Penetration Of Intermittent Renewable Energy Research Articles

Robust Time-Varying Load Modeling for Conservation Voltage Reduction Assessment

Due to the increasing penetration of intermittent renewable energy and highly stochastic load behavior, it is challenging to effectively assess conservation voltage reduction (CVR) in power distribution systems. This paper proposes a robust time-varying load modeling technique to accurately identify load-to-voltage (LTV) dependence, yielding an improved CVR assessment scheme. In particular, we propose a robust recursive least squares (RLS) approach to estimate time-varying parameters of a ZIP load model at the substation level. Based on the identified load model, we are able to effectively evaluate LTV and analyze CVR factors. We propose a RLS with variable forgetting factors to capture the variations of model parameters under different situations, including continuous and sudden changes of parameters. To further enable RLS to suppress bad or missing measurements, we advocate to use the Huber M-estimator with a convex cost function. Finally, the robust RLS is solved by an iteratively reweighted technique. We demonstrate the effectiveness and the robustness of the proposed method using both simulations and field tests.

Challenges in process optimization for new feedstocks and energy sources

Current and future challenges of optimization in the process industry are discussed. The gap between academic research and industrial workflow is analyzed. Moreover, issues arising from the shift from conventional fossil fuels as both feedstock and energy source to nonconventional feedstocks (shale gas, tar sands, CO2 and biomass) and penetration of intermittent renewable energy are discussed. This manuscript focuses mainly on offline model-based optimization of design and operation, including the generation and selection of promising process alternatives for new feedstocks in conceptual design, multi-objective optimization, the estimation of thermodynamic parameters of new intermediates and the optimization of process operation under the volatile availability of the new feedstocks and energy sources. Moreover, a number of opportunities and needs for research and development are identified, including the simultaneous optimization of feedstocks, processes and products and a production able to process a variety of feedstocks and to utilize energy when it is cheap.

Studies on the Electrification of the Transport Sector in the Island of Crete, Greece

The possibility of electrifying the transport sector in Crete, Greece has been investigated. Currently the conventional vehicles in Crete consume annually 316,872 tons of gasoline and diesel oil emitting 1,030,188 tons of CO2. Electrification of the transport sector in Crete will result in a decrease of imported fossil fuels use and a reduction of CO2 emissions. It will also increase the use of locally available renewable energies in electricity generation. If all the existing conventional vehicles in Crete were to be replaced by electric vehicles, the annual electricity requirements in their batteries would be 1,092,568 to 1,311,077 MWh depending on the type of battery. The energy demand of the electric cars could be covered with electricity generated by renewable energies including solar and wind energy which are abundant in the island. The batteries of the electric cars could be used as electricity storage devices facilitating the penetration of intermittent renewable energies, with distributed generation systems, into the smart electric grid of Crete. It has been estimated that the aggregated theoretical storage capacity of all the batteries would be 6.33 GWh and that the size of the solar-PV plants and wind energy systems, generating all the electricity required by electric vehicles, would be 728 to 874 MWp and 445 to 534 MW respectively.

How to build an electric power transmission network considering demand side management and a risk constraint?

The increasing penetration of intermittent renewable energy poses plenty of challenges to electricity networks. Moreover, following the applications of intelligent electricity networks, demand response (DR) has attracted a great deal of attention due to its positive effects on shaving peak demands and balancing power supply and demand. On the other hand, when DR reaches a critical market level, the market behavior of DR becomes a meaningful uncertainty to the networks as well. Therefore, power transmission expansion planning (TEP) becomes a complicated decision-making process requiring risk analysis. This paper proposes a probabilistic approach to TEP contemplating risk. The conventional reliability criterion is replaced by a risk constraint. In addition, the TEP problem is decomposed into a master investment problem and two slave subproblems, i.e., optimal operation and feasibility check subproblems. The proposed TEP model is tested on the Garver’s six-bus and the modified IEEE 24-bus RTS and Polish 2383-bus systems. According to the numerical results, the proposed TEP model is superior compared to the conventional reliability-driven TEP from three perspectives: (1) It has incorporated a risk constraint and hence can help network planners understand the variants of risk and provide the opportunity to make trade-offs between cost, reliability and risk. (2) It still enforces the reliability criterion and is more cost-effective when the wind power uncertainty becomes higher in the future. (3) It allows risk-analysis, giving decision-makers the flexibility to choose a plan according to their individual risk-aversion levels and understand the multiple outcomes.

