Volume 4, Number 1, September 2003

 

An Introduction to Electricity Market Auctions Using a Spreadsheet
 
 
John Farr
Farr Consulting
5 Tavern Lane
Lexington, Massachusetts 02421
USA
 
 
Frank A. Felder
School of Business
Manhattan College
Riverdale, New York 10471
USA
 
   

Abstract

This paper presents a spreadsheet model of an electricity market that can be used to simulate two types of auctions, a single price auction and a paid your bid auction. This model can be used in a variety of pedagogical applications. From the perspective of management science and operations research (MS/OR), this application emphasizes model use and integrates several important concepts. From a business perspective, users can explore various bidding strategies and their implications, depending on the auction rules. From a public policy perspective, students can learn how market design decisions may influence market outcomes and the exercise of market power.


1. Introduction

The electric power industry is one of the largest industries in a modern economy. In the United States, the electric power industry represents $216 billion-plus in revenues from sales to ultimate customers and approximately 4% of the real gross domestic product (Edison Electric Institute, 2003). It has been undergoing fundamental changes of late as it is restructured from a vertically integrated and regulated industry to a mixture of market-based generation companies and regulated transmission companies. Thanks to almost daily coverage on the network news programs of the electricity disaster in California that began in June 2000, the wider public has learned of the challenges and missteps that have occurred with restructuring in the United States (Borenstein, 2001).

Part of this restructuring involves creating markets in which owners of generation units submit bids indicating the prices at which they would be willing to produce energy (measured in megaWatt-hours, or MWh). The organization that administers the wholesale markets determines the least-cost combination of bids to meet hourly demand and thus clear supply and demand. The bidding strategies generation unit owners employ depend fundamentally on the rules of the auction and the ownership profiles of the various generation units, which determine the profitability of exercising market power. Here, we use the term market power to refer to situations in which there is insufficient competition, allowing one or more generation owners to raise profitably the market clearing price by bidding above marginal cost.

The electric power industry is of special interest to MS/OR professionals. It provides a wide range of applications spanning planning and operation. The industry’s large-scale challenges require the use of linear, non-linear, mixed, and stochastic programming as well as reliability analysis. Depending on the interests of the analysts, the application of stock-in-trade MS/OR techniques might focus on computational, engineering, economic, or public policy issues. The analysis and design of auctions is also an important MS/OR topic (e.g., Rothkopf and Park, 2001), although anecdotal evidence based on the authors’ experience and a review of textbooks suggests that auction theory is not as commonly taught at the undergraduate and MBA levels as are other MS/OR techniques.

The model presented in this paper combines many important MS/OR topics, which can be examined in several contexts depending on the users’ interests. Model users can focus on auction design, market power, microeconomic analysis, strategic interaction, or decision-making under uncertainty in a setting of either a single or multiple auction rounds, the latter allowing for the possibility of learning by the decision maker. Courses in energy economics, environmental operations research, public policy, or business economics may benefit from the use of an electricity market simulation. 

The model is easy to use and explain. Its flexibility allows it to be used in a lecture, as an in-class group activity, or as an assignment beyond the classroom. To use the model as a market simulation requires at least four people in addition to someone serving as the market administrator, who collects the bids from the various generation unit owners, enters them into the model, and reports the results to the market participants. Four or more generation owners provide sufficient competition to put some limit on the potential for the exercise of market power, although five to nine generation owners is ideal. Preferably, there should be a team of two to four people per generation owner. This will afford users the opportunity to learn through interaction with their teammates as they develop bids for their portfolio of generation units.

The authors have used this model successfully with first-year MBA students, industry and business personnel, regulators, and attorneys. Users have found the exercise informative and enjoyable. By forcing users to make specific bids and then experience the simulated market outcomes, the model drives home key points regarding bidding strategy, market analysis, and the ability to exercise market power. Active learning in MS/OR (e.g., the use of student teams to solve problems cooperatively and discuss theoretical issues with instructors as facilitators) has been recommended by many authors (e.g., Ladson and Liebman, 1998; Liebman, 1998; Powell, 1998). This group simulation exercise is an example of how “teams will learn how to learn together while engaging their most important business issues” (Senge, 1990). The authors’ experience using this simulation confirms the benefits claimed for active learning.

The model also helps serve the MS/OR objective to “teach business students the essential skills of analytical reasoning, especially how to use models to think through business problems” (Powell, 2001). The focus is on formulating a bidding strategy to price a firm’s output, not on the technical details of programming an auction-clearing mechanism. In this example, those details are not difficult and can be handled easily in a spreadsheet (Gass et al., 2000).

