Phake Nick wrote:
there's a report from Japanese government back in year 1999 that said the total reduction of energy consumption due to summer time would be about 5 million liter petroleum
Unfortunately I have no easy access to that 1999 report by the Japanese National Council to Think About Global Environment and Daylight-Saving Time, which is archived in the US Library of Congress <https://memory.loc.gov/cgi-bin/query/r?frd/jdc:@field(DOCID+@lit(LRSJ1999-30...>. However, independent scientific research tends to be more reliable than government-sponsored reports for this sort of thing. And as far as I can tell, recent research has not demonstrated significant energy saving for DST in Japan. Admittedly I am hampered by the language barrier as I don’t read Japanese; that being said, I looked for publications in Japanese or English and found only two, cited below: one suggests DST would waste electricity and the other suggests DST would save electricity, and both studies are of course merely simulations, not empirical results. For what it’s worth, the Havranek meta-analysis attempted to assess research study quality, and reported “The difference in implied DST savings between a study from a journal with a zero impact factor and an impact factor of one is 0.96; better journals publish more pessimistic estimates of DST savings.” The two studies I mentioned are consistent with this finding.
Havranek T, Herman D, Irsova Z. Does Daylight Saving Save Electricity? A Meta-Analysis. Energy J. 2018;39(2). https://doi.org/10.5547/01956574.39.2.thav with preprint at https://meta-analysis.cz/dst/dst.pdfyo
That last URL should be: https://meta-analysis.cz/dst/dst.pdf The two studies I mentioned above are: Fong W, Matsumoto H, Lun Y, Kimura R. Energy savings potential of the summer time concept in different regions of Japan from the perspective of household lighting. J Asian Arch Build Engr. 2007;6:371-8. https://doi.org/10.3130/jaabe.6.371 Shimoda Y, Asahi T, Taniguchi A, Mizuno M. Evaluation of city-scale impact of residential energy conservation measures using the detailed end-use simulation model. Energy. 2007;32(9):1617-33. https://doi.org/10.1016/j.energy.2007.01.007