arXiv subjects

Rafael Kelman

Publications and source records attributed to Rafael Kelman.

6 recordsLinked to original sources

arXiv2026

Co-Optimized Generation, Transmission, and Storage Expansion: System Value and Optimal Duration of Pumped-Storage Hydropower

Expansion planning models usually fix storage duration before optimization, setting how much storage power to build but not for how long it can discharge. We present a generation-transmission-storage expansion framework in which candidates of many durations compete on annualized cost, making the duration mix an optimization outcome. It is a rolling-horizon, two-stage stochastic linear program, each five-year stage is a full year at hourly resolution under ten coherent inflow, wind, and solar scenarios. We apply it to the Brazilian Interconnected System over 2030-2050, where demand roughly doubles to 1,716 TWh/year and variable renewable energy (VRE) supplies most new capacity. Two cases are compared: 36 pumped-storage hydropower (PSH) candidates over four subsystems and nine durations (4-144 h) alongside 4-h battery energy storage systems (BESS), and BESS alone. With PSH available, the model builds 31.2 GW / 755 GWh of PSH and no BESS, dominated by 12-h capacity with 4.9 GW of 72-h units. Without PSH it builds 38 GW / 152 GWh of BESS and 7.8 GW more gas-fired capacity, mostly open-cycle peakers. PSH lowers 2050 annualized system cost by US$ 5.0 billion/year (6.8%), operating cost by 23.5%, thermal generation by 34 TWh/year, and long-run marginal cost by 20%; 2035 VRE curtailment falls from 8.4% to 3.2%. The magnitudes are specific to Brazil, but the underlying mechanism is general: limiting storage candidates to a single duration understates the system's optimal energy-storage requirement and overstates its residual need for thermal capacity.

math.OC↗

arXiv2026

Optimization of Closed-Loop Pumped-Storage Hydropower Siting

Accelerating variable renewable energy integration introduces substantial operational challenges to modern power grids. Frequent curtailment of surplus renewable generation highlights the pressing need for long-duration energy storage capable of shifting generation to high-demand periods while providing essential ancillary services and grid inertia. Socio-environmental constraints increasingly limit conventional hydropower development; however, closed-loop pumped-storage hydropower (PSH) presents a viable alternative because its off-river reservoirs avoid natural watercourses. This paper introduces HERA-S, a computational modeling framework developed by PSR (supported by EDF, CTG, Brookfield, and Rio Light) to streamline and standardize regional PSH site prospecting. HERA-S automates spatial screening, dam optimization, cost estimation, and socio-environmental impact scoring. Applied to a case study in Rio de Janeiro, Brazil, the framework employs an integer programming model to optimize dam-fill and excavation mass balances against inter-reservoir distance, significantly improving pre-feasibility planning agility.

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arXiv2026

Integrated Investment and Operational Planning for Sugarcane-Based Biofuels and Bioelectricity under Market Uncertainty

Sugarcane biomass is a strategic resource for the energy transition, particularly in Brazil, where it underpins electricity and ethanol production. Investment planning is challenged by diverse production pathways, price volatility, and feedstock variability. This work develops a two-stage stochastic optimization model integrating investment and operational decisions for sugarcane facilities. The model aims to support robust planning for diversified biomass plants, aiding the sector's decarbonization. The first stage defines capacity expansion under economies of scale through a power-law cost function. The second stage defines operational decisions under price and feedstock uncertainty, modeled via scenarios and Conditional Value-at-Risk. \answer{From an investor's perspective, the objective is to minimize risk-adjusted net costs. In addition to its methodological contributions, this work also provides an open-source implementation of the proposed capacity expansion planning framework, referred to as \textit{OptBio}.} A Brazilian case study shows risk-neutral strategies favor sugar/ethanol but are vulnerable, whereas risk-averse strategies promote diversification. Sensitivity analyses indicate biomethane and hydrogen may become viable with favorable prices, while biochar boost productivity and profitability.