The body of this paper focuses on explaining the simulation and its classroom use for the benefit of instructors. Appendix I provides students the necessary information to participate in the simulation even if they are not familiar with electricity markets. It is a standalone document that can be distributed electronically to students.

2. Model Details

The electricity market auction simulation model, Electricity Auction Spreadsheet, comprises one spreadsheet with four worksheets. The first worksheet, labeled Data and Bids, contains the data for 28 generation units. The units, each of which is named for a color, are listed alphabetically. Data provided for each unit are total capacity in megawatts (MW), the unit type and fuel, age (a rough proxy for the efficiency of a unit, older units being less efficient). This worksheet also contains confidential information for all units on the amount of available capacity (e.g., which units are on outage and unavailable), variable costs ($/MWh), expected hours of operation per year assuming the unit bids its variable costs, and the unit’s average fixed costs presented in both dollars per kiloWatt ($/kW) and $/MWh. The first units listed are baseload units, which are expected to be dispatched (i.e., to operate) most hours in a year. They are followed by intermediate units, which operate roughly 40-60% of the time. Peaking units, which typically operate up to several hundred hours per year, are listed last.

The second portion of the Data and Bids worksheet comprises six rounds of bidding, with Round 3 in two parts. Each round is a single clearing price auction, meaning that the highest bid accepted sets the clearing price and all generators whose bids are accepted are paid this single clearing price. Figure 1 illustrates this type of auction. Different generation units, represented by different color blocks, submit energy bids (which are ranked lowest to highest). The point at which demand intersects supply establishes the market clearing price. Figure 1 presents the demand curve as a “staircase.” The vertical portion of the demand curve reflects the lack of demand price elasticity in wholesale electricity markets, and the two “stairs” indicate two blocks of price-responsive demand.

All rounds incorporate price-responsive demand. These load blocks are defined by the amounts of load (MW) and the price ($/MWh) that triggers each load block not to consume electricity. For example, a load block may consist of 50 MW that for electricity prices of $500/MWh or higher does not consume. When generation unit bids needed to serve demand exceed the prices of these load blocks, the blocks are “dispatched,” meaning that they do not consume. Although the blocks are modeled as “resources,” this is equivalent to load being reduced by the size of the block. This is a commonly used technique to model blocks of price-responsive load, and its details do not need to be shared with the students.

The model does handle situations in which only a portion of a unit is needed; this occurs when the total available capacity of the marginal unit exceeds the amount of residual demand after all the infra-marginal units have been selected. Sometimes, different generation units submit the same bid, which turns out to be the marginal bid, but the total amount of capacity from these units is not needed to meet demand. To avoid ties, the spreadsheet adds a different small random number between 0 and 0.0001 to each unit’s bid. Since each random number has 15 significant figures, it is practically impossible that even if several generation units have the same numerical bid, their bids randomly adjusted by the spreadsheet would be identical. The added number is so small that it does not visibly affect the clearing price or the associated revenues reported to the participants.

Round 3b, and only this round, is a paid your bid auction clearing mechanism. In contrast to an auction with a single clearing price, in Round 3b winning bidders are paid their bid. This auction design is not currently used in the United States. We include a paid your bid auction design to illustrate that this different design would, at first glance, seem to produce results substantially different from the single price auction. Participants, however, adjust their bids to the different auction rules, resulting in similar results. Instructors that have the time to employ Round 3b can use it to make sure students understand appropriate bidding strategies and the strategic interaction between auction rules and competitors’ strategies.1 Instructors who do not want to focus on auction design issues or have limited time can skip Round 3b.

A separate file, Electricity Auction Bid Sheets, provides the bid sheets for each generation unit. Prior to the simulation, the market administrator prepares a sheet for each generation unit by printing out each worksheet. Each owner of generation in the simulation receives one of these sheets for each generation unit in its portfolio. These sheets contain private information pertaining to each unit’s costs and are also used to submit bids for each unit for each round of the simulation. The information in these bid sheets must be kept confidential.

