Principal Software Engineer with a Java backend / full-stack experience to take a lead role in designing and architecting the SaaS platform for an early-stage clean-tech startup on a mission to accelerate the shift to a greener energy world by optimising complex grid-scale battery 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-driven systems Deep understanding of software architecture, patterns, scaling/resilience and 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 Principal Engineer, 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 you’ll be doing as a Principal Engineer: Lead on software design, architecture, and coding to shape a scalable, resilient full-stack SAAS platform. Build cloud-native Java microservices (Spring Boot / Micronaut) and drive engineering practices. Drive continuous improvement in engineering culture, mentoring/coaching other engineers and guiding technical decisions. Collaborate across product, engineering, and customer teams to deliver impactful solutions to the SaaS platform. You’ll 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-functional team. 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. You’ll 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.