ENSEMBLE
Modeling to Generate Alternatives
A framework that explores the universe of near-optimal energy system futures. Rather than finding a single least-cost pathway, ENSEMBLE reveals the full landscape of viable solutions — showing where decisions are robust across futures and where they depend on assumptions. Built on top of RIO, it transforms optimization from answer-finding to decision support.
How It Works
Optimal Solution
RIO first solves for the least-cost energy system configuration under a given set of assumptions — the traditional single-answer approach.
Near-Optimal Exploration
ENSEMBLE then systematically explores the space of solutions within a defined cost tolerance of the optimum — typically 5–10% above least cost — generating dozens to thousands of alternative futures.
Landscape Mapping
The resulting ensemble of solutions is analyzed to reveal which decisions are robust across futures (they appear in nearly every solution) and which are sensitive to assumptions (they vary widely).
Decision Support
Stakeholders can see the full range of viable options rather than a single prescribed pathway — making it easier to identify no-regrets investments, hedge against uncertainty, and build consensus.
What Makes ENSEMBLE Different
Beyond Single-Answer Optimization
Traditional models produce one "optimal" answer that depends heavily on input assumptions. ENSEMBLE reveals that many different energy futures are nearly equally cost-effective — shifting the question from "what is the answer?" to "what is the range of good answers?"
Uncertainty Without Scenarios
Instead of manually constructing a handful of scenarios, ENSEMBLE algorithmically explores the solution space. This captures interactions and trade-offs that hand-crafted scenarios miss, without requiring analysts to pre-specify what might vary.
Robust vs. Sensitive Decisions
Some investments appear in virtually every near-optimal solution — those are robust, no-regrets decisions. Others swing dramatically — those are where assumptions matter most and where flexibility has the highest value.
Stakeholder Alignment
When multiple pathways lead to similar costs, the choice becomes about values and priorities rather than economics alone. ENSEMBLE gives stakeholders a map of the viable solution space to navigate together.
Where It's Been Used
ENSEMBLE has been deployed in some of our most ambitious analyses, fundamentally changing how clients think about energy system planning.
University of Melbourne & Princeton
Net-Zero Australia
First deployment of ENSEMBLE at national scale, generating hundreds of near-optimal decarbonization pathways for Australia. Revealed that clean energy export ambitions are robust across futures, while the mix of export carriers (hydrogen vs. ammonia vs. synthetic fuels) is highly sensitive to assumptions.
EER Research
OBBBA Policy Analysis
Applied ENSEMBLE to assess clean energy futures under policy uncertainty, showing that dozens to thousands of near-optimal pathways persist even under rollback scenarios — challenging single-scenario pessimism.
Multiple clients
Technology Portfolio Assessment
Used to identify where specific technologies appear consistently across near-optimal futures (signaling robust market opportunity) versus where they are displacement-sensitive (signaling competitive risk).
What ENSEMBLE Has Revealed
The least-cost solution is one of many good solutions
In most energy systems we've analyzed, thousands of configurations fall within 5% of the true optimum. The "optimal" answer is far less special than traditional modeling implies.
Transmission and electrification are robust across futures
Across every ENSEMBLE analysis we've run, grid expansion and electrification of buildings and transport appear in nearly every near-optimal solution — making them true no-regrets investments.
Scenario analysis understates real uncertainty
Hand-crafted scenarios explore a handful of futures. ENSEMBLE typically finds orders of magnitude more viable configurations — revealing blind spots that even well-designed scenario sets miss entirely.
The most valuable insight is knowing what doesn't matter
When ENSEMBLE shows that a decision barely changes across thousands of futures, stakeholders can stop debating it and focus attention on the choices that actually drive outcomes.
Interested in ENSEMBLE analysis?
ENSEMBLE is available as part of our RIO modeling platform. We provide training, documentation, and technical support for clients exploring near-optimal futures.
Get in Touch