• Electrical India
  • Mar 23, 2017

Power Grid of the future

Smart grid technologies ,in future, will focus on increasing the grid’s efficiency, reliability, and resilience...

- C S Indulkar 


 It is necessary to operate a reliable, affordable and efficient power grid, and attract capital for the power grid to increase its operational efficiency. Wind and solar power have created new challenges and opportunities for operating the grid. Energy storage technologies have helped the consumer electronics industry in developing hybrid and electric vehicles.

Coal plant requirements

  In future, green-house gas policies will lead to a significant retirement of coal-fired generation. It will be necessary to reduce air and water pollution, due to greenhouse gas emissions and coal combustion residual disposals. For continuing the operation of coal –fired power plants, plant owners need to retrofit their plants with environmental control technology, or close down the affected units completely.

Fig.1 Wind and Solar Resources

Wind and Solar generation

  Wind and solar resources (Fig.1) will increasingly constitute a significant portion of the generation mix. However, the grid of the future should be able to manage the variability and uncertainty of wind and solar power. Numerous wind integration studies are being carried out all over the world to examine the performance and the economic impact of integrating high levels of wind power in the energy resources.

  Studies have shown that integrating enough wind power to generate more than 30% renewable by energy is possible, provided the system has adequate generation flexibility, transmission capacity, control area co-operation, and grid requirements for wind plants. The uncertainty and variability of wind and solar power demands flexibility from the rest of the generating plants. Flexible generation in the rest of the generating plants will be needed as more wind and solar plants are built. Faster starting times, capability to reduce generation quickly from the existing fleet, and higher unit ramping capabilities are the key needs to bring in significant levels of wind and solar power.

Electric Vehicles

  EVs and plug-in hybrid EVs (PHEVs) are emerging as alternatives to conventional petrol vehicles but will need strong incentives and a relatively high cost of petrol to be viable. Electric vehicles are a boon in reducing the dependence on oil and reducing the tailpipe emissions. EVs and PHEVs substantially cover the cost of the existing battery systems. If the cost of batteries is substantially reduced and a new car buyer who drives significantly lower km per year can still opt for a petrol vehicle if economics is the main reason for the buyer. At today’s fuel prices, lower battery costs and stronger incentives are needed for electric vehicles to make substantial inroads into the transportation sector. If EVs form a substantial share of the transportation market, they will lead to a substantial load growth. Further, the implementation of the charging infrastructure for EVs and PHEVs will present a new business opportunity. Smart vehicle charging costs much less than uncontrolled charging. These savings can be used to invest in technologies needed to enable smart charging, provide incentives to customers for promoting controlled charging, and thus provide savings to customers. In areas which experience sudden increases in EV charging loads, it may be necessary to replace overloaded transformers, reconfigure heavily loaded distribution lines, and build new substations. These system modifications and upgrades are manageable and are relatively small relative to the cost of EV s and of the appropriately managed charging infrastructure.

Energy Storage

  The grid serves the customer load with generation that is dispatched and controlled precisely to match the load. Earlier, the power systems were designed and controlled to manage load variations by increasing or decreasing the generation output. Wind and solar power aggravate the variable power needed from the rest of the generation. However, the variability of wind and solar power, when these resources generate more than 30% of the annual energy, can be managed by the grid, without requiring energy storage equipment. But, the grid with wind and solar resources would require a greater need for frequency regulation and reserves. For this purpose, wind turbine manufacturers are offering hybrid wind turbines with integrated battery energy storage which can self-supply incremental ancillary services. Grid Scale Energy Storage Applications are shown in Fig. 2.

  The grid with wind and solar resources would require a greater need for frequency regulation and reserves. For this purpose, wind turbine manufacturers are offering hybrid wind turbines with integrated battery energy storage which can self-supply incremental ancillary services. Storage can be used for capturing lower cost energy to displace higher cost energy at a later time, or for shifting energy from one time to another to avoid overloading the equipment. Battery storage systems can be used if expensive diesel-fired generation is to be reduced. In congested cities, which experience line or transformer overloads, and where there is no room available for new equipment, storage equipment may be used near the loads to avoid expanding the substation or reconfiguring the lines. Storage technology is employed to maximize existing generation and transmission investment and operation, integrate renewables, and minimize greenhouse gas emissions. A storage device provides flexibility to the grid, especially when the grid expands and flexibility requirements increase.

  The grid with wind and solar resources would require a greater need for frequency regulation and reserves. For this purpose, wind turbine manufacturers are offering hybrid wind turbines with integrated battery energy storage which can self-supply incremental ancillary services. Storage can be used for capturing lower cost energy to displace higher cost energy at a later time, or for shifting energy from one time to another to avoid overloading the equipment. Battery storage systems can be used if expensive diesel-fired generation is to be reduced. In congested cities, which experience line or transformer overloads, and where there is no room available for new equipment, storage equipment may be used near the loads to avoid expanding the substation or reconfiguring the lines. Storage technology is employed to maximize existing generation and transmission investment and operation, integrate renewables, and minimize greenhouse gas emissions. A storage device provides flexibility to the grid, especially when the grid expands and flexibility requirements increase.

