- Email: [email protected]
Emerging microcomputer technology for electrical energy management
Journal of Microcomputer Applications (1986) 9, 253-260
Emerging microcomputer technology for electrical energy management Barney L. Capehart Department of Industrial and Systems Engineering, University of Florida, Gainesville, Florida 32611, USA
With new utility rates based on flexible time-of-use, demand levels, inverted blocks and need for energy conservation, utilities and their customers require more generalized services than those offered by currently available, low-cost energy management systems. Sophisticated metering products using microprocessor technology allow flexible design functions for metering kWh and kW values with time variable rates, displaying costs of electric energy under complex rates, controlling appliances directly and indirectly, signalling information to both customers and the utility, and generally controlling electric energy use to minimize billing costs. The purpose of this paper is to discuss the technological needs and functions of generalized microcomputer energy management systems in response to new rate structures and operational characteristics of modem electric utilities. These functions are categorized in the areas of metering, cost monitoring, direct and indirect load control, communications and real-time control for small power producers.
1.
Introduction
For many years electric utility service was taken for granted, with few people knowing or caring about electric rate structures or energy management. In the mid-1970s the economics of electrical energy changed drastically with previously declining electric bills reversing and showing rapid increases. Declining block rates, which favoured large users, began to disappear and were replaced by flat rates or inverted block rates. Entirely new residential, commercial and industrial rates involving time of day, demand level and seasonal factors are now coming into general use. Customers who may not even know how to read standard electric meters are now being confronted with complex meters and rapidly changing rates involving these new factors. In response to increasing costs, and shortages of petroleum fuels, utilities all across the nation are developing and implementing new electric rate structures designed to promote energy conservation, to charge all classes of customers equitably and to allow customers who produce their own electrical energy to sell it back to the utility (PURPA, n.d.). A multitude of sophisticated microcomputer-based devices has come on the market to aid customers in monitoring and controlling their use of electricity (Capehart, 1982). The technology for managing energy consumption has improved dramatically over the past decade, opening up new opportunities for microcomputer-based energy management systems to aid in reducing the cost of electrical energy. Typical functions of present management systems involve time-of-day scheduling of on-off times for certain loads, duty cycling of appropriate loads and demand limiting to minimize billing based on demand rates (Capehart, Muth & Storm, 1982). Capabilities and costs of such energy 253 0745-7138/86/040253+ 08 $03.00/O
0 1986 Academic Press Inc. (London) Limited
254
B. L. Capehart
management systems vary widely, with prices ranging from several hundred dollars for simple products to tens of thousands of dollars for large-scale systems (BNL, 1978). However, even the most expensive energy management systems are restricted in the functions they perform in terms of the totality of functions desirable for general energy management. With new utility rates based on flexible time-of-use, demand levels, inverted blocks and need for energy conservation, utilities and their customers require more generalized services at a lower cost than those offered by currently available energy management systems (EPRI, 1977). Systems are needed which perform the tasks of electrical metering, cost monitoring, direct and indirect load control and communication between the utility and the customer. New devices using microprocessor technology can be developed easily to produce a new energy management system that can perform all of these functions at a reasonable price. With the appearance of customers who generate some of their own power, an entirely new function for energy management exists. These self-generators, or small power producers, require a real-time control system to aid them in their buy/sell decisions from and to the utility. Since many of the small power producers may have battery storage, the operation of their system involving decisions to buy, sell and/or store is very complex. A microcomputer energy management system could also perform the functions of a decision maker to maximize the profit of a customer who produces excess power or to minimize the energy bills for one who produces less power than he uses himself. Sophisticated metering products using microprocessor technology allow flexible design functions for metering kWh and kW values with time variable rates, displaying costs of electric energy under complex rates, controlling appliances directly and indirectly, signalling information to both customers and the utility, and generally controlling electric energy use to minimize billing costs. In addition, such technology can also perform other desirable functions such as monitoring intrusion and fire alarms, manually alerting police, fire or medical assistance, and connecting to cable or satellite information sources, as well as providing buy/sell decisions for operators of self-generation facilities. All of these functions can be performed by a flexible energy management system with control, communication and display capabilities. What is needed is an integrated microcomputer system, produced at low cost, which will satisfy all of these requirements. The purpose of this paper is to discuss the technological needs and functions of generalized microcomputer energy management systems in response to new rate structures and operational characteristics of modern electric utilities. These functions are categorized in the areas of microprocessor technology, metering, cost monitoring, direct and indirect load control, communications and real-time control for small power producers. Technology for generalized energy management functions is described from a system integration view rather than from a detailed hardware level. Future research needs are also described.
