(415e) Green-Hydrogen Production: Systematic Superstructure-Based Approach for Technology Selection

Decarbonization of the economy is a universal goal to keep global warming under 1.5°C [1]. Green-hydrogen is expected to play an important role in achieving this goal in the transport sector. In particular, it can be employed as a fuel in heavy duty electric vehicles (trucks, buses), or as raw material to produce synthetic fuels. Green-hydrogen is defined as H₂ produced by electrolysis of water employing clean renewable energy such as wind/sun as the power source. The main drawback of these “new” power sources is their time-varying and non-programmable behavior, which poses challenges when coupled to processes that are desired to operate continuously.

In previous works [2] we have addressed the trade-off between the usage factor of energy and the usage factor of the hydrogen production facilities/stations when employing a given time-varying power source. For that work, it was assumed that the electrolyzer would have such a flexible operation that it could operate at any partial load and sustain any number of on/off cycles. Proton Exchange Membrane Electrolyzers (PEME), may operate under those assumptions, however, they are currently very expensive. These and other low-temperature devices (under 100°C), have fast on/off dynamics (minutes or tens of minutes [3,4]). The most mature ones are Alkaline Electrolyzers (AE), which are cheaper but cannot run at low current densities (i.e. low partial loads) due to safety issues. In addition, other alternatives such as solid oxide electrolyzers (SOE) which operate at high temperatures (over 700°C), may not offer the flexibility of frequent on/off cycles, but reach higher efficiencies while employing lower cost and more abundant catalysts. Then, the selection of the technology or set of technologies to produce hydrogen in systems powered by time-varying energy sources is not straight-forward.

In this presentation, we will present the results of our work on the systematic selection of an optimal technology or a combination of them for the production of green-hydrogen to be used as a fuel or natural gas replacement [5]. First, a power-to-hydrogen superstructure is proposed and modelled. The superstructure considers different power sources: (renewable) energy surplus, (renewable) energy from the grid, installation of new solar/wind power generators, different energy storage strategies (hydrogen tanks and batteries), and different electrolysis technology (AE, PEME and SOE). Then, the superstructure is optimized for cost (capital and operation) minimization.

Simulations were performed using data from Uruguay, a country that has already decarbonized the power sector and is working towards decarbonization of the transport sector [6,7]. The results show that the optimal solution is to combine energy sources to obtain a more stable energy input, which in turns depends on the number and type of energy sources available. The system can also take advantage of combining high and low temperature electrolysis to exploit both higher efficiency for base loads and flexibility for peaks. Our results also show that integration of high temperature electrolysis requires the presence of energy storage devices (batteries). Sensitivity analysis further showed that their presence in the optimal solution strongly depends on the cost of these batteries.

[1] UNFCCC , “Glasgow Climate Pact. Decision -/CP.26.” Glasgow Climate Change Conference, 2021.

[2] M. Corengia, N. Estefan, A. I. Torres, “Analyzing Hydrogen Production Capacities to Seize Renewable Energy Surplus”, Computer Aided Chemical Engineering, 2020, 48, pp. 1549–1554.

[3] M. Corengia, A. I. Torres, “Two-phase dynamic model for PEM electrolyzer,” Computer Aided Chemical Engineering, 2018, 44, pp. 1435–1440.

[4] M. Carmo, D. Stolten, 2019. Energy Storage Using Hydrogen Produced From Excess Renewable Electricity: Power to Hydrogen, in Science and Engineering of Hydrogen-Based Energy Technologies.

[5] M. Corengia, A. I. Torres, “Coupling time varying power sources to production of green-hydrogen: a superstructure based approach for technology selection and optimal design”. Under review

[6] https://moves.gub.uy/en/

[7] https://www.gub.uy/ministerio-industria-energia-mineria/green-hydrogen