As we make greater use of information technology in developing the Smart Grid of the Future, careful consideration should be given to the substantial savings in energy and reductions in CO2 emissions – potentially thousands of tons per day – that can be realized with systems capable of shedding loads in a matter of seconds. These systems can be used in place of the generators that are currently kept online to meet spinning reserve requirements and can also be used to smooth the intermittence of renewable energy sources. Moreover, when properly designed, grid security can actually be enhanced using the methods described here.
Last year – as a demonstration project – Southern California Edison (SCE) asked Visionary Electronics to design a Demand Response system that would allow them to monitor the load at remote customer sites and schedule curtailment events during peak loading emergencies when SCE needed the customers to use less energy. The customer selected for this demonstration was the Mazda Corporate headquarters and Mazda R&D facilities in Irvine, California. Mazda agreed to participate in order to help SCE develop technologies that would lead to greater energy efficiency.
The resultant system uses SCE’s existing SCADA network. There were two communication channels that were used for the demonstration. The first was a K-Band satellite network and the second was a UHF radio network. Events could be independently scheduled through either network. A block diagram of the system is shown in Figure 1.
Demand Response System Operating Modes…
Figure 2 is a screen shot of the computer program that resides at SCE to control the remote Energy Management System at Mazda.
Figure 2: Screen Shot of Mazda’s Load Shedding Events (as seen from utility)
The primary function of the program is to define a future event by entering the start time, duration, and demand level, where higher demand levels represent more aggressive load shedding. In this case, the different demand levels are implemented by changing the set-points on the HVAC systems at the two locations. As a matter of policy, however, SCE does not specify how or which loads are to be shed. It is up to the customer to decide how they want to conserve energy during an active event.
Once an event is defined, it can be posted through either the radio link or over the satellite network. For the radio link, the system supports posting a new event, canceling a pending or active event, changing the demand level on a pending or active event, or reading the meters in real time. Communication from the program to the remote site goes through the corporate LAN to the radio server, over the radio link to the remote station, and through the Ethernet switch at the customer’s site to the customer’s Energy Management System. For this link, the XML commands that are native to the customer’s EMS are generated by the program and sent (as is) over the radio network.
While the event is active, the program reports the baseline KW, the KW drop that is expected, the actual average KW, and the actual kWh reduction that is occurring to date. Event details can also be viewed for past events. Using the spinner wheel in the upper left-hand corner of the Event Details box can bring up a past event, and the data for a particular time of the event can be selected with the tracker bar in the lower right-hand corner.
The satellite link also supports posting, changing, or canceling events and reading the meters in real time. Communication over the satellite link goes from the program over the corporate LAN to the satellite hub server. Electronics inside the satellite hub server translate the commands received into commands that are in the protocol native to the satellite terminal (bitwise CDC Type-1 commands). The commands are then transmitted over the satellite network to the remote satellite terminal.
The remote satellite terminal has a specially designed interface card, which is installed inside the terminal as shown in Figure 3.
This interface card has an Ethernet port that acts as a client to the Ethernet switch at the customer’s site. Commands that are received over the satellite network that are meant for the customer’s EMS are translated from the CDC Type-1 commands into the XML commands that are native to the customer’s EMS.
The interface card also has output relays, so this link also supports direct control of the customer’s load. With this control, the load can be shed without the delays associated with the customer’s EMS and it can be shed in less than 3 seconds. In California, the footprint for the satellite system covers the entire state, allowing loads to be shed from multiple locations anywhere in the state in less than 3 seconds.
Load shedding is increasingly seen as a valuable resource for managing the grid. And, the faster a load can be shed, the more valuable it becomes. Two areas where load shedding can be valuable are to meet spinning reserve requirements and for regulation.
Figure 3: Special interface module installed inside remote satellite terminal
To meet the spinning reserve requirements, the current practice is to keep generators on line synchronized to the grid in order to deal with any sudden spikes in load or loss of generation. In the western United States, the WECC (Western Electricity Coordinating Council) spinning reserve criterion is that sufficient resources need to be available to be able to deal with the simultaneous outage of the two largest generators in the Western Interconnection – a NERC “Category C” event.