2.
Microprocessor
technology
The basic technology that allows a wide range of metering capabilities at low cost is the microprocessor, which is one of the most significant technological advances of the past decade. The development of microprocessors which have extremely great capabilities,
Electrical energy management
255
but occupy very small physical spaces and can be purchased at cheap prices, has opened the door to production of metering devices with an almost unlimited range of functions. Simple digital display devices offered today with microprocessor components can easily be expanded to perform far wider ranging functions at little increase in price. The electronic components which must be included to create a highly flexible microcomputer metering device are: a microprocessor, RAM and ROM memory, I/O controllers, input switches or a keyboard, some output display and finally the sensors and switches to measure and control energy use. The microprocessor is the ‘brain’ of the device which controls the entire operation and performs all of the computations needed for accomplishing the various functions. ROM is read-only memory and represents a fixed piece of memory where relatively permanent instructions can be stored and called into use whenever desired. The ROM is contained on a plug-in chip which can be easily changed when desired. This gives the flexibility to have the overall device respond to periodic changes in rates or rate structures, for example. RAM is random-access memory and is like ‘scratch pad’ memory in that it is not permanent. RAM is used to store data collected by- the device which will later be processed into some final display or control action. The I/O, or input-output, controllers allow inputs from keys or sensors to be communicated to the microprocessor, and allow the microprocessor to control some switch or display. Some form of switch input or keyboard is necessary to tell the metering device what functions the user desires, and possibly such data as time, electric rate and what appliances are under control. An output display is also required in order to present cost data and consumer behaviour signals, as well as other operational data desired by the user. Finally, the input sensors and output switches are necessary in order to get data on kWh, kW and time-of-day; the information needed to determine control actions and cost displays, and allow for turning off and on appliances and other controlled devices. This input and output is necessary to perform such tasks as direct and indirect load control. The application of this microcomputer technology considered here is to a single control/display metering box that would be installed in a home, office or factory. The box would have to be easily accessible so that information could be input and the displayed cost data could be seen. Signals produced by the box could be displayed in some other location. For example, audio or visual signals conveying information that the peak load time rate was in effect would probably be best displayed in a frequently-used room or location. The use of a TV set would allow a very general and flexible display which could give detailed information if desired. Data on consumption, cost, status of controlled devices and consumer information could easily be displayed. If a cable or satellite information network were available, the TV set could be used to display very extensive, current information transmitted by the utility. Such information on utility system loads, status of power plants and general energy use tips could be transmitted regularly. The main point of this discussion is that the microcomputer technology to accomplish a wide variety of metering control/display functions is presently available and at relatively low cost. The current constraints to development and implementation of such a metering device are not technological, but are economic and behavioural. The cost of such a control/display device is not high based on capabilities that exist in present
256
B. L. Capehart
consumer devices such as home computers or video recorders. A present-day cost of $500-$1000 should adequately cover the electronic components of the metering control/display box. The installation cost would be quite variable, depending on whether it was installed in a new or an existing building.
3.
Metering
functions
The metering functions that can be performed by such a microcomputer control/display include all of those available in present meters and present automatic meter-reading devices. The measurements of kWh and kW form the basic elements of any metering task, along with a time measurement for handling time differentiated rates. With values of kWh, kW and time, the metering device can compute and display usage under constant cost per kWh rates, constant cost per kWh plus a demand cost, time-of-use rates with fixed periods for peak, shoulder and off-peak (as well as any number of other periods of interest), time-of-use rates where the various periods of interest are flexible and are communicated by the utility, and seasonal rates. The metering data measured, computed and stored by the device can then be displayed for the benefit of the customer, or can be read by the utility for its use. Depending on the utility’s needs, the data can be read at frequent intervals for purposes of load research or can be checked less often to be used only for billing purposes. A battery back-up would be required in order to preserve this meter data in the event of a loss of power. The use of a ROM chip containing basic rate structure data would allow the metering device to be completely flexible. When rate levels or rate structures changed, the ROM chip could be replaced with a newly programmed chip or an erasable ROM could be reprogrammed to reflect the change. For example, introduction of, or changes in, an inverted block rate could be handled easily by such a device.
4.
