Prices stabilization for inexact unit-commitment problems

International audienceA widespread and successful approach to tackle unit-commitment problems is constraint decomposition: by dualizing the linking constraints, the large-scale nonconvex problem decomposes into smaller independent subproblems. The dual problem consists then in finding the best Lagrangian multiplier (the optimal "price''); it is solved by a convex nonsmooth optimization method. Realistic modeling of technical production constraints makes the subproblems themselves difficult to solve exactly. Nonsmooth optimization algorithms can cope with inexact solutions of the subproblems. In this case however, we observe that the computed dual solutions show a noisy and unstable behaviour, that could prevent their use as price indicators. In this paper, we present a simple and easy-to-implement way to stabilize dual optimal solutions, by penalizing the noisy behaviour of the prices in the dual objective. After studying the impact of a general stabilization term on the model and the resolution scheme, we focus on the penalization by discrete total variation, showing the consistency of the approach. We illustrate our stabilization on a synthetic example, and real-life problems from EDF (the French Electricity Board)

Optimal food price stabilization in a small open developing country

In poor countries, most governments implement policies aiming to stabilize the prices of staple foods, which often include storage and trade measures insulating their domestic market from the world market. It is of crucial importance to understand the precise motivations and efficiency of those interventions, because they can have consequences worldwide. This paper addresses those issues by analyzing the case of a small, open developing country confronted by shocks to both the crop yield and foreign price. In this model, government interventions may be justified by the lack of an insurance market for food prices. Considering this market imperfection, the authors design optimal public interventions through trade and storage policies. They show that an optimal trade policy largely consists of subsidizing imports and taxing exports, which benefits consumers at the expense of producers. Import subsidies alleviate the non-negativity of food storage. In other words, when stocks are exhausted, subsidizing imports prevents domestic price spikes. One striking result: an optimal storage policy on its own is detrimental to consumers, since its stabilizing benefits leak into the world market and it raises the average domestic price. By contrast, an optimal combination of storage and trade policies results in a powerful stabilizing effect for domestic food prices.Markets and Market Access,Economic Theory&Research,Emerging Markets,Access to Markets,Trade Policy

Large-scale unit commitment under uncertainty: an updated literature survey

The Unit Commitment problem in energy management aims at finding the optimal production schedule of a set of generation units, while meeting various system-wide constraints. It has always been a large-scale, non-convex, difficult problem, especially in view of the fact that, due to operational requirements, it has to be solved in an unreasonably small time for its size. Recently, growing renewable energy shares have strongly increased the level of uncertainty in the system, making the (ideal) Unit Commitment model a large-scale, non-convex and uncertain (stochastic, robust, chance-constrained) program. We provide a survey of the literature on methods for the Uncertain Unit Commitment problem, in all its variants. We start with a review of the main contributions on solution methods for the deterministic versions of the problem, focussing on those based on mathematical programming techniques that are more relevant for the uncertain versions of the problem. We then present and categorize the approaches to the latter, while providing entry points to the relevant literature on optimization under uncertainty. This is an updated version of the paper "Large-scale Unit Commitment under uncertainty: a literature survey" that appeared in 4OR 13(2), 115--171 (2015); this version has over 170 more citations, most of which appeared in the last three years, proving how fast the literature on uncertain Unit Commitment evolves, and therefore the interest in this subject

Fixed-Point Approaches to Computing Bertrand-Nash Equilibrium Prices Under Mixed Logit Demand: A Technical Framework for Analysis and Efficient Computational Methods

This article presents a detailed technical framework for modeling with Bertrand-Nash equilibrium prices under Mixed Logit demand. Two coercive fixed-point equations provide more stable computational methods than those obtained from the literal first-order conditions. Assumptions to justify derivation and use of these equations are provided. A brief discussion of a GMRES-Newton method with hookstep globalization strategy originally due to Viswanath is also given. This article can be considered a supplement to an article by the authors forthcoming in the journal {\em Operations Research}.Comment: 57 page