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arXiv2025

From fields to fuel: analyzing the global economic and emissions potential of agricultural pellets, informed by a case study

Agricultural residues represent a vast, underutilized resource for renewable energy. This study combines empirical analysis from 179 countries with a case study of a pelletization facility to evaluate the global potential of agricultural pelletization for fossil fuel replacement. The findings estimate a technical availability of 1.44 billion tons of crop residues suitable for pellet production, translating to a 4.5% potential displacement of global fossil fuel energy use, equating to 22 million TJ and equivalent to 917 million tons of coal annually. The economically optimized scenario projects annual savings of $163 billion and a reduction of 1.35 billion tons of CO2 equivalent in emissions. Utilizing the custom-developed CLASP-P and RECOP models, the study further demonstrates that agricultural pellets can achieve competitive pricing against conventional fossil fuels in many markets. Despite logistical and policy challenges, agricultural pelletization emerges as a scalable, market-driven pathway to support global decarbonization goals while fostering rural economic development. These results reinforce the need for targeted investment, technological advancement, and supportive policy to unlock the full potential of agricultural pellets in the renewable energy mix.

econ.GN↗

arXiv2022

Sustainable Hydropower Planning in Gabon

Hydropower is a renewable, controllable, and flexible source of electricity. These are instrumental features to support decarbonization efforts, as an enabler of non-controllable and variable sources of renewable electricity. Sometimes hydropower is accompanied by other services provided by multipurpose reservoirs, such as water supply, irrigation, navigation, flood control and recreation. Despite all these benefits, hydropower can be a polarizing issue. A large sample of projects with poor planning and execution provides numerous arguments for its opponents. Large and complex projects frequently suffer overcost and delays. The direct impacts are related to the disruption of river ecosystems and surrounding habitats due to the flooding of large areas, and the fragmentation of rivers caused by the construction of dams and the reduction of sediment transport that impoverishes aquatic life. People displacement and compensation are always a complex issue. Hydropower projects can also cause indirect impacts, such as additional deforestation related to the construction of workers' villages, access roads and transmission lines. Finally, reservoirs may also become a significant source of methane emission, especially in tropical areas. This paper offers an analytical approach for sustainable hydropower planning at the river basin scale called HERA: Hydropower and Environmental Resource Assessment. Built on three main components, namely geoprocessing, engineering, and optimization, HERA screens and compares hydropower development alternatives to guarantee social and environmental objectives while maximizing mentioned economic benefits. It was designed to encourage a transparent and participatory hydropower planning process from the early stages. Experience has shown this approach increases the chances of better and balanced outcomes. A case study is presented in the Ogooue river basin in Gabon.

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arXiv2021

An integer programming model for the selection of pumped-hydro storage projects

Energy storage systems - in particular, Pumped Hydropower Storage (PHS) - will be increasingly important to support the transition of power systems toward zero emissions. The reason is that PHS can mitigate the variability and uncertainty of renewable energy production from solar and wind power to balance electricity demand with supply. In this paper, we propose an integer programming problem for PHS siting that uses a Digital Elevation Model (DEM) to meet an energy storage requirement. It assumes the existence of a reservoir, lake, or river, and decides where to build a reservoir that will constitute the PHS with the existing body of water. This model finds minimum-cost project candidates given parameters such as desired head, power, and operation time. The paper discusses different solution methods to assure reservoir closure and avoid its fragmentation. A heuristic explores the representations of the DEM, from more aggregate to more precise, to sequentially refine the solution based on the last selected site, which reduces computational effort. The formulation is general and the objective function includes both construction and equipment costs. Constraints are related to the energy storage target and reservoir closure based on the DEM. We illustrate the methodology by selecting multiple PHS projects next to the reservoir of the Sobradinho hydropower plant in Brazil. The result of this model can be seen as a bottom-up step that prepares PHS candidate projects to be considered by an integrated resource planning model in a top-down step, that would select from these shortlisted projects.

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