Energy Return on Investment (EROI)

EROI is the ratio of energy a plant delivers over its life to the energy invested to build and run it — a measure fusion aims to score highly on.

Definition

Lifetime energy out ÷ energy invested

Why it matters

High EROI means a genuine net energy source

Fusion

High energy density → high potential EROI

Kronos aids

Long wall life, no blanket changeouts, abundant fuel

Energy return on investment (EROI) asks a fundamental question of any energy technology: over its whole life, how much energy does it deliver compared with the energy spent to build, fuel, and run it? A source with low EROI is barely worth having; a high EROI is what makes a technology a genuine net contributor to society's energy.

Fusion's enormous energy density gives it a high potential EROI, and several Kronos design choices push in that direction: a first wall that lasts the full 30 full-power-years, no breeding-blanket changeouts, abundant deuterium fuel, and direct energy conversion that avoids a large thermal plant. Each reduces the lifetime energy invested per unit delivered.