The electricity duck curve is a design-stage problem

If you design buildings for a living, you've probably heard someone mention the duck curve at a conference and nodded along. Fair enough. It sounds like something for Eskom's planners to lose sleep over, not you.

We'd argue it's landed on your desk. Quietly, and probably somewhere between the electrical layout and the DB board schedule.

First, the duck

Picture a graph of how much power the country pulls from the grid over a day. As more solar goes up, the middle of the day sinks, because buildings are running off their own roofs. Then the sun goes down, everyone gets home, kettles and geysers and aircons all go on at once, and demand shoots up.

Squint and it looks like a duck. Fat belly at lunchtime, long neck at night. Somebody in California named it, and it stuck.

The belly is mostly fine. It's the neck that costs money... that steep climb into the evening is the hardest stretch for a grid to keep up with, and the priciest power you can buy.

Ours is hiding on the roof

South Africa's duck has a twist. Most of our solar isn't sitting in big farms, it's on rooftops. Eskom's estimate passed 9 GW in June this year (The Outlier), and rooftop solar on its own is already bigger than the solar running under the government's flagship procurement programmes (Engineering News).

Eskom can't see most of it. From where it sits, demand just goes missing at midday and turns up again at dinner time, hungry. Isabel Fick, General Manager of the National Transmission Company South Africa, has said Eskom has to find an extra 4,000 to 5,000 MW between 16:00 and 19:00, and that behind-the-meter solar makes the job harder (Energize). That's a lot of power to conjure up in three hours.

And the tariff noticed

Pricing has followed the duck. When NERSA approved Eskom's tariff restructure for 2025/26, the evening peak got longer, from two hours to three, and the morning peak got shorter (Eskom). In winter the evening peak runs 17:00 to 20:00. Right now, in the low-demand season, it's 18:00 to 21:00 (Energize).

So a development that runs its geysers, aircon and pool pumps flat out in that window pays peak rates for it. Every month. For as long as the building's standing. Funny how that never makes it into the sales brochure.

Which is why it's your problem, sorry

Moving load out of the evening peak sounds like something you sort out after handover. Mostly, it isn't.

Whether a site can shift its load depends on fairly boring decisions made very early. Are the geysers, aircon and pool pumps on their own circuits, or bundled in with everything else? Is there room in the DB board for the devices that do the switching? Can they talk to anything once they're in? How does the hot water meet SANS 10400-XA (which you're declaring at plan submission anyway)?

Get that right on the drawings and shifting load later is a few settings in an app. Get it wrong and someone has to open DB boards in occupied units, rewire circuits and negotiate access with residents who'd rather you didn't. Most sites never bother. The duck keeps its neck, and the bill stays where it is.

This is the bit we keep banging on about. Gecko Switch measures and controls each high-draw circuit. Geyser Gecko heats water from solar first and only leans on the grid when it has to. Gecko Hub runs the rules across the whole site. They all work a lot better on the drawings than on the snag list.

What we can honestly show you

We haven't got a before-and-after duck curve from one of our sites yet, and we're not going to dress something up as one. What we do have is load control running at scale. At Fleurhof, with Tri-Star Construction, 260 Geyser Gecko units are live, 600 more are on the way, and projected annual savings sit at R1.08M. Across Gecko Hub, over 2,000 geysers on more than 150 sites are connected and managed today.

Geysers, in our experience, are some of the easiest loads to move without anyone noticing. Nobody checks what time their water heated, as long as the shower's hot. Which makes them a pretty good place to start chipping away at the neck.

Over to you

We'd genuinely like to know. On the projects you're working on right now, whose job is the evening peak? Is it in the brief? Does the engineer quietly sort it out? Or is it one of those things everybody assumes somebody else has covered?

Tell us in the comments, we read them all. And if the honest answer is "nobody's", talk to us before the drawings are final. www.darkline.co.za

Sources

• Big increase in Gauteng rooftop solar pushes South Africa's total past 9GW, The Outlier, July 2026

• Capacity of rooftop solar installed in South Africa has passed 8 GW mark, Engineering News, June 2026

• South Africa's growing renewable energy capacity fuels grid balancing concerns, Energize

• Connect 2025/26: FY2026 Eskom standard tariffs, Eskom

• NERSA approves Eskom tariff restructure, Energize