Cost display
functions
Because of a microprocessor’s computational capability and its data storage, the control/display device can determine and display virtually any cost data desired. The current rate of usage on an hourly basis, or using any other time unit, can be presented, as can the cost accumulated since the previous billing. Projected billing cost can be displayed on any time basis such as daily, weekly, monthly. All of these cost computations require the metering device to have a ROM chip which specifies the appropriate rate structure. For example, an inverted block kWh consumption rate would require the ROM chip to be programmed with a specification of rate levels as a function of consumption. The main purpose of the cost display function is to present the billing amount incurred by the customer. However, as long as adequate wiring connections are installed, the device could also compute and display cost and consumption data for individual appliances, machines or devices. Devices could be grouped for cost and consumption data presentation.
Electrical energy management
5.
Direct
load control
257
functions
The control/display devices could easily handle direct utility load control tasks, presently envisioned or currently in operation (Morgan & Talukdar, 1979). The box would simply have one or more receivers to take information from whatever communication method is used and feed that to the microprocessor as well as to the on-off switches controlling the selected appliances, machines or devices. The utility control signals could arrive by power line, by telephone line, by radio, by cable or by satellite reception (Russell, 1980). Display information could be presented in the box itself, in some room of the customer’s house via a special display, or even on an ordinary TV set. The control/display box could have expansion room available so that additional devices or additional receivers could be accommodated. This would allow easy changes or additions to the direct load control task, as future technological advances occurred.
6.
Indirect
load control
functions
The probable implementation of innovative rates such as time-of-use, flexible time-of-use, demand rates and inverted block rates means that a customer needs a device to control his loads in order to minimize his electric bills. With direct load control the utility issues the signals, but with indirect load control the customer must issue the control signals. Simple devices, such as timers and interlocks, are useful but the ability of a microprocessor metering control/display box to accomplish indirect load control automatically under changing rate structures is highly desirable (Kennedy & Turner, 1984). The control/display device would behave as an energy management system which controlled usage under such rates as time-of-use or demand rates. Thus, the metering device would schedule and control the use of appliances and other devices in a manner to reduce or minimize the electric bill. With time-of-use rates, the goal of the system would be to shift low-valued uses out of high-cost periods. With demand rates, one goal could be to schedule the operation of consuming devices so that their total use rate did not exceed some present level. The control function could also try to reduce total kWh consumption where an inverted block rate was in effect. This same control philosophy would also be appropriate for a flat rate with a constant cost per kWh.
7.
Buy/sell
decisions
for small power
producers
Section 210 of PURPA and recent FERC rules establish procedures whereby small power producers must receive fair rates both for power sold to a utility and for back-up power purchased from a utility. The utility buy-back rate can be as high as the incremental cost to the utility for alternative electric energy, and may include a capacity credit if the small power producer generates energy of sufficient reliability. These FERC rules are encouraging significant development of many self-generation projects which qualify as small power producers under Section 210 of PURPA. Small power producers face a need for sophisticated control and communications, functions to aid them in deciding whether to buy or sell their self-generated electrical energy. Since many small power producers will have battery or other equivalent electric energy storage capability, the overall buy/sell decision-making process is very involved.
258
B. L. Capehart
(Sullivan, 1980). In addition, the price the utility pays for produced power, and the price it asks for back-up power, may vary considerably as a function of time (Yamayee & Peschon, 1981). Thus, a dynamic situation exists where, at each instant of time, the customer is faced with a decision to buy or sell in order to maximize his total profit or minimize his total cost. This dynamic decision process to buy/sell may be labelled as a Small Power Producer/Broker system where the current cost of electricity is treated as a commodity price (Schweppe et al., 1980). Separate buy and sell prices might be quoted, or a base price quoted with a ‘commission cost’ for buy or sell; there must be a two-way communication link between the utility and the customer in order for each to be aware of the resulting decision (Sterling, Williams & Kirtley, 1981). Under this Small Power Producer/Broker system, the small power producer with storage will have a variety of options available to him depending on his present capability to produce power, the present level of his storage and his own present needs for energy. Some of these options are as follows:
(1) buy energy from the utility to supply present needs in excess of self-generation plus storage;
(2) buy energy to supply present needs and to charge storage; (3) sell energy from self-generation and from storage; (4) use self-generated energy to supply present needs and to charge storage; (5) simultaneously buy and sell energy because of a higher buy-back rate than sell rate. Many more combinations are possible because of the number of factors involved in this complex system. The general nature of the problem can be seen from the block diagram in Figure 1. The utility/customer interface for this SPP/Broker system would require a two-way communication link plus a control program for an on-site microcomputer. This control program would compute in real time the optimum buy/sell decisions necessary to maximize the customer’s utility bill if net energy consumption were involved (Capehart, Mahoney & Sivazlian, 1983).
