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)