When people talk about the smart city of the future, the conversation often turns to visible infrastructure: transport networks, renewable-energy installations, smart meters, digital services and data platforms.
These are all important, but some of the most powerful opportunities are far less visible. They are already sitting inside our homes, plugged into the wall, and quietly consuming electricity every day.
In many countries, the smart-city conversation is about adding intelligence to an energy system that already works reliably. South Africa does not have that luxury. Our grid remains constrained, electricity tariffs have risen sharply over time, and years of load shedding have shown households what happens when the system cannot keep up with demand.
That pressure has also accelerated change. Solar panels have appeared on rooftops, batteries have moved into garages, and inverters have become familiar household infrastructure. South African homes are already becoming part of a distributed energy system.
The next question is whether we can coordinate these assets more intelligently.
Homes should no longer be passive consumers
Historically, homes have been treated as passive endpoints in the electricity system. Energy flows into a household, a meter records the usage, and the resident receives a bill.
Industrial and commercial customers have received more attention because their energy demand is concentrated and easier to manage. Residential demand is more fragmented. A single household may appear insignificant when viewed in isolation.
But this overlooks the collective impact of millions of homes, particularly during peak-demand periods.
Technology is changing what is possible. Connectivity has become more affordable, intelligent software can coordinate large numbers of devices, and ordinary household appliances can now respond to changing conditions in the energy system.
This means homes can move beyond being passive electricity consumers. They can become active participants in a smarter, more flexible grid.
The shift should be largely invisible to the resident. That is the point.
A smart home should not require people to constantly monitor electricity tariffs, adjust timers or compromise on comfort. The technology should operate quietly in the background, making better decisions while people continue with their daily routines.
A geyser is a battery most South Africans already own
The electric geyser is a useful place to start.
A geyser is effectively a thermal battery. It stores energy as hot water, holds that energy for several hours and gives households flexibility over when electricity is consumed.
Most people do not care exactly when their geyser heats. They care that hot water is available when they turn on the tap.
That gap between the moment electricity is consumed and the moment hot water is needed creates a valuable opportunity. A geyser can heat during the middle of the day when rooftop solar generation is abundant, reduce its consumption during expensive peak periods and respond when the grid is under pressure.
This matters because geysers are among the largest electricity consumers in residential settings, accounting for up to 40% of electricity usage.
One geyser may not change the energy system. Thousands of coordinated geysers can.
What residential communities can teach us about smart cities
Over the past three years, Plentify has worked with Balwin Properties to deploy more than 8,800 intelligent geyser controllers across 13 residential developments.
The technology manages when water is heated by considering factors such as resident needs, electricity tariffs and the availability of solar energy.
The results offer a practical glimpse into the role residential demand management could play in future-ready cities. Across the developments, peak electricity usage was reduced by 46%, short-term demand spikes fell by 36%, and the use of solar energy for water heating increased by 79%.
The peak-demand result is particularly important.
Electricity infrastructure must be designed to cope with the periods when demand is at its highest. Reducing those peaks means existing infrastructure can be used more effectively. It can also reduce the pressure to invest in additional capacity that may only be required for a limited number of hours each year.
The increase in solar utilisation matters for a related reason. If there is nowhere for solar energy to go, panels will not generate. By intelligently heating geysers at times when there is excess solar, each panel yields more energy – accelerating paybacks and enabling electricity to be sold to residents for less.
Put simply: flatten the peak and soak up the sun.
The Virtual Power Plant is already taking shape
This is where the concept of a Virtual Power Plant becomes relevant.
Imagine thousands of homes across South Africa, each with an electric geyser. Individually, each geyser is a relatively small electricity load. But when the appliances are connected and coordinated, they can begin to behave like a single flexible energy asset.
The collective system can absorb solar generation during the day, reduce demand during peak periods and respond more intelligently following power outages. They can work as one cohesive unit to serve the national grid, or target interventions through clusters of geysers on nodes of the distribution network.
There is no new power station. There is no large battery container in the parking lot. The “plant” is the software layer coordinating devices that households already own. From the perspective of an estate, municipality or electricity provider, the combined effect can be significant.
From a resident’s perspective, service delivery has the potential to simultaneously improve. As demonstrated by Project Smart Geyser, hot water can remain consistently available when it is needed while electricity consumed drops by 24%. Of course, this requires choosing the right technology – the same study showed that ripple relays and connected switches are more likely to cause frequent cold showers while offering limited efficiency benefits.
Building cities that respond intelligently
The lesson extends beyond geysers.
As homes become more connected, there is an opportunity to manage other flexible energy loads, including solar and battery systems, pool pumps, heat pumps, heating and cooling systems, and electric-vehicle chargers.
This does not mean batteries and new infrastructure are unnecessary. South Africa will need investment across the energy system. But physical infrastructure should be complemented by intelligence that helps us get more value from the assets already in place.
Property developers can build smarter energy systems into developments from the outset. Municipalities can begin to see residential communities as potential partners in grid resilience. Utilities can consider how coordinated household demand may support a more flexible energy system.
The smartest thing a city can do is recognise that the grid of the future will not be built only from concrete and copper. It will also be shaped by the coordinated intelligence of millions of ordinary devices already plugged in.