Daylight Saving - Does it really save energy?

For a more thorough analysis of this subject, there are some studies currently underway and other useful info around the web, but I'm not sure if they make this point well enough. Try this link or Google "daylight saving energy" for more info.

Based on some of the information about peak electrical demand in California (see my other posts about some data that came out of UC-Davis) I'm not convinced that daylight saving actually saves energy as much as it used to. When previous studies were done, central air conditioning was not nearly as common as it is today (many of the studies date back to the 1970s). I believe that central air is a large contributor to the peak demand when people return home from work in the afternoon, even more so when they use a programmable thermostat to set the temperature higher while they are at work. Without a programmable thermostat, the overall energy usage is much higher, because the A/C unit runs more during the day. However, a programmable thermostat changes the setpoint around the time you get home, effectively turning on the A/C for an extended period right at that time, increasing demand a lot, even though the overall usage throughout the day is lower.

Daylight saving effectively gets everyone home from work one hour earlier (as far as where the sun is in the sky) and therefore closer to the hottest part of the day. At this point, more energy is needed to cool the home to a comfortable temperature, while if people returned home an hour later (without daylight saving) the house wouldn't be as hot because the sun is lower in the sky. Of course the evening lighting load will be greater, because the sun goes down, but certainly that's a smaller load (overall) than the A/C unit.

This is an idea that may sound completely backward, but consider it for a moment. Assume for a moment that it is true that programmable thermostats cause most A/C units in California to turn on at about the same time each summer afternoon (within an hour or two of each other) and then they run for an extended period of time to cool the buildings. Now what if, instead of using demand response controls to disable some of those A/C units to reduce peak demand, you instead use a demand response control to turn some of those A/C units on earlier, cooling some of the homes earlier than others, so they won't need it later when all the other units kick on. It's the exact opposite of a typical demand response system, but in terms of reducing peak demand, it may be exactly the right thing to do.

I really think that new studies will show that daylight saving is no longer helping our energy usage (especially on the basis of peak demand) as much as it used to (if at all).