Determining the Market Clearing Price in a Single Clearing Price Electricity Auction with a Staircase Demand Curve
Figure 1: Determining the Market Clearing Price in a Single Clearing Price Electricity Auction with a Staircase Demand Curve

The Results tab summarizes the market results for each round of bidding. The information on this tab is shared with the generation owners after each round of the simulation. The results report the “perfect competition price,” that is, the price that would clear the market were each generation unit bid its variable costs. The Actual Price or clearing price is also reported, and in the case of the pay your bid auction, the “Actual Price” is the average price paid to generation owners weighted by the capacity of accepted generation units. The Perfect Competition Price and the Actual Price, respectively, are then used to calculate the “Perfect Competition” Total Margin and the Actual Total Margin. These margins are the amount of money above variable costs that all of the generation units earned, assuming perfect competition and based on the actual bids. The Change In Margin is the difference between the Perfect Competition Total Margin and the Actual Total Margin. Of course, some generation units may be better or worse off than the Perfect Competition Case; the number of units and the collective amounts of all generation units of being better and worse off are also reported.

In the file Electricity Auction Sample Results, we provide actual results from a simulation involving five rounds with both versions of Round 3. This spreadsheet of results contains the actual bids for each round and the overall results for each round. We strongly recommend not providing this spreadsheet to students.

The last tab of the simulation spreadsheet, labeled Curve, is a graph of the supply curve assuming all units bid their variable costs. Because it contains proprietary cost data for each of the competing generation units, this information is not provided to participants until after all of rounds of the simulation. When working through this simulation, participants should be trying to construct such a curve to inform their bidding strategies.

All of the worksheets in the simulation spreadsheet are “protected,” allowing editing only in the cells of the Data and Bids sheet containing bids for each round (so that bids can be entered). Results of the simulation and other information are presented in locked cells to avoid inadvertent errors. Users wishing more control over the content of the workbook can unprotect sheets as they desire by selecting “Protection” under the Tools Menu. Sheets are not password-protected.

3. Teaching Approach and Experience

We have used this simulation in several training sessions for first-year MBA students, managers, regulators, and attorneys in the electric power industry. Our approach has been as follows. Divide market participants into approximately four to nine groups of two to four people each, depending on the total number of participants. Assign each group a portfolio of generation units consisting of some baseload, intermediate, and peaking units. The 28 generating units can be divided in any manner to accommodate the number of participants; however, the market administrator should seek to ensure that each generation owner has a variety of units with differing characteristics. In addition, inform everyone that some generation units may not be available due to unit outages, but do not make this quantity public. Only the individual groups should know whether their generation units are available to bid into the market. The amount of demand for each round will be known by all participants and is listed on the unit’s bid sheet.

After explaining the basics of a single clearing price auction and the mechanics of submitting bids, allow each group 10-15 minutes to determine their first-round bids for each generation unit in their portfolio. In the first round, the discussions among the team members usually involve gaining an understanding of the information and figuring out whether and how to recover a unit’s fixed costs in its bid. The primary benefit of the first round is to make the mechanics of the simulation clear and begin to provide some information regarding how the market clears given the bids of all of the other participants. Our experience is that most participants tend to bid in the first round an amount close to the variable cost of each unit, though some will include an adder in hopes of recovering some fixed costs. Usually, the first-round results are somewhat above the perfectly competitive price (but not by much), with most generation units better off as a result. Consequently, there are usually one or two generation units that are worse off due to bidding above their variable costs and not being selected, despite that the units were economic (i.e., they had a variable cost below the market clearing price and would have been better off producing).

In the second and third rounds, participants begin to account for the fact that they hold a portfolio of units and for the potential bidding strategies of competing generation owners. After a round or two of market clearing prices, participants have determined – to some extent – how aggressive other participants are bidding. That information, combined with both the ability to coordinate the bids of a group of generation units within their portfolio and increasing demand in the market, typically leads participants to experiment with bidding margins above the Perfect Competition Total Margin. The overall trend may be increasing prices and margins, but generation owners that were made worse off in earlier rounds compared to bidding their variable costs tend to stick close to bidding their marginal costs in an attempt to maximize their profit. In earlier rounds, where ample supplies tend to be available, attempts to raise prices by raising bids often only benefits those participants not pursuing this strategy. As a result, competition can be quite effective in limited bids in initial bidding rounds.

At this point, the participants have enough experience with the single clearing price auction to switch to a paid your bid auction. This requires participants to make a fundamental change in their bidding strategies. In the single clearing price auction, a strategy exists to obtain a generation unit’s margin (clearing price minus variable costs). The generation unit could bid its variable costs, which would ensure that an economic unit would run while earning the difference between the clearing price and its variable costs. To the extent that the generation unit thought it could raise the clearing price, either because that unit was the marginal unit or because it could exercise market power, it would raise its bid above its variable cost. In the paid your bid auction, however, the generation owner must estimate the highest acceptable bid and bid close but below that amount to earn as much margin as possible.

