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Smart grid or green grid?03 May 2010What exactly is a ‘smart grid’ and is it synonymous with the so-called ‘green grid’ concept? Senior IEEE member, David Bassett provides some answers and describes recent smart grid projects undertaken in the United StatesToday, there is a lot of discussion about ‘smart grids’, but what are they exactly? We could define the ‘smart grid’ as a collection of equipment that enables an electrical utility grid to operate in a more economical and functional manner – and one that also allows for the rapid restoration of power to customers during abnormal conditions or emergency situations. The ‘green grid’ is a logical side effect of the more efficient operation of the grid, resource generation and load control.
The initial implementation of a smart grid will typically result in improved operation of an electrical power distribution system, in terms of voltage control, reactive control and the efficient allocation of residual energy, all resulting in a greener grid with savings in power, and a reduction in carbon dioxide emissions.
For example, in the US, PPL Electric Utilities has a smart grid project that will implement this type of control and the company is expecting some 2.5 percent savings in energy use for customers. PPL Electric applied for, and won, a $19 million Department of Energy federal grant funded by the American Recovery and Reinvestment Act (Stimulus Bill).
The grant was awarded under the US Smart Grid Investment Grant funding opportunity, and PPL Electric Utilities will partner with Drexel University and technology leaders GE Energy, Lockheed Martin Corporation and Alcatel-Lucent to design and install the system.
The initial implementation will automate the operation of the grid so that faults will not only be de-energised but also isolated, allowing power to be restored faster to customers on non-fault line sections. The smart grid will actually detect the status of the entire system, allowing the transfer of non-fault line sections to alternate sources, restoring these customers to service. This requires bi-directional communication between equipment controlled and owned by the utility, which will enable real-time operational data to be collected. An assessment of this data is expected to lead to further optimisation of the grid.
The additional information collected on the grid, and the additional controlled equipment, will allow for dynamic control of system voltage, enabling optimal service voltage for all customers, and ultimately saving energy. Currently, the service voltage tends to be set during the installation of the line, with periodic adjustments as loads change significantly.
This can lead to some customers having voltage that is higher than necessary, while others experience lower than optimal voltage. In either case, this can result in energy waste. The current designs tend to have regulation equipment that operates independently, but this independent operation, while generally effective, is not optimal.
Consumer involvement
The initial implementation of a smart grid will typically provide information to customers (the electricity consumers) and it is up to customers to use this information. As a result, the exercise may not yield as much savings as initially expected or predicted. Without direct control of customer equipment, the customer must take action to achieve savings.
There was a recent case where a glowing orb was provided to indicate the cost of power and to signal the need for customers to cut back on their consumption. This type of feedback did not work well, presumably because many customers were either at work during those times, or were unwilling to manually adjust their electrical usage or comfort levels.
There is considerable opportunity to extend communication to the customer, and allow direct control of customer equipment. Some customers may perceive this automatic control as more convenient if they prefer ‘set it and forget it’ technology.
This option will allow for a significant increase in operational efficiencies of the grid. During periods of very high loading, selected loads can be turned off, resulting in cost savings for each load, reduced emissions, and more efficient use of existing facilities. Most utilities plan on cycling the controlled loads; for example, turning loads off for 15 minutes and on for 45 minutes, has the potential to produce a 25 percent load reduction. Operations that lower the peak loading on the grid will result in a greener grid.
Generation is typically run on a cost basis, with the lowest cost base load units dispatched first; then higher cost units like CTGs (Combustion Turbine Generators) next, and ultimately for peak conditions, the highest cost generation facilities. The lower cost generation facility - not necessarily the lower carbon footprint - will be dispatched first.
As green generation technologies become more efficient and more distributed, smart technologies to allow monitoring and management of bi-directional power flow on the distribution system will be a necessity in order to integrate these distributed systems.
Many utilities will explore time-of-day rates, where electricity is priced according to actual cost. For example, during peak hours, such as from 7.00am to 7.00pm, electricity may be priced at twice that for off peak time (7.00pm to 7.00am). The use of time-of-day rates is expected to lower the daytime peak usage. This will lower the amount of generation required.
Lowering peak generation usage may have an additional benefit in that the highest cost generation, which is used to cover the peaks, tends to be the least efficient, and could have a higher carbon footprint. This is a win – win situation; the utility experiences a reduced load and the customer receives a smaller bill.
As utilities move forward with new grid infrastructure and governments roll out smart meters for electricity and gas in all homes and small businesses (the UK government has a target date of 2020 for this), smart system innovations, including new hardware and communications, will begin to accelerate. In turn, this will lead to reduced consumer bills and significant reductions in environmental emissions.
David Bassett is an IEEE senior member and a member of the IEEE Standards Board. He is currently a Senior Staff Engineer/Scientist at PPL Electric Utilities (EU) where he assists with all large generation projects proposing to connect to the PPL EU system
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