Principal Software Engineer with a Java backend / full-stack experienceto take a lead role in designing and architectingthe SaaS platform for an early-stage clean-tech startup on a mission to accelerate the shift to a greener energy worldby optimising complex grid-scalebattery assets for asset owners through data, ML, and SaaS innovation. Proximity to Cambridge would be ideal, although a remote role across the UK / with some company meetups. Salary £70-90k Bens Options Key skills you will bring as a Principal Software Engineer would include : Proven track record in building enterprise-grade Java / Microservices backend systems (Spring Boot or Micronaut preferred) Cloud Native development ideally with AWS Proven experience in distributed systems / Kafka / event-drivensystems Deep understanding of software architecture, patterns, scaling/resilienceand ideally with domain-driven design. Hands-on expertise with platform engineering/ DevOps practices (Kubernetes, Terraform, containers, CI/CD, ECS, Gitlab etc). A proactive, startup mindset with the ability to balance strategy and execution. Nice to have skills as a PrincipalEngineer, includes some of Experience with frontend UI design and frontend development (MUI / React/JavaScript / TypeScript preferred). Familiarity with Data Engineering patterns, Data Products / Kafka / Kafka streams, and Data Pipelines. Experience with platform-as-a-product delivery or platform engineering. Familiarity with Machine Learning Engineering tools and frameworks. Experience with microservice networking and service meshes (such as Istio). Well-informed on security considerations in a cloud native environment, with prior experience with related tooling (e.g. OPA, IRSA) Experience of working within startup environments What youll be doing as a Principal Engineer: Lead on software design, architecture,and coding to shapea scalable, resilient full-stackSAAS platform. Build cloud-native Java microservices (Spring Boot / Micronaut) and driveengineering practices. Drive continuous improvement in engineering culture, mentoring/coachingother engineers and guiding technical decisions. Collaborate across product, engineering, and customer teams to deliver impactful solutions to the SaaS platform. Youll bring strong software engineering practices to a fast-moving, collaborative environment, setting technical direction while staying hands-on with code within a small, focused cross-functionalteam. Why join? This is a rare opportunity to be part of the early days of a high-growth renewable energy startup, shaping both the product and the engineering culture. Youll have the freedom to make architectural decisions that matter while contributing directly to the clean energy transition. Cambridge-based office, with flexibility to work fully remote across the UK. Interested? Apply now or reach out to Opus Resourcing for more details.