Making A Transformerless Solar Inverter Circuit

Sun is a major and an unlimited source of raw power which is available on our planet absolutely free. This power is fundamentally in the form of heat, however humans have discovered methods of exploiting the light also from this huge source for manufacturing electrical power.

Today electricity has become the life line of all cities and even the rural areas. With depleting fossil fuel, sun light promises to be one of the major renewable source of energy that can be accessed directly from anywhere and under all circumstances on this planet, free of cost. Let's learn one of the methods of converting solar energy into electricity for our personal benefits.

In one of my previous posts I have discussed a solar inverter circuit which rather had a simple approach and incorporated an ordinary inverter topology using a transformer.

Transformers as we all know are bulky, heavy and may become quite inconvenient for some applications.

In the present design I have tried to eliminate the use of a transformer by incorporating high voltage mosfets and by stepping up the voltage through series connection of solar panels. Let's study the whole configuration the with the help of the following points:

Looking at the circuit diagram, we can see that it basically consists of three main stages, viz. the oscillator stage made up of the versatile IC 555, the output stage consisting of a couple of high voltage power mosfets and the power delivering stage which employs the solar panel bank, which is fed at B1 and B2.

Since the IC cannot operate with at voltages more than 15V, it is well guarded through a dropping resistor and a zener diode. The zener diode limits the high voltage from the solar panel at the connected 15V zener voltage.

However the mosfets are allowed to be operated with the full solar output voltage, which may lie anywhere between 200 to 260 volts. On overcast conditions the voltage might drop to well below 170V, So probably a voltage stabilizer may be used at the output for regulating the output voltage under such situations.

The mosfets are N and P types which form a pair for implementing the push pull actions and for generating the required AC.

The mosfets arenot specified in the diagram, ideally they must be rated at 450V and 5 amps, you will come across many variants, if you google a bit over the net.

The used solar panels should strictly have an open circuit voltage of around 24V at full sunlight and around 17V during bright dusk periods.

Parts List

R1 = 6K8

R2 = 140K

C1 = 0.1uF

Diodes = are 1N4148

R3 = 10K, 10 watts,

R4, R5 = 100 Ohms, 1/4 watt

B1 and B2 = from solar panel

Z1 = 5.1V 1 watt

Use these formulas for calculating R1, R2, C1....