What a UPS costs to run
A double-conversion UPS is one of the few things in a plant that runs at full duty every hour it is switched on. Four points of efficiency, on a 100 kVA load, is roughly a lakh a year — which is frequently more than the price difference that bought it.
Purchase price is the number that gets compared and the smaller of the two costs. A UPS protecting a continuous load converts power twice, twenty-four hours a day, for a working life of ten years or more. What it wastes doing that is a running cost, and it is large enough to change which machine is actually cheaper.
The arithmetic, on a real load
Take a 100 kVA machine at 0.8 power factor carrying 80 kW, running continuously. At 96% efficiency it dissipates about 3.3 kW. At 92% it dissipates about 7.0 kW. The difference is 3.7 kW, every hour.
Over a year that is roughly 32,000 units. At industrial tariffs across Maharashtra — call it eight to nine rupees — the gap is somewhere near two and a half to three lakh rupees annually, before you have cooled any of it.
| Efficiency | Heat dissipated | Units per year | Approx. annual cost |
|---|---|---|---|
| 96% | 3.3 kW | ~29,000 | ₹2.4–3.0 lakh |
| 94% | 5.1 kW | ~45,000 | ₹3.6–4.0 lakh |
| 92% | 7.0 kW | ~61,000 | ₹4.9–5.5 lakh |
| 90% | 8.9 kW | ~78,000 | ₹6.2–7.0 lakh |
The figures assume continuous full load, which few sites run. Halve the load and you halve the gap — but you also move down the efficiency curve, because most UPS designs are least efficient at light load. Ask for the efficiency at your actual load point, not the headline number.
The cost you pay twice
Every watt a UPS wastes becomes heat in the room it sits in, and in a panel room with air conditioning you then pay to remove it. At a coefficient of performance around three, each kilowatt of loss costs roughly a third of a kilowatt in cooling. The 3.7 kW difference above is closer to 4.9 kW once the air conditioning is counted.
This is also why an oversized UPS is not a free safety margin. A 100 kVA machine carrying 30 kVA sits at the inefficient end of its curve and dissipates more, proportionally, than a right-sized one would.
The comparison worth making
Take the price difference between two machines and divide it by the annual energy difference. If it pays back inside two years on a ten-year asset, the cheaper machine was not cheaper.
Where efficiency claims come apart
Headline efficiency is quoted at full load, at nominal input, in normal mode. Three things move it: the load point, the input voltage, and whether the machine is in eco mode. Eco mode figures are not comparable with double-conversion figures, because in eco mode the machine is not double-converting — it has stopped doing the thing you bought it for.
Ask for efficiency at 50% and 75% load as well as 100%. A curve tells you what a single number cannot, and a supplier who has the curve has measured the machine.
What this does not justify
Choosing a line-interactive unit for a load that cannot take the transfer, on the grounds that it is more efficient. It is, and it will also let the CNC controller reset. One scrapped job frequently costs more than a year of the efficiency difference.
Efficiency is the tie-breaker between machines that both suit the load. It is not a reason to pick one that does not.
Questions we get asked
Anything not covered here, call us — most of it is faster to answer on the phone.
How much electricity does a UPS use?
A UPS consumes what it wastes, which is its load divided by its efficiency, minus the load. An 80 kW load on a 96% efficient machine wastes about 3.3 kW continuously; at 92% it wastes about 7.0 kW. Over a year at Maharashtra industrial tariffs, those four points are worth roughly two and a half lakh rupees.
Is eco mode worth using?
It depends entirely on the load. Eco mode runs the machine in bypass and switches to inverter only when the supply degrades, which recovers most of the conversion loss and reintroduces a transfer time. On tolerant loads it is real money for no risk. On anything that cannot take a break, it undoes the reason you bought a double-conversion machine.
Does an oversized UPS waste more power?
Yes, proportionally. Most designs are least efficient at light load, so a 100 kVA machine carrying 30 kVA sits at the poor end of its curve. Twenty-five per cent headroom is sensible; a hundred per cent is paid for twice, once at purchase and again every hour it runs.
Should I count air conditioning in the running cost?
Yes, and it is usually forgotten. Every watt a UPS wastes becomes heat in the panel room, and removing it costs roughly a third of a watt again in cooling at typical coefficients of performance. A four-kilowatt difference in loss is closer to five and a half once the air conditioning is counted.