Someone has quoted you a battery. The savings number at the bottom looks good.
It’s probably wrong.
Not by a little. On a typical quote, by about R47,000 a year.
You can check it yourself in five minutes. You don’t need an engineer. You need one line off your electricity bill.
The short version
- A peak shaving battery earns money two different ways.
- Which way works depends on your tariff. Most quotes assume the wrong one.
- There’s also a charge that looks like it will fall and never does.
- Counting it adds about R3,913 a month of savings that will never appear.
- Three questions tell you which kind of battery you’re actually being sold.
First, what a battery does not do
It doesn’t make electricity. It doesn’t reduce how much you use. It won’t fix a bad tariff choice.
All a battery does is change when you take power from the grid.
That’s it. Everything else follows from that one idea.
So the only question that matters is simple. On your bill, what is timing actually worth?
Your bill charges you two different ways
Every business bill has two kinds of charge. They behave nothing alike.
The first is the demand charge. It’s priced in rand per kVA, per month. It’s based on the single biggest moment of your month — not your total use.
Think of a dam wall. The wall has to be built for the flood, not the average flow. You pay for the wall.
The second is the energy charge. It’s priced in cents per kWh. On some tariffs the price changes by the hour.
Think of petrol. Same fuel, different price depending on when you fill up. If you could fill up cheap and drive expensive, you would.
A battery can attack either one. But not equally, and not on every tariff.
Way one: cutting the demand charge
This works best on a tariff called Nightsave Urban. Many medium-sized industrial sites are on it.
Here’s what happens to the demand charge when the seasons change:
Nightsave Urban — the charge a battery can move
Winter (Jun–Aug): R332.91 + R26.29 = R359.20 per kVA, per month
Summer (Sep–May): R77.88 + R26.29 = R104.17 per kVA, per month
Rates exclude VAT. Eskom Schedule of Standard Prices, 1 April 2026.
Cut your peak by 100 kVA and you save R35,920 in a winter month. The same 100 kVA saves R10,417 in a summer month.
Over a year that’s (3 × R35,920) + (9 × R10,417) = R201,513.
Notice something. More than half that money is earned in three months.
A quote that spreads the saving evenly across the year is telling you a comfortable story. Your bill won’t match it.
Way two: buying cheap, using expensive
This works best on Megaflex, a time-of-use tariff.
In winter, a unit of electricity costs 720.19c in the peak hours. Overnight the same unit costs 120.03c.
That gap is 600.16c. About R6 for every kilowatt-hour you move out of the peak.
So you charge the battery at night. You discharge it during the peak blocks. You buy cheap and use expensive.
Here’s a worked month. Assume the battery delivers 400 kWh into each of the two daily peak blocks, on 22 weekdays.
- Avoided in the morning block: 400 × 720.19c = R2,880.76
- Cost to charge overnight: 444 kWh × 120.03c = R533.47
- Net for the morning: R2,347
- Evening block, refilled mid-day at the standard rate: net R2,081
- Per weekday: R4,428. Per winter month: R97,412
In summer the peak rate drops to 298.89c and the same battery earns R24,437 a month.
Full year: (3 × R97,412) + (9 × R24,437) = R512,169.
Those numbers rest on assumptions we should name. We assume 90% round-trip efficiency, so every 1 kWh delivered costs 1.11 kWh bought. We assume the battery is available all 22 weekdays. Treat the figure as an upper bound.
Now the part that catches people
Look at a bill for a Nightsave Urban site. You’ll see three charges sitting near each other:
- Energy demand charge — R332.91 per kVA
- Network demand charge — R26.29 per kVA
- Network capacity charge — R39.13 per kVA
They look like the same kind of thing. They are not.
The first two are based on your peak this month. Shave the peak and they fall.
The third one is based on your capacity for the whole year. Shaving one month’s peak does not move it.
Now go and look at your quote.
If the savings model adds all three together, it’s claiming R398.33 per kVA. The honest number is R359.20.
The difference is R39.13 per kVA. On a 100 kVA shave that’s R3,913 a month. Call it R47,000 a year of savings that will never arrive.
That’s not a rounding error. It’s the difference between a project that works and one that doesn’t.
Three questions to ask before you sign
1. Is my energy rate time-of-use?
Megaflex is. Nightsave Urban isn’t — it’s 177.20c in winter and 170.21c in summer, flat all day. There’s nothing to arbitrage.
If someone shows you peak-versus-off-peak energy savings on a Nightsave site, they’re describing a tariff you’re not on.
