In winter, yes, as long as the sun is shining. Solar panels actually produce more when it's cold. At night the panels stop, but your water stays hot, because the geyser tank stores the heat they made during the day. The real limit is cloud. A long cloudy spell cuts production, and the grid has to top the tank up.

That's the short, honest answer. Here's what it looks like in practice.

Cold is good for solar panels

Solar panels turn light into electricity, and they work better when they're cool. A cold, clear winter's day is good for them. A cold wind on a sunny day is even better.

PowerOptimal co-founder Dr. Sean Moolman learnt the difference the hard way. He has had one of the older solar thermal systems, the kind that heats water in pipes on the roof, and in the Western Cape it produced almost nothing in winter. Cold, cloud and wind cut its output fast, and the little heat it does collect is lost again on the way through the pipes to the tank.

Solar PV is the opposite. "Even when it's cloudy and windy, as soon as there's a little bit of sun, it starts ticking," Sean says.

Cloud is the real limit

Cloud cuts the light, and less light means less electricity. A grey morning costs you some solar. A week of heavy cloud costs a lot more, and we won't pretend otherwise.

So the grid stays available. The heating element is the same one the grid has always heated, and how it steps in depends on which Elon you have.

On Elon Smart, the connected version, Top-Up Rules in the app decide when the grid is allowed to heat the water, so you can hold off until you actually need it. The app also shows your savings in rands.

Does a solar geyser work at night?

The panels don't produce anything at night. Your hot water still does its job, because the geyser is a well-insulated tank. The sun heats it during the day, and it keeps that heat for your evening bath and your morning shower.

The tank does lose a little heat overnight through its insulation, the same as any geyser. Engineers call this standing loss, and every geyser has it, solar or not.

What the measurements show

We monitor real homes. The Pretoria East numbers cover a full winter.

A home in Pretoria East got 74% of its water heating from the sun across eight months, including a full winter. That's the honest winter benchmark: even with the cold months in the mix, the sun did about three quarters of the work, and the grid covered the rest.

A home in Centurion reached 99%. One in Roodepoort has held 73% over nine months of monitoring. You can see all four monitored homes here.

The downsides, plainly

Every option has trade-offs. These are ours:

• Cloudy spells mean grid top-ups. Expect some grid use in a wet winter week.

• You need sun on your roof. Heavy shade rules it out.

In return, there's no roof tank or pump to look after, and the panels carry 30-year performance warranties.

Where to start

If winter is the thing holding you back, look at the Pretoria East results first. Then, if your roof gets sun, ask for a quote for your home.