Risk-based methods for sustainable energy system planning: a review

The value of investments in renewable energy (RE) technologies has increased rapidly over the last decade as a result of political pressures to reduce carbon dioxide emissions and the policy incentives to increase the share of RE in the energy mix. As the number of RE investments increases, so does the need to measure the associated risks throughout planning, constructing and operating these technologies. This paper provides a state-of-the-art literature review of the quantitative and semi-quantitative methods that have been used to model risks and uncertainties in sustainable energy system planning and feasibility studies, including the derivation of optimal energy technology portfolios. The review finds that in quantitative methods, risks are mainly measured by means of the variance or probability density distributions of technical and economical parameters; while semi-quantitative methods such as scenario analysis and multi-criteria decision analysis (MCDA) can also address non-statistical parameters such as socio-economic factors (e.g. macro-economic trends, lack of public acceptance). Finally, untapped issues recognised in recent research approaches are discussed along with suggestions for future research

Weak States and Global Threats: Assessing Evidence of Spillovers

A key motivation behind recent donor attention and financial resources devoted to developing countries is the presumed connection between weak and failing states, on the one hand, and a variety of transnational threats, on the other. Indeed, it has become conventional wisdom that poorly performing states generate multiple cross-border “spillovers,” including terrorism, weapons proliferation, organized crime, regional instability, global pandemics, and energy insecurity. What is striking is how little empirical evidence underpins such sweeping assertions. A closer look suggests that the connection between state weakness and global threats is less clear and more variable than typically assumed. Both the type and extent of “spillovers” depend in part on whether the weakness in question is a function of state capacity, will, or a combination of the two. Moreover, a preliminary review suggests that some trans-border threats are more likely to emerge not from the weakest states but from stronger states that possess narrower but critical gaps in capacity and will. Crafting an effective U.S. and international strategy towards weak states and the cross-border spillovers they sometimes generate will depend on a deeper understanding of the underlying mechanisms linking these two sets of phenomena. The challenge for analysts and policymakers will be to get greater clarity about which states are responsible for which threats and design development and other external interventions accordingly. This working paper represents an initial foray in this direction, suggesting avenues for future research and policy development.weak state, failing state, regional instability, global threats

Carbon markets, institutions, policies, and research

The scale of investment needed to slow greenhouse gas emissions is larger than governments can manage through transfers. Therefore, climate change policies rely heavily on markets and private capital. This is especially true in the case of the Kyoto Protocol with its provisions for trade and investment injoint projects. This paper describes institutions and policies important for new carbon markets and explains their origins. Research efforts that explore conceptual aspects of current policy are surveyed along with empirical studies that make predictions about how carbon markets will work and perform. The authors summarize early investment and price outcomes from newly formed markets and point out areas where markets have preformed as predicted and areas where markets remain incomplete. Overall the scale of carbon-market investment planned exceeds earlier expectations, but the geographic dispersion of investment is uneven and important opportunities for abatement remain untapped in some sectors, indicating a need for additional research on how investment markets work. How best to promote the development and deployment of new technologies is another promising area for study identified in the paper.Carbon Policy and Trading,Energy and Environment,Environment and Energy Efficiency,Climate Change,Transport and Environment

The politics of automatic stabilization mechanisms in public pension programs

"Demographic and fiscal pressures have increased pressures on governments in most wealthy countries to reduce the generosity of their public pension programs. Mechanisms that automatically adjust public pension levels to take account of factors such as increased life expectancy and slower economic growth are appealing to politicians because it saves them from having to take loss-imposing actions that are likely to incur political blame. This paper analyzes the financial and political potential of automatic stabilizing mechanisms (ASMs), beginning with a discussion of design issues and alternatives. This is followed by a discussion of potential adoption, implementation, and sustainability challenges for automatic stabilizing mechanisms and a review of experiences with stabilization mechanisms in three countries: Canada, Sweden and Germany. The paper argues that ASMs are vulnerable to erosion over time, especially when the losses that the ASM would impose are substantial, and when elections are impending. Preserving the integrity of ASMs is most likely where the parties that initially supported their adoption continue to be able to sustain cartel-like behavior with respect to pension policymaking. Overall, the analysis in this paper suggests that automatic stabilizing mechanisms are no panacea for the problems of countries facing serious long-term pension financing problems." (author's abstract