2. Which season did you model?
R332.91 behaves nothing like R77.88. A model that averages the two flatters itself in summer and disappoints in winter. Ask for winter and summer separately.
3. Am I Eskom-direct or municipal?
Megaflex, Nightsave Urban and Ruraflex are Eskom-direct tariffs. They went up 8.76% on 1 April.
If your bill comes from Johannesburg, Cape Town or eThekwini, you’re on that municipality’s tariff instead. Those moved on 1 July. eThekwini went up 9%.
Different structure. Different arithmetic. Ask which one your quote used.
When a peak shaving battery is wrong for you
If your connection is 100 kVA or smaller, you’re likely on Businessrate.
Businessrate has no rand-per-kVA demand charge at all. Its network demand charge is 15.81c per kWh — an energy charge.
There is nothing for a peak shaving battery to cut. If someone is pitching you one, they haven’t read your tariff.
Farmers and agri-processors, take note too. Ruraflex has the widest peak gap in the country at 610.82c. But its network demand charge of 45.56c per kWh applies in every period, all day. Moving load doesn’t touch it.
Why we won’t give you a payback number
You’ll notice there’s no “pays back in 18 months” line here.
That’s on purpose.
The savings side is checkable. Every rate above comes from Eskom’s published schedule and you can look it up.
The cost side isn’t. Battery prices move with the rand and with cell prices. Your switchgear and civils are specific to your yard. A number we publish in July is one we’d have to defend in October, on a site we’ve never seen.
So here’s the method instead. Take twelve months of bills. Work out which charges respond to a battery on your tariff. Model winter and summer apart. Leave the capacity charge alone. Then put a price against it.
Do it in that order and the answer will hold up.
Next April is the number to watch
One more thing worth knowing.
NERSA made a R54.7 billion error working out what Eskom is owed. They’re recovering it over three years. This year’s share is R12 billion. Next year’s is R23 billion.
Without it, this year’s increases would have been 5.36% and 6.19%. They were 8.76% and 9.01%.
The instalment nearly doubles next year.
So a payback modelled on today’s rates is the cautious one, not the hopeful one. That’s the opposite of how most energy quotes are built.
There are about five weeks of winter rates left. That matters more than it sounds.
Right now your meter is recording a battery working at full stretch. Model it in October and everything looks cheap, and the case looks weak. Use the data while the winter peaks are still on it.
Frequently asked questions
What is peak shaving?
It’s using a battery to hold your site below a set level of demand. Your meter records the biggest half hour of the month and charges you for it. Keep that number down and the charge comes down with it.
What’s the difference between peak shaving and energy arbitrage?
Peak shaving lowers the demand figure your rand-per-kVA charges are based on. Arbitrage moves units of electricity from an expensive hour to a cheap one. They’re different charges on your bill, and a battery built for one isn’t automatically good at the other.
Which Eskom tariff suits a peak shaving battery best?
Nightsave Urban, for cutting demand charges. Its winter demand charge is R332.91 per kVA against R77.88 in summer. For arbitrage it’s Megaflex, where the winter peak-to-off-peak gap is 600.16c per kWh.
Will a battery reduce my network capacity charge?
No. That charge is based on your annual capacity, not your monthly peak. It’s R39.13 per kVA and it stays. The network demand charge of R26.29 does fall. Check which one your quote counted.
Should I wait for the April tariffs before deciding?
Waiting doesn’t make it cheaper. You’d absorb another winter at today’s rates and then face a bigger step-up. Modelling now uses the more conservative numbers.
How do I check a quote myself?
Ask the supplier to name the charge codes they expect to change, and why. Then find those lines on your bill. If they can’t name them, they haven’t read your bill. Our savings calculator is a useful sanity check before a meeting.
Send us the bill, not the brochure
Send twelve months of bills and your meter data. We’ll tell you which of the two mechanisms your site can actually earn.
Charge codes named. Winter and summer modelled apart. Capacity charge left where it is.
If a battery doesn’t pay on your tariff, we’ll say so, and tell you what does.
Check your quote against your bill
Send us the quote and twelve months of bills. We’ll show you which charges actually move, and which ones were counted twice. No pitch until the numbers say there’s something worth doing.
Tariff figures are from Eskom’s 2026/27 Schedule of Standard Prices, effective 1 April 2026: non-local-authority supply, transmission zone under 300 km, 500V–66kV, excluding VAT. Your rate band may differ. Efficiency and throughput figures are Terawatt modelling assumptions. Further reading: how winter tariffs work, 1MWh versus 500kWh sizing, and our tariff forecast.
