Solar photovoltaic (PV) systems are considered as promising renewable technologies and they are expanding rapidly in recent years. The country’s solar installed capacity was 71.61 GWAC as of 31st August 2023. Solar power generation in India ranked fourth globally in 2021. Solar PV systems convert solar energy into direct current electricity using solar cells, which are normally made by semiconducting materials. Common technologies used in PV industries include crystalline silicon, thin-film, compound semiconductor, and nanotechnology. Photons of light hitting the solar panel knock electrons in the substrate material into a higher level of activity; these electrons are then channelled off of the panel to create DC electricity.
In most cases, an inverter will be used to convert the DC power into AC power, making it more directly usable to consumers – as most modern electric appliances operate only on AC power. We can also use charge controllers DC-DC conversion to use in village where AC 3-phase line is not available to supply DC operated home appliances like LED, TV, Mobile charging etc., which are our basic needs.
Solar PV system performance is generally characterized in terms of the cost per kilowatt-hour of energy generated for a comparison of energy costs from other distributed technologies. This cost is a function of the system’s efficiency at converting light into electricity, the availability of direct sunlight at the point of installation and myriad costs that influence the total installation price (e.g. the cost of the panels and other equipment, labour, permitting fees, etc.). The max irradiance received in India is 1000W/m2. Below figure describes the V-I curve of PV module for max o/p DC voltage.
Solar PV system for smart grid-tie type
A solar photovoltaic system consists of various energy conversion stages in which the DC-generated electricity is first converted to the desired DC voltage incorporating the maximum power point tracker. Depending upon the requirements, the voltage is either boosted up or bucked down using one of the DC choppers like a step-down buck converter, step-up boost converter, buck-boost converter, single-ended primary inductor converter (SEPIC converter), flyback converter, and Cuk converter. The other conversion is DC to AC conversion to feed the AC load or the grid. The inverter is used to convert DC from the solar panels to AC. Both these conversions contain power electronic converters and inverters. See the next figure.
Parts of solar PV system
- PV module/panel
- DC-DC converter
- Solar inverter (standalone or grid-tie)
- Grid
- Load
PV module: Photovoltaic modules are made up of many individuals, interconnected photovoltaic cells. To ensure the modules are tilted correctly and facing the sun, they are housed in support structures. Every module has two output terminals that collect the generated current and transfer it to the management systems at a solar power station.
A photovoltaic module’s efficiency is quantified as the ratio between the electrical power going out of the terminals and the power of the sun’s rays striking the module’s surface. The standard value used to indicate solar radiation is 1,000 watt/sqm. If every square meter is struck by 1,000 watts of sunlight, the percentage of energy actually converted into usable electricity is what constitutes the efficiency. The average life of a photovoltaic module is around 30 years.
Types:
- Monocrystalline Solar Panels (Mono-SI)
- Polycrystalline Solar Panels (Poly-SI)
- Thin Film (TFSC)
- Amorphous Silicon Solar Cell (A-Si)
- Biohybrid Solar Cell
- Cadmium Telluride Solar Cell (CdTe)
- Concentrated PV Cell (CVP and HCVP)
Monocrystalline solar panels (Mono-SI): This type of solar panels (made of monocrystalline silicon) is the purest one. One can easily recognise them from the uniform dark look and the rounded edges. The silicon’s high purity causes this type of solar panel have one of the highest efficiency rates, with the newest ones reaching above 20%.
Monocrystalline panels have a high-power output, occupy less space, and last the longest.
Polycrystalline solar panels (Poly-SI): These panels can be distinguished because these types of solar panels have squares, their angles are not cut, and they have a blue, speckled look. They are made by melting raw silicon, which is a faster and cheaper process than that used for monocrystalline panels.
This not only leads to a lower final price but also lowers efficiency (around 15%), lower space efficiency, and a shorter lifespan since they are affected by hot temperatures to a greater degree.
However, the differences between mono- and polycrystalline types of solar panels are not so significant and the choice will strongly depend on your specific situation. The first option offers slightly higher space efficiency at a slightly higher price but power outputs are basically the same.
Thin-film solar cells (TFSC): Thin-film solar panels are manufactured by placing one or more films of photovoltaic material (such as silicon, cadmium or copper) onto a substrate. These types of solar panels are the easiest to produce and economies of scale make them cheaper than the alternatives due to less material being needed for their production.
They are also flexible – which opens a lot of opportunities for alternative applications – and are less affected by high temperatures. The main issue is that they take up a lot of space, generally making them unsuitable for residential installations. Moreover, they carry the shortest warranties because their lifespan is shorter than the mono- and polycrystalline types of solar panels. However, they can be a good option to choose among the different types of solar panels where a lot of space is available.