Instead of keeping generators online, the Demand Response system could drop load elsewhere on the grid to meet this criterion. And, since the Demand Response system has zero emissions, a system of this sort would save the CO2 that is being emitted by the spinning reserve generators.
Such a system would have very little impact on the customers whose load was being dropped. If the event were short lived, the affected customers would be back online in a few minutes. If the load needed to be off for a longer period, the system could cycle through to other customers such that no single customer would experience prolonged down time. It is anticipated that most of the load that would be put on such a system would be HVAC systems. Therefore, the affected customer(s) would typically be completely unaware that their load had been dropped, resulting in little or no customer inconvenience.
To get a rough estimate of the amount of CO2 that would be saved, we can conservatively say that the savings in energy would be in the 1-2% range or even as high as 3-4%.
We can use the state of California as an example of what the actual savings might be. If we use the most conservative (1%) value and take a statewide estimate of load to be 25,000 MW for 20 hours on a typical day, the estimated potential savings would be:
25,000 MW x .01 = 250 MW x 20 hrs/day = 5,000 MWh/day
It is generally accepted that 1 ton of CO2 is generated for every 1,200 kWh of electricity. Thus, our conservative (1%) estimate of CO2 savings is:
5,000 MWh/day x 1 ton CO2 / 1.2 MWh 4,200 tons CO2 / day
If the actual savings were in the 3-4% range the savings would climb to 12,000 or 16,000 tons of CO2 per day. Remember that these are the savings that would be realized in just one state; expanded use would increase these savings substantially.
There are also other advantages of such a system. First, since it would replace the need for peaking power plants, fewer power plants would need to be built which would save money and lower pollution levels.
A satellite-based demand response system would also be useful in dealing with the intermittence of the renewable energy sources that will play an increasingly important role in future energy strategies. It could be used to store energy while the sun is shining and the wind is blowing and decrease the load when the opposite is true. Two areas where the energy can be stored are in the batteries of the coming fleet of plug-in hybrid cars and as thermal energy in HVAC systems and refrigerators.
While installing such a system will be labor intensive, demand response systems create jobs and ultimately result in significant economic benefits. The cost of the hardware itself is dropping, further improving economically feasibility. At today’s prices, the cost of a satellite system would be under $2,000 per remote terminal, including amortizing the cost of the hub. Then, once a satellite terminal is in place, it can communicate with numerous sites via less expensive radio links.
Radios with a range of a mile currently sell for less than $100 each. As the number of radios hosted by a particular satellite terminal surpasses 50-100 units, the cost of the satellite terminal component becomes increasingly insignificant in relation to the overall cost per site.
Demand response systems need not create a security risk. In fact, if properly designed, the security and system integrity of a system like the one described here can be very high since the system can be completely segregated from the Internet, and there are no wires to cut. Also, there could be any number of completely redundant, overlapping hubs, any or all of which could be placed in secret locations, if warranted. And finally, because the redundant hubs are always in continuous communication with the main hubs, the redundant hub can take over in a few seconds should any of the mains fail. Thus, there would be no disruption in functionality at all, even in the event of a primary failure.
In conclusion, it is technically feasible to build a demand response system that could be used to meet the spinning reserve requirement. It could also be used to smooth out the intermittence of renewable energy sources, would be very secure and would result in substantial savings in money and in CO2 emissions.
Brad McMillan is President of Visionary Electronics Inc., which designs and manufactures hardware and software solutions for the electric power industry. His interest in alternative energy technology began in the early 1980s when he chaired conferences on the subject at San Francisco State University, testified before the House Subcommittee on Energy Development and Applications and provided a report on the subject for the Appropriate Energy Technology program of the U.S. Department of Energy. McMillan holds an MSEE from the University of California, Berkeley.
Edwin Hornquist is Project Manager, Design & Engineering Services at Southern California Edison where his focus has included managing projects related to the utility’s Advanced Metering Infrastructure (AMI) initiative, Codes & Standards program, and Demand Response and Energy Efficiency emerging technology assessment projects. Hornquist has over 18 years of experience in the energy industry across a diverse spectrum on companies. He began his career working for municipal and investor-owned utilities focusing on energy efficiency, demand-side-management, supply resource planning, and meter data acquisition systems. He holds a Mechanical Engineering Degree and a Masters Degree in Business Administration.
