电转气地质储能技术的经济性分析

电转气（Power-to-gas）是一项将电能转化为高能量密度可燃气体的化学储能技术，与地质储能相结合，有望满足未来大容量储能需求，并成为未来有效储能技术选择之一。电转气地质储能技术中涉及电离制氢、甲烷化、二氧化碳（CO2）地质储存和人工合成甲烷（CH4）地质储存四个阶段。由于电转气地质储能技术发展处于初步阶段，且涉及多个技术环节，其技术整体的经济性分析相对较少，有必要对电转气地质储能技术的经济性展开分析，便于探索电转气地质储能技术在中国的应用潜能。本文基于大量文献调研，首先对电离制氢与甲烷化过程展开技术经济性分析，随后分别对CH4与CO2地质储存的技术经济性展开分析，进而将整个流程按照不同工况下的估算结果进行统计分析，并通过与抽水蓄能和压缩空气储能进行技术经济对比，明确了电转气地质储能的技术成本，最后针对该技术在中国应用的机遇与挑战做出了分析。研究发现，碱性电解液电解技术（AEL）目前以较低投资成本更具优势，大约为7850元/kW，聚合物电解质膜技术（PEM）的投资成本在技术进步的基础上，有望于2050年降低投资成本至约为当前AEL技术的一半；生物甲烷化以及催化甲烷化的技术中的三相甲烷化技术仍处于实验和示范阶段，催化甲烷化的技术中的绝热固定床甲烷化技术因为有较成熟的商业应用更具技术优势，该技术有望于2050年成本降低至目前的50%-60%；CH4地质储能设施的开发成本变化浮动很大，因为这些成本受储能的类型及各项特性参数的影响。不过基于已发表数据可知，CH4地质储能中含水层储能与枯竭油气田储能的投资成本相当，在1.88-3.30元/m3范围内浮动。盐穴储能相对投资成本较高，约为其他两种地质储能技术的两倍。CO2地质储存成本变化范围很广，除个别高成本案例外，储存成本通常低于53.38元/吨，以3.38-53.38元/吨CO2的储存成本具有很大的潜力。整体技术经济性来看，人工合成甲烷发电成本比传统化石能源如天然气的发电成本高出很多，相较于化石能源发电不存在竞争性，但与当前太阳能热电厂发电成本相当。相较于目前处于应用阶段的抽水蓄能和压缩空气储能，电转气地质储能技术投资成本相当。当前，电转气地质储能在中国应用的机遇与挑战并存。随着未来电离制氢与甲烷化技术的创新，系统能效、地质储能模式、选址模型的优化，与现有储气库、天然气管网、电网结合方法的优化以及低碳政策的积极影响等，都将提升电转气地质储能技术在中国应用的可能性。

Economic Analysis of Power-to-Gas based Subsurface Energy Storage Technology

Power-to-gas is a chemical energy storage technology that converts electrical energy into combustible gas with high energy density. Combined with subsurface energy storage, it is expected to meet the demand for a large capacity of energy storage, and it will become one of the most effective energy storage technologies in the future. Power-to-gas based subsurface energy storage includes four stages: hydrogen production from electrolysis, methanation, geological storage of carbon dioxide (CO2), and geological storage of synthetic methane (CH4). Since the development of Power-to-gas based geological energy storage technology is at a preliminary stage and involves multiple technical aspects, the overall economic analysis is relatively rare. It is necessary to carry out an economic analysis and further explore the application potential of this technology in China. Based on a large amount of literature research, a technical and economic analysis of electrolysis and methanation are firstly carried out, and then the technical and economic analysis of the geological storage of CH4 and CO2 are carried out respectively, and then the whole process is statistically analyzed according to the estimated results under different assumptions and conditions. The results are compared with pumped hydro storage and compressed air energy storage, and the technical cost of Power-to-gas based geological energy storage is clarified. Finally, the application opportunities and challenges of this technology in China are pointed out. This study has found that Alkaline electrolysis (AEL) currently has advantages at lower investment costs, which is about 7850 yuan/kW, the investment cost of Polymer electrolyte membrane (PEM) is expected to reduce the investment cost to about half of the current AEL in 2050. The biological methanation and isothermal catalytic methanation technology is still in the experimental and demonstration stage. The adiabatic fixed-bed methanation technology has more technical advantages because of its more mature commercial applications. It is expected that the cost will be reduced to the current 50%-60% in 2050. The cost of geological CH4 storage fluctuates greatly, because the cost is affected by different reservoirs and various operating parameters. However, based on published data, it can be seen that the investment cost of energy storage in aquifers is equivalent to that of energy storage in depleted oil or gas fields, which fluctuates in the range of 1.88-3.30 yuan/m3. The investment cost of geological CH4 storage in salt caverns is relatively high, about twice that of the other two geological reservoirs. CO2 geological storage costs varies widely, except for individual high-cost cases, the storage cost is usually less than 53.38 yuan/tonne. At present, the opportunities and challenges for the application of Power-to-gas based geological energy storage in China coexist. However, the innovations of electrolysis and methanation technology in the future, the optimizations of geological energy storage efficiency, mode, site selection, the improvements of integration method with existing gas storage sites, natural gas pipeline network, power grid, and the impacts of low-carbon policy, will enhance the possibility of applying Power-to-gas based geological energy storage technology in China.