• Electrical India
  • Jan 5, 2016

A Necessity Of Hybrid AC/DC Microgrids In Indian Electricity Sector

The grid collapse can cause half of the population to face darkness focusing a need of reliable well monitored supply system. Hybrid AC/DC microgrid can be the answer to resolve this problem of energy scarcity and uncertainity of supply – particularly for remote, sparsely geographically rural population...

- Dr. Mrs. G. A. Vaidya,

Prof. Mrs. Kalyani M. Kurundkar

 In India, 300 million i.e. quarter of the country’s population do not have access to electricity. About 70% energy generation capacity of India is from fossil fuel, with coal accounting for 40% of India’s energy consumption followed by crude oil and natural gas respectively. India is largely dependent on imports of fossil fuels.

  Due to rapid economic expansion, India is world’s largest energy market and going to be second largest in global energy demand by 2035. About 10-15% of villages in India are still to be electrified.

  The grid collapse can cause half of the population to face darkness focusing a need of reliable well monitored supply system. Hybrid AC/DC microgrid can be the answer to resolve this problem of energy scarcity and uncertainity of supply particularly for remote, sparsely geographically rural population. Hybrid AC/DC microgrids have high reliability, high efficiency, low emissions and affordable cost.

  Therefore, a universal access to energy services through Hybrid microgrid systems can be India's enduring contribution to human development.

  In past several years India has seen significant growth in the renewable energy generation. At present, 12% of energy in Indian Electricity sector is from renewable energy sources. With the financial assistance from MNRE, solar power plants in coordination with bio power plants have been installed at some locations. As India is having the world’s highest solar intensities with annual solar energy yield of 1,700 to 1,900 kilowatt hours per kilowatt peak of the installed capacity, the Jawaharlal National Solar Mission has set the ambitious target of deploying 20,000 MW of grid connected solar power by 2022 and aims at reducing the cost of solar power generation in the country through (i) long term policy; (ii) large scale deployment goals; (iii) aggressive R&D; and (iv) domestic production of critical raw materials, components and products. It has been envisaged to achieve grid tariff parity by 2022. Many Private players like Softbank, Airtel, Foxconn are investing $20 billion for grid tied solar, wind power and other renewable power projects. Also, entrepreneurs like Mera Gao Power, Gram Power, Minda Next Gen Tech, Sun Edison have electrified many households in the state like Uttarpradesh, Bihar and Madhya Pradesh. Although a rise in renewable energy generating sources have been observed, due to the dependency on solar power projects the grid experiences the sudden drop in the supply at certain hours that have to be met by conventional fossil fuel based power plants.

  This phenomenon is called as 'duck curve.' This shortage of power for only certain hours can be overcome using storage in the grid or system typically by using batteries or a flywheel. Such storage helps to quickly restore the supply, but are costlier.

  A system therefore consisting of Solar-Biogas Mix or Solar-Wind-Diesel generation mix or sometimes Solar-Hydro power generation mix called as ‘Hybrid AC/DC Microgrid’ is the need of the hour.

  Nearly all microgrids in India run on power from photovoltaic panels. Few Hybrid AC/DC Microgridsare installed in Karnataka and Uttarakhand which are networks based on Solar-Hydropower generation mix; in Bihar and Uttarpradesh these Hybrid microgrids are Solar-Biomass based. All these cover only a tiny part of the overall power needs of rural India.

Fig 1: Block diagram of Hybrid AC/DC Microgrid...

  A study has revealed that with DC Load and AC Source or AC load with DC source, many power conversion stages are to be incorporated which contribute to the total losses of the system. Therefore, instead of having only DC microgrid with Solar panel as the source and only the LED lamps and Solar fans as the load, one can have a combination of AC microgrid and DC microgrid with variety of linear and non-linear load i.e., the ‘Hybrid AC/DC Microgrid’. Hybrid AC/DC microgrids have separate supply lines and reduce the total conversion losses of the system. There are benefits and limitations for both DC and AC systems when considered as a supply system alone.

