C. Genesi

Generation Expansion Planning in the Age of Green Economy

Generation expansion planning (GEP) is the problem of finding the optimal strategy to plan the construction of new generation plants while satisfying technical and economical constraints. It is a challenging problem due to its nonlinearity, large-scale, and to the discrete nature of the variables describing unit size and allocation. Originally, GEP was faced by vertically integrated utilities with the aim of minimizing production and capital costs. After deregulation, generation companies were forced to consider GEP from the viewpoint of market shares and financial risk. In recent years, increasing concern for environmental protection has driven lots of countries all over the world to promote energy generation from renewable sources. Different incentive systems have been introduced to support the growth of the investments in generation plants exploiting renewable energy. In the present paper, the impact of some of the most popular incentive systems (namely feed-in tariffs, quota obligation, emission trade, and carbon tax) on generation planning is considered, thus obtaining a comprehensive GEP model with a suitably modified objective function and additional constraints. The resulting problem is solved by resorting to the generalized Benders decomposition (GBD) approach and implemented in the Matlab programming language. Tests are presented with reference to the Italian system.

Risk management in long term generation planning

Constraints on renewable energy production and CO(in2} emissions are being imposed to generation companies (GENCOs) by growing environmental concern and compelling regulatory directives. These constraints impact on the economy of generation acting as a bias towards the adoption of novel generation technologies, mostly in the field of renewable energy generation. In the present work, the mathematical model of generation planning is presented aiming at the maximization of the net present value of the investment made in generation expansion. A general model is developed to find the present and the future generation mix of a given GENCO and the Lagrangian relaxation method is used to solve the ensuing large scale mixed integer programming problem. Although this problem is interesting in its own right, its results cannot be really useful to define a generation planning strategy unless the uncertainties in costs, prices, construction times are considered. For this reason a Monte Carlo simulation procedure is set up including an expansion planning computation at each step of the procedure. Results are presented with reference to an hypothetical GENCO, by employing reasonable data.

Impact of renewable energy quotas and emission trade on generation planning

Growing environmental concern and compelling regulatory directives have forced Generation Companies (GEN-COs) to revise criteria previously used for long term generation expansion planning. Constraints on renewable energy production and on CO2 emission affect the economy of generation acting as a powerful drift towards the adoption of novel generation technologies. In the present work, the mathematical model of generation planning is presented aiming at the maximization of the net present value of the investment made in generation expansion, taking all the above limitations into account. A model is developed with reference to the present and the future generation mix of a given GENCO. The Lagrangian Relaxation method is used to solve the generation planning model requiring the solution of many sub-problems each relative to one generation plant a time. The solution of these sub-problems, obtained by dynamic programming, is interesting in its own right since it allows the decision maker to gauge the economic impact of the different generation technologies now available.

A multilateral market coupling procedure for the internal electricity market simulation

Afterwards the energy market liberalization in European countries, the issue of optimal allocation of cross border interchanges has gained a notable importance. The most widely accepted method for the congestion management among several interconnected countries is the “Decentralized Market Coupling” (DCM), which was successfully implemented by the Power Exchangers of France, Belgium and the Netherlands. In this paper an iterative procedure that applies the DMC method to a large interconnected network is presented and the solution is compared with that achieved by a single pool simulated by means of a market splitting method.

Strategic bidding in a day-ahead market by coevolutionary genetic algorithms

In the present work, the problem of energy market price clearing and generation company (Genco) strategic bidding is considered in the framework of existing day-ahead markets with system marginal price auction. The situation of imperfect competition arising when one of the Gencos is large enough to exert market power is considered in detail, showing what bidding behaviors are to be expected when such a market arrangement occurs. The impact that inter-area transmission system congestions may have on the mechanism of system pricing is also addressed. The bidding problem faced by each Genco is formulated as a strategic multi-player game in which the choice between different bidding levels and energy amounts to be sold at the market has to be made. The large size of the problem due to the number of competitors and to the presence of transmission constraints makes the application of classical game theory troublesome. Therefore, an agent based method belonging to the category of coevolutionary genetic algorithm was selected for the solution of this problem. Test cases illustrate the different strategies that the Gencos may implement to optimize their performance at the day-ahead market. Beside some small didactical examples, the situation of the Italian day-ahead market is considered in detail.

