Solid oxide electrolysis cell (SOEC) technology offers advantages such as high efficiency and reversible operation

but its scale-up is constrained by the limited power rating of individual stacks

high-temperature operation

and consistency issues among multiple stacks. This paper reviews the progress in SOEC system integration and engineering scale-up. Planar

tubular

and flat-tubular configurations and their stacking approaches are compared

and key issues in stack scale-up

including material and interface compatibility

electro-thermal-flow field uniformity

and mechanical reliability

are analyzed. Multi-stack modular integration

thermal management

balance-of-plant (BOP) configuration

and integration with external heat sources are summarized

together with key enabling technologies such as online diagnostics

balancing control

and lifetime management. The analysis indicates that multi-stack modularization and efficient thermal integration are the principal engineering pathways toward large-scale SOEC systems

while multi-stack operational consistency

the reliability of high-temperature BOP components

and long-term lifetime management remain critical challenges for further scale-up.