The remaining rounds usually (but not always) result in the dramatic exercise of market power. Participants now have a solid grasp of how to bid and how others will bid. The exercise of market power usually results when one or more portfolio owners figure out that demand has reached a level such that some portion of each portfolio is needed to have sufficient supply. At this point, the clearing price can rise markedly as one or more portfolio owners bid very high prices – knowing that at least some of their high-priced generation is required. This effect is limited somewhat by the presence of price-responsive load (i.e., load that will not consume if prices reach above a certain level). Price-responsive load can be used to complicate later rounds and add a new dimension to the participants’ analyses. Depending on how much information participants are provided about the amount of load reduction, the price at which such reduction will occur and the probability of it occurring may influence how aggressively participants bid in the final round.

4. Extending the Use of the Simulation

Many authors have recognized the importance of using spreadsheet simulations for solving various MS/OR problems (e.g., Bodily, 1986; Leon et al., 1995; Seal et al., 2000). Hence, we propose extending the use of this simulation to introductory MS/OR undergraduate and graduate courses. The simulation could be used as part of an interactive lecture or in a group exercise.

The simulation can be used to support learning objectives in model use. It provides an interactive tool to enhance instruction in the importance of distinguishing between fixed and variable costs, some auction basics (including why and how changes in auction rules result in changes in bidding strategy), decision making under uncertainty, and strategic thinking. Unlike instructional tools that emphasize only one aspect of MS/OR, this auction model integrates several key ideas and requires students to move among these concepts as they formulate their bidding strategies. The simulation also permits group interaction and learning among students, which is more representative of what will confront students in non-academic settings.

This simulation helps meet the learning objective of having students gain an understanding of the following specific aspects of markets and auctions.

  • In a single clearing price auction in a perfectly competitive market,
    • the profit-maximizing bidding strategy for each generation unit is to bid its variable (marginal) costs;
    • bidders do not need to know the cost structure of their competitors to determine their bid; and
    • the market-clearing price will be the variable costs of the highest-cost bidder selected to satisfy demand.
  • The details of how auctions work can fundamentally change bidding strategies, as evidenced by the difference in strategies between the two types of auctions presented in this simulation.
  • In a paid your bid auction, a reasonable bidding strategy is to forecast the highest accepted bid and to bid that amount (or slightly less depending on one’s risk preference).
  • The ability to exercise market power increases with ownership concentration, demand, and the ability of competitors to anticipate and implicitly collude based on the experience of multiple bidding rounds – but price-responsive demand can mitigate market power.

Depending on the interest of the instructor and students, the learning objective can be approached from several different perspectives. Students can be asked to use the model in a pure business context and play the role of profit-maximizing companies. Students can also use the simulation to study the implication of two different auction designs or different market structures (i.e., concentration and type of ownership) on market power in electricity markets. In this case, the simulation can be used either to conduct systematic experiments to draw conclusions (e.g., along the lines, but less sophisticated than, Weiss, 2002) or as an analytical tool that allows students to test various assumptions and bidding strategies.

We have described the use of the simulation as part of an interactive lecture. The simulation can also be used outside the classroom, for example, as a group project or homework assignment. As a homework assignment, students could be asked either to create a spreadsheet simulation or be provided the spreadsheet and use it to answer questions regarding how they anticipate market participants might bid in different situations. After playing the game, the students, either as individuals or groups, could write up or present their conclusions, including the students who were the market maker.

It is important to note that the simulation is not intended to cover auction theory in detail or to provide a comprehensive model of electricity markets. For example, transmission congestion and the need for reserve capacity significantly complicate real electricity markets. In addition, auction applications in the electric power industry are not limited to electric energy markets; auctions are also used to allocate transmission capacity. Students should be made aware of the simulation’s limitations by being asked to assess the spreadsheet’s weaknesses, which should help reinforce the MS/OR reasoning and the instructor’s key learning objectives.

5. Step-by-Step Notes for the Instructor to Implement the Electricity Market Simulation

5.1 Pre-Class Preparation

The instructor first needs to determine the number of teams and then assign to each team specific generation units. All 28 generation units should be assigned. Using the generation handout file, Electricity Auction Generation Units, print out each worksheet and assign each worksheet to a team. To provide each team with a variety of generation units (baseload, intermediate, and peaking), we suggest that the instructor sequentially assign the units to each team. For instance, if there are six teams, Unit 1 is assigned to Team 1, Unit 2 is assigned to Team 2, …, Unit 7 is assigned to Team 1, Unit 8 is assigned to Team 2, and so on until all units have been assigned.

