Renewable Energy Payback: Carbon Debt vs Avoided Emissions

Simulated Site

Displaced grid carbon intensity 450 g/kWh

Resource quality (sun/wind/flow) 1.00×

Years per second 2

Technologies (1 kW installed each)

☀️ Solar PVYr 0.0

EPBT –C-payback –

💨 Wind TurbineYr 0.0

EPBT –C-payback –

💧 Small HydroYr 0.0

EPBT –C-payback –

Simulated year

0.0

Fastest carbon payback

–

How it works

Manufacturing any power plant burns carbon before it generates a single clean kWh. Two clocks track when that debt is repaid:

EPBT = E_embodied / (8760 × CF)
Carbon payback = C_embodied / (8760 × CF × I_grid)

where E_embodied is the manufacturing energy per kW installed (kWh/kW), CF is the capacity factor (fraction of the year the plant runs at full output), and I_grid is the carbon intensity of the electricity it displaces (kg CO2/kWh). After the carbon-payback year, every further year of generation is a net climate benefit — the bar keeps climbing instead of just refilling a hole.

Displaced grid carbon — a coal-heavy grid (~900 g/kWh) pays back the embodied carbon far faster than an already-clean one (~150 g/kWh), because each avoided kWh is worth more.
Resource quality — scales each technology's capacity factor, modelling a sunnier/windier/wetter site; it shortens both EPBT and carbon payback identically since output scales linearly.
Default assumptions — Solar PV: 1900 kWh/kW embodied, CF 18%. Wind: 1500 kWh/kW embodied, CF 34%. Small hydro: 3200 kWh/kW embodied, CF 45% (concrete-heavy civil works cost more energy to build but the plant runs almost continuously). Embodied carbon assumes the manufacturing grid itself emits ~500 g CO2/kWh.
Particles rising from each plant represent tons of CO2 avoided so far — count and rise speed scale with each technology's live avoided-emission rate.

Year 0.0

Solar PV Wind turbine Small hydro

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