Jorge Sousa

Negotiating Bilateral Contracts in a Multi-agent Electricity Market: A Case Study

Electricity markets are systems for effecting the purchase and sale of electricity using supply and demand to set energy prices. Three major market models are often distinguished: pools, bilateral contracts, and hybrid models. This article addresses the challenge of using software agents with negotiation competence to help manage the complexity of electricity markets, particularly the issues associated with the negotiation of bilateral contracts. Specifically, it presents a multi-agent energy market and describes a case study on forward bilateral contracts.

Evaluation of energy storage devices for renewable energies integration: Application to a Portuguese wind farm

This paper evaluates the benefits of energy storage systems applied to renewable intermittent sources like wind. With this objective, a 144 MW Portuguese wind farm is used as a case-study. The storage system design and evaluation processes use a computational tool developed in MatLab to simulate the wind farm operation with an energy storage system and computes the remuneration tariff. The energy storage design settles on a system of 5 MW with 30 MWh. The simulation results show a 2.1% gain in wind farm tariff and a improved adjustment on generation to the typical electricity demand curve. Considering the storage system design and an available storage technology survey, one concludes that redox flow batteries are the best suited to application, in spite of their present prices being not the most advantage.

Price forecasting in the day-ahead Iberian electricity market using a conjectural variations ARIMA model

Price forecast is a matter of concern for all participants in electricity markets, from suppliers to consumers through policy makers, which are interested in the accurate forecast of day-ahead electricity prices either for better decisions making or for an improved evaluation of the effectiveness of market rules and structure. This paper describes a methodology to forecast market prices in an electricity market using an ARIMA model applied to the conjectural variations of the firms acting in an electricity market. This methodology is applied to the Iberian electricity market to forecast market prices in the 24 hours of a working day. The methodology was then compared with two other methodologies, one called naïve and the other a direct forecast of market prices using also an ARIMA model. Results show that the conjectural variations price forecast performs better than the naïve and that it performs slightly better than the direct price forecast.

Contribution of energy storage systems for power generation and demand balancing with increasing integration of renewable sources: application to the Portuguese power system

Increasing integration of renewable sources introduce some new issues on the operation of the power system, such as potential unbalancing between generation and demand, especially in off-peak periods with high levels of hydro generation. This scenario can get worse when associated with the installation of a nuclear powerplant, which operates on a must run basis. This paper analyses the contribution of energy storage systems use to avoid future power generation and demand unbalance in the Portuguese power system. Moreover it is also presented an overview of the available energy storage technologies and the role of power electronics on its appropriate operation.

How market power affects the behavior of a pumped storage hydro unit in the day-ahead electricity market?

The integration of large amounts of wind energy in power systems raises important operation issues such as the balance between power demand and generation. The pumped storage hydro (PSH) units are seen as one solution for this issue, avoiding the need for wind power curtailments. However, the behavior of a PSH unit might differ considerably when it operates in a liberalized market with some degree of market power. In this regard, a new approach for the optimal daily scheduling of a PSH unit in the day-ahead electricity market was developed and presented in this paper, in which the market power is modeled by a residual inverse demand function with a variable elasticity. The results obtained show that increasing degrees of market power of the PSH unit correspond to decreasing levels of storage and, therefore, the capacity to integrate wind power is considerably reduced under these circumstances.

Optimal renewable generation mix of hydro, wind and photovoltaic for integration into the Portuguese power system

In spite of the advantages of renewable energy sources (RES), their variability and uncertainty raises important issues in power systems operation, such as the need to balance demand with a highly variable and uncertain power generation. In this context, is of utmost importance the choice of the optimal renewable generation mix to be integrated in the power system in order to accomplish the established renewable energy targets with the lowest technical impacts. With this aim, this paper presents a methodology that supports decision making on the renewable energy policy by deriving the optimal renewable generation mix from different available technologies - hydro, wind and photovoltaic - that integrates a given amount of electricity from renewable sources, taking into account the variability of the renewable generation mix and the target share of renewable generation. This methodology is applied to a case study of one month using renewable generation data of the Portuguese power system.

