Benefit Evaluation of Hydrogen Production System Harnessing Curtailed Wind Considering Integrated Demand Response

With the continuous increase of wind power installed capacity in China in recent years, the problem of wind curtailment has become increasingly serious. Using curtailed wind power for hydrogen production is an effective way to reduce wind curtailment. In this paper, based on the complementary characteristics of various energies in the electric-hydrogen system, a capacity planning model of the energy system considering wind curtailment wind-to-hydrogen technology and integrated demand response is established. The proposed model utilizes a fast unit commitment technology, with the function of solving the optimum capacity of various equipment in the electrolytic hydrogen production system under different wind curtailment utilization rates and different wind power installed capacities. A case study based on Xinjiang province, which has rich wind energy resources, is conducted to obtain the optimal composition of new-built capacities of the electrolytic hydrogen production system. In light of the simulation results, the levelized cost of hydrogen is proportional to the wind power installed capacity and inversely proportional to the utilization rate of wind curtailment.


Introduction
With the rapid development of renewable energy, the proportion of renewable energy in power systems is increasing.Wind power technology has developed rapidly, and the cost of wind power has been continuously reduced, which makes the scale of wind farms expand, as well as the continuous growth of wind power generation has been achieved, which deteriorates wind curtailment.The wind curtailment issue is getting worse due to uncertainty in wind power and increasing wind power capacity [1][2][3][4][5].
To reduce wind curtailment, scholars from various countries have carried out a lot of research.In [6], an optimized wind and water combined curtailment strategy is proposed, which can keep the wind curtailment within a certain range.To increase the utilization rate of wind power in power systems, in [7], an integrated optimization model that maximizes the utilization rate of wind power from the perspective of transaction energy control is proposed.
As a kind of clean energy, hydrogen energy has received extensive attention, and utilizing curtailed wind to produce hydrogen is an effective means to reduce wind curtailment.In [8] a power system network constrained day ahead scheduling scheme based on cogeneration devices and HES technology is proposed, taking into account the high integration of wind resources.At low wind power generation, the HES system converts the stored hydrogen into electricity through gas power plants, reducing the system's operating costs and wind power curtailment.A P2H system model considering hydrogen sales is proposed in [9], considering the constraints of electric power systems, hydrogen storage, sales of hydrogen, and regional heating systems.Integrating this model into the optimization scheduling model of the electric thermal hydrogen multi-energy flow system, the results of the simulation show that electricity-heat-hydrogen systems can reduce system operating costs and improve wind power integration.
Integrated demand response considers the complementary characteristics of different energy sources in the integrated energy system, which can realize the interaction between the demand and supply of various energies in the electric-hydrogen system.Aiming at the coordination and optimization scheduling problem of the CCHP microgrid, in [10], a CCHP-SESS two-layer supply and demand coordination optimization model is built, which considers the incentive effect of comprehensive demand response and the coupling characteristics of different types of loads.An electricity consumption behavior portrait method is proposed in [11] based on optimal feature collection and improved k-means clustering analysis.By adding the annual comprehensive cost, etc. as the optimization objectives in the decision-making objectives, in [11], a distribution network expansion planning model with a differentiated demand response scheme is constructed.
In this paper, a capacity planning model of the energy system considering wind curtailment wind-tohydrogen technology and integrated demand response is established.The goal of the capacity planning model is to minimize the operating cost of an electric hydrogen system.In this article, a case study based on Xinjiang province is simulated with MATLAB, and the optimum capacity of the electrolytic hydrogen production system under different wind curtailment utilization rates and different wind power installed capacities is obtained.
This paper comprehensively considers electricity, heat, and hydrogen, and Figure 1 shows the overall architecture of the integrated energy system.Two highlights of the paper will be represented as follows: 1) Capacity planning of hydrogen production system considering integrated demand response 2) Obtaining the optimum capacity of the electrolytic hydrogen production system under different wind curtailment utilization rates and different wind power installed capacities.

Objective Function
where f W is the operation and maintenance (O&M) costs of thermal units, solar power units, and wind power units; v W represents both the start-up costs and fuel costs; h W represents the levelized cost of hydrogen.
f W , v W and h W are given as follows: In the above formulas, N indicates the number of thermal units types; i f , h f , w f , and s f are the O&M costs for type i thermal units, electrolysis unit, wind units, as well as solar units; i I , w I and s I indicate the total capacity for type i thermal units, wind units, and solar units; i c is the fuel costs for type i thermal units; i SD is the start-up costs; represent the wind and solar power outputs at time t.In this formula, i t p is continuous variable obtained by using the fast unit combination method, indicating the capacities that are online, which satisfy the following formula: where i t s and i t u represent the start-up and shut-down capacity for i -type thermal units at time t respectively.
2) Minimum on/off Time Constraints In the above formulas, In the above formulas, α represents the water required for unit hydrogen production; β and γ are the oxygen and heat generated simultaneously by unit hydrogen production; wat p , o p and heat p indicate the prices of wind power, water, oxygen, and thermal energy.
3) Hydrogen Balance Constraints where ( ) P t , ( ) E t , ( ) H t represent the electric, thermal, and hydrogen energy supplied by the comprehensive energy system; p  , e  , and h  are the proportion coefficient of electrical energy used for power supply, heat generation, and hydrogen production; e  is the proportion coefficient of thermal energy used for heat generation; p  , e  , and h  are the proportion coefficient of hydrogen energy used for power supply, heat generation, and hydrogen production.
The constraints of integrated demand response are as follows.

