I’m no party animal, but I attended four social events this weekend. My takeaway from a dozen or so conversations is that South Africans are seriously looking for ways to save energy. People were telling me about their new efficient fridges and gas stoves. A property developer explained how Standard Bank is saving thousands of tons of carbon dioxide by generating its own power from gas in Rosebank.
One question came up at two different parties: Does it save energy to switch off the geyser for part of the day? This is a query I’ve heard so often that one could be forgiven for thinking that it was the Number 1 issue in energy efficiency. People take passionate stands on either side of the debate. One person told me that he’s saving hundreds of rands each month by switching the geyser on and off. Another said she had heard that it uses more electricity to heat the water back up than to keep it hot.
Here’s the disappointing answer to the most-discussed issue in home energy conservation:
It’s no big deal.
You can save a little electricity with daily switching, but you could save a lot more by lowering the temperature of your geyser thermostat, buying low-flow shower heads, or insulating the tank—not to mention the even larger savings from installing a solar water heater or heat pump.
If your geyser were perfectly insulated, switching would save nothing. Because it is not, the element will reheat the water from time to time even if no one is using hot water. If the element is off, however, the tank loses heat more slowly as the water gradually cools. All of that water has to be reheated when you turn the geyser back on, but because overall tank losses were lower than if the tank had been kept hot, it requires a little less energy than repeatedly heating the water over that same period of time.
What about the guy who said he was saving hundreds of rands? If your geyser has been off for several hours and you switch it back on, any shower you take or dish you wash before the water has been fully re-heated is saving you significant energy, because switching off and on is effectively lowering your thermostat setting. These savings can be large, but you could have saved that same energy more consistently and easily by simply lowering the thermostat on the geyser. Unconvinced? You can read more here.
Electrical engineer TC Venter has a long, technical article on the subject of options for saving electricity with hot water heaters in Watt Now and comes to this conclusion: “short switch-off periods (less than a day) do not really contribute meaningfully to energy saving.” But Venter did bring up one exception to this rule.
There is one special situation, if one thinks it through carefully, in which a timer can be used daily to eliminate practically all standby power. If the occupant of the flat is single and a creature of habit, who only needs hot water to bath or shower at 07:00 each day, a small (50L) geyser could be run like an electric kettle: an electronic timer could be set to switch the geyser on for one hour at 06:00 every morning, to ensure hot water at 07:00, but not to reheat the geyser after its hot water has been used. The geyser remains cold until the next morning at 06:00, thus no standby power is required.
Of course switching off the geyser when you leave home on a trip can add up to real savings. Switching off during Eskom’s peak hours of 5 to 9 pm is also good for the country, if not for your utility bill. And timers are essential with solar water heaters to avoid using electricity to heat up the tank after morning showers, just before the sun has a chance to do its work. Finally, if you really want to switch your old-fashioned electric geyser on and off every day during idle hours, go right ahead. Just don’t imagine that your hot-water electricity consumption is solved.