Presentation Information
[O02-02]Research on "Renewable Thermal Energy" -Shallow ground source heat energy and Solar Thermal Assessment and Demonstration in Saitama★Invited Papers
*Hideki Hamamoto1,2, Takashi Ishiyama1, Takashi Kakimoto1, Hiroaki Yamato1, Tomohide Shimada1, Satoshi Tomigashi3 (1.Center for Environmental Science in Saitama, 2.Sitama University, Graduate School of Science and Engineering, 3.National Institute of Advanced Industrial Science and Technology)
Keywords:
Renewable Thermal Energy,Ground Source Heat Pump (GSHP),Solar Thermal Energy,Potential Assessment,Local Government
1. Introduction
Transitioning from conventional fossil fuels to renewable energy is an urgent mandate for realizing a decarbonized society. When examining final energy consumption within the residential sector, "thermal demand"—including water heating, space heating, cooling, and cooking—accounts for approximately 70% of total energy consumption. Rather than converting electrical energy into heat (as is done with photovoltaics), the utilization of "renewable thermal energy," which uses heat directly, is a rational and promising approach that minimizes energy conversion losses.
Shallow geothermal energy and solar thermal energy, which represent renewable thermal energy, hold immense installation potential globally. However, Japan’s current implementation lags significantly behind leading nations such as those in Europe, the United States, and China. For instance, regarding the installed capacity of Ground Source Heat Pump (GSHP) systems, the United States and China both exceed 20,000 MWt, whereas Japan remains at only 226 MWt. Even Germany, with a smaller population than Japan, has reached 5,000 MWt, indicating a substantial margin for expansion in Japan.
Against this backdrop, local governments are required to implement promotion strategies for renewable thermal energy tailored to regional characteristics. This presentation reports on the research outcomes regarding geothermal and solar thermal energy utilization conducted at the Center for Environmental Science in Saitama (CESS).
2. Research on Geothermal Energy Utilization
2.1 Geothermal Potential Assessment and GIS Publication
Our reserach center evaluates geothermal potential for each region based on subsurface environmental data within the prefecture and publishes this information via a Geographic Information System (GIS). The evaluation methodology involved collecting and analyzing borehole logs from approximately 4,800 locations within the prefecture to identify the stratigraphy up to a depth of 100 meters. By applying empirical specific heat extraction rates (heat extraction per unit length) corresponding to typical geology (rock and soil types), we calculated the weighted average in the depth direction for each location. This allowed us to estimate and evaluate the expected heat extraction rate per standard borehole heat exchanger.
2.2 Demonstration Tests of Heat Pump Systems
We installed closed-loop GSHP systems and Air Source Heat Pumps (ASHP) in parallel at five model facilities within the prefecture to conduct comparative demonstration tests. Analysis of the measured data confirmed that the GSHPs demonstrated high efficiency, achieving a seasonal Coefficient of Performance (COP) approximately 1.5 to 2.0 times higher than that of the ASHPs. Furthermore, for agricultural applications, we conducted demonstration tests of open-loop geothermal systems, which utilize groundwater directly as a heat source, in cooperation with farmers in Kumagaya City (strawberry cultivation) and Kuki City (herb cultivation). The results confirmed the effectiveness of geothermal heat compared to conventional fossil fuel use. Additionally, the study suggested co-benefits in cultivation, such as higher crop quality due to advanced temperature control and the extension of harvest periods.
3. Research on Solar Thermal Energy Utilization
Regarding solar thermal energy utilization, we conducted long-term monitoring using a vacuum tube solar thermal collection system installed at our center. The study demonstrated that the vacuum tube type is less susceptible to ambient temperature due to minimal heat loss from temperature differences, enabling high-temperature collection even in winter. A high system-wide energy conversion efficiency exceeding 50% was confirmed, validating the potential for highly efficient heat utilization.
