Introduction
The use of renewable energy sources, especially photovoltaic (PV) and wind power generation, is now expanding on a global scale. Japan has set high goals for the introduction of these technologies, which have attracted more and more attention following the Great East Japan Earthquake and the Fukushima nuclear accident in March 2011. However, PV and wind power generation are characterized by seasonal and hourly variations as well as irregular variations caused by Komaba II Campus of the University of Tokyo in changes in the weather. Therefore, in addition to balancing supply and demand, to ensure a sufficient and stable power supply we have to also solve various technical problems such as voltage increases and frequency changes.
The Problem
To achieve a supply-demand balance in future power systems, it is imperative that we should not only apply pumped-storage power generation or large-scale batteries on the supply side but also focus on residential power usage, storage, and generation on the demand side.
The Ogimoto Laboratory is a leader in studies about using the Home Energy Management System (HEMS) to better manage energy through the use of optimization techniques across both supply and demand, including controlling equipment on the demand side to contribute energy to the overall electric power system.
Figure one shows the system for balancing supply and demand where centralized and decentralized energy management work together to address the needs of both the overall power system, as well as the needs of a single building or community.
Under a centralized energy management system, power companies forecast the amount of PV generation and electricity demand in the service area and calculate the optimal load dispatch across the power plants. In situations where there is insufficient capability to balance supply and demand through equipment controlled by the power company, a signal for managing residential power usage could be sent directly to customers prior to the fact. For example, if an increase in demand is desired, a method could be used in which the price for electrical power would be lowered and customers notified a day in advance, or a higher price for power set when a decrease in demand is desired.
On the other hand, the decentralized energy management calculates the most economical operation schedules of domestic electric appliances, within a range that will not interfere with the comfort of living or working environments, by using forecasted energy demand and PV generation and also using next-day electricity prices sent from the utility.
By coordinating localized optimization, attained by implementing decentalized energy management for residences and office buildings, with overall regional optimization, based on centralized energy management performed by power companies, we aim for a system that can fully benefit both consumers and power companies.
Results
The Ogimoto Laboratory is engaged in development of a scheduling model for optimized household appliance operation (see Fig. 2), which would utilize the functions of the Gurobi Optimizer mixed integer linear programming method (MILP) to quantitatively evaluate effects of the optimal control of household appliance, using forecasted levels of next-day energy service and PV generation demand, as well as information on demand adjustment incentives from power companies.
As a result of the application of actual residential data, it was discovered that setting lower daytime power rates for clear weather days in May, when the supply-demand adjustment is most difficult in Japan, can create more daytime power demand for residential heat pump water heaters or storage batteries, thus consuming surplus PV power and suppressing reverse flow (see Fig. 3). In addition, it was confirmed that residential power demand can be used to adjust the supply-demand balance, through a suitable setting of power prices in response to weather conditions.
