1cFE · Envelope explorer

The 1¢ envelope for fusion electricity

Levelized cost is held at the target. Move any parameter and the unlocked ones move toward their limits to compensate. When every unlocked parameter reaches its limit, the target is out of reach.

Target LCOE
1.00¢/kWh

Plant and finance parameters

Drag a slider, or use the arrow keys. The lock holds a parameter at its value while the others compensate. Cost of capital and plant life start locked at 7% and 30 years, the 1cFE reference finance case.

Limit: the most ambitious value allowedOut of reach, even with every other unlocked parameter at its limit

Where the budget goes

    How much ambition is used

    Each axis runs from the relaxed end of its range at the centre to its limit at the rim. The dashed shape is the least ambition each parameter needs, with every other unlocked parameter at its limit.

    Current settingMinimum needed

    What each step is worth

    The capital cost, in $/kW, that each change would pay for at the current point while LCOE stays the same.

      Cost surface

      LCOE across two parameters, with the rest at their current values. Drag on the surface to move both; the unlocked parameters rebalance and the surface redraws.

      ¼×target4× LCOE equals the target, other parameters as set Envelope edge: other unlocked parameters at their limits Outside the envelope Current point

      How the arithmetic works

      Single-plant screening arithmetic in constant 2025 dollars. For each kW of net output:

      E = 8.76 × CF MWh per kW-year CRF = r / (1 − (1 + r)^−life) IDC = ((1 + r)^T − 1) / (T × ln(1 + r)) even spending over T years SFF = r / ((1 + r)^N − 1) replacement every N years LCOE = C × (CRF × IDC + s × SFF) / (E × (1 − f)) + F / E + V
      • C is capital cost per kW of gross electric output; f is the recirculating fraction, so net output is gross × (1 − f). Engineering gain QE is 1/f.
      • F is fixed O&M per kW of net output per year; V is variable O&M and fuel per MWh.
      • Replacements recur every N years at share s of the original capital cost for the life of the plant, annualized as a sinking fund.
      • Compensation is shared evenly: every unlocked parameter moves the same fraction of its remaining travel toward its limit, or back toward its relaxed end when there is slack.
      • Check: $1,000/kW at 7% real, 30 years and 95% capacity factor, with no construction interest, O&M, recirculation or replacements, gives 0.97¢/kWh.

      Excluded: taxes, decommissioning, land, fuel-price risk, grid and firming costs, and revenue from heat or other products. For a full plant model, use 1costingFE.

      For scale: 1cFE's working estimate is that a Rankine steam block alone contributes about 0.5¢/kWh to a D-T plant, half of the 1¢ budget. See what if the core were free and material multipliers and learning curves for what a low capital cost would have to rest on.

      Limits and references

      The limits are screening assumptions chosen for this tool. They are neither forecasts nor engineering floors. Change them here and the envelope redraws.

      Edit limits
      ParameterLow endHigh endUnitLimit at

      Reference marks on the sliders are from EIA, Capital Cost and Performance Characteristics for Utility-Scale Electric Power Generating Technologies (AEO2025), Table 1-2, in 2023 dollars: combined cycle $868 to $921/kW, fixed O&M $12.12 to $15.51/kW-yr, variable O&M $3.33 to $3.41/MWh excluding fuel; two AP1000 units $7,861/kW, $156.20/kW-yr and $2.52/MWh. Those are per kW of net output; the capital slider is per kW of gross output.

      The starting point is illustrative. On load and on reset, the tool solves capital cost so that LCOE equals the target.