We also suggest that the instructor write the unit number on the back of each of the generation unit bid sheets assigned or print out each team’s bid sheets on different color paper. This will facilitate the distribution of the bid sheets from the market administrator (usually the instructor) to each team after each round of bidding.

Each student should also be given a copy of the Instruction for Students, Electricity Auction Instructions, to read before the simulation, preferably at least several days ahead of time. We recommend that the instructor review with students the Summary of Key Instructions provided at the bottom of the Instruction for Students immediately prior to the simulation. 

To expedite the processing of bids, the instructor may want to appoint a student to assist in the market-making functions. This student can aid in collecting the bid sheets, arranging them in sequential order to facilitate data entry, reading the entries to the instructor who inputs them into the spreadsheet, and redistributing the bids sheets to the appropriate teams.

5.2 During the Simulation

Teams should be given at least 15 minutes to prepare their bids for the first round. This can be  done either during the class time in which the simulation takes place, or teams could be required to meet beforehand to prepare their bids for the first round. Even if teams are responsible for preparing their bids ahead of time, the instructor may want to provide some class time during the simulation to provide clarifying instructions and allow the teams to finalize their bids. We recommend that the instructor not provide any bidding suggestions during the first round. It is important for teams to struggle with how to formulate their bids.

After the first-round bids have been collected, the market administrator should enter the bids, clear the market, and present the results using the Results tab in the simulation spreadsheet. We recommend hooking the computer used by the market administrator to an LCD projector to display the results. Remember when entering the bids to turn off the LCD display so that the teams cannot see the bids of the other teams.

We recommend running the first three rounds without any class discussion of the results. It takes two to three rounds for the teams to get the mechanics down, understand the information on their bid sheets, and understand the results. When presenting the results of each round, some students will want to discuss bidding strategies or seek confirmation on their approach. We recommend avoiding these discussions at this point of the simulation so that teams are required to work through these issues.

If the instructor plans to use Round 3b, the paid your bid round, the students should be told prior to Round 3 to submit two sets of bids per unit and reminded of the differences in auction rules between Round 3a and 3b. After Round 3, the instructor should engage in a short discussion comparing the bidding strategies between Round 3a and 3b.

Rounds 4 through 6 can proceed at a quicker pace than the first three rounds. Our experience is that after three rounds, the teams understand the mechanics and basic strategies and have internalized a process to prepare their bids. Not only can they prepare their bids more quickly, but they start to think strategically about them. The instructor may want to encourage teams to develop a rough estimate of the total supply curve as a means of focusing team discussions. In the final round, the instructor may want to permit teams to collude by sharing their confidential information and prepare bids jointly. This adds an additional dimension to the simulation and increases the energy level of the participants.

5.3 After the Simulation

It is up to the instructor to determine the total number of rounds and the tradeoff between the length of the final discussion and the number of rounds played. We recommend leaving 15 minutes or so to debrief after the exercise. This allows each team to summarize their strategies to the group, contrast their approaches, and digest what they have learned. We typically summarize the game with the following points, along with the reasoning behind them:

  • Never bid below a unit’s marginal cost;
  • The single-clearing price auction during periods of low demand and substantial competition provides a strong incentive to bid a unit’s marginal cost;
  • The paid your bid auction requires estimating bid of the highest unit that is selected to be dispatched and then bidding the higher of that estimate and a unit’s marginal cost;
  • As demand increases, the ability to exercise market power, that is, the ability to raise prices above their competitive levels by bidding above marginal costs, increases; and
  • Much of the recovery of fixed costs occurs during periods of high demand and not equally across all hours.

6. Conclusions

The importance of spreadsheet modeling in MS/OR practice and as a pedagogical method is a given. The simulation presented provides a hands-on introduction to auction design, which is an important area within MS/OR research and in practical applications such as supply chain management. It also provides an application in one of the largest industries in a modern economy – one that is undergoing rapid and fundamental change in many countries. This simulation requires students to integrate several skills that they develop in their introductory MS/OR course and to work in a team environment. Students enjoy, and we think learn, from the interactive exercise and the immediate feedback of learning the consequences of their bidding strategies.

Acknowledgements

The authors would like to thank the editor, associate editor, and three anonymous reviewers for their comments. In addition, the authors would like to thank the many players of this game for their participation and input.

References

Bodily, S. (1986), “Spreadsheet Modeling as a Stepping Stone,” Interfaces, Vol. 16, No. 5, pp. 34-52.

