South Africans who want to save money on monthly energy spend without significant investments in self-generation must focus on what is often the biggest power user in local homes: water heating.
South Africans who want to save money on their monthly energy bills can significantly reduce costs by installing a smart geyser controller.
Several studies have shown that conventional electric geysers are the single largest consumers of household electricity in South Africa.
These devices typically come with a 3kW element that takes about two and a half to three hours to heat 150 litres of water from a cool 15℃ to a “standard hot” of 65℃.
A 10-minute shower with a low-flow showerhead uses about 60-80 litres of water. Therefore, one heating session would only be sufficient for around two people’s hot water needs.
The power consumed would be roughly 7.5kWh to 9kWh per day, costing R26.70 to R32.04 on Eskom’s Homepower 4 tariff, the most common plan for the power utility’s residential customers.
Over a month, the usage would reach 225kWh to 270kWh, costing R801 to R961. The average Eskom Homepower 4 customer consumes roughly 656kWh per month.
That means a geyser accounts for between 34% to 41% of the average Homepower 4 user’s home’s electricity demand.
One common device that many a salesman claimed could cut down this usage is a geyser timer. However, the claimed savings using such devices are debatable.
Modern geysers are well-insulated and only lose about 1℃ to 2℃ of heat per hour. Reheating a cold geyser back to its target temperature often requires as much power as maintaining the warm water.
In addition, turning off a geyser for long periods to let water rest within the 20℃ to 45℃ range creates the ideal breeding ground for harmful Legionella bacteria.
In more recent years, more advanced smart geyser controllers have been presented as the better solution, with data to back it up in some cases.
By shifting from purely time-based toggling to live temperature and consumption monitoring, they can eliminate unnecessary standing loss, avoid bacterial growth, and protect plumbing hardware.
These devices use additional sensors and machine learning to adapt heating sessions and lengths based on an individual household’s unique water usage habits.
They also feature additional sensory capabilities that enable them to detect leaks, dry burns, and element failures. This lets them cut power to the geyser and prevent more expensive damage.
The table below summarises some of the differences between conventional geyser timers and smart geyser controllers.
Conventional geyser timerSmart geyser controllerTemperature sensingNoneProbe to track exact water temperatureControl and flexibilityFixed clock switchesWi-Fi app access, custom triggers, and dynamic schedulesGrid power outagesClock desynchronises without batteryAuto-resyncs and adjusts to power availabilitySolar and tariff integrationStatic heating windowsDirects excess solar PV power to water and targets off-peak ratesDamage preventionNoDetects leaks, dry burns, and element failure
One prominent example of a smart geyser controller in South Africa is Plentify’s HotBot, which claims to save most users between 15% and 20% on their water heating, with some saving up to 30%.
“This is about double the savings you can expect with a simple timer or by manually switching your geyser at the distribution board,” the company said.
“Actual savings depend on many factors — most notably how well insulated your hot water system is, and how much hot water you use relative to your tank size.”
The company asserts the device is suitable for households that use a geyser with an electric or thermosyphon solar thermal element, which spend on average R1,000 per month on electricity.
The HotBot costs R849 once-off, and users must also pay a R149 subscription fee for access to its intelligent cost-reduction capabilities.
To determine whether the HotBot would make sense for your household, you must first ascertain how much you spend on water heating per month.
Some smaller households might not see much benefit or need to run the system for an extended period to recover the initial upfront cost.
Savings are not guaranteed and depend heavily on individual consumption habits and the tariff the customer uses.
With Plentify’s 15% to 30% savings on water heating bills, Homepower customers would save between R120.15 and R288.42 per month.
The HotBot can significantly increase savings if a customer is on a time-of-use tariff, where certain periods have much lower rates, making it ideal for running the geyser at a lower cost.
