• Energy Research

Low-inertia, isolated power systems face the problem of resiliency to active power variations. The integration of variable renewable energy sources, such as wind and solar photovoltaic, pushes the boundaries of this issue further. Higher shares of renewables requires better evaluations of electrical system stability, to avoid severe safety and economic consequences. Accounting for frequency stability requirements and allocating proper spinning reserves, therefore becomes a topic of pivotal importance in the planning and operational management of power systems. In this paper, dynamic frequency constraints are proposed to ensure resiliency during short-term power variations due to, for example, wind gusts or cloud passage. The use of the proposed constraints is exemplified in a case study, the constraints being integrated into a mixed-integer linear programming algorithm for sizing the optimal capacities of solar photovoltaic and battery energy storage resources in an isolated industrial plant. Outcomes of this case study show that reductions in the levelized cost of energy and carbon emissions can be overestimated by 8.0% and 10.8% respectively, where frequency constraints are neglected. The proposed optimal sizing is validated using time-domain simulations of the case study. The results indicate that this optimal system is frequency stable under the worst-case contingency.

With the introduction of massive renewable energy sources and storage devices, the traditional process of grid operation must be improved in order to be safe, reliable, fast responsive and cost efficient, and in this regard power flow solvers are indispensable. In this paper, we introduce an Interior Point-based (IP) Multi-Period AC Optimal Power Flow (MPOPF) solver for the integration of Stationary Energy Storage Systems (SESS) and Electric Vehicles (EV). The primary methodology is based on: 1) analytic and exact calculation of partial differential equations of the Lagrangian sub-problem, and 2) exploiting the sparse structure and pattern of the coefficient matrix of Newton-Raphson approach in the IP algorithm. Extensive results of the application of proposed methods on several benchmark test systems are presented and elaborated, where the advantages and disadvantages of different existing algorithms for the solution of MPOPF, from the standpoint of computational efficiency, are brought forward. We compare the computational performance of the proposed Schur-Complement algorithm with a direct sparse LU solver. The comparison is performed for two different applicational purposes: SESS and EV. The results suggest the substantial computational performance of Schur-Complement algorithm in comparison with that of a direct LU solver when the number of storage devices and optimisation horizon increase for both cases of SESS and EV. Also, some situations where computational performance is inferior are discussed. 24 pages, 15 figures, Accepted for publication in IEEE Transactions on Power Systems

Abstract Previous research has identified flexible Norwegian hydropower as one potential key resource for managing variations in wind and solar power in Northern Europe. There is, however, a need for further detailed examination of this potential role of Norwegian hydropower based on updated future scenarios and using the latest data and model tools available. We analyze potential power system impacts of expanding Norwegian hydropower flexibility and Norway-Europe transmission, considering renewable energy variability based on a simulation for the historical weather years 1991-2020. The simulations are performed using FanSi, a stochastic optimization model for analyzing large-scale power systems with significant shares of hydropower combined with high shares of wind/solar power. A year 2050 scenario for Europe from the integrated energy system model SCOPE SD is used as framework for our analysis with FanSi. Our results highlight how expanded hydropower and transmission can potentially reduce price spikes during periods of low wind/solar output, reduce wind/solar energy curtailment during periods of high wind/solar output; and reduce price differences between interconnected areas during periods of either low or high wind/solar output. We demonstrate that these effects are attributable to more dynamic operation and expanded operational ranges of hydropower and transmission in the simulations assuming expanded hydropower and transmission capacities. We acknowledge high fundamental uncertainty in modelling a future system for the year 2050.

This paper presents a systematic procedure for partitioning smart distribution systems into supply-sufficient microgrids. First, renewable distributed generations (DGs) are optimally allocated in the distribution system. A multiobjective performance index including voltage profile and energy losses indices is utilized in this problem as the objective function. Two alternative control approaches of future smart grids, including on load tap changer control and adaptive power factor control are assessed to maximize potential benefits and increase the penetration level of DGs. Then, optimal allocation of protection devices and energy storage systems for constructing supply-sufficient microgrids is presented for a feeder equipped with capacity-constrained DGs. To this end, two different optimization problems are formulated and proper indices are developed for minimizing power exchange between microgrids and minimizing generation-load imbalance within microgrids. Finally, test results of the proposed models on 33-bus IEEE radial distribution system are presented and discussed.

This work highlights the importance of process flexibility in industry decarbonization, showing it can enhance transmission grid capacity at costs comparable to other grid reinforcement measures, thereby enabling faster electrification of demand.

The demand for low carbon energy calls for close to 100% renewable power systems, with decarbonization of other energy sectors adding to the anticipated paradigm shift. Rising levels of variable inverter-based renewable energy sources (VIBRES) are prompting questions about how such systems will be planned and operated when variable renewable generation becomes the dominant technology. Here, we examine the implications of this paradigm shift with respect to planning, operation and system stability, also addressing the need for integration with other energy vectors, including heat, transport and Power-to-X. We highlight the knowledge gaps and provide recommendations for improved methods and models needed as power systems transform towards 100% VIBRES.

In Norway, environmental constraints applying to hydropower may become stricter to safeguard local ecosystems. At the same time, Norwegian hydropower can facilitate the transition to more renewable energy within Northern Europe. This study quantifies the aggregated impact of environmental constraints on the Norwegian power system and its interactions with neighbouring countries up to 2050. Requirements for augmented protection of the local environment affect hydropower operation and, hence, the power system. For example, a loss of 3% in production combined with a 4% reduction in average hourly ramp for the Norwegian hydropower fleet results in our case study in up to a 14% increase in average Norwegian power prices and 4% increase in congestion on transmission lines towards neighbouring countries. The abundance of cheap renewable energy can mitigate price augmentation, but losses in flexibility can be difficult to recover completely within the existing hydropower infrastructure. While prioritizing hydropower plants with vulnerable surrounding ecosystems for adding new environmental targets helps limit their constraining effect on the power system, it also leads to an economic disparity between individual plants; stricter environmental constraints on parts of the hydropower fleet increase the revenues of the unaffected part (by up to 10% in our case study). Do we have to choose between the ecosystems and the energy transition? Environmental trade-offs with operation of Norwegian hydropower