Intermittent Electricity Sources Research Articles

Energy-efficient monosaccharides electrooxidation coupled with green hydrogen production by bifunctional Co9S8/Ni3S2 electrode

Water electrolysis is a sustainable strategy for renewable energy conversion and storage that can be replenished by intermittent electricity sources. Despite the decades-long progress, the commercialization of water electrolysis remains fraught with difficulties owing to its high electricity consumption. We couple the hydrogen evolution reaction with the electrooxidation of xylose obtained from regenerated hemicellulose to organic acids, utilizing a bifunctional electrode consisting of Co9S8/Ni3S2. The electrochemically activated anodic sites, including Co2+/Co3+, Co3+/Co4+, Ni2+/Ni3+, and Ni3+/Ni4+ redox species, are responsible for xylose electrooxidation, with the required potential reduced by 290 mV at 100 mA cm−2 compared with water oxidation. Moreover, the process yields over 60% towards formic acid at the anode, is accompanied by the production of hydrogen at the cathode. Xylose oxidation is kinetically and thermodynamically more favorable than water oxidation, significantly reducing the overall energy consumption relative to conventional water electrolysis. This study provides a promising strategy for the scalable and energy-efficient process of biomass electrooxidation coupled with hydrogen production.

(Invited) Progress in Nafion™ Membrane Development for Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzers (PEMWE) have received significant recent attention in order to address the burgeoning need for low/zero-carbon sources of hydrogen at scale. PEMWE devices are an attractive source of “green” hydrogen due to their relatively compact size, scalable construction, high efficiency, and proven durability. They also integrate well with intermittent electricity sources and can deliver elevated hydrogen outlet pressures to reduce parasitic efficiency losses associated with hydrogen compression.1 Membranes made from Nafion™ perfluorosulfonic acid (PFSA) polymer have been the leader in PEMWE device application for decades, due to their high proton conductivity and chemical durability in the hot, acidic PEMWE environment. Traditional Nafion™ membranes in this application, however, comprise thick films (>100 µm) where ohmic-driven voltage losses due to proton transport resistance are high.To maximize the electrical efficiency and hydrogen production of PEMWE applications, and help drive hydrogen costs below $2/kg, new membranes – specifically engineered for low proton transport resistance and high durability in a PEMWE environment – are required. A multigenerational plan has been established to improve the performance of Nafion™ membranes while maintaining their best-in-class durability. One major contributor to membrane improvement is a reduced proton transport resistance inherent in thinner membranes. However, as membranes become thinner, they invite higher gas crossover, especially in a differential pressure environment. Novel mitigation strategies are required to ensure safe operation and long lifetimes of the thinnest membranes in advanced PEMWE membrane concepts.2-3 In this presentation, an overview of the activities and strategic developments within Nafion™ membranes for water electrolyzers will be summarized. The multigenerational product development program will be discussed, highlighting the significant contribution possible from Nafion™ membrane development to green hydrogen proliferation. Ayers, K.; Danilovic, N.; Ouimet, R.; Carmo, M.; Pivovar, B.; Bornstein, M., Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale. Annual Review of Chemical and Biomolecular Engineering 2019, 10 (1), 219-239.Klose, C.; Trinke, P.; Böhm, T.; Bensmann, B.; Vierrath, S.; Hanke-Rauschenbach, R.; Thiele, S., Membrane Interlayer with Pt Recombination Particles for Reduction of the Anodic Hydrogen Content in PEM Water Electrolysis. J. Electrochem. Soc. 2018, 165 (16), F1271-F1277.Baker, A. M.; Babu, S. K.; Mukundan, R.; Advani, S. G.; Prasad, A. K.; Spernjak, D.; Borup, R. L., Cerium Ion Mobility and Diffusivity Rates in Perfluorosulfonic Acid Membranes Measured via Hydrogen Pump Operation. J. Electrochem. Soc. 2017, 164 (12), F1272-F1278. Figure 1

Optimization of parabolic trough power plant operations in variable irradiance conditions using all sky imagers

The continuously growing penetration of intermittent electricity sources will increase the future demand for dispatchable power plants, which balance out fluctuations within the electrical grids. Parabolic trough power plants with thermal energy storages could be one renewable solution for regions with a high yearly direct normal irradiance (DNI) sum, but in order to compete against other renewable as well as non-renewable technologies, the economic competitiveness must be ensured. Price reductions can be achieved for example by optimizing the plant operation. One shortcoming of state of the art plant controllers is that they only use the DNI measured at one or a few positions in the solar field. Due to the spatial variability of the DNI throughout the solar field this DNI information can be misleading.In this paper, we investigate the optimization potential of solar field control strategies with access to spatially resolved DNI information from all sky imagers (ASI). Uncertainties of the ASI system are considered by introducing additional independent spatial DNI information from a shadow camera system. The spatial and temporal DNI variability of the DNI seen by the controller is classified in distinct DNI variability classes. Two new control strategies are developed, with optimized control parameters for distinct combinations of the spatial and temporal DNI variability classes.These new variability class dependent control strategies are benchmarked in a simulation environment. A relative increase in revenue in excess of 1.9% is observed over a test period with 22 days, compared to a state of the art reference controller.