Small Power Producer On-site generation
Small Power Producer On-site storage Figure 1.
l
*
Utility grid system
Smal I Power Producer On-site usage
Diagram of operation for a Small Power Producer/Broker
system.
Electrical energy management
8.
Other
259’
functions
In addition to the electrical energy metering, control and display functions of such a utility/customer interface device, there are other unrelated functions which could be incorporated to increase the customer appeal and increase the cost-effectiveness of the device (Capehart & Storin, 1982; Truxal, 1983). Typical functions which could be performed with the technology of the device and its communication and control links are: automatic alarms for intrusion, smoke and lire detection; manual alarms for police, fire and medical assistance; and consumer information displayed on the customer’s TV set. The device could easily be expanded to handle metering and cost display for other utility services such as water, gas and steam (if district heating is available). The only additions required would be appropriate sensors, a new ROM, and possibly a new display.
9.
Conclusion
In the aggregate, existing devices have most, if not all, of the features described, However, there are no single devices which accomplish all of these functions. Specific meters, digital cost indicators, direct load control and automatic meter-reading systems, and small energy management systems all have individual features that are desirable, but there is a need to combine the appropriate functions into a single microcomputer-based device and market it for widespread use. There is presently no technological limit to constructing the device described here. The cost is within reason when compared with sophisticated consumer devices such as home computers, microwave ovens and home video systems. The only limitation is that of consumer acceptance which is related to overall interest and overall cost-effectiveness.
References BNL 1978. Automated energy management systems for small buildings. Brookhaven National Laboratory Final Report BNL 50970, prepared for US Department of Energy, August. Capehart, B. L. & Storin, M. 0. 1982. Technological advances in metering. In Innovative Electric Rates: Issues in Cost Benefit Analysis (S. V. Berg, ed.), ch. 15. Lexington Press. Capehart, B. L., Mahoney, J. F. & Sivazlian, B. D. 1983. Optimum operation of a small power production facility. Electric Power Systems Research, No. 6, 225-233. Capehart, B. L., Muth, E. J. & Storin, M. 0. 1982. Minimizing residential electrical energy costs using microcomputer energy management systems. Computers and Industrial Engineering, 6 (3) 261-269.
Capehart, B. L., Storin, M. O., Berg, S. V. & Sullivan, R. L. 1982. Metering technology fat innovative electric rates. International Journal of Energy Systems, 2 (2) 87-92. EPRI l977. Rate design and load control. Electric Utility Rate Design Study Project, Electric Power Research Institute, Palo Alto, California, November. Kennedy, W. J. & Turner, W. C. 1984. Energy Management. Englewood Cliffs, NJ: Prentice-Hall. Morgan, M. G. & Talukdar, S. N. 1979. Electric power load management: some technical economic, regulatory and social issues. Proceedings of the IEEE, 67 (2), 241-312. PURPA n.d. Public Utility Regulatory Policies Act, 16 U.S.C. et seq. Russell, B. D. (ed.), 1980. Communication alternatives for distribution metering and load management. IEEE Transactions on Power Apparatus and Systems, PAS-9!I(4), 1448-1455. Schweppe, F. C. et al. 1980. Homeostatic utility control. IEEE Transactions on Power Apparatus and Systems, PAS-99 (3), 1151-1163.
260 B.L.Capehart Sterling, T. L., Williams, R. D. & Kirtley, J. L. 1981. Control and monitoring communications for effective energy use. IEEE Transactions on Power Apparatus and PAS-lOO(1 l), 4407-4412. Sullivan, R. L. 1980. Power system planning and the new technologies. Proceedings of Annual Allerton Conference. Truxal, C. 1983. The very high-tech home. IEEE Spectrum, 20 (I), 6467. Yamayee, Z. A. & Peschon, J. 1981. Financial transactions between the electric utility solar photovoltaic system owner. IEEE Transactions on Power Apparatus and
system Systems, the 1980
and the Systems,
PAS-100 (8), 3950-3958.
Barney L. Capehart received his BS and MEE degrees in electrical engineering and a PhD in systems engineering from the University of Oklahoma in 1961, 1962 and 1967, respectively. Since 1968 he has been with the department of Industrial and Systems Engineering at the University of Florida, Gainesville, Florida, where he is presently a professor. His main research area is energy systems analysis and he is particularly interested in energy policy, electric utility rate design, energy conservation, integration of solar technology and microprocessor-based energy management systems. He is a Senior Member of the Institute of Electrical and Electronic Engineers and the Institute of Industrial Engineers, a Fellow of the American Association for the Advancement of Science, and is listed in Marquis’s Who’s Who in The World. He is presently editor of the International Journal of Energy Systems.