Edison Electric Institute (2003), “Key Facts About the Electric Power Industry,”

Fabra, N., Nils-Henrik von der Fehr, and D. Harbord, (2003), ”Designing Electricity Auctions:  Uniform, Discriminatory and Vickrey,”

Gass, S. I., D. S. Hirshfeld, and E. A. Wasil (2000), “Model World: The Spreadsheeting of OR/MS,” Interfaces, Vol. 30, No. 5, pp. 72-81.

Harvey, S. M., and W. W. Hogan, (2002), “Market Power and Market Simulations,”

Kahn, A., P. Cramton, R. Porter, and R. Tabors (2001), “Pricing in the California Power Exchange Electricity Market:  Should California Switch from Uniform Pricing to Pay-as-Bid Priding,” commissioned by the California Power Exchange,”

Joskow, P., and E. Kahn. (2002), “A Quantitative Analysis of Pricing Behavior in California’s Wholesale Electricity Market During Summer 2000:  The Final Word,”

Ladson, L., and J. S. Liebman (1998), “The Teachers’ Forum: Teaching Nonlinear Programming Using Cooperative Active Learning,” Interfaces, Vol. 28, No. 4, pp. 119-132.

Leon, L., Z. H. Przasnyski and K. C. Seal (1995), “Spreadsheets and MS/OR Models: An End-User Perspective,” Interfaces, Vol. 26, pp. 92-104.

Liebman, J. S. (1998), “Teaching Operations Research: Lessons from Cognitive Psychology,” Interfaces, Vol. 28, No. 2, pp. 104-110.

Mount, T. D., W. D. Schulze, R. J. Thomas, and R. D. Zimmerman, (2001), “Testing the Performance of Uniform Price and Discriminative Auctions,

Powell, S. G. (2001), “Teaching Modeling in Management Science,” INFORMS Transactions on Education, Vol. 1, No. 2, pp. 62-27.

Powell, S. G. (1998), “The Teachers’ Forum: Requiem for the Management Science Course,” Interfaces, Vol. 28, No. 2, pp. 111-117.

Seal, K. C., Przasnyski, Z. H., and Leon, L. (2000), “A Literature Review of MS/OR Models in Spreadsheets,” OR Insight, Volume 13, No. 4, pp. 21-31.

Senge, P. (1990), The Fifth Discipline, Doubleday, New York.

Rothkopf, M. H. and S. Park (2001), “An Elementary Introduction to Auctions,” Interfaces, Vol. 31, No. 6, pp. 83-97.

Weiss, J. (2002), “Market Power and Power Markets,” Interfaces, Vol. 32, No. 5, pp. 37-46.


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Farr, J. and F.A. Felder (2003), "An Introduction to Electricity Market Auctions Using a Spreadsheet," INFORMS Transactions on Education, Vol. 4, No 1,  http://ite.pubs.informs.org/Vol4No1/FarrFelder/

 

Appendix
 
 
Instructions for Simulation Participants
 
   

1. Introduction

This paper provides the necessary background and instructions for students to participate effectively in the electricity market simulation described in An Introduction to Electricity Market Auctions Using a Spreadsheet.

2. Background

The electric power industry is one of the largest industries in a modern economy. In the United States, the electric power industry represents $216 billion-plus in revenues from sales to ultimate customers and approximately 4% of the real gross domestic product (Edison Electric Institute, 2003). It has been undergoing fundamental changes of late as it is restructured from a vertically integrated and regulated industry to a mixture of market-based generation companies and regulated transmission companies. Thanks to almost daily coverage on the network news programs of the electricity disaster in California that began in June 2000, the wider public has learned of the challenges and missteps that have occurred with restructuring in the United States (Borenstein, 2001).

Part of this restructuring involves creating markets in which owners of generation units submit bids indicating the prices at which they would be willing to produce energy (measured in megaWatt-hours, or MWh).1 The organization that administers the wholesale markets determines the least-cost combination of bids to meet hourly demand and thus clear supply and demand. The bidding strategies generation unit owners employ depend fundamentally on the rules of the auction and the ownership profiles of the various generation units, which determine the profitability of exercising market power. Here, we use the term market power to refer to situations in which there is insufficient competition, allowing one or more generation owners to raise profitably the market clearing price by bidding above marginal cost.

