واکنش مصرف کننده انرژی صنعتی کل به قیمت عمده فروشی در ساختار بازار برق تگزاس

The aggregate response of consumers to wholesale price signals is very limited in the restructured Electric Reliability Council of Texas (ERCOT) market. An overall average own-price elasticity of demand of − 0.000008 for industrial energy consumers served at transmission voltage is estimated using a Symmetric Generalized McFadden cost function model. To date, ERCOT has sought to promote demand response to price signals without reliance on “stand alone” demand response programs, but with a market structure that is designed to facilitate economic demand response. This very limited responsiveness to wholesale price signals may prove problematic in light of policy decisions to pursue an “energy only” resource adequacy mechanism for ERCOT.

As noted by U.S. Federal Energy Commission (2002): “Demand response is essential in competitive markets, to assure the efficient interaction of supply and demand, as a check on supplier and locational market power, and as an opportunity for choice by wholesale and end-use customers.” Through the Energy Policy Act of 2005, the U.S. Congress affirmed the importance of expanding demand response opportunities as a matter of national policy.3 Nearly-vertical demand curves contribute to price spikes and volatility and can provide suppliers with greater market power if competition is imperfect. Studies repeatedly demonstrate that even a small amount of demand response to wholesale electricity prices can mitigate price spikes.4 In markets where an “energy only” approach is adopted to maintain resource adequacy, demand response plays an important role in maintaining a balance between supply and demand. This is particularly important in light of the cyclical nature of power plant construction activity. During periods when a market is left with inadequate reserve margins, demand response can provide an important backstop. As electricity markets are redesigned to foster competition, stakeholders and policymakers are faced with the challenge of ensuring that consumers are presented with accurate price signals and the appropriate incentives to react to those prices in a manner that promotes economic efficiency and the efficient operation of the electricity market. As the ERCOT market was redesigned in the 1999 to 2001 period to introduce retail competition and to refine wholesale operations, fostering demand response emerged as a policy objective. The Public Utility Commission of Texas (PUCT) ordered ERCOT to “Develop new measures and refine existing measures to enable load resources a greater opportunity to participate in the ERCOT market” (PUCT, 2000). Due to features of the new market structure, some larger energy consumers who were formerly insulated from wholesale price signals through regulated tariffs with fixed pricing are now exposed to market-based wholesale market prices via creative contractual arrangements between retail electric providers (REPs) and consumers. A number of REPs offer “MCPE products” which enables a consumer to purchase power from the near-real-time balancing energy market through the REP and its scheduling entity. This is facilitated by ERCOT's “relaxed balanced schedule” policies, particularly since this policy was formalized in October 2002. The direct assignment of transmission costs to industrial energy consumers based on their contribution to monthly system peak demand in four summer months also provides a strong price signal. Consequently, all of the industrial energy consumers in this market have an economic incentive to reduce their consumption during the peak periods upon which transmission prices are assessed. All have the ability to procure power through a widely-available MCPE product (similar to a spot market pricing arrangement). Yet the extent to which they procure power through this approach, as opposed to procurement through a fixed-price contract or a hedging instrument, is not known to the market. The degree to which energy consumers react to wholesale price signals is not well known. Energy consumers do not presently announce to the market that they are responding to prices. There presently is no active economic demand response program which would encourage demand response to prices and quantify the magnitude of such responses. Customer-specific load data are regarded as confidential. Prior to the completion of this study, analyses of the price elasticity of demand in ERCOT were limited to a study of the twenty largest industrial energy consumers in the Houston area (Zarnikau et al., 2007), and some observations provided by ERCOT's system operations staff (Jones et al., 2006, Wattles, 2007a and Wattles, 2007b). While the response of energy consumers to price signals in ERCOT is not well understood, this is a topic that is increasing in importance. The PUCT has adopted an “energy only” resource adequacy mechanism (with a number of backstops) which relies greatly on demand response to price signals to maintain planning reserves and reliability. ERCOT has suffered from unacceptably high errors in its short-term load forecasts (which contributed to blackouts in April 2006), and some insight into aggregate price elasticities could potentially improve forecast accuracy. There is presently a debate over whether the present strategy of fostering demand response without formal demand response programs attracts an adequate level of demand response or whether a stand-alone program based on priority service concepts should be established. Finally, ERCOT's transition to a nodal market structure will eliminate any advance notice of real-time wholesale market prices, and some have questioned whether the level of demand response that the market presently enjoys will be sacrificed as a result. In each of these applications, some insight into the aggregate demand curve in the market is essential. A quantification of the magnitude of aggregate demand response in the ERCOT market may be of considerable interest to researchers outside of Texas. ERCOT is widely viewed as the most successful of North America's attempts at electricity market restructuring and is often studied as a model for restructuring initiatives elsewhere. Thus, the success or failure of the Texas market in fostering demand response to wholesale prices may have lessons for other markets struggling with this same task.

In the aggregate, the demand side of ERCOT's market exhibits very little responsiveness to wholesale electricity prices. A number of factors may be responsible for this limited response, including the types of service typically offered by REPs, the short notice period that consumers receive of price changes, constraints on the ability of interruptible energy consumers providing ancillary service to respond to prices, and the difficulties and costs inherent in monitoring and responding to price signals. The results reported here are consistent with Zarnikau et al. (2007) which found that only a couple of the twenty largest industrial energy consumers in Houston were actively responding to wholesale prices. The findings reported here are also consistent with three recent analyses by the staff of ERCOT. Based on some simple comparisons of the aggregate load levels of transmission voltage energy consumers between days of likely 4 CP charges and adjacent days, the ERCOT staff has identified about 600 MW of aggregate demand response, or about a 1% reduction in demand (Jones, Wattles, and Krein, 2006). An ERCOT staff analysis of the trend in total ERCOT load during a day of multiple price spikes in the market for balancing energy suggested no discernable response to the price changes during the first couple price spikes and some small but noticeable deviations from trends during some later price spikes within April 3, 2007 (Wattles, 2007a). ERCOT recently completed a survey of all load-serving entities participating in the ERCOT market to collect further insights into the demand response activities, including pricing programs and load management programs which are operated on a bilateral basis between load-serving entities and energy consumers and not visible to the wholesale market and ERCOT's system operators. Preliminary results from that survey suggest that over 12,000 commercial and industrial energy consumers (including over 800 industrials) in ERCOT are served through MCPE Products or similar arrangements, providing 431 MW of price-responsive load. Additionally, 91 MW of load responds to critical peak pricing. 222 MW of load responds to transmission prices, although it is not clear whether these consumers are also responding to balancing energy prices or critical peak prices (Wattles, 2007b). Market changes are presently being implemented which may increase demand response in ERCOT. The “offer cap” on wholesale prices was increased from $1000 per MWh to $1500 per MWh on March 1, 2007. This increase was designed in part to provide energy consumers with a greater incentive to respond to prices. This price cap will eventually be raised to $3000 per MWh. A day-ahead energy market will be implemented around 2009. New metering infrastructure will provide the technology necessary to reward residential energy consumers who respond to price signals. Yet other market changes could further limit demand response. For example, the notice period prior to calculation of a real-time wholesale market price will be eliminated when the ERCOT market transitions to a nodal structure in 2009.