Emerging microcomputer technology for electrical energy management Barney L. Capehart Department of Industrial and Systems Engineering, University of Florida, Gainesville, Florida 32611, USA
With new utility rates based on flexible time-of-use, demand levels, inverted blocks and need for energy conservation, utilities and their customers require more generalized services than those offered by currently available, low-cost energy management systems. Sophisticated metering products using microprocessor technology allow flexible design functions for metering kWh and kW values with time variable rates, displaying costs of electric energy under complex rates, controlling appliances directly and indirectly, signalling information to both customers and the utility, and generally controlling electric energy use to minimize billing costs. The purpose of this paper is to discuss the technological needs and functions of generalized microcomputer energy management systems in response to new rate structures and operational characteristics of modem electric utilities. These functions are categorized in the areas of metering, cost monitoring, direct and indirect load control, communications and real-time control for small power producers.
1.
Introduction
For many years electric utility service was taken for granted, with few people knowing or caring about electric rate structures or energy management. In the mid-1970s the economics of electrical energy changed drastically with previously declining electric bills reversing and showing rapid increases. Declining block rates, which favoured large users, began to disappear and were replaced by flat rates or inverted block rates. Entirely new residential, commercial and industrial rates involving time of day, demand level and seasonal factors are now coming into general use. Customers who may not even know how to read standard electric meters are now being confronted with complex meters and rapidly changing rates involving these new factors. In response to increasing costs, and shortages of petroleum fuels, utilities all across the nation are developing and implementing new electric rate structures designed to promote energy conservation, to charge all classes of customers equitably and to allow customers who produce their own electrical energy to sell it back to the utility (PURPA, n.d.). A multitude of sophisticated microcomputer-based devices has come on the market to aid customers in monitoring and controlling their use of electricity (Capehart, 1982). The technology for managing energy consumption has improved dramatically over the past decade, opening up new opportunities for microcomputer-based energy management systems to aid in reducing the cost of electrical energy. Typical functions of present management systems involve time-of-day scheduling of on-off times for certain loads, duty cycling of appropriate loads and demand limiting to minimize billing based on demand rates (Capehart, Muth & Storm, 1982). Capabilities and costs of such energy 253 0745-7138/86/040253+ 08 $03.00/O
0 1986 Academic Press Inc. (London) Limited
254
B. L. Capehart
management systems vary widely, with prices ranging from several hundred dollars for simple products to tens of thousands of dollars for large-scale systems (BNL, 1978). However, even the most expensive energy management systems are restricted in the functions they perform in terms of the totality of functions desirable for general energy management. With new utility rates based on flexible time-of-use, demand levels, inverted blocks and need for energy conservation, utilities and their customers require more generalized services at a lower cost than those offered by currently available energy management systems (EPRI, 1977). Systems are needed which perform the tasks of electrical metering, cost monitoring, direct and indirect load control and communication between the utility and the customer. New devices using microprocessor technology can be developed easily to produce a new energy management system that can perform all of these functions at a reasonable price. With the appearance of customers who generate some of their own power, an entirely new function for energy management exists. These self-generators, or small power producers, require a real-time control system to aid them in their buy/sell decisions from and to the utility. Since many of the small power producers may have battery storage, the operation of their system involving decisions to buy, sell and/or store is very complex. A microcomputer energy management system could also perform the functions of a decision maker to maximize the profit of a customer who produces excess power or to minimize the energy bills for one who produces less power than he uses himself. Sophisticated metering products using microprocessor technology allow flexible design functions for metering kWh and kW values with time variable rates, displaying costs of electric energy under complex rates, controlling appliances directly and indirectly, signalling information to both customers and the utility, and generally controlling electric energy use to minimize billing costs. In addition, such technology can also perform other desirable functions such as monitoring intrusion and fire alarms, manually alerting police, fire or medical assistance, and connecting to cable or satellite information sources, as well as providing buy/sell decisions for operators of self-generation facilities. All of these functions can be performed by a flexible energy management system with control, communication and display capabilities. What is needed is an integrated microcomputer system, produced at low cost, which will satisfy all of these requirements. The purpose of this paper is to discuss the technological needs and functions of generalized microcomputer energy management systems in response to new rate structures and operational characteristics of modern electric utilities. These functions are categorized in the areas of microprocessor technology, metering, cost monitoring, direct and indirect load control, communications and real-time control for small power producers. Technology for generalized energy management functions is described from a system integration view rather than from a detailed hardware level. Future research needs are also described.
