What is an inverter?

Inverters (inverter) is a device whose function is to convert the continuous DC electricity coming from the panels or batteries into an alternating current of 110/220/380 AC to operate home appliances or pumps or connect the solar energy system to the national electricity grid. Basic Technical Characteristics of Solar Inverters:

1. Characteristics of AC Output waves

   The household current operates on a pure sine wave called the Pure Sine Wave, and there is another wave called the Modified Sine Wave.As the picture shows, the red color shows the normal current, and the other colors show other forms of waves. This will make a difference with you in operating some devices that only work on the real sine wave. So when buying an inverter, we will find that some devices are described as producing a pure or modified sine wave or pure sine wave. Modified Sine Wave, and this will have a difference in the price and also in the quality of the devices that can be operated. It used to operate it sometimes, but a change occurred in the behavior of the device, for example the fan worked, but a change was noticed in its sound and the motor cycle, and this is a negative point that is compensated by the low price. Modified sine wave inverters are not suitable for operating all devices that have AC motors, such as:

2. Inverter capacity – Rated Power

   It is noted that the devices often express their consumption in watts, and some inverters express their capacity in volt-ampere VA, and this calls for attention when calculating the capacity and converting volt-ampere into Watt requires multiplication in the electrical power factor. The devices that can be loaded on it have a total of 600 watts.For the motors that are loaded on the inverter, the actual current must be calculated when starting the motor by making the necessary correction for the electrical power factor, and here you will calculate the loads that are expected to be loaded. Set a margin of increase in order to avoid overloading. The user must be careful and aware of the nature of the device, not to overload it, and respond to the warnings issued by the device when increasing the load by reducing loads, turning off some devices, or turning off the device altogether if it cannot bear it, especially with frequent power outages.

3. Low frequency and high frequency inverters

   Low frequency vs High Frequency There are two types of inverters and without diving into theories, it can simply be said that there are differences in weight, cost, maximum capacity and noise.

   1. A low frequency inverter uses large copper coils to convert current and is therefore heavy and expensive
   2. A high frequency inverter uses electronic transistors to convert current.

   The difference between high and low frequency inverters

   clause	Low Frequency Inverter	High frequency inverter
   Weight and size	Large and heavy, weighing up to 10 kg per kilowatt capacity	Small and light, weighing about 2.5 kg per kilowatt capacity
   price	beloved	Cheap
   Maximum power – Surge Power	The maximum capacity is 4-8 times the continuous capacity. That is, the 3 kilowatt inverter has a maximum capacity of at least 12 kilowatts, and this number is valid for starting induction motors such as air conditioners and washing machines. For example, a 3 kilowatt inverter has a maximum capacity of 12 kilowatts. This number is sufficient to operate a 3-horsepower air conditioner	The maximum power does not exceed twice the continuous power, and for the operation of rectifying motors, careful care must be taken in designing the size of the inverter
   the noise	It causes a lot of noise, so it must be connected in a place far from living places	He does not make noise and his voice is very low

Types of inverters (inverters)

1. On Grid Inverter

   

   • This type is used in systems connected to the electricity grid
   • There are sizes starting from 2 kilowatts to 1 megawatt
   • Small sizes up to 5 kilos have a 1-phase 220 volt output type
   • Sizes larger than 5 kilos have an AC output type of 3 phase, 380 volts
   • This type of inverter disconnects the electric current automatically and turns off completely when the network is out of power, and this feature ensures safety for workers in the event of maintenance work on the electricity network during a power outage.
   • It is not possible to benefit from solar energy electricity when the power is cut off from the network, as the inverter is completely turned off
   • The inverter synchronizes the frequency of the output current (50-60 Hertz) with the frequency of the network current using an internal oscillator, and adjusts the voltage with the same network voltage, and this process is called Synchronization
   • This inverter outputs  a pure sine wave current  , so that the electricity coming out of the inverter matches the network electricity in all characteristics.
   • Most of the types of inverters connected to the network now come from the high frequency type that does not contain copper coils, as previously explained.
2. Off Grid Inverter and Hybrid

   

