Effect of the installation of natural-gas fuel-based on-site technologies on grid power in terms of investment and operation costs

摘要

Since the Great East Japan Earthquake, the experience of the Fukushima Daiichi nuclear accident and the need for blackouts to avoid power shortages has caused the Japanese government to reconsider the most suitable combination (best mix) of energy sources. The improvement of the so-called "3E+S" conditions, namely, economy, environment, energy security, and safety, is required for the energy system of each country. The installation of gas systems, such as on-site combined heat and power (CHP), fuel cells, and gas air-conditioning (gas enginedriven heat pumps and absorption chillers), can contribute to this improvement. An evaluation of the whole energy system as a whole, including the gas and grid power systems, will offer significant information to the gas industry and facilitate governmental discussions. Furthermore, with effect from 2016, deregulation has been planned for all sectors of the electric power industry in Japan. In the near future, gas companies will not only retail natural gas, but also electricity. Therefore, following deregulation, the gas companies will need to evaluate the whole energy system, including the gas and grid power systems, in order to establish and utilize their most appropriate energy supply combination. Based on these circumstances, we evaluated the effect of installing the gas systems on grid power in terms of investment and operation costs by using the Electric Load Curve Estimation Model and the Grid Power Supply Simulation Model. For this purpose, it was necessary to calculate the hourly electric load curves of grid power both with and without the gas systems. However, as gas systems vary widely according to each sector, e.g. residential, commercial, and industrial, it was necessary to calculate separate load curves before combining the results to estimate a total load curve. Although a large number of studies have been performed on the hourly electric load curve of an individual customer, little is known about the total hourly electric load curve of an area or of various sectors. Hence, in this study, we developed the Electric Load Curve Estimation Model, which can be used to calculate both individual and total hourly electric load curves. This data was subsequently input into the Grid Power Supply Simulation Model, which enabled us to calculate the investment and operation costs for electricity supply. Accordingly, the costs with and without the gas systems could then be compared. Following on from this, a case study focusing on the Tokyo metropolitan area was performed. Results indicate that including gas systems, alongside other energy sources, can limit total investment and operation costs. In particular, on-site CHP can be economically competitive where nuclear power plants are out of service. Overall, these results suggest that an energy supply system that includes gas systems is more economically efficient than those that rely on grid power only.