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Suitable alternative

The demand for energy in India is consistently increasing and over the next decade, it is expected to grow at an annual rate of 6 per cent. What has also risen is the demand for power and estimates reveal that currently the country is experiencing a huge deficit between demand and supply, i.e. peak power shortage of 12 per cent and energy shortage of 11 per cent. As per the Ministry of Power's plan till 2011-12, India will need about 100,000 MW of additional capacity installation to meet its power requirement.

Presently, the supply of energy to satisfy this ever-increasing demand is a challenge. Spiralling power demand, huge Transmission and Distribution (T&D) losses etc, are affecting the reliability and efficiency of the existing grid network and thus managing the power grid has become one of the major concerns for the officials concerned. Also, the gap between energy requirement (MU) and energy available (MU) is expected to increase. Therefore, to meet the existing as well as future power demand, installation of few central power stations of the desired capacity could be proposed. However, with this option, a significant amount of power would be lost (as the existing average T&D loss is around 30 per cent) before delivering at the required sites, especially when power is transported over a larger distance, thus reducing the overall efficiency of the system. Hence, this option may not seem feasible in all cases, particularly for meeting relatively small dispersed loads at far flung areas.

In such a scenario, generating power through distributed generation (DG)/renewable energy resources and interfacing it with existing conventional grid could be a more feasible alternative. The DG-based power system can be added to increment generation capacity, whenever and wherever required. The distributed energy sources can not only deliver power to the local areas (where it is installed and distributed) more efficiently and reliably, but it can also feed excess power, if any, to the utility grid. Additionally, such an option has additional advantages like being cleaner and environmentally benign and also augmenting the supply of conventional grid while reducing the T&D loss.

Evolution of distributed generation based mini-grid system in India

In India, Distributed Generation (DG) is not a recent phenomenon. Diesel-based standalone DG systems (gensets) are commonly used by individual shopkeepers and house owners to provide back-up power during power failure. Large-scale power-intensive industries and commercial buildings have also installed their own captive power plants. If the history of distributed generation technologies/renewable energy technologies in India is observed, it is largely seen that it is either used in off-grid standalone mode to provide electricity access to remote villages or promoted in grid connected mode (such as largescale wind, small hydro projects and biomass power/cogeneration projects) with the aim of feeding electricity to the grid and augment the electricity supply situation.

In 1980s, the renewable power systems were used either as standalone systems such as solar lantern, solar home systems, solar street lighting system, wind pumps etc. or as large-scale grid interactive system such as large-scale wind or micro-hydro power system. The small-scale standalone solar home systems have been used for meeting the minimum lighting demand of rural remote dispersed community for a period of three to four hours in a day. However, these systems are limited to household lighting application only and were not able to cater to productive activity requirement.

In the '90s, several DG-based mini-grid systems (solar PV-based, biomass gasifier-based, micro hydro- based etc.) were installed. Power generation in the mini grid could be from a diverse range of small local generating resources, i.e. either through conventional generators, such as a diesel gensets or from renewable generators like micro hydro power plants, wind turbines, biomass gasifier, solar PVetc. or from a combination of both. These mini grids are typically of 10 to 250 kW and spread over 2 to 3 km to provide power through low-tension distribution lines. Here, availability of power in villages helps to improve the quality of life of the rural people through lighting of rural homes, streets, community areas, public places, helping trigger economic development and generating employment. In a DGbased mini-grid system, from a user's perspective, it has all the features of grid power supply, e.g. overhead Low Tension (LT) lines and service connections, which brings it close to the conventional power supply system. An appropriately designed mini grid can easily supply power for 8 to 10 hours daily. Though there is no limit on the capacity of the mini grid, these are typically in the range of 10 to 250 kW. A mini grid with more than one renewable energy resource were used in the late '90s to deliver more quantum of electricity at a cost-effective manner as compared to a single resource-based mini grid. The combination also provides better demand-side management.

Distributed generation based smart mini grid

In recent years, the options of integrating various DG technologies together more effectively through smart technologies to provide power in a grid connected as well as isolated mode, has gained attention. Also, with time, the smart grid has evolved as one of the solutions to tackle the existing energy challenges. The basic concept of a smart grid is to add monitoring, control and communication capabilities into the existing electricity delivery system, thereby improving the reliability, security and efficiency of the overall system. Advanced sensing, communication and control technologies in smart grids not only facilitate generation and transmission of power, but also distribution and utilization of electricity more intelligently and effectively. Smart grid is a significant technology enabler, allowing the consumer to participate in energy usage decisions while optimizing grid operations, fostering grid security and opening markets for alternate energy production. However, if the approach of smart grid projects and its development in India is observed closely, then, it is mainly aimed for large-scale power generation, transmission and distribution. The use of these advanced technologies to generate, distribute and consume electricity in the small-scale distribution network, i.e. in mini grid, is not a common practice, although the same tools and techniques can be applied in a mini grid to create a smart system for an efficient operation. Such an application will foster the effective interconnection and utilization of multiple renewable energy resources.

Smart mini grid elucidated

A Smart Mini Grid (SMG), or Micro Grid, is an intelligent electricity distribution network, operating at or below 11 KV, where the energy demand is effectively and intelligently managed by a diverse range of Distributed Energy Resources (DERs) such as solar pv. micro-hydro power plants, wind turbines, biomass, small conventional generators (diesel gensets) in combination with each other through smart control techniques. It may or may not be connected to a conventional utility grid. Large-scale implementation of such smart mini-grid systems in India can well be integrated with the existing programmes of MNRE such as the JNNSM and the national rural electrification programme.

Case study by TERI

TERI has designed, developed, and demonstrated the country's first of- its-kind smart mini-grid system. The aim is to have a better control of distributed energy sources combined with intelligent management of loads to improve the efficiency and reliability of the overall mini-grid system. This facility combines various Distributed Energy Resource (DERsl. i.e3.3 kWp wind generator, 1 kWp thin-film solar pv. 12.5 kWp solar PV, 100 kWe biomass gasifier, 600 Ah, 48 V storage battery, and a diesel generator. The diesel generator has been added to meet the intermittency of the renewable resources and hence, ensure reliable power supply.

Based on the integration of these multiple DERs into the same grid, the system has been designed with local controllers for each of the DER as well as a central controller called Intelligent Dispatch Controller ODC) which communicates with each of the local controller. While the local controllers ensure maximum utilisation of energy resources with permissible output power, the IDC performs complex system control functions and takes critical decisions such as automating the demand response, dynamically adding or removing DERs in a seamless manner (based on the existing demand) without affecting the grid stability. The system also has the capability to respond automatically to network problems and minimise network disruptions. Such smart mini-grid systems have scope in commercial complexes, hospitals, apartments, educational institutions and un-electrified locations.

Conclusion

Since distributed generation based smart mini grids are evolving as one of the enabling technologies for future dynamic energy needs and are immensely advantageous in terms of the multi-sectoral benefits, currently the focus should be to implement several pilot projects, while showcasing the applications and benefits of these smart mini grids. What is also needed is providing a conducive policy and regulatory regime for this concept to flourish and the market to develop.

Tags: smart mini grid, renewable energy, India energy crisis, distributed generation

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