Amorphous silicon solar cell (A-Si): Have you ever used a solar powered pocket calculator? Yes? Then you have definitely seen these types of solar panels before. The amorphous silicon solar cell is among the different types of solar panels, the one that is used mainly in such pocket calculators. This type of solar panel uses a triple layered technology, which is the best of the thin film variety.
Just to give a brief impression of what ‘thin’ means, in this case, we’re talking about a thickness of 1 micrometre (one millionth of a metre). With only 7% efficiency rate, these cells are less effective than crystalline silicon ones – that have an efficiency rate of circa 18% – but the advantage is the fact that the A-Si-Cells are relatively low in cost.
Biohybrid solar cell: The Biohybrid solar cell is one of the types of solar panels, that is still in the research phase. It has been discovered by an expert team at Vanderbilt University. The idea behind the new technology is to take advantage of the photosystem 1 and thus emulate the natural process of photosynthesis. By combining the multiple layers of photosystem 1, the conversion from chemical to electrical energy becomes much more effective (up to 1000 times more efficient than the 1st generation types of solar panels).
Cadmium telluride solar cell (CdTe): Among the collection of different types of solar panels, this photovoltaic technique uses Cadmium Telluride, which enables the production of solar cells at relatively low cost – and thus a shorter payback time (less than a year). Of all solar energy technologies, this is the one requiring the least amount of water for production. Keeping the short energy payback time in mind, CdTe solar cells will keep your carbon footprint as low as possible. The only disadvantage of using Cadmium Telluride is its characteristic of being toxic, if ingested or inhaled. In Europe especially, this is one of the greatest barriers to overcome, as many people are very concerned about using the technology behind this type of solar panel.
Concentrated PV cell (CVP and HCVP): Concentrated PV cells generate electrical energy just as conventional photovoltaic systems do. Those multi-junction types of solar panels have an efficiency rate up to 41%, which, among all photovoltaic systems, is the highest so far.
The name of such CVP cells is related to what makes them so efficient, compared to other types of solar panels: curved mirror surfaces, lenses and sometimes even cooling systems are used to bundle the sun rays and thus increase their efficiency. By this means, CVP cells have become one of the most efficient solar panels, with a high performance and efficiency rate of up to 41%. What remains is the fact, that such CVP solar panels can only be as efficient if they face the sun in a perfect angle. In order to reach such high efficiency rates, a solar tracker inside the solar panel is responsible for following the sun.
DC-DC converter in PV system
DC-DC converters are widely used in photovoltaic generating systems as an interface between PV module and the load. The DC-DC converter is provided to regulate the constant output under various operating conditions of photovoltaic cells. These converters must be chosen to be able to match the Maximum Power Point (MPP) of PV module when climatic conditions change with different resistive load values. So DC-DC converters must be used with MPPT controller in order to reduce losses in the PV system. The power from the solar which is not depleting in nature is unpredictable and greatly fluctuating. One serious component of any PV is the effectiveness of its maximum power point tracker (MPPT).
Solar inverter
Grid-Interactive or Grid Tie Inverter (GTI) is an electronic device that converts Direct Current (DC) voltage to Alternating Current (AC) voltage – and that can operate in parallel with the electric utility grid, normally 120 V RMS at 60 Hz or 240 V RMS at 50 Hz.
The grid tie inverter must match the phase voltage of the grid and maintain the output voltage slightly higher than the grid voltage at any instant for not flowing any current to grid or vice versa while grid power is ON & only current flows to Home or ANY LOAD. Grid-tie inverter has a fixed unity power factor (PF=1), which means its output voltage and current are perfectly lined up.
Grid-tie inverters are also designed so that they can quickly (within 2secs) disconnect from the grid, if the utility grid goes down or any fault created on grid side. This phenomenon is called ANTI-ISLANDING.
Advantages of a solar inverter
Solar energy has always helped in reducing global warming and greenhouse effect. Use of solar energy helps in saving money. Many people have started using solar-based devices.
- A solar inverter helps in converting the direct current into batteries or alternating current. This helps people who use limited amount of electricity.
- There is this synchronous solar inverter that helps small homeowners and power companies as they are large in size.
- Then there is this multifunction solar inverter, which is the best among all – and works efficiently. It converts the DC power to AC very carefully which is perfect for commercial establishments.
- This inverter is cost effective i.e., less expensive than generators.
- Apart from solar inverters there are other devices too that make use of solar energy namely, solar cooker, heater.
- Solar inverters are the best way and they are better than the normal electric ones. Also, their maintenance does not cost much money.
Nirod Ranjan Samantaray is a Senior Product Compliance Specialist at Vimta-Emtac Laboratories Pvt. Ltd.