On the other hand, solar thermal energy possesses characteristics of a variable energy source dependent on weather and geographic conditions. Since high spatiotemporal resolution data, such as global solar radiation, is essential for efficient regional planning, we are currently advancing spatial analysis (detailed mapping using techniques such as spatial interpolation) of solar radiation distribution within the prefecture.
Acknowledgments
portion of this work was supported by the New Energy and Industrial Technology Development Organization (NEDO).
Transitioning from conventional fossil fuels to renewable energy is an urgent mandate for realizing a decarbonized society. When examining final energy consumption within the residential sector, "thermal demand"—including water heating, space heating, cooling, and cooking—accounts for approximately 70% of total energy consumption. Rather than converting electrical energy into heat (as is done with photovoltaics), the utilization of "renewable thermal energy," which uses heat directly, is a rational and promising approach that minimizes energy conversion losses.
Shallow geothermal energy and solar thermal energy, which represent renewable thermal energy, hold immense installation potential globally. However, Japan’s current implementation lags significantly behind leading nations such as those in Europe, the United States, and China. For instance, regarding the installed capacity of Ground Source Heat Pump (GSHP) systems, the United States and China both exceed 20,000 MWt, whereas Japan remains at only 226 MWt. Even Germany, with a smaller population than Japan, has reached 5,000 MWt, indicating a substantial margin for expansion in Japan.
Against this backdrop, local governments are required to implement promotion strategies for renewable thermal energy tailored to regional characteristics. This presentation reports on the research outcomes regarding geothermal and solar thermal energy utilization conducted at the Center for Environmental Science in Saitama (CESS).
2. Research on Geothermal Energy Utilization
2.1 Geothermal Potential Assessment and GIS Publication
Our reserach center evaluates geothermal potential for each region based on subsurface environmental data within the prefecture and publishes this information via a Geographic Information System (GIS). The evaluation methodology involved collecting and analyzing borehole logs from approximately 4,800 locations within the prefecture to identify the stratigraphy up to a depth of 100 meters. By applying empirical specific heat extraction rates (heat extraction per unit length) corresponding to typical geology (rock and soil types), we calculated the weighted average in the depth direction for each location. This allowed us to estimate and evaluate the expected heat extraction rate per standard borehole heat exchanger.
2.2 Demonstration Tests of Heat Pump Systems
We installed closed-loop GSHP systems and Air Source Heat Pumps (ASHP) in parallel at five model facilities within the prefecture to conduct comparative demonstration tests. Analysis of the measured data confirmed that the GSHPs demonstrated high efficiency, achieving a seasonal Coefficient of Performance (COP) approximately 1.5 to 2.0 times higher than that of the ASHPs. Furthermore, for agricultural applications, we conducted demonstration tests of open-loop geothermal systems, which utilize groundwater directly as a heat source, in cooperation with farmers in Kumagaya City (strawberry cultivation) and Kuki City (herb cultivation). The results confirmed the effectiveness of geothermal heat compared to conventional fossil fuel use. Additionally, the study suggested co-benefits in cultivation, such as higher crop quality due to advanced temperature control and the extension of harvest periods.
3. Research on Solar Thermal Energy Utilization
Regarding solar thermal energy utilization, we conducted long-term monitoring using a vacuum tube solar thermal collection system installed at our center. The study demonstrated that the vacuum tube type is less susceptible to ambient temperature due to minimal heat loss from temperature differences, enabling high-temperature collection even in winter. A high system-wide energy conversion efficiency exceeding 50% was confirmed, validating the potential for highly efficient heat utilization.
On the other hand, solar thermal energy possesses characteristics of a variable energy source dependent on weather and geographic conditions. Since high spatiotemporal resolution data, such as global solar radiation, is essential for efficient regional planning, we are currently advancing spatial analysis (detailed mapping using techniques such as spatial interpolation) of solar radiation distribution within the prefecture.
Acknowledgments
portion of this work was supported by the New Energy and Industrial Technology Development Organization (NEDO).