The effect of intermittent renewables on the electricity price variance

The dominating view in the literature is that renewable electricity production increases the price variance on spot markets for electricity. In this paper, we critically review this hypothesis. Using a static market model, we identify the variance of the infeed from intermittent electricity sources (IES) and the shape of the industry supply curve as two pivotal factors influencing the electricity price variance. The model predicts that the overall effect of IES infeed depends on the produced amount: while small to moderate quantities of IES tend to decrease the price variance, large quantities have the opposite effect. In the second part of the paper, we test these predictions using data from Germany, where investments in IES have been massive in the recent years. The results of this econometric analysis largely conform to the predictions from the theoretical model. Our findings suggest that subsidy schemes for IES capacities should be complemented by policy measures supporting variance absorbing technologies such as smart-grids, energy storage, or grid interconnections to ensure the build-up of sufficient capacities in time.

The Effect of Intermittent Renewables on the Electricity Price Variance

The dominating view in the literature is that renewable electricity production increases the price variance on spot markets for electricity. In this paper, we critically review this hypothesis. Using a static market model, we identify the variance of the infeed from intermittent electricity sources (IES) and the shape of the industry supply curve as two pivotal factors influencing the electricity price variance. The model predicts that the overall effect of IES infeed depends on the produced amount: while small to moderate quantities of IES tend to decrease the price variance, large quantities have the opposite effect. In the second part of the paper, we test these predictions using data from Germany, where investments in IES have been massive in the recent years. The results of this econometric analysis largely conform to the predictions from the theoretical model. Our findings have wide-ranging implications for policy makers coordinating subsidy schemes for renewables, flexible production capacities, and electricity storages.

Regulatory road maps for the integration of intermittent electricity generation: Methodology development and the case of The Netherlands

The envisaged increase in the share of electricity generation from intermittent renewable energy sources (RES-E) like wind and photovoltaics will pose challenges to the existing electricity system. A successful integration of these sources requires a cost-efficient use of system flexibility. The literature on the options to improve system flexibility, and thus the costs of successfully integrating intermittent electricity generating units, is still growing but what is lacking is an overarching systematic view on when to adopt which option in particular energy systems. This paper aims to bridge this gap in literature. We use existing insights on market and network integration of intermittent electricity sources within a regulatory road map framework. The framework allows policy makers and other electricity system stakeholders to arrive at a consistent strategy in dealing with integration issues over a longer period of time. In this contribution we present and explain the framework and apply it for the case of The Netherlands.

Exploring the impact on cost and electricity production of high penetration levels of intermittent electricity in OECD Europe and the USA, results for wind energy

Abstract In this study we explore for the USA and OECD Europe (OECD Europe includes the countries that participate in the Organisation of Economic Cooperation and Development, among which Western Europe, USA and Japan) dynamic changes in electricity production, cost and CO 2 emissions when intermittent electricity sources are used with increasing penetration levels. The methodology developed can be applied for both solar photovoltaic (PV) and wind energy. Here the focus of the results is on penetration of wind electricity in the electricity system as simulated in a long-term model experiment in which the electricity demand is kept constant over time. All important parameter are included in a sensitivity analysis. With increasing penetration levels the cost reduction of wind electricity caused by upscaling and technological learning is counteracted by the cost increase due to (1) the need for additional back-up capacity, (2) the need to generate wind electricity at less favourable sites, and (3) discarded wind electricity because of supply–demand mismatch. This occurs after about 20% wind electricity production as percentage of current electricity production. At this level about 500 (OECD Europe) and 750 (USA) TWh yr −1 wind electricity is absorbed in the system with the electricity demand of the year 2000. Wind electricity is found to be discarded when the production is about 55 (USA) to 10 times (OECD Europe) the present electricity produced from wind power. Beyond 30% of present electricity production, cost increases most significantly because of discarded wind electricity, excluding storage. In both regions the use of wind electricity would mainly avoid use of natural gas. The CO 2 emissions abatement costs range from 14 (OECD Europe) to 33 (USA) $ per ton CO 2 differ in both regions due to a faster wind electricity cost increase in OECD Europe.

Network Requirements of Future Energy Conversion Technologies

Especially the introduction of intermittent electricity sources and the diffusion of distributed generation will make it necessary to improve the electricity network capacities and control mechanisms and will make the introduction of completely new dispatching philosophies necessary. The paper discusses the expected problems of the UCTE net introduced by the possible installation of 25 GW off-shore wind power in the North and Baltic sea. An up-grade of the transport capacities will become necessary to make the power available all over Germany. Control problems might especially arise, if a rapid shut down of the wind turbines in a storm situation would occur. The dispatching philosophy has to be changed from a demand driven to a supply driven philosophy, which distinguishes between renewable – primary – supplies and back-up – secondary – supplies.