Technology readiness level, which according to the International Energy Agency follows a 1-11 scale defined as:
- 1 – Initial idea (basic principles have been defined)
- 2 – Application formulated (concept and application of solution have been formulated)
- 3 – Concept needs validation (solution needs to be prototyped and applied)
- 4 – Early prototype (prototype proven in test conditions)
- 5 – Large prototype (components proven in conditions to be deployed)
- 6 – Full prototype at scale (prototype proven at scale in conditions to be deployed)
- 7 – Pre-commercial demonstration (prototype working in expected conditions)
- 8 – First of a kind commercial (commercial demonstration, full-scale deployment in final conditions)
- 9 – Commercial operation in relevant environment (solution is commercially available, needs evolutionary improvement to stay competitive)
- 10 – Integration needed at scale (solution is commercial and competitive but needs further integration efforts)
- 11 – Proof of stability reached (predictable growth)