Risk-Constrained Optimal Bidding Strategy for Pairing of Wind and Demand Response Resources

Wind power represents a significant percentage of the Spanish generation mix and this trend will increase due to the commitment of the European Union to the full deployment of Directive 2009/28/EC. The increasing penetration of intermittent renewable energy, and the development of advanced information and communication technologies, give rise to questions on how additional flexibility obtained from loads can be used in order to optimize the use of resources and assets. This paper proposes a comprehensive stochastic decision making model for the coordinated operation of wind power producers and demand response (DR) aggregators participating in the day-ahead market. In order to account for the uncertainty around the true outcomes of day-ahead prices and wind power, a minimum conditional value at risk term has been included in the model formulation. Numerical results illustrate how the proposed bidding strategy for wind and demand response (DR) pairing increases the expected benefit of both resources and reduces the related risk.

Process control strategies for flexible operation of post-combustion CO2 capture plants

With increasing penetration of intermittent renewable energy into the electricity grid, one can expect thermal power plants to be required to operate in a more dynamic fashion, with more frequent departures from design point operation. However, the application of optimal control strategies can offer solutions to these operational challenges, associated with the integration of the power plant with the capture plant. In this paper a process control strategy is developed in order to select the optimal control variables for a PCC process. In addition, economically efficient control structures for operation of a post-combustion capture process with minimum energy requirements for coal and natural gas power plant are designed. The results have shown that with an appropriate and well-tuned control strategy, it is possible to maintain critical parameters, such as the degree of CO2 capture, at the desired set-point, even during periods of significant fluctuation in the power plant load and even if based on simple and well established control technologies, such as PID, avoids the need for more risky solutions such as adding solvent storage tanks to the process.

Swiss pumped hydro storage potential for Germany’s electricity system under high penetration of intermittent renewable energy

In order to cut greenhouse-gas emissions and increase energy security, the European Commission stimulates the deployment of intermittent renewable energy sources (IRES) towards 2050. In an electricity system with high shares of IRES implemented in the network, energy balancing like storage is needed to secure grid stability and smooth demand satisfaction. Pumped hydro storage (PHS) is at this moment the best option for large scale storage. Switzerland has strong ambitions to further develop their PHS sector and become the battery of Europe. In this research, the potential of the Swiss PSH plants is explored, whilst taking inflow into the upper reservoirs of the PHS plants into consideration. To simulate electricity imbalance, Germany is used as a case study. Germany already has a high penetration of IRES and has plans to increase installed IRES capacity. By using an energy planning model (PowerPlan), three future scenarios of the German electricity system were designed, each with a different set of IRES installed (solar, mixed and wind). Results show that the Swiss battery ambition offers most benefits to a wind-oriented scenario, reducing both shortages as well as surpluses. Water inflow in Swiss PHS-reservoirs is of minor importance when looking at security of supply, although it was shown that the solar-scenario profits more from inflow in terms of system stability. However, a potential conflict was observed in the solar-scenario between the need for electricity storage and the storage of natural inflow, resulting in more surpluses in the system when inflow was taken into account.

On the Multicycle Activity of Natural Limestone/Dolomite for Thermochemical Energy Storage of Concentrated Solar Power

AbstractCheap, efficient, and non‐toxic energy storage technologies are urgently needed to handle the rapidly increasing penetration of intermittent renewable energies into the grid. This work explores the use of limestone and dolomite for energy storage in concentrated solar power (CSP) plants by means of the calcium looping (CaL) process based on the multicycle carbonation/calcination of CaO. An efficient integration of the CaL process into CSP plants involves high temperature carbonation and calcination at moderate temperatures in a close CO2 cycle for power generation. These conditions differ from those of the CaL process for CO2 capture, which lead to CaO deactivation as extensively reported in recent years. In contrast, we show that limestone‐ and dolomite‐derived CaO give rise to a high residual conversion at CaL–CSP conditions and in short residence times, which would facilitate the development of a competitive and clean CSP technology with permanent energy storage.

