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気候変動を考慮した日本の水力発電ポテンシャル評価 Potential of hydropower development as the renewable enegy in Japan and evaluation of long term effects of climate change

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気候変動を考慮した日本の水力発電ポテンシャル評価

Assessment of hydropower potential in Japan with consideration of climate change

○角 哲也・桑田光明・石田裕哉・丹羽尚人・小島裕之・井上素行・佐藤嘉展・竹門康弘・Sameh Kantoush ○Tetsuya SUMI, Mitsuaki KUWATA, Hiroya ISHIDA, Naoto NIWA,

Motoyuki INOUE, Yoshinobu SATO, Yasuhiro TAKEMON, Sameh KANTOUSH In the big trend of shifting energy sources from nuclear power and thermal generation to renewable energy, hydropower has been paid attention in Japan. In this study, targeting existing 93 multipurpose dams belong to MLIT and JWA, it is shown how much potential it generates in Japan only by changing the maximum water use and how it changes by the effect of the climate change.

1. Introduction

Hydropower generation is pure domestic energy and operated at more than 500 existing dams in Japan. Making use of them in better way1, more electricity can be obtained, and it is

defined as “potential” in this study. 2. Methodology

Draw a flow duration curve for each dam by using past 10 years outflow data2(Q) and

calculate electricity generation by using the equation P=9.8QHη 3,4. Assume the outflow

more than the maximum usage water (Qmax) is

equal to the Qmax, and ignore outflow less than

20% of Qmax. The hydropower production “P”

become the largest one at a certain Qopt value.

The difference between Popt and current P is

the current potential of the hydropower at the dam. Future and current flow data for 25 years is calculated by substituting climate data which is given by MRI-AGCM 3.2S into Hydro-Beam. In this study, the worst scenario RCP8.5 is applied to check the change clearly.

1 By changing maximum discharge. 2 It can be less than 10 years. 3 H:=effective head difference×2/3 4 η: coefficient of efficiency =0.82

After making average flow duration curve both for current/future climates, climate factors can be obtained by dividing 365 elements of future duration curve by current ones. Calculate P’ for the future duration curve, which is obtained by multiplying the climate factor to the actual current flow duration curve, with the same Qmax setting and get P’opt at certain Q’opt value.

Fig.1 Comparison of current/future flow duration curves at the Tamagawa dam

Fig. 2 Current/future flow ratio at the Tamagawa dam 0 100 200 300 1 24 47 70 93 116 139 162 185 208 231 254 277 300 323 346 Flow (m 3/s ) Dairy Flow Rank Current Outflow Future Outflow 0 0.5 1 1.5 2 1 24 47 70 93 116 139 162 185 208 231 254 277 300 323 346 ratio Dairy Flow Rank

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3. Results

Fig.1 shows comparison of current/future flow duration curves at the Tamagawa dam. Fig. 1 can be converted to current/future flow ratio as shown in Fig.2. In this case, higher flow rate larger than 10 will increase but lower than 280 will decrease drastically. Fig.3 shows difference of annual hydropower production by changing Qmax. Since current value is 40 m3/s, around

2,000MWh can be increased from Qmax = 40 to

55-60 m3/s.

Fig. 3 Difference of annual hydropower production based on the maximum usage water

Based on changing Qmax, total calculated

hydropower potential of 92 dams can be calculated as follows:

① Current: P=4,104,010MWh

② Current optimized: Popt=4,415,461MWh

③ Future: P’=3,633,497MWh

④ Future optimized: P’opt=3,865,488MWh

⑤ Popt-P (MWh): Current potential by

changing the maximum discharge (Qmax)

⑥ P’-P (MWh): Current/Future change without optimization

⑦ P’opt-P (MWh): Current/Future change with

optimization 4. Conclusion

1) Hydropower generation at existing dams still have huge potential to develop in Japan. 2) Proper Qmax can maximize the potential.

3) Regional trend of the effect of climate change should be taken into consideration for future scheme of hydropower generation.

5Fig. 4 Total calculated hydropower potential of 93 dams based on Popt-P (left), P’-P (middle) and

P’opt-P (right).

Fig. 2 Current/future flow ratio at the  Tamagawa dam 01002003001244770 93 116 139 162 185 208 231 254 277 300 323 346Flow(m3/s)Dairy Flow RankCurrent OutflowFuture Outflow00.511.52124477093116139162185208231254277300323 346ratioDairy Flow Rank
Fig. 3 Difference of annual hydropower  production based on the maximum usage water

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