isolated micro-grid for smart cogeneration of electricity/cold – RECIF

In order to optimize the dynamic coupling of the two storage technologies at the scale of that smart micro-grid, our approach will combine numerical and experimental developments. We will first rely on component-scale modeling to characterize the intrinsic dynamic behavior of the reactor, compressor, electrolyser, hydrogen storage, fuel cell and electrochemical accumulator. In particular, we will take into account the heat and mass transfers coupled to chemical kinetics within the reactor, the evolution of the isentropic and volumetric efficiencies of the compressor as a function of the variation of the compression ratio and its rotational speed, the thermal behavior of the fuel cell and the electrolyser in relation to the electrical demand / power supply). Second, a global model of the process will be developed based on the REM formalism (Macroscopic Energy Representation), with intrinsic physical causality, allowing to analyze the dynamic interactions between the components and to optimize performance at the process scale.
Solar power forecasting will be studied for several time horizons. In a very short time (intra-hour), the forecast will be made from ground-based sky imager output processed by artificial neural network technologies. For short lead times (up to 6 hours), the forecast will be based on GOES 17 satellite image analysis. Finally, for longer lead times (up to a few days), the forecast will be based on a fine-mesh regional atmospheric model forced by a global weather forecast model.
We will conduct several local measurement campaigns of electrical consumption in Polynesia by distinguishing the energy devoted to the production of cold. We will consider different types of buildings that consume between 1 and 100 kW and are air-conditioned during the night.
French Polynesia is a relevant region due to its abundance of solar energy resources and its high electricity consumption for air conditioning.

Expected results :
- REM model of the complete H2 system
- Energy management algorithm for the H2 system
- Component models: thermochemical reactor, compressor, evaporator, condenser
- Global model coupling the thermochemical reactor exploiting a variable heat source and the compressor of the refrigerating cycle
- Principles and assumptions, parameters and target values, parametric sensitivity studies
- Multi-horizon photovoltaic energy forecasting tool: intra-hour, intra-day, intra-week
- Typical consumption profiles of buildings with air conditioning and refrigeration needs
- REM model + simulation software (Matlab / Simulink) of the complete system
- Energy flow monitoring algorithm, implementable in real time
- Implementation and installation plans of the prototype

The issues related to the valorization and the transfer of the results obtained will be treated in close connection with H2SYS. On the basis of the results obtained, a prospective technical-economic analysis will be conducted considering the use of HT-PEMFC and SOFC fuel cells in place of the PEMFC fuel cell considered in the project. Indeed, the use of such fuel cells, operating at a higher temperature, coupled with the use of other salts for thermochemical storage, can allow the production of cold at negative temperatures, compatible with freezing and deep freezing applications for long-term food conservation. To do this, the simulation models will be adapted (macroscopically) and the costs of the systems will be compared using data available in the literature and/or among project partners.

The communication and dissemination of the results will be carried out over the entire duration of the project. An objective of 6 publications in international journals with impact factor, 6 papers in international peer-reviewed conferences, 1 patent and 1 software repository are set.
Currently, three publications are being written on the following topics:
- “Cogeneration, trigeneration and energy management of fuel cell systems : a review”
- “Technical economic analysis of PV–driven Electricity / Cold cogeneration systems using Particle Swarm Optimization algorithm”,
- “Intra-hour GHI forecasting using ground-based sky imager and convolutional neural network”.
Depending on the project progress, the consortium will consider the possibility of protecting the technology through other intellectual property titles (patents, protection of software / algorithms ...).
An international workshop on smart micro-grids will be organized in December 2022 in Polynesia.

The urgency to significantly reduce the production of greenhouse gases is today unequivocal. The substitution of carbon-based energies by clean and renewable energies sources (RES) is one of the technical solutions that will minimize climate change. However, the production of electricity from these resources is intermittent, not controllable and not always in phase with demand. It no longer allows for a straightforward production of electricity of quality.

To overcome these difficulties, the combination of different energy storage systems, electrical and/or thermal, has proven to be an effective solution. Storage techniques are very varied and are characterized by their nature (e.g. electrical, chemical, mechanical and thermal) and by their performance in terms of energy efficiency, storage capacity, charging/discharging time, life span and return on investment, among others. The diversity of quality criteria and services they provide is such that, to date, there is no "ideal" storage system.
Within this context, thermochemical storage processes and fuel cells coupled to hydrogen storage represent innovative and promising solutions because of their competitive energy storage and long lifetime.
Thermochemical processes are based on reversible chemical reactions between a solid and a gas. They allow the storage of energy in the form of chemical potential for a deferred cold production. They are particularly relevant for cold storage/production, due to their operational flexibility and their high energy density. The advancement of the chemical reaction can be controlled mechanically by a compressor and/or thermally, by an external heat input.

Electricity storage in the form of hydrogen is very competitive with conventional electrochemical technologies, such as lead-acid and lithium-ion batteries (.energy density is 150 times higher for hydrogen). It is even more interesting if the energy used for the electrolysis of water and therefore the production of hydrogen, is of renewable origin. The electricity is then produced through a fuel cell system (FC) whose electrical efficiency is generally much higher than thermal machines. However, an important part of energy is dissipated in the form of heat during this energy storage / retrieval process.

The main idea of this project is to study and implement the coupling of the two aforementioned storage systems in order to revalorize the thermal energy released by the hydrogen fuel cell during its operation to increase the energy efficiency of the overall system.
The core of the project is the study of the integration and coupling of these two storage technologies in a solar-powered, smart micro-grid for building and industrial sectors. The approach aims at optimizing the performance of the micro-grid in terms of autonomy, efficiency, energy supply and consumption and nowcasting of solar power. The innovative aspect concerns the development and the optimal integration of a system of storage/production of electricity/cold, by hydrogen-energy vector and by thermochemical process and by the strategy of piloting and management of this micro-grid faced with intermittent resources and a variable load profiling. The goal is to provide proof of the technological concept both through a numerical and experimental approach. Based on a complete dynamical system modeling, a representative small-scale pilot demonstrator will be implemented, which will permit to evaluate the feasibility and performance of the system. The site chosen to build the pilot plant is French Polynesia, a relevant region due to its abundance of solar energy resources and its high electricity consumption for air conditioning (especially in the hotel, administration and industry sector).

This project brings together one SME and three research teams with complementary area of expertise: electricity storage (hydrogen, fuel cells), cold production and thermochemical storage and weather modeling.