If you live on the Highveld, you know the rhythm of winter. Mornings are icy, evenings demand a blanket and a warm fireplace, and somewhere in between the sun pours down with that high-altitude intensity we take for granted.
Now, with Eskom’s Homeflex time-of-use tariff rolling out to direct Eskom households, compulsory for those with installed solar, that daily rhythm has a price tag — and a growing opportunity for those willing to think differently about heat and energy storage.
Eskom’s Homeflex tariff ramps electricity costs during winter peak hours — from 6 to 8am and again from 5 to 8 pm — to more than six times the off-peak rate. It’s a strong price signal: shift your usage, or pay through the nose for the privilege of staying warm at the same time as everyone else.
Many households already responded by installing solar and batteries, but batteries are mostly tasked with keeping essential loads running — lights, routers, security systems, fridges. Heating circuits, including space heating and geysers, are typically left out because they’re just too demanding. The alternative is very expensive electricity, LPG water and space heaters, or closed combustion wood stoves — but what if you live in a complex or apartment where that isn't possible? Or if you have more rooms that require heating?
This challenge — high demand in the early morning and evening, and limited heating options in communal or constrained settings — is especially relevant for residential complexes and estates. These environments typically see synchronized energy use as residents get ready for work or school and return home in the evening.
Crucially, many of these developments have large, underutilised roof or parking areas that can support extensive solar PV installations.
By shifting energy use for heating into the middle of the day or overnight, the solar system size can be increased and its output better utilised — maximising both self-consumption and savings for the community.
What’s ironic is that most residential battery systems are already fully charged by midmorning in winter. With limited discharge capacity, they often sit idle through the sunniest hours of the day. That’s when an opportunity opens up: using your excess solar generation to charge thermal storage for later use.
Energy storage heaters, long used in the UK to take advantage of night tariffs, could be a perfect fit for the South African winter Homeflex environment. These are not complex systems — just heavy electric heaters filled with ceramic bricks that soak up heat when power is cheap or abundant, and release it slowly later in the day. A well-insulated model can be charged overnight using off-peak grid electricity, and topped up again during the day using solar PV that would otherwise be curtailed or wasted.
We ran the numbers on a typical Highveld winter day. Charging a storage heater between 8pm and 6am at off-peak rates costs just a few rands. With the addition of free solar charging from 11am to 3pm, the system easily covers the morning and evening heating needs — all without drawing a single watt from the grid during peak hours.
Even when you factor in the current capital cost — R10,000 for an imported system – if amortised over twenty years, thermal storage remains dramatically cheaper than any comparable electric space heating solution. These heaters are typically 60–80% efficient, but that modest energy loss is more than offset by the dramatic price gap between off-peak and peak electricity. When electricity costs six times more during peak hours, even a 70% efficient system can deliver major savings.
It’s also worth noting that thermal storage can work hand-in-hand with a geyser controller. These smart devices already help households shift hot water heating to solar-rich or off-peak periods. Together with a storage heater, they allow you to align both your space heating and water heating with solar availability, creating a home that’s warm, efficient, and cost-effective.
Strikingly, these thermal storage heaters are not yet widely available in South Africa. Despite a small number of imports recorded in recent years, they remain virtually unknown in the local residential heating market. This presents a clear opportunity: with the right manufacturing and distribution effort, South African suppliers could introduce a product that directly addresses a growing need. In a country with abundant solar energy and punishing winter peak tariffs, thermal storage heaters could become the missing link in truly affordable, sustainable home energy — particularly for complex and estate living where centralised solutions could serve many households at once.
The conclusion is simple: batteries may power your essentials, but your heat should come from the sun — either directly, or by storing its warmth in tank of water and box of bricks. In a country blessed with solar and cursed with winter tariffs, thermal storage could be one of the smartest moves a household can make.
