Projects / Programmes
Optimization based control of P2G converter connected to hydro power plant
| Code |
Science |
Field |
Subfield |
| 2.06.01 |
Engineering sciences and technologies |
Systems and cybernetics |
Control systems technology |
| Code |
Science |
Field |
| T125 |
Technological sciences |
Automation, robotics, control engineering |
| Code |
Science |
Field |
| 2.02 |
Engineering and Technology |
Electrical engineering, Electronic engineering, Information engineering |
Optimal control of systems to convert electric power to gas
Renewable power sources
Storage of excess electric power
Researchers (14)
Organisations (2)
Abstract
The need for decarbonisation and reduction of fossil fuels use requires the installation of a number of renewable power sources (hydropower plants, photovoltaic fields and wind turbines). The inherent issue of these technologies (especially photovoltaic and wind) is their dependency upon the weather, which leads to fluctuating power production not following actual power demands. Thus, a need to store the energy emerges in periods of the excess production. For long term and high capacity storage, one possible solution is conversion of electric energy to hydrogen, which can be added to the natural gas grid or it can be stored and converted to electric energy in periods of increased demand, or it can be used in other ways. Systems, converting electric power to hydrogen, are referred to as Power to gas systems (P2G) and they are composed of two main components: electrolyser and hydrogen storage tank.
In the project, we are focusing to the optimal control problem of a special case of P2G system linked to the hydro power plant. In periods of excess electric power in the electric system, dispatchable power sources (including hydro power plants) may be required to decrease or even stop their production. If hydro power plant decreases or stops power generation and if the water accumulation is full, then incoming water flow has to bypass the turbine generators. This leads to energy loss (spilled turbinable energy) and consequent financial losses. An upgrade of hydro power plant by a P2G system can convert a part excess hydroelectric energy into hydrogen and in this way prevents or reduces these losses.
The objective of the project is to develop an optimal control of P2G system, linked to the hydro power plant, which will maximize energy and economic efficiency and consequently the profitability of an investment into P2G system. High enough efficiency can only be achieved by optimal control, which means perfect accommodation to the electric energy and natural gas market, environmental conditions (time profile of available hydro energy) and by operation in a way to achieve maximum efficiency and long life time of the system (steady operation without numerous starts and stops of the system).
We will develop a system for optimal control of P2G, which will search for the most efficient operation condition by means of online optimization. Optimization will use embedded mathematical models of P2G system, hydro power plant and it will take into account a number of information inputs: the current state of charge of water accumulation, the current state of charge of hydrogen accumulation (pressure), predicted time profiles of input water flow into the accumulation, electric energy and gas demands and prices, predicted time profile of maximum hydrogen flow, which natural gas network can accept (network restrictions), efficiency of P2G system depending on load and pressure in the hydrogen tank and other constraints.
The system for optimal control will determine optimal P2G power (hydrogen production rate), flow rate of hydrogen into natural gas grid and, optionally, a hydrogen flow rate into the fuel cells to convert hydrogen back to electricity in the periods of electric energy deficits.
The development and demonstration will be performed in the simulation environment, where hydro power plant, P2G system, and electric energy and natural gas markets will be simulated by mathematical models. By simulation we will test the operation efficiency at varying of several parameters (nominal power of P2G system, hydrogen storage tank volume and maximum pressure, several constraints of electric and natural gas grids). Results of the simulation study will serve as decision support for investment into P2G system. Co-financer (hydropower plant operator ''Hidroelektrarne na Spodnji Savi'' - HESS) recognized potentials of P2G technology and it will invest in such system after the end of the research project if sufficient profitability will be proven.
Significance for science
The proposed project is focused to optimization of hydro power plant operation by means of the system for conversion of electric energy to gas (P2G). Energy losses due to spilled turbinable power in periods of excess electric energy can be reduced by installing P2G system, which converts excess energy into hydrogen. To achieve maximum energy and economic efficiency and the profitability of investment, installed P2G system must be controlled in an optimal way by taking into account predictions of the electric energy and natural gas markets, predictions of input water flow into hydro power plant and many other conditions and constraints. The proposed project combines two research and engineering fields: 1. Process control and optimization technology and 2. Energy storage and grid balancing field. In the literature, the optimization of P2G systems linked to wind and photovoltaic power plants is addressed, but cases linked to hydro power plants are rare ##. The project will open a new special multi-disciplinary research and development direction, which will analyse potentials of use and optimization of P2G system linked to the hydro power plant and develop a methodology for optimization. This is an extremely relevant research topic, which directly affects the ecology and energetics and it will have an influence to the development of future flexible grids. The development and study will be performed in simulation environment, which will be developed in the project. Simulation environment will represent a benchmark for the development and comparison of different optimization approaches and it will be used also ##outside the proposed project. It will provide the possibility of including other researchers, scientific collaboration and testing of alternative optimization approaches. Project’s co-financer, hydro power plant company ''Hidroelektrarne na Spodnji Savi'' (HESS), will provide all the necessary information about hydro power plant and electric energy market operation. In this way, the project will be based on realistic assumptions and information. The implementation will represent a reference, which will help Slovenian research partners to enter the international research consortia and projects, e.g. the projects, initiated by FCH-JU (Horizon 2020, Fuel cell and hydrogen joint undertaking).
Significance for the country
Slovenia generates over 25 % of electric energy from renewable sources and 70 % of this energy comes from hydro power plants. The motivation for the proposed applied research comes from the company ''Hidroelektrarne na Spodnji Savi'' (HESS), which faces energy losses due to spilled turbinable power in the periods of excess of electric energy. Company HESS recognized the potential of P2G technology as a way to decrease energy losses and it will invest into the implementation of the P2G system, if the proposed project will demonstrate that sufficient profitability of the investment can be achieved. To achieve sufficient profitability it is necessary to achieve maximum possible energy and economic efficiency of the system, which is only possible by optimal control of P2G system and by considering the predictions of electric energy and natural gas markets, predictions of input water flow into the hydro power stations and several other conditions and constraints. The implementation of the project will bring the following benefits to the users in Slovenia and abroad:
Methodology and prototype of the system for optimal control of P2G system, which provides maximum possible energy and economic effects.
A simulation environment that will allow the study of the influence of different parameters on energy and economic effects and on the system's profitability. The simulation environment will support decision-making about the optimal size of the P2G system, the mode of operation of the P2G system and the method of using the hydrogen produced.
The project has a wider social significance from the following aspects:
Market opportunity: Hydropower optimizer and P2G system can be installed on hydro power plants in Slovenia and on global market. The motivation for the proposed project also comes from Slovenian hydro power plant operator, which recognized the requirements of new energy systems and potential of P2G energy storage systems.
Economic benefits: Upgrading hydro power plant with P2G system makes possible to reduce energy loss (spilled turbinable energy). By proper optimal control, additional saving can be achieved. For example, in study [11] after applying optimization based predictive control, economic efficiency of P2G system linked to electric and natural gas network was increased by over 30 % and number of starts and stops of the electrolyser reduced by almost 50 %.
Ecologic benefits: The proposed project allows for greater utilization of hydropower and its share in the total amount of energy produced. This will help to reduce environmental impacts (lower environmental indicators to LCA methodology) since hydrogen is a very pure fuel in the phase of its use and it will be produced from hydropower, which has the lowest environmental impact among all energy generation technologies.
Clean hydrogen production: P2G process is cost effective, clean and geographically distributed way of hydrogen supply, which meets the needs of various consumers [7], [9].