Multi-market optimal scheduling of a power generation portfolio with a price-maker pumped-storage hydro unit

The increasing integration of renewables in the energy markets has been raising some challenges to generating companies (GENCOs), in terms of operation and planning of their generation portfolios. A GENCO aiming at maximizing its profits has to deal with offers to several available markets, among which are the Day-ahead Market (DAM) and the Secondary Reserve Market (SRM). This paper presents a scheduling solution of a price-maker GENCO whose portfolio includes a pumped-storage hydro unit, acting simultaneously in the DAM and SRM. The results were obtained for six different scenarios, where the portfolio may include a thermal generation unit and compares the GENCO behavior in both markets either as a price-taker or as a price-maker. The results put in evidence the portfolio effect when the GENCO takes into account its influence on price, which is seen in the price-maker scenarios, whereas the scheduling remains unchanged under the price-taker behavior.

Comparing wind generation profiles: A circular data approach

The importance of wind power energy for energy and environmental policies has been growing in past recent years. However, because of its random nature over time, the wind generation cannot be reliable dispatched and perfectly forecasted, becoming a challenge when integrating this production in power systems. In addition the wind energy has to cope with the diversity of production resulting from alternative wind power profiles located in different regions. In 2012, Portugal presented a cumulative installed capacity distributed over 223 wind farms [1]. In this work the circular data statistical methods are used to analyze and compare alternative spatial wind generation profiles. Variables indicating extreme situations are analyzed. The hour(s) of the day where the farm production attains its maximum daily production is considered. This variable was converted into circular variable, and the use of circular statistics enables to identify the daily hour distribution for different wind production profiles. This methodology was applied to a real case, considering data from the Portuguese power system regarding the year 2012 with a 15-minutes interval. Six geographical locations were considered, representing different wind generation profiles in the Portuguese system.In this work the circular data statistical methods are used to analyze and compare alternative spatial wind generation profiles. Variables indicating extreme situations are analyzed. The hour(s) of the day where the farm production attains its maximum daily production is considered. This variable was converted into circular variable, and the use of circular statistics enables to identify the daily hour distribution for different wind production profiles. This methodology was applied to a real case, considering data from the Portuguese power system regarding the year 2012 with a 15-minutes interval. Six geographical locations were considered, representing different wind generation profiles in the Portuguese system.

Optimal scheduling of a pumped storage hydro unit in the day-ahead and secondary reserve electricity market

Ancillary services play a major role in power systems security and stability. The transmission systems operators contract some of these services at minimum cost in competitive markets. This is the case of the secondary reserve market (SRM). Besides the day-ahead market (DAM) generating companies, aiming at maximize their profits, can increase their revenues by selling available capacity in the SRM. This paper presents the solution of a price-taker generating company, owning a pumped-storage hydro (PSH) unit, acting in DAM and SRM. The results were obtained for three case studies: the generating company acts only in the DAM; the generating company acts in both markets with a fixed pumping capacity of the PSH unit; the generating company acts in both markets with a variable pumping capacity of the PSH unit. Results show that higher profits are obtained when acting in both markets with a variable pumping capacity of the PSH unit.

Risk Analysis and Behavior of Electricity Portfolio Aggregator

The scope of this paper is to adapt the standard mean-variance model of Henry Markowitz theory, creating a simulation tool to find the optimal configuration of the portfolio aggregator, calculate its profitability and risk. Currently, there is a deep discussion going on among the power system society about the structure and architecture of the future electric system. In this environment, policy makers and electric utilities find new approaches to access the electricity market; this configures new challenging positions in order to find innovative strategies and methodologies. Decentralized power generation is gaining relevance in liberalized markets, and small and medium size electricity consumers are also become producers (“prosumers”). In this scenario an electric aggregator is an entity that joins a group of electric clients, customers, producers, “prosumers” together as a single purchasing unit to negotiate the purchase and sale of electricity. The aggregator conducts research on electricity prices, contract terms and conditions in order to promote better energy prices for their clients and allows small and medium customers to benefit improved market prices.