What is Solar Energy?
"Energy neither can be created nor can be destroyed" is a famous statement that all of us know. We also know that the sun is the ultimate energy source, as constant exothermic reactions co-occur and heat releases. The Earth receives the sun's solar energy in the form of sunlight. Sunlight contains packets of energy, called photons which can be used for various purposes. This energy coming from the sun is called solar energy.
Now, energy is indestructible, but we can convert it from one form to another. Solar energy can be used for various purposes, but one of the best use of solar power is to convert it into electric energy and use it for our daily needs. It is the best way of generating electricity, as it is renewable, and no pollution is involved. So, valuable resources like coal and petroleum are preserved.
How to convert solar energy into electrical energy?
Solar radiation can generate voltage, or a potential difference, resulting in electricity generation. There is a junction between the metal and semiconductor in a photovoltaic/solar cell. When solar radiation strikes this junction, a potential is created, called the photovoltaic effect. Every cell generates a small amount of electrical power with very low efficiency. Still, when many of these solar cells are connected, electrical energy can be developed much higher value.
Generally, silicon panels are used in solar cells, consisting of a thin film, and are installed on the roof of households. They have an efficiency of 15-20%, and since many have to be installed for sufficient power, the cost eventually increases.
It is to be noted that the amount of electricity generated is proportional to the temperature and radiation intensity. The intensity and temperature of surroundings are different in different places. As a result, obtaining the same electrical power in other regions is impossible.
The Working Model of the Solar Cell in Energy Generation
Firstly, for generating electricity with the help of solar power, we need a solar cell to convert solar radiation into electrical energy. In Simulink, "PV Array" is the solar cell block we will also use. The inputs for the temperature and irradiation need to be given to the PV Array, after which it will start capturing the radiation and converting it.
However, as we had discussed earlier, the electrical energy generated isn't enough, as a solar cell's efficiency is very low. In this case, we have also attached a display to the PV Array, showing the input and output magnitudes parameters. We need a voltage of around 240 Volts, which is the ideal household voltage. But on simulation, the voltage comes to be about 100-130 volts, which is insufficient to run household appliances. Moreover, household appliances run on AC power, but the output obtained from a PV Array Solar Cell is DC voltage, which means conversion from DC to AC is also required. A detailed breakdown of the circuit is explained below.
We will be using two signal builder blocks. The signal builder blocks will contain values of temperature and irradiance, which change during the day and night. So, more solar energy will be generated during the day compared to night.
Boosting up the low voltage output to a higher value:
Boosting the voltage is the first step after solar energy is converted to electrical power. The step-up of voltage is carried out by installing a boost converter. A boost converter is a component/circuit responsible for increasing the voltage. It steps up DC voltage and returns the output as a DC voltage. Voltage is stepped up by stepping down the current. It works on the principle of conservation of power. As power is the product of voltage and current, as voltage increases, current reduces to keep the power constant.
A boost converter consists of 4 components, a capacitor, an inductor, a diode and a MOSFET/IGBT switch. The boost converter has two working modes: the Conduction Mode and the OFF mode. The mode on which the boost converter works depends on whether the switch is ON or OFF.
We use a Pulse Generator or a Pulse Waveform Generator and connect it with the MOSFET or the IGBT switch. The role of the pulse generator is to send pulses to the switch. It is required for the functioning of the boost converter.
So, the low voltage provided by the PV Array is now converted to a high voltage DC power source.
Converting the DC Voltage to AC voltage:
The second step is to convert the high voltage DC to high voltage AC, which is done with an inverter's help. An inverter consists of an oscillator, control circuit, drive circuit, and transformer for step-up. The conversion of DC to AC is done by mainly turning ON and OFF the switching devices. The DC inp[put given to the inverter is constantly switched ON and OFF by the MOSFET. The pulses are transferred to the transformer.
MOSFET and internal diode in parallel with a series RC snubber circuit. When a gate signal is applied, the MOSFET conducts and acts as a resistance (Ron) in both directions. If the gate signal falls to zero when the current is negative, the current is transferred to the antiparallel diode.
Below is the diagram of a three-phase inverter circuit:
The switching devices' constant turning ON and OFF is called Pulse Width Modulation and is achieved by attaching the Pulse Width Modulation Generator to the inverter. The PWM generator, in our case, is a single-phase full-bridge(4 pulses) type with a modulation index of 0.8.
Passing the wave through a passive filter:
After converting to an AC signal, the wave is given to a passive filter connected to a resistive load. The role of a passive filter is that it filters the frequencies so that the output waveform generated is a pure sine wave.
Implementation in Simulink:
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Solar Intelligent Power Generation System is a circuit modelling that harvests the solar power provided by the sun. Learn how solar radiation is converted to electrical energy and used in our household; Developed in MATLAB R2021a with Simulink and Simscape.
We use various components in Simulink to design an ideal system where the solar energy is trapped by the cell, boosted up and then converted to AC. Below are the blocks needed, which are categorized based on the function they perform:
Capturing the Solar Energy and converting it to DC:
- PV Array
- 2 Signal Builder Blocks(for generating varying temperature and irradiation throughout day and night)
- Display attached to PV Array
Boosting Up the DC Voltage(Boost Converter):
- A switching device like MOSFET or IGBT
- Gate pulse connected to the switching device
Converting the DC Voltage to AC Voltage:
- Universal Bridge
- PWM generator connected to the universal bridge
- Resistance/ load
Adding a passive filter:
Note that the powergui block is also needed for the simulation to run.
Then, we connect all the blocks and get the final circuit as shown below:
We have also attached three scopes at three sites. The scope will help us see the voltage waveform in all three steps; thus, we can analyze the circuit.
The first scope is connected to the PV array output, and here is the waveform obtained:
Then we have to pass this low voltage wave to a boost converter. We get the output from the boost converter as shown below:
Now, we have to convert this DC voltage to AC voltage with a passive filter, and the waveform from the third scope is shown below:
Hence, we get the desired output of 230-240 volts pulsating AC, which concludes our solar power generation.
In this blog, we have successfully covered the following topics:
- What is Solar Energy?
- Components and working of a solar power circuit for electricity generation.
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