Energy Management Strategies in hydrogen Smart-Grids: A laboratory experience

As microgrids gain reputation, nations are making decisions towards a new energetic paradigm where the centralized model is being abandoned in favor of a more sophisticated, reliable, environmentally friendly and decentralized one. The implementation of such sophisticated systems drive to find out new control techniques that make the system “smart”, bringing the Smart-Grid concept. This paper studies the role of Energy Management Strategies (EMSs) in hydrogen microgrids, covering both theoretical and experimental sides. It first describes the commissioning of a new labscale microgrid system to analyze a set of different EMS performance in real-life. This is followed by a summary of the approach used towards obtaining dynamic models to study and refine the different controllers implemented within this work. Then the implementation and validation of the developed EMSs using the new labscale microgrid are discussed. Experimental results are shown comparing the response of simple strategies (hysteresis band) against complex on-line optimization techniques, such as the Model Predictive Control. The difference between both approaches is extensively discussed. Results evidence how different control techniques can greatly influence the plant performance and finally we provide a set of guidelines for designing and operating Smart Grids.Ministerio de Economía y Competitividad DPI2013-46912-C2-1-

Experimental validation of an optical and thermal model of a Linear Fresnel Collector

2nd European Conference on Polygeneration – 30th March 1st April, 2011– Tarragona, SpainThis paper describes the design and validation of a mathematical model for a solar Fresnel collector. The function of the model is to simulate the optical and thermal dynamics of a Fresnel system for heating water. The model is validated using real data gathered from a cooling plant with double effect absorption chiller located in the School of Engineering University of Seville, Spain (Experimental cooling plant is also described in the paper). Comparison of calculated and plant measured data shows that the error is lower than 3% in the optical model and within 7% in the thermal model. The model uses a new approach to include a solar tracking mirror mechanism in one axis. This tracking has been designed to maximise the reception of available solar radiation by the absorption pipe. The thermal model used is based around classical models for solar receivers and it is validated with real operating data gathered from a supervisor system. The Fresnel model has been designed with sufficient flexibility to consider different geometries and thermal parameters, and may be used to simulate the performance of a proposed Fresnel collector system at any location

Biomimetic flow fields for proton exchange membrane fuel cells: A review of design trends

Bipolar Plate design is one of the most active research fields in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) development. Bipolar Plates are key components for ensuring an appropriate water management within the cell, preventing flooding and enhancing the cell operation at high current densities. This work presents a literature review covering bipolar plate designs based on nature or biological structures such as fractals, leaves or lungs. Biological inspiration comes from the fact that fluid distribution systems found in plants and animals such as leaves, blood vessels, or lungs perform their functions (mostly the same functions that are required for bipolar plates) with a remarkable efficiency, after millions of years of natural evolution. Such biomimetic designs have been explored to date with success, but it is generally acknowledged that biomimetic designs have not yet achieved their full potential. Many biomimetic designs have been derived using computer simulation tools, in particular Computational Fluid Dynamics (CFD) so that the use of CFD is included in the review. A detailed review including performance benchmarking, time line evolution, challenges and proposals, as well as manufacturing issues is discussed.Ministerio de Ciencia, Innovación y Universidades ENE2017-91159-EXPMinisterio de Economía y Competitividad UNSE15-CE296

Analytical approach to ground heat losses for high temperature thermal storage systems

A new approach to estimate the heat loss from thermal energy storage tank foundations is presented. Results are presented through analytical correlations based on numerical solutions for the steady-state heat conduction problem for thermal energy slab-on-grade tanks with uniform insulation. Model results were verified with other well-established benchmark problems with similar boundary conditions and validated with experimental data with excellent agreement. In addition to the TES foundation heat loss, new correlations for the maximum temperature and for the radial evolution of the temperature underneath the insulation layer are also provided, giving important information related to the tank foundation design. The correlated variables are of primordial importance in the tank foundation design because, due to the typical high operating storage temperatures, an inappropriate tank foundation insulation would lead not only to a not desired loss of energy but also to an inadmissible increase of the temperatures underneath the insulation layer, affecting the structural stability of the tank. The proposed correlations provide a quick method for the estimation of total tank foundation heat losses and soil maximum temperature reached underneath the insulation layer, saving time, and cost on the engineering tank foundation design process. Finally, a comprehensive parametric analysis of the variables of interest is made and a set of cases covering a wide range of tank sizes, insulation levels, depths to water table, and storage temperatures are solved

Integration of Fuel Cell Technologies in Renewable-Energy-Based Microgrids Optimizing Operational Costs and Durability

In this paper, a Model Predictive Control (MPC) approach is proposed to manage a grid-tied hydrogen microgrid (μG) . The μG testbed is equipped with a 1-kW polymer electrolyte membrane (PEM) electrolyzer and a 1.5-kW PEM fuel cell as main equipment. In particular, we present a formulation that includes the cost of the electricity exported/imported, the aging of the components, and the operational constraints. The control objective is to satisfy user demand, as well as extend the lifespan of expensive equipment, as is the case of the fuel cell or the electrolyzer. μG performance is investigated under realistic scenarios in three experiments. The experimental results illustrate how the proposed control system is able to manage the fuel cell and the electrolyzer through smooth power references, as well as to satisfy the power demanded. Finally, benchmarking is carried out between hysteresis band (HB) control and the proposed MPC in regard to efficiency and cost of the operation. The results obtained show that the MPC approach is more effective than HB for this type of μG , with a reduction in operation cost of up to 30%

Innovative concepts of Integrated Solar Combined Cycles (ISCC) using a Solid Oxide Fuel Cell (SOFC)