Fig.2 Grid Scale Energy Storage Applications

Distributed Generation

  The term, Distributed Generation (Fig.3), is applicable to non-despatchable solar PVs located on the customer side of the meter and to co-generation facilities by large industrial sites with ratings of 100MW or more. Independent power producers and utilities may choose to connect at the distribution level when their magnitude of development is small. Distributed generation built close to load can generate greater revenue in the wholesale market. DGs can also be used for alleviating localized overloads of existing substation capacity. However, the DG output must be available at the time of system peak. This requires that the DG output be despatchable. Wind generation and hydro power are currently the largest renewable energy sources in the grid. Therefore, solar PVs are currently the most rapidly growing DG segment. When the PVs are connected on the customers’ roofs, the energy produced displaces the energy provided by the utility. However, the grid service is still needed on cloudy days when PVs are unable to displace the utility energy. Therefore, much of the fixed service costs of the utility remain unchanged. Hence, the utilities need to consider alternative tariff structures. Alternative tariff structures can recover the fixed costs without burdening the non-self -generating customers.

  Large scale wind and solar power, along with distributed generation, and coal-plant retirements in future, will also affect the performance of the transmission system. Many old thermal units are located near large urban centres. These units provide essential voltage support and needed short-circuit strength. This dynamic support maintains a strong and rigid voltage for system stability during disturbances such as loss of a major transmission line. Unlike active power, the need for reactive power is highly location-dependent. Wind and solar plants are usually built away from load centres. The reactive power produced at a remote wind plant or a sunny desert is of little value to maintaining voltage in urban load centres. Previously, electricity transmitted through the grid was delivered via synchronous generators equipped with excitation systems. Wind and solar energy use asynchronous generating technologies with nil contribution to the short-circuit strength of the grid. Wind and solar energy can, however, provide necessary dynamic reactive power to the grid and support voltage at normal operating conditions, but the asynchronous generators(wind and solar) do not provide the same level of voltage stiffness during grid disturbances as conventional synchronous generators. There is, therefore, loss of dynamic reactive capability at load centres due to wind and solar power. Modern electronic loads, air-conditioning and computers also increase the requirement of dynamic reactive support. The retirement of conventional generators and displacing them with wind and solar power would alter the present systems’ capabilities to manage grid disturbances. For voltage problems, shunt capacitors are a relatively inexpensive solution and can be installed quickly. However, shunt capacitors cannot regulate voltage dynamically. Static voltage compensators (SVCs) have been used successfully to control dynamic voltage regulation, but require stiff grid voltage that is created by nearby generation. STATCOMS can provide improved performance in a weaker grid, but in a very weak grid they will not be able to stabilize voltage during a disturbance. The only viable option is synchronous condensers, which replicate the dynamic reactive power capability of generating power for the grid. For this purpose, the conversion of retired generators to synchronous condensers is possible, which involves removing the turbine and operating the synchronous generator to produce only reactive power.

Demand Management

  Direct load control, where operators can disconnect load on demand, is possible. This is based on dynamic pricing where price schedules and signals are passed on to customers to incentivize load reduction. Dynamic pricing is making possible more flexible and advantageous response for both customers and system operators. In future, retail demand management will be possible by state regulatory commissions and utilities that need to manage the peek demands and reduce long-term capacity costs. Demand management (Fig.4) benefits utilities, customers, and the power system by deferring new investment in generation and transmission, increased reliability, and increased economic efficiency due to dynamic pricing.

  In recent times, there is a vital need for preventing power disruptions and blackouts which paralyze the key necessities of the population which include services provided by police departments, fire houses ,hospitals, elderly care facilities, and other essential government and business operations. Microgrid systems, which include a combination of distributed generation, energy storage and demand management, with a system that enables system integration, communication, monitoring, and smart control can function seamlessly during contingencies to ensure continuous operation of critical loads.

Fig.4 Demand management

Conclusions

  Smart grid technologies ,in future, will focus on increasing the grid’s efficiency, reliability, and resilience. Microgrids will be a useful means of providing service resiliency in certain areas by providing sustainable operations and uninterrupted functioning of critical loads in the event of widespread interruptions in power supply. New technologies, variable market conditions, extreme weather events, and new regulations and policies will shape the future of the grid. The factors described in this article are some of the key drivers that will affect the power grid of the future.


C S Indulkar is retired from IIT Delhi as Professor and Head of Electrical Engineering Department.

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