The electric power industry is of special interest to MS/OR professionals. It provides a wide range of applications spanning planning and operation. The industry’s large-scale challenges require the use of linear, non-linear, mixed, and stochastic programming as well as reliability analysis. Depending on the interests of the analysts, the application of stock-in-trade MS/OR techniques might focus on computational, engineering, economic, or public policy issues. The analysis and design of auctions is also an important MS/OR topic (e.g., Rothkopf and Park, 2001), although anecdotal evidence based on the authors’ experience and a review of textbooks suggests that auction theory is not as commonly taught at the undergraduate and MBA levels as are other MS/OR techniques.

3. Electricity Market Simulation

You will be a member of a team whose objective is to determine the hourly energy bids of the several generation units in your company’s portfolio. Your objective is to make as much money as possible given your portfolio. You will be competing against other groups that have similar, but not identical, portfolios of generation units.

There are a maximum of six hourly rounds in this market. Each round is for one hour. All of the rounds except Round 3b use a single clearing price auction. Round 3b, and only this round, is a paid your bid auction clearing mechanism. In contrast to an auction with a single clearing price, in Round 3b winning bidders are paid their bid. This last auction design is not currently used in the United States. Your instructor will inform you if Round 3b is to be used in the simulation.

Each team is provided a separate bid sheet for each of its generation units in its portfolio. Since the demand for electricity varies considerably over a day, a variety of generation units are dispatched – that is, turned on to produce electricity to meet demand. Fundamentally, the tradeoff is between fixed costs and variable costs. Typically, units that are designed to be dispatched frequently have higher fixed costs but lower variable costs than those units designed to be dispatched less frequently.

For each round, each team submits a generation unit bid sheet for each unit in its portfolio. Each generation unit is numbered and has a name. It is important that each team records the unit number of each of their generation units that they own in order to collect the appropriate sheets back from the market administrator after each round. It is also recommended that teams write the generation unit’s number on the back of its respective bid sheet so that the market administrator can return the sheets by placing them face down on a table. The bids are determined one round at a time. After the bids for a particular round have been submitted, the market administrator posts the public results (such as the electricity clearing price) for that round. The bid sheets are returned to the appropriate teams with additional information regarding the amount of money each generation unit made in that round. The process is repeated for each of the rounds.

The demand for electricity increases in each round (hour). Not all generation units are expected to run in each round. Moreover, the rounds cover only 6 hours of a year’s total of 8,760 hours. All generation units compete to serve the hourly demand, which is the market demand for electricity. The bid for each generation unit is submitted in $/MWh, that is, the price at which the owner of that unit is willing to be paid per megaWatt-hour of production to operate that unit.

The following information is public and hence available to all teams: the demand for each hour; the type of auction mechanism for a given round: the clearing price for the single-clearing price round after the market is cleared; and the total amount of generation installed (6,930 MW), which does not vary from round to round. Generation units may be unavailable due to maintenance, but this information is known only to the owners of that unit. Other private information is the fixed cost, variable cost, generation technology, age, and the expected number of hours that the unit will be dispatched. All of this private information must remain confidential during the rounds.

Each of the units is named for a color. Data provided for each unit are total capacity in megawatts (MW), the unit type and fuel, and age (a rough proxy for the efficiency of a unit, older units being less efficient). This worksheet also contains confidential information for all units on the amount of available capacity (e.g., which units are on outage and unavailable), variable costs ($/MWh), expected hours of operation per year assuming the unit bids its variable costs, and the unit’s average fixed costs presented in both dollars per kiloWatt($/kW) and $/MWh. For example, if a 100 MW unit is expected to be dispatched 50 hours per year and its total fixed costs is $100,000, then its fixed costs in dollars per kiloWatt is $100,000/(100 MW*1000kW/1MW) = $1/kW. Its fixed cost in dollars per MegaWatts is $100,000/(50 hours * 100 MW) = $20/MWh.

Each portfolio may consist of baseload units, which are expected to run most hours in a year; intermediate units, which operate roughly 40-60% of the time; and peaking units, which are dispatched only up to several hundred hours per year.

Each round is a single clearing price auction, meaning that the highest bid accepted sets the clearing price and all generators whose bids are accepted are paid this single clearing price. Figure 1 illustrates this type of auction. Different generation units, represented by different color blocks, submit energy bids (which are ranked lowest to highest). The point at which demand intersects supply establishes the market clearing price. Figure 1 presents the demand curve as a “staircase.” The vertical portion of the demand curve reflects the lack of demand price elasticity in wholesale electricity markets, and the two “stairs” indicate two blocks of price-responsive demand.

