances with motors such as refrigerators, only the power loss of these appliances increases and their life is slightly reduced. But the square wave inverter should not be used for motor devices at all because this type of inverter goes from a positive value to a negative value in a moment and this sudden sign change is very dangerous for motor devices. So, in general, pure sine and pseudo-sine inverter should be used.
Checking inverters in terms of connection to the network:
Grid connected inverter
Grid connected inverter
If you are connected to the grid and install solar energy to reduce the amount of electricity consumed from the grid, or if you cannot disconnect from the grid for any reason, these inverters are a good solution for you. By using these inverters, as much electricity as your solar system produces, the same amount of electricity consumed from the grid will be reduced, in fact, your costs will be reduced. And if your system produces more electricity than it needs, it can be sold to the grid. In these types of systems, if you don’t need backup power, you don’t need a battery, and the cost of installing your solar system will also decrease. Or if you need backup power for a short time, for example, one hour, you can choose a very low battery capacity.
In the type connected to the grid, the electricity produced from the solar panel is directly entered into the inverter. Therefore, this inverter is different from ordinary inverters. Because the electricity generated from the panel is always changing due to the effects of environmental conditions such as changes in sunlight. So the inverter does not face a uniform input power, and as a result, it must have a special pattern to convert direct current to alternating current. As a result, the price of the solar inverter is higher than the normal inverter.
Read this article : Types of solar panels
As their name suggests, these types of inverters do not have the ability to connect to the power grid and cannot be connected to the grid. Almost all inverters used in cars and for small systems are of this type.
In the off-grid type, the inverter converts the electricity stored in the battery from 12 V direct to 220 V alternating to make it suitable for use in home appliances. The more sinusoidal the inverters are, the better they will be. These inverters are not like grid connected inverters because they will convert uniform power from the battery.
Types of solar inverters in terms of solar panel connections
String solar inverters:
String solar inverters that have small capacities usually up to 125 kW, the strings are connected independently to the input part of the inverter and are paralleled to each other inside the inverter for connecting to any MPPT or may be in In special conditions and if the inverter has an MPPT, the strings are paralleled in a switchboard (Combiner Box) while protecting the voltage and current, and finally an input is connected to the inverter.
For example, we have a 20 kW inverter that has 2 MPPTs and 4 inputs, both of which belong to the same MPPT. 4 strings are connected to 4 inputs independently. 2 strings related to MPPT1 and 2 strings related to MPPT2 are paralleled to each other inside the inverter.
Central solar inverters:
Central solar inverters, which have capacities higher than 200 kW, although the number of strings in a switchboard (Combiner Box) are paralleled with each other while protecting voltage and current, and the output of the switchboard is connected to the input of the inverter.
For example, the SMA 2.2 MW central inverter has 18 inputs, so we must have 18 electrical panels, in each electrical panel there are 22 strings parallel to each other, and each string includes 20 320 watt LG panels. Therefore, 7920 panels are connected to this inverter, whose rated power is 2,534,400 watts. The total number of strings is 396.
Solar micro inverter:
Micro inverters are small inverters that are made in capacities of 200 to 500 watts and are suitable for installation on any one panel or sometimes both panels. These inverters have a small share of the market because they have a high price, they also have lower efficiency and higher harmonics, but instead they have a longer lifespan and in case of damage to one panel or creating a shadow on one panel, the performance of other panels will be overshadowed. does not place
Ease of installation is another advantage of these inverters. In case of failure of an inverter, only a small part of the set stops injecting electricity into the grid and other inverters are busy injecting into the grid.
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