Tennessee Valley Authority (TVA) developed an integrated resource plan in 2011 that recommended a strategic direction that focuses on a diverse, balanced mix of energy sources. A key element of this plan was to initiate an energy-efficient demand-response (DR) program capable of providing up to 2,600 MW of peak demand reductions through demand-side management. The DR component can be used to alleviate financial constraints associated with serving the load or for maintaining reliability, and to provide ancillary services in the balancing authority (BA) area.
Utilities normally call on their DR programs on an hours-ahead or day-ahead basis because of forecasted system load or market conditions. Since small temperature errors or unexpected thunderstorm activity can dramatically impact the system load and necessity of calling on the DR resource, TVA has focused on reducing the notification period so these important decisions can be made close to the time DR is needed to maximize value.
TVA exercises its DR programs for both economic and reliability curtailments through an internally developed demand-response management system (DRMS), which provides the system operator with the necessary information and tools to manage a diverse portfolio of DR resources effectively. These products are viewed as virtual power plants, integrated into the daily resource plan, and are dispatchable by the BA.
DR as a Virtual Power Plant
TVA dispatches resources, from the least to most expensive, based on the load requirements. This dispatchable stack is managed by an application called the block pricing compendium, which provides the BA with a quick overview of the generation resources that should be called on to increase or decrease as the load rises and falls. Units with low operating costs, such as hydroelectric and nuclear resources, are typically at the bottom of the stack with more expensive coal-fired plants and combustion turbines (gas and oil) at the top.
Current TVA Demand Response Portfolio
Future TVA Demand Response Portfolio
For DR to be viewed as a virtual power plant by the BA, it needs to be viewed within the same context as other resources so it will be used as load increases. This brings DR into the operational realm and optimizes its value as a true power plant and not just a day-ahead resource. To include DR as a dispatchable resource, the costs for each product must be calculated by TVA's power trading organization and coded in the DRMS.
In 2011, TVA evaluated the various DRMSs available on the market. It became evident these systems were designed for day-ahead, economic-based DR programs and not for implementing DR as an operational virtual power plant. To meet its vision for DR implementation, TVA decided to develop a custom solution using TVA personnel. To date, TVA has implemented several of the functional highlights:
Integration between the DRMS, BA and power trading
Near-real-time view of current load by product
Calculation of curtailable load
Event history of DR participant performance
Integration with telephony notification system
Post-operative financial evaluation of DR events
Mobile view of system and products.
Integration of Tools
The DRMS automates coordination functions between the BA and power trading. All reliability curtailments in TVA are initiated by the BA, while economic curtailments are approved by the BA but executed by the power trading organization. When power trading schedules a day-ahead economic curtailment in the DRMS, a request-for-approval window immediately appears on one of the BA displays. The BA can approve, cancel or acknowledge the request using the DRMS. Once an event is approved by the BA, it automatically goes into scheduled status, and the DRMS initiates notifications and monitors the actual load during the event.
The BA needs a near-real-time view of load available for curtailment to operate DR as a true virtual power plant. The DRMS real-time monitor uses four sources of data to obtain real-time or near-real-time information:
Supervisory control and data acquisition (SCADA). Most large TVA customers have SCADA measurements that are sent to the TVA SCADA system every two seconds and passed into the DRMS.
Inter-control center communications protocol (ICCP). All customers who sign up for the dispatchable voltage regulation product are required to transmit their current load (by feeder) to TVA through their ICCP connection. This information is then passed to the DRMS.
Meter data management (MDM). DR customers who do not have SCADA or ICCP connectivity have their billing meter interrogated every 15 minutes and passed to the DRMS.
Load forecast. If the SCADA, ICCP or MDM data does not come in on schedule, the DRMS uses the customer's load forecast as a proxy for the actual load.
Calculation of Curtailable Load
Prior to implementing the DRMS, the BA had only a rough estimate of megawatts available to interrupt. TVA DR products are designed to meld TVA system needs with customer operational attributes, which creates complex business rules for curtailment. These complex rules compounded establishing an interruptible load estimate.
Since the DRMS brings in near-real-time data, the actual number of curtailable megawatts for each customer can be calculated at any point in time. For DR events, the curtailable megawatt would use the actual customer's load and the appropriate contractual baseline. For future DR events, it would use the customer's load forecast.
In practice, the DRMS calculation for curtailable megawatts has been very accurate, based on event actualities. This accurate forecast has given TVA's power operations and energy trading group confidence in the DRMS forecasts for curtailable load and makes DR credible as an actual virtual power plant.
Integration with Telephony Notification System
To manage the multiple DR products with reduced curtailment notification periods, an automated curtailment system was needed. TVA's DRMS performs telephone notifications to all DR customers at the start and end of each event using an on-site third-party voice XML notification server. The notification system accepts voice XML as an input, which is generated by the DRMS. The actual messages are typed into the DRMS and use placeholders to fill in specific DR event information, such as product name and event start and end times. In addition to telephone notification, the DRMS also will send text messages and e-mails to customers.
While the current system uses the telephone as the primary means for DR event notification, a new standard called open automated demand-response (OpenADR) eventually will be integrated into the DRMS. The DRMS will function as an OpenADR server, communicating directly with third-party OpenADR clients at the customer sites.
Post-Op Financial Evaluation
The DRMS is able to calculate the impact to TVA of each event because all economic factors (for example, current system cost, curtailment amount, contract prices and DR credits) are fed into the DRMS from other sources. The DRMS displays this value by event, customer and product, allowing management to evaluate the benefit of each DR product to TVA. This provides immediate feedback on the effective use of DR for each event.
As TVA took to the road to market the products, the logical next step was to develop a mobile version of the DR as well as a view of the entire TVA system. With that vision a reality, the teams can now not only talk about products but show them in real time within the mobile power system summary application. Anyone with an iPad or iPhone and the necessary security privileges can see a real-time view of the system, refreshed every 10 seconds.
Fulfilling the Vision
TVA's vision of becoming one of the nation's leading providers of clean, affordable power serves as inspiration for daily work at TVA. TVA is using DR as a true virtual power plant to fulfill this vision while building on the 12th year of 99.999% reliability. DR provides a win-win opportunity for TVA and its customers. Options exist for customers to lower their electric power bill by providing operational benefits to the TVA system while continuing to receive top-tier reliability.
DR products provide tools for daily system operation, which make them an integral part of TVA's strategic direction for load management. Load management is a key component of the integrated resource plan as a low-cost method for offsetting load growth. DR, along with energy efficiency and wholesale/retail rates, provides TVA the vehicle to achieve its integrated resource plan of clean energy targets and fulfill its vision.
Clay DeLoach ([email protected]) is the senior manager of operations applications for TVA, where he has worked for 18 years. His team supports all control center software applications used by the Systems Operations Center and the Reliability Operations Centers. This application portfolio consists of more than 100 custom and vendor applications including the Demand Response Management Portal, SCADA and the Advanced Power Applications suite of tools.
Charles E. (Butch) Massey ([email protected]) is the director of demand-side pricing for TVA and a 32-year veteran of the electric power industry. His experience covers generation, distribution, transmission, demand response and pricing. Massey currently serves on the Association of Demand Response and Smart Grid board of directors and participates in other national organizations.
Tennessee Valley Authority | www.tva.gov