Optimization based control of P2G converter connected to hydro power plant

Principal investigator:

Dr. Gregor Dolanc


July 1, 2019 – June 30, 2022


ARRS - Slovenian Research Agency, L2 - 1832 (B), co-financing from Hidroelektrarne na Spodnji Savi, d.o.o.


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.

Project partners: