https://www1.eere.energy.gov/ba/pba/pdfs/epact_sec_110_edst_report_to_congress_2008.pdf
2. Key Findings: Changes in National Energy Consumption
Overall National Energy Consumption Findings
Using both heuristic2 and statistical analysis methods for measuring the national pattern of electricity changes, the study found:
• For the heuristic analysis, total savings of electricity during the four weeks of EDST time in 2007 was 1.3 TWh and the total primary energy saved associated with the changes inelectricity consumption was 17 TBtu.
• For the statistical analysis, total savings of electricity during the four weeks of EDST in 2007 was 1.2 TWh. This also corresponds to a total primary energy savings of 17 TBtu.The statistical variation on this result is ±40 percent (at a 95 percent level of confidence).
The electricity savings are small compared to the national total for the year, representing about 0.03 percent of the total national electricity consumption of 3,900 TWh in 2007.3 On a daily basis, the total electricity savings due to EDST was 0.46 to 0.48 percent per each day of EDST.
Electricity savings generally occurred over a period of three to five hours in the evening, offset slightly by small increases in energy consumption in several morning hours—typically the hours ending at 7:00 a.m. and 8:00 a.m. in the morning, and ending 5:00 p.m. through 9:00 p.m. in the evening. On a daily percentage basis, electricity savings were slightly greater during the March(spring) extension of DST (0.50 percent) than the November (fall) extension (0.38 percent).
Regionally, areas of the southern United States exhibited smaller impacts of EDST compared to areas of the North. The study found:
• Based on the heuristic analysis, electricity savings in the South as a percent per day were the same as in the North regions, 0.48 percent.
• Based on the statistical analysis, the average daily percent savings in electricity consumption for the North were 0.51 percent, while in the South the savings were 0.42percent.There is insufficient statistical evidence that the EDST period has had any measurable impact on motor gasoline consumption for passenger vehicles or traffic volume in 2007.