All rounds incorporate price-responsive demand. There are two blocks of price-responsive load as illustrated in Figure 1. These load blocks are defined by the amounts of load (MW) and the price ($/MWh) that triggers each load block not to consume electricity. For example, a load block may consist of 50 MW that for electricity prices of $500/MWh or higher does not consume. When generation unit bids needed to serve demand exceed the prices of these load blocks, the blocks are “dispatched,” meaning that they do not consume. Only the market administrator knows the size and dispatch price of these two blocks of price-responsive load.

The model does handle situations in which only a portion of a unit is needed; this occurs when the total available capacity of the marginal unit exceeds the amount of residual demand after all the infra-marginal units have been selected. Sometimes, different generation units submit the same bid, which turns out to be the marginal bid, but the total amount of capacity from these units is not needed to meet demand. To avoid ties, the spreadsheet randomly selects units to break the tie.

Determining the Market Clearing Price in a Single Clearing Price Electricity Auction with a Staircase Demand Curve
Figure 1: Determining the Market Clearing Price in a Single Clearing Price Electricity Auction with a Staircase Demand Curve

The results report the “perfect competition price,” that is, the price that would clear the market were each generation unit bid its variable costs. The Actual Price or clearing price is also reported, and in the case of the pay-your-bid auction, the “Actual Price” is the average price paid to generation owners weighted by the capacity of accepted generation units. The Perfect Competition Price and the Actual Price, respectively, are then used to calculate the “Perfect Competition” Total Margin and the Actual Total Margin. These margins are the amount of money above variable costs that all of the generation units earned, assuming perfect competition and based on the actual bids. The Change In Margin is the difference between the Perfect Competition Total Margin and the Actual Total Margin. Of course, some generation units may be better or worse off than the Perfect Competition Case; the number of units and the collective amounts of all generation units of being better and worse off are also reported.

4. Summary of Key Instructions

  1. Each team has a portfolio of generation units.
  2. Each team submits one bid sheet for each unit for each round, which is for one hour.
  3. Each team should only prepare bids one round at a time. Between each round, the market administrator clears the market and provides price-clearing information that may be helpful in preparing bids for future rounds.
  4. Each bid for each generation unit for each round should be in $/MWh, that is, a bid per unit of production and not a bid for the total output of the generation unit.
  5. The demand for electricity increases in every round.
  6. Round 3 has two versions. Round 3a is the single-clearing-price auction just like Rounds 1-2 and 4-6. Round 3b, which your instructor may or may not use, is a paid your bid auction. Rounds 3a and 3b have the same level of demand.
  7. Information on each team’s bid sheets should remain confidential.

5. References for Students to Investigate

For students who are interested in various aspects of electricity markets, a good place to start is the Harvard Electricity Policy Group (HEPG) webpage , which has numerous papers and presentations organized by topic. Many of the documents can be downloaded from the web; those that are not available electronically can be requested at no charge. In addition, this webpage has links to many other webpages that may be of interest.

For students interested in the California electricity market meltdown starting in June 2000, see

Borenstein, S. (2001), “The Trouble with Electricity Markets and California’s Electricity Restructuring Disaster,” University of California Energy Institute, PWP-081,

In addition, the HEPG has a series of papers that debate the fundamental causes of the California situation (market power versus poor market design) under its Mergers, Market Power and Antitrust section. Two examples are the following:

Harvey, S. M., and W. W. Hogan, (2002), “Market Power and Market Simulations,”

Oskow, P. and E. Kahn. (2002), “A Quantitative Analysis of Pricing Behavior in California’s Wholesale Electricity Market During Summer 2000: The Final Word,”

For students interested in electricity auctions, the HEPG has several papers:

Mount, T. D., W. D. Schulze, R. J. Thomas, and R. D. Zimmerman, (2001), “Testing the Performance of Uniform Price and Discriminative Auctions, mimeo, at

Fabra, N., Nils-Henrik von der Fehr, D. Harbord, (2003), “Designing Electricity Auctions: Uniform, Discriminatory and Vickrey,”

Kahn, A., P. Cramton, R. Porter, and R. Tabors (2001), “Pricing in the California Power Exchange Electricity Market: Should California Switch from Uniform Pricing to Pay-as-Bid Priding,” commissioned by the California Power Exchange,” .

References

Edison Electric Institute (2003), “Key Facts About the Electric Power Industry,”

Borenstein, S. (2001), “The Trouble with Electricity Markets and California’s Electricity Restructuring Disaster,” University of California Energy Institute, PWP-081,

Rothkopf, M. H. and S. Park (2001), “An Elementary Introduction to Auctions,” Interfaces, Vol. 31, No. 6, pp. 83-97.