Power-to-gas plants and gas turbines for improved wind energy dispatchability: Energy and economic assessment

Limited dispatchability of wind parks and unexpected grid power injections create unbalances between the generated electric power and the actual required power that has to be reduced for proper operation of the electrical grid. The increasing amount of renewable energy sources stresses this problem in several countries, where the responses in terms of reinforcement of transmission lines and ancillary services are not sufficiently fast or effective. In this study, we analyze the potential of a grid balancing system based on different combinations of traditional gas turbine based power plants with innovative 'power-to-gas' plants. Power-to-gas is a promising solution to balance the electric grid, based on water electrolysis, which can effectively contribute to reducing the uncertainty of dispatch plans. According to this system, the excess power produced by renewables is converted into hydrogen, which can be then injected into the natural gas grid. Different economic scenarios are assessed in this work, leading to a set of optimal sizes of the proposed system, using a statistical approach in order to estimate wind farm productivity and forecasting errors, as well as each component load conditions. Economic parameters, equivalent operating hours, CO2 emissions and lost wind energy are the main performances indexes considered in this work to compare gas turbine and electrolysis balancing systems. From an economic point of view, hybrid systems including both balancing technologies generally lead to the best performances. The scenario which leads to the highest power-to-gas capacity (with installed electrolysis power of about 6% of wind park nominal power) is determined coupling a mid-term perspective of reduction in investment costs with favorable energy market conditions or with incentives (“green-gas” or carbon taxes). In such conditions, an equivalence between the two technologies in terms of optimum installed power can be reached at an electricity-to-natural gas cost ratio between 1.8 and 2. In most interesting scenarios, the P2G system brings about a lower total wind electricity injected in the grid, due to wind-to-gas energy conversion, while it allows reducing energy losses due to grid congestion and curtailment of the wind park; however, the additional CO2 emissions due to gas turbines operation and due to the reduced electricity production tend to offset or to limit the positive effect of the carbon-free gas production.