Renewables can’t scale fast enough to replace fossil fuels without an energy shortfall, and a new open-source model built by engineering graduates shows the gap could last decades and reshape how the world plans its entire energy future

The global energy debate frequently collapses into two opposing visions: fossil fuels burning unchecked until industrial systems fracture, or a smooth, rapid handoff to renewable abundance. Yet civil engineers know that complex physical infrastructure rarely obeys political optimism or catastrophic doomerism.

To understand what lies between those extremes, researchers examined the real-world mechanics of replacing our global energy foundation. What their work uncovers is a structural reality that standard policy frameworks continuously overlook.

A model built to explore the uncomfortable middle ground

To map this uncharted territory, researchers developed the Global Renewable Energy and Sectoral Electrification model, known as GREaSE. Created at the University of South Australia by Associate Professor James Hopeward alongside civil engineering researchers Shannon O’Connor, Richard Davis, and Peter Akiki, the initiative began as an Honours project before expanding into a peer-reviewed tool published in the open-access journal Energies.

By offering open-source code, the creators intended to move critical energy forecasting beyond closed academic circles into direct public discourse.

Designed for policy analysts, grid planners, and public stakeholders alike, GREaSE provides an accessible framework to stress-test energy assumptions without proprietary algorithms. Hopeward describes it as an exploratory tool that allows users to run scenarios across major economic sectors—including manufacturing, heavy transport, and residential power.

By offering open-source code, the creators intended to move critical energy forecasting beyond closed academic circles into direct public discourse.

What the simulations actually show

The research team subjected GREaSE to a vast range of plausible future conditions: rapid fossil fuel curtailment, shifting per-capita power demands, and varying rates of electrification across heavy industry and transport. While inputs fluctuated, the structural outputs consistently converged on a single path.

As Davis observed, a striking similarity across all scenarios is the ultimate necessity of transitioning to clean energy—whether proactively to meet carbon reduction targets or reactively as fossil fuel supplies tighten.

The critical challenge is not the final destination, but the physical rate of progress. Standard energy models often assume solar panels and wind turbines can step in immediately as fossil plants close. However, when accounting for material extraction, manufacturing output, and electrical grid interconnections, clean energy expansion faces strict physical boundaries.

The inescapable trade-off at the heart of the transition

Meeting international climate benchmarks—such as holding global warming to 1.5°C (2.7°F)—requires steep, rapid emissions cuts that risk creating near-term power supply shortfalls. Extending fossil fuel operations to cushion the grid might appear pragmatic, but modeling demonstrates this merely delays the unavoidable shift while escalating climate risks.

Nuclear power is frequently highlighted as a bridge, but GREaSE indicates significant scaling limitations. Hopeward notes that nuclear deployment is restricted by extended construction timelines, capital requirements, and finite global uranium reserves. Even with expanded mineral discoveries, nuclear capacity expands far slower than modular solar and wind.

This reality forces an uncomfortable adjustment in energy consumption. As O’Connor points out, during the multi-decade build-out, nations must rebalance expectations regarding total economic energy availability.

Why this matters beyond the modeling

The modeled power gap is not a permanent state of scarcity. By roughly 2050, GREaSE projections indicate that renewable generation could successfully scale to meet global power demand, allowing modern industrial economies to run predominantly on clean energy.

Yet this framing alters the fundamental nature of the energy debate. The primary question is no longer whether to transition, but how societies manage structural disruption while building the new grid. Standard policy tools are rarely designed for managing systemic supply bottlenecks. Hopeward compares the dilemma to cardiovascular health: delaying lifestyle changes does not remove health risks; it simply forces a dangerous reckoning when the patient is least prepared.

By opening GREaSE to the public, the researchers invite policy leaders and communities to confront these operational truths. What the simulation ultimately reveals—the central, unavoidable hook at the heart of our energy future—is that even under rapid renewable expansion, replacement capacity cannot keep pace with fossil fuel phase-outs, leaving a massive 20-to-30-year energy shortfall that could last a full generation.

The full study can be found here: James Hopeward, Richard Davis, Shannon O’Connor, Peter Akiki. The Global Renewable Energy and Sectoral Electrification (GREaSE) Model for Rapid Energy Transition Scenarios. Energies, 2025; 18 (9): 2205 DOI: 10.3390/en18092205 

Kelly Lippke

Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.