Peak electricity usage in the summer is between 5pm and 9pm, that is when they tell you to conserve power. If the sun went down one hour earlier in the summer it would be one hour cooler when people get home from work and run their air conditioner. It would be cooler when people go to bed even if they only had a fan and they could sleep better. Air conditioners are probably the highest power users, so wouldn't we save power if it got cooler one hour earlier in the evening...