What is load shedding in a microgrid?

Load shedding is the deliberate, staged disconnection of lower-priority circuits during an outage or supply shortfall so that the most important loads keep running. Grouping circuits into priority tiers lets you drop deferrable loads first and protect critical ones longest.

How is battery runtime calculated?

Usable energy equals capacity in amp-hours times bank voltage times the usable depth of discharge fraction. Runtime in hours is that usable watt-hours figure divided by the connected load in watts.

How is generator runtime estimated?

Runtime equals fuel quantity divided by burn rate. Because burn rate rises with load, the tool scales the rated burn by the load fraction with an idle floor, and flags any stage whose load exceeds the generator's continuous rating as an overload.

Which loads should be deferrable?

Large discretionary loads like HVAC, EV charging, pool pumps, dryers and water heaters are usually deferrable because they can be cycled or delayed without safety impact. Refrigeration, lighting, medical equipment and communications are typically essential or critical.

Why keep lead-acid above a depth-of-discharge limit?

Deeply discharging lead-acid batteries shortens their cycle life dramatically, so the usable depth of discharge is often capped near 50 to 80 percent. Entering that limit gives a realistic usable-capacity figure rather than the full nameplate amp-hours.

Microgrid Load Shedding Priority Calculator

When grid power fails, a microgrid can only support a fraction of its normal load. Load shedding is the practice of dropping lower-priority circuits in stages so the critical ones stay energised as long as possible. This calculator groups your circuits into priority tiers, sums the load in each, and shows how long your battery or generator will last at each shedding stage.

How it works

Every circuit is tagged critical, essential or deferrable. The tool sums wattage per tier and builds three cumulative scenarios: critical only, critical plus essential, and all circuits. For each it computes runtime from your chosen source.

For a battery bank, usable energy and runtime are:

usable_Wh = Ah × V × (DoD% / 100)
runtime_h = usable_Wh / load_W

For a generator, runtime is limited by fuel. Burn rate climbs with load, so the rated burn is scaled by the load fraction with an idle floor, and any stage exceeding the continuous rating is flagged as an overload:

burn_now = burn_rated × (0.3 + 0.7 × load_fraction)
runtime_h = fuel / burn_now

Worked example

A 48V, 200 Ah bank at 80 percent usable depth of discharge stores 200 × 48 × 0.8 = 7680 Wh. With only critical loads of 400 W online it runs for 7680 / 400 ≈ 19 hours. Add 750 W of essential loads and the same bank lasts about 7680 / 1150 ≈ 6.7 hours.

Tips and notes

Order your shed from deferrable to essential, keeping critical loads online longest. Size the generator so even the all-circuits stage stays below its continuous rating to avoid an overload. Remember that motor loads draw a large starting surge, so leave headroom above the steady-state watts shown here, and verify your transfer-switch and islanding scheme meet local interconnection rules.