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JST Press Release

June 7, 2017
Japan Science and Technology Agency (JST)
5-3, Yonbancho, Chiyoda-ku, Tokyo 102-8666

Evaluation of demand response effect of heat pump water heaters

Professor Yumiko Iwafune of the University of Tokyo et al. evaluated the economic effects of demand response management using heat pump water heaters (HPWHs) and batteries with residential photovoltaic (PV) systems.

The increase in PV systems has been driven by Feed-in Tariff (FIT) incentives in Japan. As a response to the “Year 2019 Problem” which is the start of the end of purchase agreements in expensive FIT price in 2019, a model was developed for optimizing the operation of HPWHs using 24 hours advance forecasting of electricity consumption and PV generation. The goal was to minimize electricity charges by optimizing the operation of actual HPWHs. Annual electricity consumption data from 357 houses fitted with both PV and an HPWH were used in the study. Optimal operation of an HPWH was shown to yield average cost savings of $58 or 7% of the electricity cost in conventional operation. HPWH electricity consumption was reduced by 11% on average, compared with conventional operation, because running the heat pumps during the daytime increases their efficiency. The self-consumption ratio increased from 32% in conventional operation to 45% by optimizing the operation of the HPWH, which was similar to the effect of introduction of a 2–4 kWh battery. The simulation results show that the demand response of HPWHs contributes to the expansion of self-consumption of PV systems and energy conservation. Future flexibility of electric power system can be improved by the demand response effect of HPWHs.

Program Information

Research Area “Creation of Fundamental Theory and Technology to Establish a Cooperative Distributed Energy Management System and Integration of Technologies Across Broad Disciplines Toward Social Application”
Research Theme “Home energy management system with consideration of consumer acceptability”

Journal Information

Yumiko Iwafune, Junichiro Kanamori and Hisayoshi Sakakibara, “A comparison of the effects of energy management using heat pump water heaters and batteries in photovoltaic -installed houses”, Energy Conversion and Management, Published online 6 June 2017, doi: 10.1016/j.enconman.2017.05.060.


[About Research]
IWAFUNE Yumiko, Ph.D.
Institute of Industrial Science, the University of Tokyo

[About Program]
Koji Matsuo ICT Group,
Department of Innovation Research, JST


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