On the Implementation of Variable Speed in Pump-Turbine Units Providing Primary and Secondary Load-Frequency Control in Generating Mode

This paper analyses different control strategies for the speed control loop of a variable-speed pump-turbine unit equipped with a doubly fed induction generator, operating in generating mode in an isolated power system with high penetration of intermittent renewable energy. The control strategies are evaluated and compared to each other in terms of the amount of water discharged through the pump-turbine and of the wicket gates fatigue while providing primary and secondary load-frequency control. The influence of the penstock length and the initial operating point on the performance of each control strategy is studied in detail. For these purposes, several simulations have been performed with a suitable dynamic model of the pumped-storage hydropower plant and the power system. The results of the paper indicate that a proper control strategy would consist in updating the reference speed according to the power generation schedule and keeping it constant within each scheduling period (typically 1 h).

Multi-region optimal deployment of renewable energy considering different interregional transmission scenarios

Renewable energy is expected to play much more important role in future low-carbon energy system, however, renewable energy has problems with regard to load-following and regional imbalance. This study aims to plan the deployment of intermittent renewable energy in multiple regions considering the impacts of regional natural conditions and generation capacity mix as well as interregional transmission capacity using a multi-region dynamic optimization model. The model was developed to find optimized development paths toward future smart electricity systems with high level penetration of intermittent renewable energy considering regional differences and interregional transmission at national scale. As a case study, the model was applied to plan power generation in nine interconnected regions in Japan out to 2030. Four scenarios were proposed with different supporting policies for the interregional power transmission infrastructures and different nuclear power phase-out scenarios. The analysis results show that (i) the government's support for power transmission infrastructures is vital important to develop more intermittent renewable energy in appropriate regions and utilize renewable energy more efficiently; (ii) nuclear and renewable can complement rather than replace each other if enough interregional transmission capacity is provided.

HyUnder – Hydrogen Underground Storage at Large Scale: Case Study Spain

Abstract Hydrogen as an energy carrier is understood as a system capable of storing energy for a later use in a controlled manner. Surplus electricity from renewable energy serves for green hydrogen generation via electrolysis. Once produced, the hydrogen is stored for later consumption. This paper describes the Spanish Case Study of the HyUnder project which aims to evaluate the potential of underground hydrogen storage for large-scale energy storage along Europe, analysing besides the Spanish Case, France, Germany, the Netherlands, Romania, and the United Kingdom. This case study has considered for the assessment, the competitiveness of hydrogen storage against other large scale energy storage concepts, the geological potential for hydrogen storage in the region, how to embed the hydrogen energy storage in the energy market and the possible business cases in four different applications: transport, Power to Gas, re-electrification and industry, taking into account all the economic aspects such us the electrolyser OPEX and CAPEX or the cavern, electricity and water costs. It is shown that the Spanish geology can provide four technical options for hydrogen underground storage. Results have shown the interest of the technology in short – medium term especially linked to certain conditions of high intermittent renewable energy penetration in the Spanish power grid that result in surplus or residual electricity. Hydrogen storage is interesting because it can integrate renewable energy systems in other sectors which do not have overcapacity and a high use of fossil fuels as the natural gas sector and the transport sector. Moreover, all the economic issues have been analysed for two different horizons, 2025 and 2050; concluding that the average price of electricity is the main cost. From the financial results, transport application represents a business case which, although in order has enough values of hydrogen demand to be stored, combination of different applications must be needed in order to make sense to the development of the cavern.

Cost-Benefit Analysis Model of Single and Hybrid Energy Storage System in Active Distribution Network

The active distribution network is an effective approach to solve the problem such as the high penetration of intermittent renewable energy. This paper constructs single and hybrid energy storage battery systems in the active distribution network, calculates the economic benefits of the single and hybrid energy storage systems from six aspects in annual electricity sale revenue, ancillary revenue, investment cost, maintenance cost, landed cost and power shortage punishment cost. Take the lithium iron phosphate battery as single system, the lithium iron phosphate battery and Lithium titanate battery as the hybrid system to compute the cost benefit. The results show that the storage systems have effects to the intermittent renewable energy in peak shaving. Since the hybrid energy storage system can obtain more annual ancillary revenue, and the batteries’ work life is longer, it has more advantage in economic benefits than the single energy storage system.

