Electricity is what makes our modern life possible. It provides comfort- lighting, cooling and heating in our homes and offices. It runs many of our modern transport systems, hospitals, schools, factories, and more importantly our computers and the internet. In short, the modern world and economy is inconceivable without electricity. No wonder the per capita electrical consumption is an indicator of the prosperity levels of any country.
The electrical infrastructure, the grid, makes all this possible and is one of the marvels of human ingenuity. It is ubiquitous and we take it for granted. It is a complex network of interconnected electrical networks and is characterized by three important elements: Generation, Transmission and Distribution.
Generators produce electricity converting one or the other form of energy into electricity. Thermal, hydro and nuclear have been traditionally used for centralized power generation. The power flows one way from the generator all the way down to the multitudes of customers and meets their differing demand. The generator electricity cannot be stored and has to be consumed as they are generated and thus making the balancing of the supply and demand a very critical aspect of the grid operation. Typical central grid architecture is illustrated below:
The present day besides being centralized, has quite a few problems. With hundreds of thousands of interconnecting points, the controlling and protection devices in a complicated web, the vulnerability of the grid is high. A simple system fault like overload devices not activating can result in cascading failures and eventually leading to the collapse of the entire grid. The aging infrastructure only makes the problem worse.
The earliest large scale grid collapse commonly referred to as the Great “North East Blackout” plunged northern and eastern USA and a part of Canada into darkness and 30mn people were affected. A faulty relay was behind this major event.
The other most often cited collapse is the July 14, 1977 New York grid collapse for more than 25 hours which besides bringing the city to a grinding halt also resulted in arsonists setting more than 1,000 fires and looters ransacking 1,600 stores. Ironically on the same day 42 years later, this July 14th, another partial blackout took place in New York.
In our country the Great Indian Grid Collapse that took place on two successive days 30 & 31 July 2012, hit as many as 400mn people, the largest ever population to be affected by a grid shut down. Failure of the load sensors & protective relays failed in a segment of the transmission led to this collapse.
Extreme weather incidents cause extensive damage to grid infrastructure. Depending on the intensity of the impact, rebuilding the infrastructure and restoring power can extend over many days. The aftermath of Hurricane Katrina in the US, the Tsunami in Fukishima in Japan and the Pani cyclone this year in Orissa in our country are recent major incidents. These vulnerabilities reduce the resilience, which the US Department of Commerce defines as “the ability to withstand grid stress events without suffering operational compromise or to adapt to the strain so as to minimize compromise via graceful degradation”.
Besides resilience, the grid’s reliability is also under stress. Ever rising demand and extension of network causes problems in matching the supply and demand. Weak monitoring, communication and control systems and focus on response, following a fault rather on preventive measures add to the reliability issues.
Centralized power plants run by fossil fuels also impacts environment. They pollute the environment and contribute to global warming. They need large amount of water and when warm water is released into the water body, its ecosystem is damaged. The solid waste produced pose handling, storage and disposal problems. They require large space for generating stations, substations, transmission and distribution network.
The losses in generation is as high as 60% and transmission losses further adds to it. More disappointingly the consumers have little role in any of the decision making processes in the entire arrangement and choice in the absence of a thriving electricity market.
Over the past 15 and 20 years, driven by growing need to limit carbon emissions and the simultaneous steep drop in Renewable energy equipments particularly solar, there has been rising integration of RE systems of varying sizes across the grid network. This rising injection of RE power which is inherently infirm further adds to the woes of grid management. However the huge merit of RE is that these sources, present as they are everywhere, can be directly tapped into by the consumers and generate power. Together with batteries whose prices also have dropped sharply, the efficient use of RE and its reliable integration to the grid has become a reality.
These small distributed energy systems (DERs) are miniaturized grids by themselves and have come to be called the Microgrids. These microgrids can operate unconnected or off the grid and meet the entire need of the customer. It can also be connected to the grid and draw power from the grid whenever there is a shortfall or inject power whenever there is excess generation. By feeding power into the grid, the power flow is no longer unidirectional and the consumer becomes a producer and consumer, “the prosumer”. He now has a greater stake and role in the entire arrangement and also can make choices. Illustration below shows a simple microgrid architecture.
Microgrids have multiple advantages. They bring electricity to remote communities and empower them by helping them learn and also to work even after sunset. It provides secure & reliable power 24x7 in conjunction with storage/grid. It is more resilient than the centralized grid and can easily isolate itself from the grid whenever there are issues and continue to power the consumer’s loads. It can be installed quickly and easily without the need for highly skilled people. Cost of implementation and maintenance are low. Microgrids powered by RE leaves behind minimal carbon footprint.
Microgrids come in all sizes: from a 5 KW system powering a remote village to a few MW sized grid connected industrial microgrid. As for ownership it could be single or multiple, as in the case of community and utility owned. However utility need not necessarily be an owner.
There is no universally accepted definition of the Microgrid. The International Council on Large Electrical Systems CIGRÉ defines microgrids as“electricity distribution systems containing loads and distributed energy resources, (such as distributed generators, storage devices, or controllable loads) that can be operated in a controlled, coordinated way either while connected to the main power network or while islanded”
Enmeshing microgrids of varying sizes and the new and more advanced distributed loads like EV and meeting their varying demands, into the existing grid network necessitates far greater and precise monitoring and controlling of all the elements to make the grid resilient, reliable, efficient and safe. Besides that, compliance to the laws governing electricity in the states or the nations the network meanders through to reach the consumers also needs to be taken into account.
The information, communication and computing technologies have grown by leaps and bounds over the same two decades period and are cut out for this task. The emerging digitalized grid “would detect and react to local changes in usage, improve system operating efficiency, and, in turn, reduce operating costs while maintaining high system reliability” and make it truly smart and intelligent.