Cross border transmission capacity allocation by multilateral market coupling

The problem of cross border interchange and of allocation of exchange capacities between interconnected countries of the European community has gained an ever increasing importance during the most recent years. The reasons for that are to be found in the existing price gap between different countries as well as in the limited exchange capacity of some interconnection corridors. As a result, the European transmission system operators (ETSO) committee has issued a sequence of documents illustrating the guidelines for efficient and economic assignment of the available cross border capacity. In addition to the ETSOpsilas efforts, an example of successful multi-market coordination is given by the trilateral market coupling system developed by the transmission system operators of France, Belgium and the Netherlands. In the present paper, the idea of multilateral market coupling is re-considered and extended to an arbitrary number of interconnected countries. The proposed procedure elaborates the net export curves, relative to each country, by means of a suitable coordinating procedure based on linear programming. Examples of the application of the proposed procedure are given with reference to a small test network as well as to an equivalent model of the European (UCTE) system.

Identification of Critical Outages Leading to Cascading Failures in Electrical Power Systems

The extended black-outs that have occurred in the near past, have stimulated a renewed interest in the assessment of power system vulnerability. Accurate post-mortem analyses of the causes involved in a major black-out have shown that, in most cases, the outage of a line or a generator is the initiating event of cascading faults that may rapidly lead to a catastrophic failure. The role of hidden faults has been emphasized, but a systematic screening of the protection system in search for hidden faults remains a formidable and almost impossible task for today power engineers. The aim of the present paper is that of carrying out a more effective screening of single and multiple contingencies looking for those situations which are likely to jeopardize system security and to expose possible hidden faults. The problem of finding the worst branch or generator outages is recast in the form of a linear programming problem with mixed (real and binary) variables which is solved by efficient branch-and-bound techniques implemented in the CPLEX optimization package. Tests carried out with reference to the Italian EHV network and to the European UCTE system, confirm the effectiveness of the proposed contingency screening approach.

Definition of a zonal reactive power market based on the adoption of a hierarchical voltage control

The overall purpose of the paper is to suggest a suitable methodology of valuing the reactive power support in a deregulated electricity market from the point of view of Transmission System Operator (TSO). The valorization of the reactive resource available in a grid bus will be determined by means of an Optimal Reactive Power Flow (ORPF) procedure, which pursues both economic and security criteria. The methodology has been applied to a detailed model of the EHV Italian system with reference to a 2010 peak load condition and to a medium term forecast scenario (target year 2014). The results will show that an adequate Hierarchical Voltage Control (HVC) framework and above all a suitable definition of control areas may be a good way to implement a regional (zonal) reactive power market. The analysis will also investigate the possible consequences of delaying the network development planned by the Italian TSO.

A multilateral market coupling approach for the allocation of cross border transmission capacity

The problem of cross border interchange and of exchange capacity allocation has gained an increasing importance because of existing price gaps between the different countries and of limited exchange capacity. The European Transmission System Operators (ETSO) committee has issued a sequence of documents illustrating the guidelines for efficient and economic assignment of the available cross border capacity. An example of successful multi-market coordination is given by the trilateral market coupling system developed by the TSOs of France, Belgium and the Netherlands. The aim of the present paper is that of finding a procedure able to make results from market coupling as close as possible to those furnished by single electricity pool.

An online optimization algorithm for coordinated control of VSC-HVDC link and DFIGs for offshore wind applications

The aim of this paper is to find out an optimization algorithm for wind power plants, where the wind turbines are equipped by DFIG, connected to on-shore grid by means VSC-HVDC link. The off-shore grid frequency is assumed variable under a fixed range and the wind power tracking characteristic of the DFIG has to be extended to consider the additional grid frequency dependence. The highly non linear problem is solved by means of a interior point algorithm and a sequential quadratic programming algorithm. The methodology has been tested on a wind park composed by 50 turbines. Results show that the best operation point is quickly reached, demonstrating the effectiveness of the tool for online operations.