2.
Microprocessor
technology
The basic technology that allows a wide range of metering capabilities at low cost is the microprocessor, which is one of the most significant technological advances of the past decade. The development of microprocessors which have extremely great capabilities,
Electrical energy management
255
but occupy very small physical spaces and can be purchased at cheap prices, has opened the door to production of metering devices with an almost unlimited range of functions. Simple digital display devices offered today with microprocessor components can easily be expanded to perform far wider ranging functions at little increase in price. The electronic components which must be included to create a highly flexible microcomputer metering device are: a microprocessor, RAM and ROM memory, I/O controllers, input switches or a keyboard, some output display and finally the sensors and switches to measure and control energy use. The microprocessor is the ‘brain’ of the device which controls the entire operation and performs all of the computations needed for accomplishing the various functions. ROM is read-only memory and represents a fixed piece of memory where relatively permanent instructions can be stored and called into use whenever desired. The ROM is contained on a plug-in chip which can be easily changed when desired. This gives the flexibility to have the overall device respond to periodic changes in rates or rate structures, for example. RAM is random-access memory and is like ‘scratch pad’ memory in that it is not permanent. RAM is used to store data collected by- the device which will later be processed into some final display or control action. The I/O, or input-output, controllers allow inputs from keys or sensors to be communicated to the microprocessor, and allow the microprocessor to control some switch or display. Some form of switch input or keyboard is necessary to tell the metering device what functions the user desires, and possibly such data as time, electric rate and what appliances are under control. An output display is also required in order to present cost data and consumer behaviour signals, as well as other operational data desired by the user. Finally, the input sensors and output switches are necessary in order to get data on kWh, kW and time-of-day; the information needed to determine control actions and cost displays, and allow for turning off and on appliances and other controlled devices. This input and output is necessary to perform such tasks as direct and indirect load control. The application of this microcomputer technology considered here is to a single control/display metering box that would be installed in a home, office or factory. The box would have to be easily accessible so that information could be input and the displayed cost data could be seen. Signals produced by the box could be displayed in some other location. For example, audio or visual signals conveying information that the peak load time rate was in effect would probably be best displayed in a frequently-used room or location. The use of a TV set would allow a very general and flexible display which could give detailed information if desired. Data on consumption, cost, status of controlled devices and consumer information could easily be displayed. If a cable or satellite information network were available, the TV set could be used to display very extensive, current information transmitted by the utility. Such information on utility system loads, status of power plants and general energy use tips could be transmitted regularly. The main point of this discussion is that the microcomputer technology to accomplish a wide variety of metering control/display functions is presently available and at relatively low cost. The current constraints to development and implementation of such a metering device are not technological, but are economic and behavioural. The cost of such a control/display device is not high based on capabilities that exist in present
256
B. L. Capehart
consumer devices such as home computers or video recorders. A present-day cost of $500-$1000 should adequately cover the electronic components of the metering control/display box. The installation cost would be quite variable, depending on whether it was installed in a new or an existing building.
3.
Metering
functions
The metering functions that can be performed by such a microcomputer control/display include all of those available in present meters and present automatic meter-reading devices. The measurements of kWh and kW form the basic elements of any metering task, along with a time measurement for handling time differentiated rates. With values of kWh, kW and time, the metering device can compute and display usage under constant cost per kWh rates, constant cost per kWh plus a demand cost, time-of-use rates with fixed periods for peak, shoulder and off-peak (as well as any number of other periods of interest), time-of-use rates where the various periods of interest are flexible and are communicated by the utility, and seasonal rates. The metering data measured, computed and stored by the device can then be displayed for the benefit of the customer, or can be read by the utility for its use. Depending on the utility’s needs, the data can be read at frequent intervals for purposes of load research or can be checked less often to be used only for billing purposes. A battery back-up would be required in order to preserve this meter data in the event of a loss of power. The use of a ROM chip containing basic rate structure data would allow the metering device to be completely flexible. When rate levels or rate structures changed, the ROM chip could be replaced with a newly programmed chip or an erasable ROM could be reprogrammed to reflect the change. For example, introduction of, or changes in, an inverted block rate could be handled easily by such a device.
4.
Cost display
functions
Because of a microprocessor’s computational capability and its data storage, the control/display device can determine and display virtually any cost data desired. The current rate of usage on an hourly basis, or using any other time unit, can be presented, as can the cost accumulated since the previous billing. Projected billing cost can be displayed on any time basis such as daily, weekly, monthly. All of these cost computations require the metering device to have a ROM chip which specifies the appropriate rate structure. For example, an inverted block kWh consumption rate would require the ROM chip to be programmed with a specification of rate levels as a function of consumption. The main purpose of the cost display function is to present the billing amount incurred by the customer. However, as long as adequate wiring connections are installed, the device could also compute and display cost and consumption data for individual appliances, machines or devices. Devices could be grouped for cost and consumption data presentation.