Case study
The installed capacity of wind turbines in Xinjiang accounts for a large proportion of the country, as shown in Figure 2.This paper conducts a case analysis based on the data of Xinjiang Province.The GUROBI solver was used to simulate the power generation and load data of Xinjiang Province, China on MATLAB.The relevant unit capacity and operational constraints data of Xinjiang Province are described in Table 1.
There are many different types of electrolyzers used for the electrolysis of hydrogen production.When the hydrogen production simulation is carried out in this paper, three different types of electrolyzers (AEC, PEMEC, SOEC) are used for simulation.The characteristics of three types of electrolyzers are shown in Table 2. Two operation scenarios are set to analyze the economy of integrating the power-to-hydrogen technology.

Only use the curtailed wind to produce hydrogen
In this scenario, , 0 g t P  .Figure 3 and Figure 4 show the optimized hourly output of various power generation units in 72 hours.Figure 3 indicates the optimization results without the electrolysis hydrogen production system, and the optimization results with the electrolysis hydrogen production system are shown in Figure 4.It is not difficult to see that the use of curtailed wind to produce hydrogen by electrolysis can effectively reduce wind curtailment.Figure 3 Hourly output without electrolysis hydrogen production system Figure 4 Hourly output with electrolysis hydrogen production system Figure 5 shows the optimal capacity of the electrolysis device and levelized cost of hydrogen under different wind power installed capacities under the scenario only using curtailed wind to produce hydrogen.It can be seen that among the three types of electrolyzers, SOEC has the best economy.Under the condition that the utilization rate of wind curtailment remains unchanged, as the wind power capacity increases, the levelized cost of hydrogen for all three types of electrolytic cells is reduced.
Figure 6 indicates the optimal capacity of the electrolysis device and levelized cost of hydrogen under different utilization rates of curtailed wind under the scenario only using curtailed wind to produce hydrogen.It can be shown that under the condition that the wind power installed capacity remains unchanged, as the utilization rate of curtailed wind power increases, the levelized cost for all three types of electrolytic cells increases.
Figure 5 The capacity of the electrolysis device and levelized cost of hydrogen under different wind power installed capacities Figure 6 The capacity of the electrolysis device and levelized cost of hydrogen under different utilization rates of curtailed wind 3.2.Using on-grid wind and curtailed wind to produce hydrogen Figure 7 demonstrates the levelized cost of hydrogen under different wind power installed capacities under the scenario using on-grid and curtailed wind to produce hydrogen.Under the condition that the utilization rate of curtailed wind remains unchanged, the levelized cost of hydrogen for all three types of electrolytic cells decreases as the wind power capacity increases.Figure 8 shows the optimal capacity of the electrolysis device and levelized cost of hydrogen under different utilization rates of curtailed wind under the scenario using on-grid and curtailed wind to produce hydrogen.As the utilization rate of wind power curtailment and wind power capacity remains unchanged, the levelized cost of hydrogen for all three types of electrolytic cells increases.Figure 9 compares the optimal capacity of the electrolysis device under the scenario only using curtailed wind for hydrogen production and the scenario using on-grid and curtailed wind for hydrogen production.With the improvement of the utilization rate of curtailed wind, the optimal capacity of the electrolyzer under the scenario using on-grid and curtailed wind to produce hydrogen is smaller than that under the scenario only using curtailed wind to produce hydrogen.
Figure 9 The capacity of the electrolysis device

Conclusion
This paper establishes a capacity planning model of the curtailment wind-to-hydrogen system.The goal of the capacity planning model is to minimize the cost of the Power-to-hydrogen integrated energy system.By simulating a one-year hourly operation that is incorporated into the proposed model, the optimal newly built capacity of the electrolytic hydrogen production system under different wind curtailment utilization rates and different wind power installed capacities can be obtained.
1) Whether it is the scenario only using curtailed wind to produce hydrogen or the scenario using ongrid wind and curtailed wind to produce hydrogen, as the wind power installed capacity increases, the cost of hydrogen will decrease.
2) Whether it is the scenario only using curtailed wind to produce hydrogen or the scenario using ongrid wind and wind curtailment to produce hydrogen, as the utilization rate of wind curtailment increases, the cost of hydrogen will increase.
3) When the same amount of hydrogen is generated, the electrolyzer capacity required in the scenario where only curtailed wind is used is bigger than that in the scenario where both on-grid wind and curtailed wind are utilized.The reason is that when on-grid wind and curtailed wind are used at the same time, the capacity of the electrolyzer can be better utilized because the impact of the wind curtailment fluctuation on the electrolyzer will be reduced.At this time, the capacity factor for the electrolysis increases, and as a result, the required electrolysis capacity is smaller.

Figure 1
Figure 1 Integrated energy system

Figure 2 Figure
Figure 2 Figure with short caption (caption centered)

Figure 7 Figure 8
Figure 7 Levelized cost of hydrogen under different wind power installed capacities

Table 1
Installed Capacity and Operation Characteristics of Thermal Power Units in Xinjiang Province

Table 2
Data of Different Electrolysis Technologies in 2030