N+1 Redundancy
N+1 means one spare beyond what the load needs, so any single unit can fail or be serviced without dropping power — the base pattern for making the burner firm.
One more than you need
If a campus needs N units of firm capacity to carry its load, an N+1 design installs one extra. Any single unit can trip or go into maintenance and the remaining N still cover the load. 2N doubles everything for two fully independent supplies; N+1 is the lighter, common compromise. Both convert individually imperfect machines into a collectively firm supply.
N+1 is the direct answer to the burner's availability gate. A single burner at 0.86-0.995 is not a Tier III source, but several burners plus a grid feed and storage, arranged so that no single failure drops the compute bus, can reach far higher combined availability. The redundancy multiplies the small probabilities of simultaneous failure down toward the Tier III floor.
The tradeoff in redundancy is capacity you carry but do not always use, and here that is stated as an engineering fact rather than an economic one: N+1 requires spare firm capacity to sit ready. For fusion that also interacts with the helium-3 supply gate, since more units mean more fuel demand — another reason the commercial case leans on breeder-bred and lunar He-3.
The practical rule for MetroVolt sites: size the burner fleet to N+1 at minimum, treat the grid tie and battery layer as additional independent members, and compute the combined availability explicitly rather than assuming it.
- N+1 = one spare beyond load; 2N = full duplication
- Turns imperfect units into a firm collective supply
- Directly answers the 0.86-0.995 gate
- Carries spare capacity and extra fuel demand as the price