Decentralized Generation - Distributed Generation and Micro Grid
When energy is generated and distributed using small scale technologies closer to its end users, it is termed as Decentralized Generation. These generations are based on the technologies, mainly renewable, including but not limited to, wind turbines, photovoltaic cells, geothermal energy and micro hydro power plants. Onsite power generation has many benefits over the centralized power generation systems, as it eliminates the costs associated with the transmission and distribution of power over long distances. These small scale technologies can yield power from 1KW to as much as 100MW.
Figure 1 Centralized vs. Decentralized Generation (Source: www.jcwinnie.biz)
Decentralized generation can take place at two scales. At a local level, site specific energy sources are used to generate electricity, constituting a Micro-Grid which is a cluster of generations serving a limited number of consumers. It can be either connected to the grid at a single point or can be totally independent of it. At the second level, the same technologies are used at much smaller scale and are installed by an individual energy consumer. Such a system is called Distributed Generation. These sources can be individually connected to grid, so that they can supply power to the grid when required – creating a prosumer, i.e., a producer and a consumer of electricity.
Benefits of Decentralized Generation
Decentralized generations are small and offer numerous benefits in comparison to the conventional centralized systems. Few of its benefits are discussed as follows:
No high peak load shortages -Distributed generation systems can reduce the peak demand and offer an effective solution to the problem of high peak load shortages.
Reduced high transmission and distribution losses - It can greatly reduce the losses during transmission and distribution of power from central location and hence improve the reliability of the grid network. In India, the current losses amount to about 35% of the total available energy.
Linking remote and inaccessible areas - Distributed generation can play a major role in providing power to remote and inaccessible areas. For a country like India, it offers a solution towards rural electrification.
Faster response to new power demands – The micro-grid systems are small scaled and often require lower gestation periods, it enables faster and easy capacity additions when required.
Improved supply reliability and power management - With independence from utility grid systems, distributed generation systems offer easy maintenance of power, voltage and frequency. It also offers the possibility of combining energy storage and management systems, with reduced congestion.
Technologies for Decentralized Generation
A decentralized generation system is very flexible, as it can be based on renewable or non-renewable energy sources. The decentralized generation technologies include but are not limited to the following:
Reciprocating Engines: Reciprocating engines can be fueled either by diesel or natural gas, with varying emission outputs. Almost all engines used for power generation are four-stroke and operate in four cycles of intake, compression, combustion, and exhaustion. Reciprocating engines are manufactured in various size ranges. Their typical usage is in providing continuous power supply or backup emergency power.
Microturbines: Microturbines are an emerging class of small-scale distributed power generation system in the size range of 30-400 kW. Microturbines consist of a compressor, combustor, turbine, and a generator. The compressors and turbines have radial-flow designs, and resemble automotive engine turbochargers. Most designs are single-shaft and use a high-speed permanent magnet generator producing variable voltage, variable frequency alternating current (AC) power. Most microturbine units are designed for continuous operation with higher electric efficiencies.
Combustion Gas Turbines: Simple cycle combustion turbine units start at about 1MW. These turbines can also be configured as combined cycle power systems to achieve upto 15MW, also called as industrial turbines or miniturbines. Combustion turbines have relatively low installation costs, low emissions, and require infrequent maintenance. However, their low electric efficiency has limited turbines to primarily peaking unit and combined heat and power (CHP) applications. Cogeneration DG installations are particularly advantageous when a continuous supply of steam or hot water is desired.
Fuel Cells: There are many types of fuel cells currently under development in the 5-1000+ kW size range, including phosphoric acid, proton exchange membrane, molten carbonate, solid oxide, alkaline, and direct methanol. Fuel cells have very low levels of NOx and CO emissions because the power conversion is an electrochemical process.
Photovoltaics (PV): Photovoltaic systems are most commonly known as solar panels. Photovoltaic solar panels are made up of smaller cells connected together that convert light radiation into electricity. The PV cells produce direct-current (DC) electricity, which must then be inverted for use in an AC system. Photovoltaic systems produce no emissions, are reliable, and require minimal maintenance to operate.
Wind Turbines: Wind turbines utilizes wind to produce electricity and require no additional investments in setting up large infrastructure such as new transmission lines, and are thus commonly employed for remote power applications.
Role of Decentralized Generation in Smart Grid
Decentralized Generations are natural extensions of smart grids. Their ability for on-site decentralized power generation helps in reducing peak loads and hence better system management of the central grid. In future, both smart micro grids and smart decentralized generations will be able to sell their generation back to the utilities from whom they buy the power thus providing additional revenue stream. This will help utilities to reduce the need for massive investments in building new high-voltage transmission lines to carry renewable power from far-off plants to towns and cities. Locally based solar, wind, biomass generators, fuel cells and other decentralized generation systems are much more convenient sources of power, thereby cutting down on the line losses associated with long-range transmission.
A key feature of a micro-grid is its ability to separate and isolate itself from the utility seamlessly during a utility grid disturbance with little or no disruption to the loads within the micro-grid. The micro-grid can automatically resynchronize itself when the utility grid returns to normal functioning, and reconnects itself to the grid, in an equally seamless fashion. Additionally, it reduces carbon emission and thus supports sustainable livelihood.
Decentralized Generation in India
In India, many renewable energy technologies are being employed in a number of decentralized generation projects. The figure below illustrates the technology options for decentralized power generation.
Figure 2: Technology options for Decentralized Generation
In typical Indian rural areas, smart micro-grids can provide clean, reliable, affordable, and scalable electrical power. For Indian economy rising fuel costs, under investment in old infrastructure and climate change are some of the biggest challenges being faced by the energy industry today. A Micro-Smart Grid can deliver benefit by use of renewable energy sources, while improving the reliability, security, and useful life of electrical infrastructure. The development of basic smart grid technologies can be accelerated by bring together all stakeholders namely, state and local governments, utility companies, public electricity regulators, and IT companies towards a common goal.
The Government of India has adopted an integrated energy policy which aims to provide energy security to all its citizens through conventional as well as alternative sources of energy. Some of the policies adopted by the Indian Government are as follows.
- The Electricity Act, 2003 has given a thrust to distributed generation particularly in the context of rural electrification. The Act specifies distributed generation and supply through stand-alone conventional and renewable energy systems.
- The National Electricity Policy notified on 12 February 2005 recommends under the Rural Electrification component, that to provide a reliable rural electrification system, wherever conventional grid is not feasible, decentralized distributed generation facilities (using conventional or non-conventional sources of energy) together with local distribution network be provided.
- Two specific schemes, the Rajiv Gandhi Grameen Vidyutikaran Yojna and the Remote Village Electrification Scheme, will provide up to 90% capital subsidy for rural electrification projects using decentralized distributed generation options based on conventional and non-conventional fuels.