Electrical energy management
5.
Direct
load control
257
functions
The control/display devices could easily handle direct utility load control tasks, presently envisioned or currently in operation (Morgan & Talukdar, 1979). The box would simply have one or more receivers to take information from whatever communication method is used and feed that to the microprocessor as well as to the on-off switches controlling the selected appliances, machines or devices. The utility control signals could arrive by power line, by telephone line, by radio, by cable or by satellite reception (Russell, 1980). Display information could be presented in the box itself, in some room of the customer’s house via a special display, or even on an ordinary TV set. The control/display box could have expansion room available so that additional devices or additional receivers could be accommodated. This would allow easy changes or additions to the direct load control task, as future technological advances occurred.
6.
Indirect
load control
functions
The probable implementation of innovative rates such as time-of-use, flexible time-of-use, demand rates and inverted block rates means that a customer needs a device to control his loads in order to minimize his electric bills. With direct load control the utility issues the signals, but with indirect load control the customer must issue the control signals. Simple devices, such as timers and interlocks, are useful but the ability of a microprocessor metering control/display box to accomplish indirect load control automatically under changing rate structures is highly desirable (Kennedy & Turner, 1984). The control/display device would behave as an energy management system which controlled usage under such rates as time-of-use or demand rates. Thus, the metering device would schedule and control the use of appliances and other devices in a manner to reduce or minimize the electric bill. With time-of-use rates, the goal of the system would be to shift low-valued uses out of high-cost periods. With demand rates, one goal could be to schedule the operation of consuming devices so that their total use rate did not exceed some present level. The control function could also try to reduce total kWh consumption where an inverted block rate was in effect. This same control philosophy would also be appropriate for a flat rate with a constant cost per kWh.
7.
Buy/sell
decisions
for small power
producers
Section 210 of PURPA and recent FERC rules establish procedures whereby small power producers must receive fair rates both for power sold to a utility and for back-up power purchased from a utility. The utility buy-back rate can be as high as the incremental cost to the utility for alternative electric energy, and may include a capacity credit if the small power producer generates energy of sufficient reliability. These FERC rules are encouraging significant development of many self-generation projects which qualify as small power producers under Section 210 of PURPA. Small power producers face a need for sophisticated control and communications, functions to aid them in deciding whether to buy or sell their self-generated electrical energy. Since many small power producers will have battery or other equivalent electric energy storage capability, the overall buy/sell decision-making process is very involved.
258
B. L. Capehart
(Sullivan, 1980). In addition, the price the utility pays for produced power, and the price it asks for back-up power, may vary considerably as a function of time (Yamayee & Peschon, 1981). Thus, a dynamic situation exists where, at each instant of time, the customer is faced with a decision to buy or sell in order to maximize his total profit or minimize his total cost. This dynamic decision process to buy/sell may be labelled as a Small Power Producer/Broker system where the current cost of electricity is treated as a commodity price (Schweppe et al., 1980). Separate buy and sell prices might be quoted, or a base price quoted with a ‘commission cost’ for buy or sell; there must be a two-way communication link between the utility and the customer in order for each to be aware of the resulting decision (Sterling, Williams & Kirtley, 1981). Under this Small Power Producer/Broker system, the small power producer with storage will have a variety of options available to him depending on his present capability to produce power, the present level of his storage and his own present needs for energy. Some of these options are as follows:
(1) buy energy from the utility to supply present needs in excess of self-generation plus storage;
(2) buy energy to supply present needs and to charge storage; (3) sell energy from self-generation and from storage; (4) use self-generated energy to supply present needs and to charge storage; (5) simultaneously buy and sell energy because of a higher buy-back rate than sell rate. Many more combinations are possible because of the number of factors involved in this complex system. The general nature of the problem can be seen from the block diagram in Figure 1. The utility/customer interface for this SPP/Broker system would require a two-way communication link plus a control program for an on-site microcomputer. This control program would compute in real time the optimum buy/sell decisions necessary to maximize the customer’s utility bill if net energy consumption were involved (Capehart, Mahoney & Sivazlian, 1983).
Small Power Producer On-site generation
Small Power Producer On-site storage Figure 1.
l
*
Utility grid system
Smal I Power Producer On-site usage
Diagram of operation for a Small Power Producer/Broker
system.