Concentrating Solar Power (CSP) is one of the most promising ways for electricity production of the upcoming years with high penetration of intermittent renewable energy sources such as wind and solar-photovoltaics. This is due to the fact that CSP when coupled to Thermal Energy Storage (TES) system enables large, inexpensive and flexible energy dispatch, which contributes to energy grid stabilization. At the same time, TES allows for steady operation of the power block by reducing undesirable fluctuations due to weather transient conditions and increasing the number of hours that the power block operates at design conditions 1. Despite the abovementioned advantages of CSP systems, a step further is needed for increase overall system efficiency and decrease CO2 emissions. Several studies have been performed considering high efficiency plant layouts such as combined cycle. For the latter, several works have been investigated about solar integration of combined cycle using parabolic trough and solar tower technologies. In both cases, solar energy was used for water/steam preheating and evaporation steps of the Rankine cycle in combination with the exhaust gases of fossil-fuel gas turbine engine. However, no research has been performed considering ISCC coupled with a Solid Oxide Fuel Cell (SOFC). In this research, two innovative layouts of ISCC power plants will be analyzed. First considers a ISCC based on solar tower and second a ISCC with a parabolic trough collector field coupled to the Heat Recovery Steam Generator (HRSG). The objective of this research is analyze the energy behavior of both layouts, selecting the best ISCC scheme to be coupled with a SOFC. The simulations will be performed using Thermoflex software. In both layouts, a SOFC is introduced before the combustion chamber at the topping cycle, and a Rankine cycle (bottoming cycle) with 2 pressures is considered.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Direct radiation estimates from horizontal global irradiance values

One of the main factors determining the economic feasibility of a solar thermal power plant is the availability of direct radiation at the plant site. During last years, two Central Receiver Power Plants (Solgas and Colon Solar) have been proposed in the South West of Spain (Huelva). For this area only global solar radiation data are available in a historical representative database. Based on an 11 years radiation database gathered at a nearby location, distance less than 100 km, 12 correlations, (one per month), between Mt and Md have been obtained. Solar global radiation data from the power plant site and generated correlations have allowed the "construction" of a Direct Radiation Design year that has been used both to design the solar plant heliostat field and receiver and to estimate annual energy produced by the solar plant

Experiences in teaching Hydrogen Technologies in the framework of the International Campus of Excellence Andalucia TECH

The increasing importance of hydrogen technologies is demanding prepared professionals in the numerous topics related to this energy vector. Apart from some basic and advanced courses given by actual experts in these topics, universities must play an important role in the general formation of future professionals. In this way, the International Campus of Excellence (ICE) Andalucía TECH has created several degrees taught jointly by its participating universities of Seville (US) and Málaga (UMA). Among those degrees, Energy Engineering is the best suited to the field of this conference because this degree provide future engineers with specialized training in energy generation, transformation and management. In relation to hydrogen technologies this degree includes a cross sectional optional unit named Hydrogen Based Systems (4.5 ECTS/112.5 h), which is placed in the last term of the fourth year and sharing space with work placement and mobility courses. This paper will present some author’s experiences as teachers of that unit during its short history of only three years. In spite of being a joint degree, which is coordinated between both universities (US and UMA) trying to give similar contents, it is interesting to highlight the differential experiences coming from the teachers of both universities in relation to the teaching methodologies and academic results.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Experimental and numerical Investigation on the design of a bioinspired PEM fuel cell

Proton exchange membrane fuel cells (PEMFCs) are promising energy devices that directly convert chemical energy of fuels such as hydrogen to useful work with negligible environmental impact and high efficiency. The channel geometry of the Bipolar Plate (BP) has a considerably impact on the PEMFC performance. BP designs based on nature-inspired structures such as leaves, lungs or sponges have been explored to date with success but have not yet achieved their full potential. With the objective of researching new flow field designs with enhanced operation, this work presents an experimental analysis of a novel bioinspired design of the channels of a PEMFC. Starting from a CFD fluid flow analysis of different novel initial biomimetic designs, the most promising one was selected, manufactured and tested experimentally. Experimental results comprise polarization and power curves for a comprehensive set of operating conditions. Results were analysed and compared against a reference parallel-serpentine model. Results indicated that the proposed novel biomimetic design is particularly suited for improving water management at high reactants humidity reaching out a peak power a 6.0% higher in comparison with the reference design. Future research should further develop novel design variants and analyze water distribution within the channels

Experimental testing of multi-tubular reactor for hydrogen production and comparison with a thermal CFD model

AIP Conference Proceedings, 2033, Nov. 2018, Article number 130013-1-130013-9This study presents a comparison of the experimental tests and CFD results for a multi-tubular solar reactor for hydrogen production in a pilot plant in the Plataforma Solar de Almería. This paper describes the methodology used for the solar reactor design and the experimental tests carry out during the testing and characterization campaign of the plant. The CFD model which has been used to design the solar reactor has been validated with an error around 10%. CFD simulations also allow to solve the thermal balance in the reactor (cavity and tubes) and to calculate the percentage of reacting media inside the tubes which achieve the required temperature for the process. The temperature in the thermocouples is around 1200 °C for the experimental data and a 90% of the ferrite inside the tube is above 900 °C. The multi-tubular solar reactor, which has been design with CFD techniques, has been built and operated successfully.Ministerio de Ciencia e Innovación, Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica 2008-2011Fondo Europeo de Desarrollo Regional IPT-2011-1323-920000Fondos FEDER Andalucía 2007-2013 Proyecto RNM 612