The solar inverter is one of the most important power electronic devices that make the modern solar panel system installed by EBR Energy widely usable. It makes the DC power from the modules usable for all the appliances of our house. Although these appliances might internally either work on DC or AC, all of them are used to an AC current. To know what an inverter is we must first understand its precise function in the solar panel system.
The output of the solar panel module is direct current. DC or direct current is the unidirectional flow of electric charge. Dc is produced by power sources like batteries, laptop chargers and solar panels. The symbol of dc power is “=”.
AC or alternating current, on the other hand, is the flow of electric charge such as it constantly reverses its direction. The usual form of an AC power is a sine wave the symbol for an AC signal is “~”.
Almost all electric grids across the world are AC based. Most households have, what is known as AC sockets. Consequently, most household electric appliances expect to be fed AC power even though the internal circuitry of the appliances might use DC. Nonetheless, the fact remains that solar power produced needs to be converted to an AC form so that it is more usable in the electricity frame we have today.
How do we make this DC power into easily usable AC power?
Working of an Inverter
By using an inverter. The inverter converts DC electric signal into the AC one. In an inverter, an oscillator is connected to switch DC current to AC. Then amplification for AC current takes place and finally to step up the voltage a step-up transformer is connected.
Let’s have a brief look at the features of solar inverter and it’s applications in the modern solar panel system. Inverters are classified based on their mode of operation, their size or implementation technology. Let’s first discuss the classification based on the mode of operation.
Classification on the mode of operation:
There are inverters for grid-connected systems, one for stand-alone systems and inverters that can be applied in situations that can have both connection types, called bi-model inverters. The first two types are the most commonly used.
Here a typical grid-connected PV system is shown:
The DC PV modules are connected to the regular AC electricity grid via a grid converted inverter (Sometimes called grid type inverter). In this case, the PV system is grid-connected, this means that the load can be supplied either by the solar panels system or the grid system. The inverters latch onto the grid’s frequencies and voltage. So the inverter that supplies AC power to the grid acts as a current source while the role of the voltage source is fulfilled by the grid.
Grid-connected technology can only be applied when there is a grid available. In some places, there is no grid available. Here we have to apply the stand-alone system technology. Take a look at the following diagram:
Here a typical solar grid or stand-alone solar panel system is shown consequently the inverter is a stand-alone inverter. In this case, the solar panel system is not connected to the grid which means the load can only depend on the solar panel system or solar power. So the inverter that supplies AC power to the load has to be a voltage source with a stable volt and a frequency supplying at 240 VAC or 110 VAC, whichever is the standard at the location.
In an off-grid system excess energy has to be stored in order to the system still be able to operate even at night when there is no solar power generation. Which types of storage are available and which are most suitable for solar systems, is the discussion of another time.
Apart from the mode of operations, inverters are classified on the basis of their implementation topology. There are 4 different categories of this classification.
Central inverters: Usually function around several kilowatts to a hundred megawatts range.
Module inverter or micro-inverters: Typically rated 50-500 watts range.
String inverters: Typically rated around 500 watts to few kilowatts. The string is nothing but a number of PV modules connected in series.
Multi string inverters: Typically rated around 1k watt to the 10-kilowatt range.
Click here to have a detailed explanation of inverters classified on the basis of their implementation topology.
Characteristics of a solar inverter:
Certainly, the choice of topology for your solar system will entirely depend on your system needs, size, etc. But in general, while choosing the solar inverter for your solar panel system, what are requirements that need to be considered. There are several characteristics of a good solar inverter:
- Solar inverters are expected to be as efficient as possible. This is because we wish to deliver maximum PV generated power to the load or to the grid. Typical efficiencies are in the range of more than 95% at rated conditions.
- It is expected for the inverter to have a built-in maximum power point tracker(MPPT mechanism). In power electronics, it is common to have inverters that implement maximum power point tracking before inverting the voltage. This ensures that the PV modules or arrays are operated at their maximum power point or MPP.
- Anti-islanding protection, to sense when there is a problem with the power grid.
- Since in a lot of situations solar panels are exposed to ambient conditions, it must comply with the temperature and the humidity conditions of the location.
- A good inverter will reach in favorable conditions around 10 to 12 years of lifetime.
With EBR Energy, get your solar panels installed for your homes, offices and commercial & industrial buildings, and convert them into your personal powerhouse of electricity generation. Get a free quote today.