In this article we will try to understand the basic concept of a solar inverter and also how to make a simple yet powerful solar inverter circuit.
Solar power is abundantly available to us and is free to use, moreover it’s an unlimited, unending natural source of energy, easily accessible to all of us.
Why Solar Inverter
We have discussed how to use solar panels for generating electricity from solar or sun power, in this article we are going to discuss a simple arrangement which will enable us to use solar energy for operating our household appliances.
A solar panel is able to convert sun rays into direct current at lower potential levels. For example a solar panel may be specified for delivering 36 volts at 8 amps under optimal conditions.
However we cannot use this magnitude of power for operating our domestic appliances, because these appliances can work only at mains potentials or at voltages in the ranges of 120 to 230 V.
Further more the current should be an AC and not DC as normally received from a solar panel.
We have come across a number of inverter circuits posted in this blog and we have studied how they work.
Inverters are used for converting and stepping up low voltage battery power to high voltage AC mains levels.
Therefore inverters can be effectively used for converting the DC from a solar panel into mains outputs that would suitably power our domestic equipment.
Basically in inverters, the conversion from a low potential to a stepped up high mains level becomes feasible because of the high current that’s normally available from the DC inputs such as a battery or a solar panel. The overall wattage remains the same.
Understanding Voltage Current Specifications
For example if we supply an input of 36 volts @ 8 amps to an inverter and get an output of 220 V @ 1.2 Amps would mean that we just modified an input power of 36 × 8 = 288 watts into 220 × 1.2 = 264 watts.
Therefore we can see that it’s no magic, just modifications of the respective parameters.
If the solar panel is able to generate enough current and voltage, its output may be used for directly operating an inverter and the connected household appliances and also simultaneously for charging a battery.
The charged battery may be used for powering the loads via the inverter, during night times when solar energy is not present.
However if the solar panel is smaller in size and unable to generate sufficient power, it may be used just for charging the battery, and becomes useful for operating the inverter only after sunset.
Simulation and Working
Referring to the circuit diagram, we are able to witness a simple set up using a solar panel, an inverter and a battery.
The three units are connected through a solar regulator circuit that distributes the power to the respective units after appropriate regulations of the received power from the solar panel.
Assuming the voltage to be 36 and the current to be 10 amps from the solar panel, the inverter is selected with an input operating voltage of 24 volts @ 6 amps, providing a total power of about 120 watts.
A fraction of the solar panels amp which amounts to about 3 amps is spared for charging a battery, intended to be used after sunset.
We also assume that the solar panel is mounted over a solar tracker so that it is able to deliver the specified requirements as long as the sun is visible over the skies.
The input power of 36 volts is applied to the input of a regulator which trims it down to 24 volts.
The load connected to the output of the inverter is selected such that it does not force the inverter more than 6 amps from the solar panel. From the remaining 4 amps, 2 amps is supplied to the battery for charging it.
The remaining 2 amps are not used for the sake of maintaining better efficiency of the whole system.
The circuits are all those which have been already discussed in my blogs, we can see how these are intelligently configured to each other for implementing the required operations.
A MINI solar inverter circuit with relay changeover is discussed HERE
For complete tutorial please refer to this article: Solar Inverter Tutorial
Parts List for the LM338 charger section
All resistors are 1/4 watt 5% CFR unless specified.
R1 = 120 ohms
P1 = 10K pot (2K is mistkanly shown)
R4 = replace iit with a link
R3 = 0.6 x 10 / Battery AH
Transistor = BC547 (not BC557, it's mistakenly shown)
Regulator IC = LM338
Parts List for the inverter section
All parts are 1/4 watt unless specified
R1 = 100k pot
R2 = 10K
R3 = 100K
R4, R5 = 1K
T1, T2 = mosfer IRF540
N1---N4 = IC 4093
Remaining few of the parts does not need to be specified and can be copied as shown in the diagram.
For Charging Batteries up to 250 AH
The charger section in the above circuit may be suitably upgraded for enabling the charging of high current batteries in the order of 100 AH to 250 AH.
An outboard transistor TIP36 is appropriately integrated across the IC 338 for facilitating the required high current charging.
The emitter resistor of TIP36 must be calculated appropriately otherwise the transistor might just blow off, do it by trial and error method, start with 1 ohm initially, then gradually go on reducing it until the required amount of current becomes achievable at the output.
Adding a PWM Feature
For ensuring a fixed 220V or 120V output a PWM control could added to the above designs as shown in the following diagram. AS can be seen the gate N1 which is basically configured as a 50 or 60Hz oscillator, is enhanced with diodes and a pot for enabling a variable duty cycle option.
By adjusting this pot we can force the oscillator to create frequencies with different ON/OFF periods which will in turn enable the mosfets to turn ON and OFF with the the same rate.
By adjusting the mosfet ON/OFF timing we can proportionately vary the current induction in the transformer, which will eventually allow us to adjust the output RMS voltage of the inverter.
Once the output RMS is fixed, the inverter will be able to produce a constant output regardless f the solar voltage variations, until of course the voltage drops below the voltage specification of the transformer primary winding.
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