Electrical energy management
8.
Other
259’
functions
In addition to the electrical energy metering, control and display functions of such a utility/customer interface device, there are other unrelated functions which could be incorporated to increase the customer appeal and increase the cost-effectiveness of the device (Capehart & Storin, 1982; Truxal, 1983). Typical functions which could be performed with the technology of the device and its communication and control links are: automatic alarms for intrusion, smoke and lire detection; manual alarms for police, fire and medical assistance; and consumer information displayed on the customer’s TV set. The device could easily be expanded to handle metering and cost display for other utility services such as water, gas and steam (if district heating is available). The only additions required would be appropriate sensors, a new ROM, and possibly a new display.
9.
Conclusion
In the aggregate, existing devices have most, if not all, of the features described, However, there are no single devices which accomplish all of these functions. Specific meters, digital cost indicators, direct load control and automatic meter-reading systems, and small energy management systems all have individual features that are desirable, but there is a need to combine the appropriate functions into a single microcomputer-based device and market it for widespread use. There is presently no technological limit to constructing the device described here. The cost is within reason when compared with sophisticated consumer devices such as home computers, microwave ovens and home video systems. The only limitation is that of consumer acceptance which is related to overall interest and overall cost-effectiveness.
References BNL 1978. Automated energy management systems for small buildings. Brookhaven National Laboratory Final Report BNL 50970, prepared for US Department of Energy, August. Capehart, B. L. & Storin, M. 0. 1982. Technological advances in metering. In Innovative Electric Rates: Issues in Cost Benefit Analysis (S. V. Berg, ed.), ch. 15. Lexington Press. Capehart, B. L., Mahoney, J. F. & Sivazlian, B. D. 1983. Optimum operation of a small power production facility. Electric Power Systems Research, No. 6, 225-233. Capehart, B. L., Muth, E. J. & Storin, M. 0. 1982. Minimizing residential electrical energy costs using microcomputer energy management systems. Computers and Industrial Engineering, 6 (3) 261-269.
Capehart, B. L., Storin, M. O., Berg, S. V. & Sullivan, R. L. 1982. Metering technology fat innovative electric rates. International Journal of Energy Systems, 2 (2) 87-92. EPRI l977. Rate design and load control. Electric Utility Rate Design Study Project, Electric Power Research Institute, Palo Alto, California, November. Kennedy, W. J. & Turner, W. C. 1984. Energy Management. Englewood Cliffs, NJ: Prentice-Hall. Morgan, M. G. & Talukdar, S. N. 1979. Electric power load management: some technical economic, regulatory and social issues. Proceedings of the IEEE, 67 (2), 241-312. PURPA n.d. Public Utility Regulatory Policies Act, 16 U.S.C. et seq. Russell, B. D. (ed.), 1980. Communication alternatives for distribution metering and load management. IEEE Transactions on Power Apparatus and Systems, PAS-9!I(4), 1448-1455. Schweppe, F. C. et al. 1980. Homeostatic utility control. IEEE Transactions on Power Apparatus and Systems, PAS-99 (3), 1151-1163.
260 B.L.Capehart Sterling, T. L., Williams, R. D. & Kirtley, J. L. 1981. Control and monitoring communications for effective energy use. IEEE Transactions on Power Apparatus and PAS-lOO(1 l), 4407-4412. Sullivan, R. L. 1980. Power system planning and the new technologies. Proceedings of Annual Allerton Conference. Truxal, C. 1983. The very high-tech home. IEEE Spectrum, 20 (I), 6467. Yamayee, Z. A. & Peschon, J. 1981. Financial transactions between the electric utility solar photovoltaic system owner. IEEE Transactions on Power Apparatus and
system Systems, the 1980
and the Systems,
PAS-100 (8), 3950-3958.
Barney L. Capehart received his BS and MEE degrees in electrical engineering and a PhD in systems engineering from the University of Oklahoma in 1961, 1962 and 1967, respectively. Since 1968 he has been with the department of Industrial and Systems Engineering at the University of Florida, Gainesville, Florida, where he is presently a professor. His main research area is energy systems analysis and he is particularly interested in energy policy, electric utility rate design, energy conservation, integration of solar technology and microprocessor-based energy management systems. He is a Senior Member of the Institute of Electrical and Electronic Engineers and the Institute of Industrial Engineers, a Fellow of the American Association for the Advancement of Science, and is listed in Marquis’s Who’s Who in The World. He is presently editor of the International Journal of Energy Systems.