Load shedding cost calculator: generator vs IPS vs grid

Load shedding refers to a distribution utility deliberately cutting supply to specific feeder areas for a period, usually to prevent an overloaded grid section from failing entirely. In Bangladesh it is most common in the hot summer months when air-conditioner demand spikes in the early evening, and during periods when gas supply to power plants is constrained, reducing total available generation capacity nationwide. Rural areas served by BREB palli bidyut samities and older urban feeders tend to experience it more frequently than newer, well-reinforced city networks. While national generation capacity has expanded substantially, distribution and transmission bottlenecks, along with fuel supply variability, mean outages during peak hours can still occur, particularly during heatwaves.

Households and businesses typically respond with one of two backup strategies: a diesel (or occasionally petrol) generator, or an IPS (instant power supply) battery bank charged from the grid. A generator converts diesel fuel directly into electricity on demand and can supply large loads — motors, deep freezers, whole-house circuits — for as long as fuel lasts, but diesel is expensive per unit of energy compared to grid electricity, and a generator's efficiency drops sharply when running well below its rated capacity, which is common when only a few lights and fans are running. Maintenance — oil changes, filters, servicing — adds a further ongoing cost on top of fuel that this calculator represents as a percentage markup on the fuel cost.

An IPS or battery backup system instead stores grid electricity in batteries while the grid is live, then draws on that stored energy during an outage through an inverter. Because it is essentially reselling grid electricity back to you with some conversion loss, its per-unit cost is almost always far lower than diesel — the two real costs are the electricity used to charge the batteries (increased by charging and inverter losses, typically bringing round-trip efficiency to roughly 70–80%) and the amortised cost of replacing the battery bank once it reaches its rated number of charge-discharge cycles. Lead-acid batteries are cheaper upfront but wear out faster; lithium batteries cost more initially but often last several times longer, which can make their true per-unit cost competitive or lower over the battery's life.

Sizing an IPS correctly starts with adding up the wattage of everything you intend to run during an outage — a few LED lights, a fan or two, a router, perhaps a TV — and matching that to an inverter rated comfortably above your peak simultaneous load, with battery capacity (in kWh) large enough to cover your typical outage duration without deep-discharging the battery below its recommended limit, since repeated deep discharge shortens battery life well below its rated cycle count. For most residential outages of two to six hours covering lights, fans and a router, a mid-sized battery bank is usually more economical than running a generator, while very long outages or heavy loads like water pumps and refrigerators may still justify keeping a small generator as a secondary backup.

Safety matters in both cases. Diesel generators must run in open, well-ventilated spaces — never inside a room, garage, or veranda with limited airflow — because they emit carbon monoxide, an odourless gas that can be fatal in enclosed spaces. Both generators and IPS units must be wired through a proper change-over or transfer switch so that backup power can never flow backward into the grid distribution line; an energised line during a supposed outage is a serious electrocution hazard to utility workers repairing the fault. If in doubt, have a licensed electrician install the change-over wiring rather than using it as a DIY connection.