  In order to incorporate the advantages of both the systems the pairing of AC output source and DC output source i.e., Hybrid AC/DC microgrid is necessary. Fig 1. shows the basic block diagram of Hybrid AC/DC microgrid. This ‘Hybrid AC/DC microgrid’ system uses Solar with Gas or Wind or Hydro or Biomass as a source of energy in combination with each other with a battery or flywheel as storage, this can address the issue of variability, uncertainty and intermittent characteristics of these renewable energy sources giving a continuous and reliable electric supply.

  With a combination of AC electric system that is already existing and a low voltage DC system i.e., nearly less than 50 Volts when considered, it can simplify the setup process, reduce the cost – and will be also safer for the user for operations.

  Typical loads like lighting, charging phones, powering fans, Laptops, LCD TVs etc. are either DC System loads or can be converted to DC, and there are some non-linear loads like pumps motors etc. a separate AC supply line and a DC supply line can prove to be beneficial to reduce the tremendous conversion losses. In this condition, with a separate Biomass,Hydro, Wind or Biogas (AC source) in combination of Solar panel (DC source) and a battery as an energy storage system, a continuous and reliable supply to this type of load is possible.For this, a group of customers can contribute towards the initial installation and setup charges which can be recovered soon.

  Hybrid AC/DC Microgrids are very essential for sustainable energy required for human development with a robust economy. Due to Hybrid AC/DC Microgrids installations in near future, it will be possible to (1) supply electricity to 300 million Indians without the access to the electricity grid. This will help them, not only to increase their working hours, but also to run schools and colleges, hospitals and small scale industries. Improve their standard of living; (2) load management not only in rural areas but also in urban areas, university campuses, hospitals; (3) improve energy efficiency; (4) help with the existing grid stability, with renewable proportion increases in generation mix; (5) increase self-sufficiency of the customers, which can become ‘Prosumers’ (producers and consumers of electricity) in future; (6) reduce transmission and distribution losses by increase in number of microgrids.

  Due to these manifold benefits of Microgrids, the technological cost will also be reduced, which will cause lowered initial investment and decreased operational cost to the market, entrepreneurs and government.

  This will enable the investors to include more and more resources and create modern infrastructure.

  Even when Microgrids are essential, there are various ‘Economic’, ‘Technical’ and ‘Social issues’ to be addressed for the deployment of microgrids in India.

  Economic issues i.e., prepaid or postpaid metering system, which may lead to debts to the private player.

  This is because collection becomes a top challenge, also investment in technology optimally and cost recovery with maintenance comes under economic issues.

  Technically: Tariff mechanisms, government policies for volume scale deployment of these technologies, joint optimization of heat and electric supply, connection charges, joint optimization of demand and supply, quality and reliability of supply are the major challenges – and in addition to this there are also many social barriers.

  ‘Hybrid AC/DC Microgrids’ reflect a new way of thinking about designing and building sustainable grids, leading towards ‘SmartGrids’. Hybrid AC/DC Microgrids can have a faster implementation and can create a power system with redundancy, distributed generation and storage, cogeneration, heat and power efficient utilisation, with better consumer control.

  This will help work together with bulk power grid or system as an integrated whole to provide its consumers with maximum economic and environmental benefits. In future, the microgrids will be 'Smart' to make decisions about what clean energy source to run at what time and regulate the energy demand using power management technologies.
The Smart Hybrid AC/DC Microgrids will be able to optimize the cost reductions,energy savings and CO² emission reductions. The integration of multiple 'Smart Hybrid AC/DC microgrids' will lead this country towards Smart Grid contributing to sustainable human development..

Dr. Mrs. G. A. Vaidya is Professor and  Head of  Electrical Engineering Department, PVG’s College of Engineering and Technology, Pune. Prof. Mrs. Kalyani M. Kurundkar is Asst. Professor in Electrical Engineering Department, PVG’s College of Engineering and Technology, Pune.

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