   • Most types of off-grid inverters now come with an internal charging regulator
   • The current output is either a modified or pure sine wave. Pure wave inverters have become the most common of all inverters after their low prices, except for small inverters intended for operating lighting units only.
   • The voltage of the battery bank supported by the inverter is a specification found in the hybrid inverter or the Off Grid that contains the charging regulator inside it. The voltage of the batteries supported by the inverter is generally as follows: 12 volts for small inverters up to a capacity of 1 kilowatt 24 volts for inverters from 1 to 3 kilowatts 48 volts for inverters from 3 to 10 kilowatts 96 volts for inverters from 10 to 20 kilowatts 192 volts for inverters from 20 to 50 kilowatts 600 volts for inverters from 50 to 500 kilowatts. If it is 48 volts, for example, you will have to install 4 12-volt batteries or 8 6-volt batteries, so that they are connected in series. More than one battery can be connected to the same device, but in parallel, to give the same 12 volts, for example, with a longer operating time, which also depends on the device’s ability to charge the batteries at an appropriate time, as frequent power outages lead to insufficient time between the two outages to charge the batteries.
   • Inverter Protection – Circuit Protection Protection must ensure that the device has sufficient protections, mainly protection against overloads, especially with an audio alert Protection against low battery voltage Protection against overheating
   • Automatic switching when the power is cut off – UPS uninterrupted power support Hybrid devices support automatic switching when the power is cut off or back, which is called UPS. This feature is useful if a specific device is running on the inverter and you do not want it to stop running, such as a server or a medical device, for example.
   • The possibility of programming priority in operation, whether from panels, batteries or mains electricity
   • Some types have a circuit to operate a diesel generator in the absence of the sun, mains electricity, and low battery charge. .
3. Grid Tied with battery backup

   

   • This system combines the previously explained connected and separate systems, as these inverters accept batteries with the possibility of connecting them to the electricity grid.
   • The main difference between this type and the hybrid inverter is that this inverter can pump electricity to the grid in addition to using electricity from the grid. That is, the alternating current runs in both directions to and from the network, as shown in the picture. As for the hybrid inverter, it takes current from the network in one direction only, and it cannot pump electricity to the network.
   • This inverter performs the Synchronization process previously explained in the inverters connected to the network
   • This inverter separates the pumping of electricity to the network when the power is cut off, but it does not turn off, so here lies the benefit from solar energy electricity when the power is cut off from the network and relying on cells and batteries
4. Solar pump inverter

   

   • It is known that the power of the solar beam is variable during the day, which results in the need to change the speed of the solar-powered pump throughout the day. These inverters are characterized by the ability to control the speed of AC pumps from the moment they are turned on at sunrise to the moment they are turned off at sunset, passing through their normal operating period during the day.
   • Solar pump inverters receive a series of cells connected to each other in series with a total voltage of up to 800 volts. Where there can be 20 solar panels connected to each other in series, and there will be 60 groups of these 20 panels, so they are all connected inside the inverters, whose capacity in large sizes may reach 300 kilowatts.
   • The inverter controls the start of the motor by gradually raising the voltage and frequency from zero until it reaches the programmed initial speed or the required reference speed within a percentage of time called the acceleration time that has been determined and programmed in advance, as well as the process of stopping the motor, it gradually reduces the voltage and frequency from the value which it is at the moment of the stop request until it reaches zero within a percentage of time called the acceleration time that has been determined and programmed in advance.
   • Inverters for pumps less than 2 HP usually have a single phase current output
   • All inverters for pumps greater than 2 HP have a three phase AC output
   • Many modern types of solar pump inverters have a diesel input and AC electricity from the network, to obtain a hybrid system that works as a backup source of energy other than the energy of the panels.
   • The inverter outputs a current of variable frequency, starting from 0 to 60 Hz, according to the instantaneous intensity of sunlight.
   • The inverter is equipped with a soft starter device, which performs soft rectification of motors with large and medium capacities to reduce the starting current, which is high when direct operation of the motor through a contactor, and to gradually raise the load speed from zero to maximum speed. This feature eliminates the need for a large inverter to withstand the large surge power that occurs at the start of induction motors.

Solar inverter specifications