Load Shifting

Your panels do most of their work between about ten in the morning and three in the afternoon. Most Joburg households use most of their electricity before eight and after five. The system sits on the roof making power while the house is empty, then the house comes home and buys power from City Power.

Load shifting closes that gap. You move the loads that don't care what time they run, mainly the geyser, the pool pump and the washing, into the hours when the sun is paying for them. For most systems it needs no new equipment, and the part that does is cheap.

This guide covers which loads are worth moving, what it saves in rand on a City Power tariff, and the limits to watch so you don't trip the inverter or end up with a cold shower.

Why It Matters More Now

Most systems in northern Johannesburg went in during 2022 and 2023 to get through load shedding. Their job was to keep the lights on. With load shedding largely gone, the job is cutting the bill, and a system that cuts the bill is one whose output gets used in the house.

On City Power's standard residential tariffs, prepaid and postpaid, a unit costs the same at one in the afternoon as at seven in the evening. So this isn't about finding cheap hours on the tariff. It's about using the free hours on your roof.

The arithmetic is simple. At 2026/27 rates, a unit bought on Prepaid High costs about R3.34 including VAT. A unit your panels produce and your house uses saves you that R3.34. A unit your panels produce and send to the grid earns, at best, City Power's embedded generator rate of about R1.43 including VAT, and only if export credits are being paid on your account. On a zero-export system, which is most of them, a unit the house doesn't use at midday is simply never produced. The inverter turns the panels down and the power is lost.

Where Your Midday Solar Goes Now

On a sunny day, once the house's daytime load is covered, the rest of your panels' output has three places to go:

• Into the battery. Useful, until the battery is full. On many systems that happens before noon.
• Out to the grid. Worth less than half what you pay for a unit, and on many Joburg accounts worth nothing yet.
• Nowhere. The inverter throttles the panels back. This is the most common outcome, and the one nobody notices, because nothing on the bill shows power that was never made.

Load shifting moves that third bucket into the house.

Check You Have Surplus to Use

Before moving anything, check whether your system is wasting power at midday. Open your inverter app on a clear day and look at three things:

• Battery state of charge. If it reaches 100% before lunchtime and sits there, you have surplus.
• The shape of the production curve. A smooth hill that rises and falls with the sun means the panels are working freely. A curve with a flat top, or one that drops suddenly when the battery fills, usually means the inverter is holding the panels back.
• Exported units, if the app shows them. Anything exported is power you could have used at full value.

If the battery never fills and the curve is a clean hill, your system is already using what it makes, and shifting loads will mostly move battery use around rather than save money. If you're not sure what you're looking at, our guide to checking whether your solar system is underperforming walks through the app screens.

The Loads Worth Moving

The geyser. Usually the biggest single load in the house, and the easiest to move. A family geyser commonly uses 4 to 8 units a day. Heated between about 10:00 and 15:00, an insulated geyser holds most of that heat into the evening. A geyser timer or a smart geyser controller does the switching. Two cautions: installing either on the geyser circuit is electrical work that needs a registered electrician and a Certificate of Compliance, and the water should still reach 60°C regularly for hygiene, so don't set the thermostat lower to stretch the solar further.

The pool pump. Often 4 to 6 units a day in summer. Most pumps already have a timer; many are set to run early in the morning or in the evening, which is exactly when the panels are idle. Moving the run hours into the middle of the day is a two-minute job.

Washing machine, dishwasher and tumble dryer. A load of washing or dishes uses about a unit, most of it heating water; a tumble dryer uses two to four. Use the delay-start setting, or run them before you leave in the morning with a delayed start set for late morning.

An electric car, if you have one. A car plugged in at home over a weekend or on a work-from-home day can absorb more surplus than everything above put together. Charge it in the middle of the day rather than overnight.

Some loads aren't worth the effort: the fridge, lights, TV, Wi-Fi and cooking run when they run. Leave them alone.

What It Saves: Worked Through for a Northern Joburg House

Take a four-person house in Blairgowrie on Prepaid High, with a system that fills its battery by late morning and throttles its panels most sunny afternoons.

• Geyser moved to midday: 5 units a day, about 150 units a month. At R3.34 a unit, around R500 a month.
• Pool pump moved from early morning and evening to midday: 1.5 units a day, about 45 units a month. Around R150 a month.

That's roughly R650 a month, or close to R7,800 a year, from a geyser timer and two changed pump settings. Washing and dishes on delay start add a little more.

Two honest caveats. The saving only counts on days the panels have surplus, so it is larger in summer than in winter and smaller in a rainy week. And it depends on how your system is set up today. If your battery is already cycling fully every day, some of this is money you're already saving, just at a different time. The only way to know for your house is to look at your own data.

The Limits to Watch

Your inverter's size. A geyser element draws about 3 kW. Add a kettle, an oven or a dryer at the same moment and a 5 kW inverter can run out of headroom. Depending on how it's set up, it either pulls the difference from the grid or, on some systems during an outage, shuts down. Stagger the big loads rather than stacking them all at 11:00.

Cloudy days. A timer doesn't know the weather. On a grey day the geyser heats from the grid or the battery instead. That's fine, but it means a timer on its own won't give you the full saving. Smart controllers that watch the solar output handle this better.

Winter. The solar window is shorter and weaker from May to August. Plan the timer settings for summer and winter separately, or review them when the clocks of the season change.

The battery. Shifting loads into daylight means the battery reaches the evening fuller and does less work at night. That's usually good for it. Our guide to battery lifespan and replacement costs explains why fewer deep cycles matter.

What Load Shifting Can't Do

It can't touch your fixed monthly charge. If registering your system moved you from prepaid to a postpaid account, those fixed charges are the same whatever time you boil the kettle. Our guide to SSEG registration in Johannesburg covers what that costs.

It also won't fix a fault. If the panels are dirty, a string is down or the battery is failing, moving the geyser won't show up on the bill. And it can be undone by the inverter's own settings: a system set to hold the battery at 100% for load shedding, or to charge it from the grid overnight, works against everything above.

Where the Inverter Settings Come In

Load shifting is the part you control with a timer and the settings on your appliances. The other half is how the inverter decides what to do with the power: whether it charges the battery first or feeds the house, how low it lets the battery go, and whether it ever buys from the grid to top the battery up. Many systems still carry the settings they were given in 2023, when the only question was riding out the next outage.

Getting both halves right together is what our tariff re-optimisation does. Nothing is broken. It's a system set up for a problem that has changed.

How We Help

We work with homeowners across Blairgowrie, Linden, Randburg, Ferndale, Northcliff, Fairland, Emmarentia, Greenside, Parkhurst and the suburbs around them. A re-optimisation starts with your system's own history from the monitoring app, hour by hour, read against the tariff on your bill. From that we tell you which loads to move, what timer settings to use for summer and winter, and which inverter settings to change, with a before-and-after once the new setup has had a month to run.

If a geyser timer or controller needs installing, that's done by a registered electrical contractor you contract directly, who issues the Certificate of Compliance under their own registration.

Book a Re-optimisation

Find out how much of your solar is going to waste before the summer sun makes the most of it. Have your inverter app login handy if you have one. Book a re-optimisation.