A Unified Approach for Power System Predictive Operations Using Viterbi Algorithm

A paradigm shift in the renewable energy proliferation in the U.S. necessitates a paradigm shift in power system operations to accommodate large-scale intermittent power while keeping the grid reliable and secure. Energy management systems (EMS) will benefit from an auxiliary function, which integrates the wind and load forecasting to state estimation and forecasting. This auxiliary function will create a predictive database for the power system states using the historical states as well as wind and load forecasts. The predictive database can be utilized to provide pseudo-measurements to a static state estimator in the case of loss of observability and bad data processing, or it can be used for short-term congestion and ramping predictions. This paper proposes an auxiliary tool for look-ahead power system state forecasting in electrical power systems with high intermittent renewable energy penetration. The method utilizes Markov models (MMs) and the Viterbi algorithm (VA) with a grid of feasible power system states obtained and updated by using the past states. The proposed algorithm is evaluated on the IEEE 14-bus and 118-bus systems using wind and load data available from the Bonneville Power Administration (BPA). The results show good correlation between the predictions and the actual power system states.

Optimal control strategies for hydrogen production when coupling solid oxide electrolysers with intermittent renewable energies

The penetration of intermittent renewable energies requires the development of energy storage technologies. High temperature electrolysis using solid oxide electrolyser cells (SOECs) as a potential energy storage technology, provides the prospect of a cost-effective and energy efficient route to clean hydrogen production. The development of optimal control strategies when SOEC systems are coupled with intermittent renewable energies is discussed. Hydrogen production is examined in relation to energy consumption. Control strategies considered include maximizing hydrogen production, minimizing SOEC energy consumption and minimizing compressor energy consumption. Optimal control trajectories of the operating variables over a given period of time show feasible control for the chosen situations. Temperature control of the SOEC stack is ensured via constraints on the overall temperature difference across the cell and the local temperature gradient within the SOEC stack, to link materials properties with system performance; these constraints are successfully managed. The relative merits of the optimal control strategies are analyzed.

An Evaluation of Seawater Pumped Hydro Storage for Regulating the Export of Renewable Energy to the National Grid

A seawater inlet with a surface area of 6 km2 was assessed for the potential to be used as a 100 MW, low head, high flow, sea water pumped hydro energy storage system. The capital cost was estimated to be recouped after a number of years and the plant has a predicted energy storage capacity of 320 MWh.National and international policies are driving the increased penetration of solar and wind energy onto the electricity networks, in an effort to reduce carbon emissions. Transmissions System Operators depend on ancillary services such as spinning reserve from thermal generators or pumped hydro systems to enhance grid stability. The increased penetration of renewable energy onto the electricity grid is driving a demand for greater capacity in the area of energy storage.This research presents a case study, which is a technical and economical appraisal of using an inland sea water reservoir to store energy. This project involves building a seawater dam around an existing natural inlet, and placing turbines at the mouth of the inlet. As part of the study an evaluation of current pumped hydro, seawater storage, and tidal barrages was carried out. The optimum design of the low head, high flow rate seawater energy storage facility was determined for the seawater inlet and different scenarios for the optimum head and flow rates are presented for analysis.Using low-head, high-flow seawater storage near the coast, greatly reduces the danger of contamination of inland freshwater supplies, thus reducing the environmental impact of pumped seawater energy storage.This research indicates that sea water pumped hydro energy storage with a high flow rate and low head is technically and economically feasible for increasing the ability of national grids to allow high penetration of intermittent renewable energy.

