Who this is for
Plant owners and engineers in South Africa deciding how to back up a production line against load shedding and grid failure — and tired of vendors pushing whichever one they happen to sell. This is the neutral decision framework. It pairs with our guides on load-shedding protection and running a line on solar.
The mistake: treating them as alternatives
"Generator or battery?" is the wrong question, because they protect against different things on different timescales. A UPS responds in milliseconds but lasts minutes. A generator lasts days but takes 10–30 seconds to pick up the load. A battery sits in between. Pick one in isolation and you leave a gap; combine them and each covers the other's weakness.
Decision rule: match the technology to the timescale and the load. Milliseconds and controls → UPS. Minutes-to-hours and part of the line → battery. Hours-to-days and large/critical loads → generator. Most lines need two or three of these, layered.
UPS — instant, brief, for the controls
An uninterruptible power supply switches over with effectively no break, so sensitive electronics never see the cut. But its runtime is short (minutes) unless you pay for a large battery bank. Its job on a production line is to keep the controls — PLC, HMI, SCADA, network, key instruments — alive so they hold state and shut down cleanly, and to absorb transients.
- Strength: instant, protects against spikes/dips, cheap for small (controls) loads.
- Weakness: not for running motor loads; short runtime.
- Cost: ZAR 30 000–120 000 for a line's controls.
Battery (BESS) — instant, hours, clean and quiet
A battery energy storage system stores hours of energy and can run real loads through an outage, switching instantly. Paired with solar it also cuts the tariff bill. The catch is cost per stored hour: batteries are expensive, so you size them to the hours and loads you truly need, not the whole plant for a whole day.
- Strength: instant, silent, no fuel, no emissions, doubles as tariff-saving with solar, low maintenance.
- Weakness: expensive per kWh of storage; finite runtime; large loads need large (costly) systems.
- Cost: from ZAR 1.5 million for a meaningful system; scales with kWh.
Generator — delayed, sustained, for long and large loads
A diesel (or gas) generator makes power for as long as it is fuelled, making it the economical choice for long outages and large loads — full-line backup, big thermal demand, extended grid failure. The trade-offs are the switchover delay (covered by UPS/battery), the diesel cost, maintenance, noise, and emissions.
- Strength: sustained runtime, cost-effective for large/long loads, mature and serviceable.
- Weakness: 10–30s switchover (needs UPS/battery to bridge), diesel cost, maintenance, noise.
- Cost: critical-load genset + ATS from ZAR 250 000; full-line into the millions, plus diesel.
Side-by-side
| Dimension | UPS | Battery (BESS) | Generator |
|---|---|---|---|
| Switchover | Instant (ms) | Instant (ms) | Delayed (10–30s) |
| Runtime | Minutes | Hours | As long as fuelled |
| Best load | Controls only | Part / whole line (sized) | Large / critical / whole line |
| Running cost | Negligible | Low (free with solar) | Diesel + maintenance |
| Protects transients | Yes | Via inverter | No (needs protection) |
| Emissions / noise | None | None | Yes |
| Capex per hour of backup | n/a (controls) | High | Low |
| Indicative cost | ZAR 30–120k | ZAR 1.5m+ | ZAR 250k+ |
How they combine — the real-world setups
Most resilient factories run a layered combination, not one box:
- Minimum viable: UPS on controls + safe-shutdown logic. Protects electronics and product; line stops cleanly. Cheapest, and the non-negotiable baseline.
- Common mid-tier: UPS on controls + critical-load generator with ATS. Controls ride through the switchover delay; the generator keeps cold chain / CIP / hygiene-critical loads running.
- Modern hybrid: UPS on controls + solar-plus-battery for daytime production + generator for night, weather, and large loads. Minimises diesel, cuts the tariff bill, and keeps producing through cuts.
The UPS is in every setup because it does a job neither of the others can: protect the controls instantly and bridge the generator's start delay.
Failure mode: buying a big generator with no UPS on the controls — so every cut still crashes the PLC and every restart is dirty, despite the expensive backup. Or buying a battery sized for "the plant" without checking the load profile, and finding it lasts 20 minutes under real load.
How to choose for your line
- Always put the controls on a UPS with safe-shutdown logic. This is the baseline regardless of what else you do.
- List your critical loads — what genuinely cannot stop (cold chain, CIP, hygiene-critical process). Size a generator or battery to these, not the whole plant.
- Profile the rest of the load by hour and shift to decide how much daytime production a battery (with solar) can economically carry. See solar for a production line.
- Decide long-outage cover — a generator is usually the economical answer for extended or large-load resilience.
- Run the numbers against real downtime cost — a total-cost-of-ownership view tells you how much backup is worth buying.
What CISH does
We engineer the line side of resilience: controls UPS and safe-shutdown logic, MCC surge/undervoltage protection, automatic transfer and clean source-switching between grid, battery, and generator, so the production line runs through power events without damage. We coordinate with generator and solar suppliers on the generation side. See Line Upgrade & Digitalisation and Commissioning & Maintenance.
Frequently asked questions
What's the difference between a UPS, a battery, and a generator?
A UPS bridges milliseconds-to-minutes instantly to protect controls. A battery (BESS) stores hours and can run loads through an outage. A generator makes power for as long as it has fuel. Different timescales, different jobs — most setups combine them.
Can a UPS run my whole line?
No — a UPS is sized for the controls to ride through and shut down cleanly, not for the line's motor loads. Running production needs a battery system or a generator.
Generator or battery for load shedding?
Batteries (especially with solar) are clean, instant, and cheap to run but costly per stored hour. Generators are economical for long or large loads but cost diesel and switch with a delay. Many factories use a battery for short cuts and a generator for long ones.
Do I need all three?
Most resilient lines use at least a controls UPS plus one of battery or generator. The UPS is near-universal because it protects the controls and bridges a generator's start delay — jobs the others can't do.
How much does backup power cost?
Controls UPS: ZAR 30 000–120 000. Critical-load generator + ATS: from ZAR 250 000. Meaningful battery / solar-plus-battery: from ZAR 1.5 million. The right spend is matched to your real downtime cost.