Systems guide

Off-grid power for a bunker

Power runs the blowers, lights, water pump and fridge, and it is the system most likely to be called on. Grid outages are common, so a bunker has to make and store its own.

The short answer
  • Batteries and an inverter run the bunker day to day; a standby generator recharges them.
  • Most lithium batteries must not be charged below 32°F without heating.
  • Propane stores far longer than gasoline or diesel.

How the pieces fit

A battery bank stores power and an inverter turns it into household current. A standby generator starts when the batteries get low, runs at its most efficient load, and shuts off. Solar on the surface can extend the time between generator runs. The blowers for the air system come first on the list of loads, ahead of everything else.

Cold and lithium

Lithium iron phosphate batteries are the common choice, but charging most lithium batteries below freezing can damage them. Underground, the cubes stay well above freezing once in use, which helps. Batteries in a cold utility space need heat or a low-temperature charging cutoff.

Fuel

Gasoline and diesel break down in storage and need treatment and rotation. Propane does not degrade with age, which makes it a good standby fuel. Wherever the generator sits, its exhaust has to go outside, well away from the air intake. A separate generator room is an option in the Builder.

How much

Size the system from the loads you will actually run, for the number of days you need. In a CUBE 4, the Household power tier is the largest of the required system lines, because batteries, inverter and generator big enough for a family are a real investment in any building.

Questions

Can a bunker run on solar alone?

Solar helps, but snow, smoke and short winter days make it unreliable as the only source. Pair it with batteries and a standby generator.

How often does the grid go out?

The U.S. Energy Information Administration reports that the average customer had about 1.5 interruptions and about 11 hours without power in 2024, with major storms causing the longest outages.

Sources
  1. REDARC: Why you should not charge a lithium battery below 0°C / 32°F
  2. Ferrellgas: Propane shelf life compared with gasoline and diesel
  3. Clean fuel for generators: a drill-down of NFPA 110
  4. U.S. EIA: Customers experienced more electricity interruptions in 2024

CUBE Bunker prices are preliminary until engineering for the cube system is complete and are confirmed in writing after a site visit. This guide is general information, not engineering, legal or medical advice. Updated 2026-11-02.