Unified Stochastic and Robust Unit Commitment

Due to increasing penetration of intermittent renewable energy and introduction of demand response programs, uncertainties occur in both supply and demand sides in real time for the current power grid system. To address these uncertainties, most ISOs/RTOs perform reliability unit commitment runs after the day-ahead financial market to ensure sufficient generation capacity available in real time to accommodate uncertainties. Two-stage stochastic unit commitment and robust unit commitment formulations have been introduced and studied recently to provide day-ahead unit commitment decisions. However, both approaches have limitations: 1) computational challenges due to the large scenario size for the stochastic optimization approach and 2) conservativeness for the robust optimization approach. In this paper, we propose a novel unified stochastic and robust unit commitment model that takes advantage of both stochastic and robust optimization approaches, that is, this innovative model can achieve a low expected total cost while ensuring the system robustness. By introducing weights for the components for the stochastic and robust parts in the objective function, system operators can adjust the weights based on their preferences. Finally, a Benders' decomposition algorithm is developed to solve the model efficiently. The computational results indicate that this approach provides a more robust and computationally trackable framework as compared with the stochastic optimization approach and a more cost-effective unit commitment decision as compared with the robust optimization approach.

Two-Level Dynamic Stochastic Optimal Power Flow Control for Power Systems With Intermittent Renewable Generation

High penetration of intermittent renewable energy imposes new challenges to the operation and control of power systems. Power system security needs to be ensured dynamically as the system operating condition continuously changes. The dynamic stochastic optimal power flow (DSOPF) control algorithm using the Adaptive Critic Designs (ACDs) has shown promising dynamic power flow control capability and has been demonstrated in a small system. To further investigate the potential of the DSOPF control algorithm for large power systems, a 70-bus test power system with different generation resources, including large wind plants, is developed. A two-level DSOPF control scheme is proposed in this paper to scale up the DSOPF algorithm for this 70-bus system. The lower-level area DSOPF controllers control their own area power network. The top-level global DSOPF controller coordinates the area controllers by adjusting the inter-area tie-line flows. This two-level architecture distributes the control and computation burden to multiple area DSOPF controllers, and reduces the training difficulty for implementing the DSOPF control for a large power network. Simulation studies on the 70-bus power system with large wind variation are shown to demonstrate the effectiveness of the proposed two-level DSOPF control scheme.

An integrated model for long-term power generation planning toward future smart electricity systems

In the present study, an integrated planning model was developed to find economically/environmentally optimized paths toward future smart electricity systems with high level penetration of intermittent renewable energy and new controllable electric devices at the supply and demand sides respectively for regional scale. The integrated model is used to (i) plan the best power generation and capacity mixes to meet future electricity demand subject to various constraints using an optimization model; (ii) obtain detailed operation patterns of power plants and new controllable electric devices using an hour-by-hour simulation model based on the obtained optimized power generation mix. As a case study, the model was applied to power generation planning in the Tokyo area, Japan, out to 2030 in light of the Fukushima Accident. The paths toward best generation mixes of smart electricity systems in 2030 based on fossil fuel, hydro power, nuclear and renewable energy were obtained and the feasibility of the integrated model was proven.

Strategy for Overcoming Cost Hurdles of Plug-In–Hybrid Battery in California

Advances in electric drive technology, including lithium ion batteries as well as the development of strong policy drivers such as California's Global Warming Solutions Act, now contribute to a more promising market environment for the widespread introduction of plug-in vehicles in California. Nevertheless, battery costs remain high. This study explores a strategy for overcoming the significant hurdle to electric transportation fuel use presented by high battery costs. It describes offsetting plug-in-vehicle battery costs with value derived from post-vehicle stationary use of hybrid batteries and quantifies the possible effect the net present value that several of these benefits might have on battery lease payments. With a focus on blended-mode plug-in hybrids with minimized battery size, even the subset of values explored (regulation, peak power, arbitrage, and some carbon reduction credit) promises to lower battery lease payments while simultaneously allowing vehicle upgrades and profitable repurposing of vehicle batteries for stationary use as grid support, electrical storage and generation devices. Such stationary, post-vehicle battery-to-grid devices could not only provide valuable services needed by existing statewide grid-support markets but could also provide customer side benefits, improve utility operation, help defer costly grid upgrades, and potentially support the profitability and penetration of intermittent renewable energy.