IPS, generator or solar backup: the real cost per unit
Load shedding forces a choice between three backup options. We compare the per-unit cost of each, the hidden battery and fuel maths, and which suits a flat, a shop and a small factory.
Backup power is usually bought in a hurry, during a bad week of load shedding, on the advice of whoever is nearest. That is how households end up with an IPS too small for their real load, or a generator that costs more per hour to run than the business it protects earns. The useful way to compare the three options is not by sticker price but by cost per unit of backup electricity delivered — because that is the number that keeps charging you long after the purchase is forgotten.
The three options side by side
| Option | Upfront | Running cost | Best suited to | Real limits |
|---|---|---|---|---|
| IPS / inverter with battery | Moderate — inverter plus one or more batteries | Grid units to recharge, plus battery replacement amortised over its life | Flats and small homes needing fans, lights and a TV through short outages | Cannot realistically run an AC, pump or motor load for long |
| Petrol / diesel generator | Moderate to high depending on kVA rating | Fuel per hour, plus oil changes and servicing | Shops, clinics and small factories that must keep motors or refrigeration alive | Noise, fumes, fuel logistics, and poor efficiency at light load |
| Solar with battery backup | Highest — panels, inverter, battery bank, installation | Very low; sunlight is free, but batteries are consumable | Homes and businesses with roof space and a long ownership horizon | Output depends on weather and season; battery cost dominates the maths |
The hidden cost of an IPS is the battery, not the electricity
People assume an IPS runs on cheap grid electricity, so backup must be cheap. The grid units it consumes to recharge are indeed billed at your normal tariff — but that is only part of the cost. Charging and discharging is lossy, so you always put more units in than you get out. And the battery itself is a consumable with a finite number of cycles: divide its replacement cost by the total backup units it will deliver over its life, and add that to every unit. Once you include battery amortisation, IPS backup is several times more expensive per unit than grid supply — still worth it for essential loads, but not "nearly free".
Generators: efficient when loaded, wasteful when not
A generator's fuel consumption does not fall proportionally with load. Run a large generator to power a couple of lights and a fan and the cost per unit becomes absurd, because a substantial share of the fuel goes into simply keeping the engine turning. Matching the generator's rating to the load you actually need to carry is therefore the single most important sizing decision — oversizing is not a safe margin, it is a permanent fuel penalty. Our load shedding cost calculator and the generator sizing output in the multiple load calculator let you test that against your real appliance list.
Against that, generators do something neither of the other options does easily: start and run motor loads. Refrigeration in a shop, a water pump, workshop machinery — these have high inrush currents that a modest inverter cannot supply. For a business where those loads stopping means spoilage or lost trade, the generator's higher per-unit cost is not really the relevant comparison; the cost of the alternative is.
Solar backup: the maths depends on whether you need batteries
Solar is unusual because its economics split into two very different cases. A grid-tied system without batteries, under net metering, is primarily a way to reduce your bill — it does not keep the lights on during an outage. A battery-backed system does provide genuine backup, but the battery bank typically dominates the cost and, as with an IPS, is a consumable. Anyone comparing solar quotations should establish first which of the two they are actually being sold, because the payback arithmetic is not comparable between them. Our rooftop solar and net metering article covers the regulatory side, and the solar savings calculator lets you model the bill-reduction case.
Three typical situations
A city flat wanting fans and lights through a couple of hours of outage is almost always best served by a properly sized IPS. A generator is impractical in an apartment, and battery-backed solar rarely has the roof area allocated to it.
A shop or small clinic with refrigeration, or equipment that must not lose power mid-task, generally needs a generator sized to the motor load, sometimes paired with a small inverter so that lighting and billing systems ride through the changeover without flickering.
A small factory should treat this as a load study rather than a purchase decision: which processes tolerate interruption, what the inrush requirements are, and whether the demand charge implications of a revised sanctioned load change the picture — see demand charge and sanctioned load.
Takeaways
- Compare backup options on cost per delivered unit, not on purchase price.
- IPS backup is not cheap once battery replacement is amortised into every unit.
- Oversized generators waste fuel permanently; size to the load you must actually carry.
- Clarify whether a solar quote is grid-tied bill reduction or true battery backup.
- List your essential loads first — that list, not the salesperson, picks the technology.