Senior Java Software Engineer with proven Java, Spring Boot or Micronaut experience is required to join an early-stage green energy technology start-up building microservices-based SaaS applications for the renewable energy sector. You’ll help design, deliver and enhance a new product offering, working across full-stack scalable distributed systems, backend services, APIs, test automation, continuous delivery and cloud-native engineering, with frontend UI development experience ideally using React / MUI. This role will suit someone who has worked in a small, scale-up or product-focused SaaS software business and enjoys building resilient, maintainable software at pace. The role is potentially remote with meetups, although candidates who are accessible and can spend some time in the central Cambridge office would be an advantage. Salary £60-85k Bens Stock Key skills required for the Senior Java Software Engineer Proven experience building and operating Java-based applications in an enterprise environment. Strong experience with Spring Boot or Micronaut, ideally as microservices within a SaaS platform. Full stack engineering experience, with the ability to work across backend services, APIs and user-facing product features. Frontend development experience, ideally with React and MUI or similar modern UI frameworks/component libraries. Strong understanding of good engineering practices around resilience, scalability and maintainability of distributed systems. Familiarity with container management solutions such as Kubernetes, ECS or similar. Experience working with managed cloud platforms such as EKS, GKE or equivalent would be advantageous. Good understanding of DevOps practices and Continuous Delivery. Experience working in a small, scale-up, start-up or product-focused SaaS software business. Comfortable working in a technically challenging, cross-functional engineering team where collaboration, ownership and adaptability are key. Any experience with Domain Driven Design, data engineering, data products, data pipelines, data mesh architectures, platform engineering, ML engineering, IoT hardware, embedded systems or firmware development would be advantageous. A genuine interest in renewable energy, climate technology or building software with real-world impact. What you’ll do as a Senior Java Software Engineer Build, deliver and support green energy software as part of a product-led, continuous delivery lifecycle. Develop new Java-based services, APIs and frontend product features in collaboration with the wider engineering team. Work across microservices and customer-facing UI features to deliver increasingly valuable product capability. Contribute to scalable, resilient and maintainable distributed systems that support complex energy data use cases. Take part in pair-programming or mob-programming sessions to solve complex technical problems. Participate in product demos and feedback sessions with external stakeholders. Contribute to retrospectives, code reviews and internal continuous improvement discussions. Write appropriate test automation to support the reliability of services and product features. Help operate and support the services you build as part of a team-wide approach. Contribute more broadly to the success of the business where your skills and enthusiasm can make an impact. Why this role? This is a chance to join a mission-led start-up at an early stage and play a meaningful role in shaping both the product and engineering culture. You’ll work alongside a diverse team combining renewable energy expertise, modern software engineering and operational delivery experience, with colleagues across the UK, Europe and North America. The environment is collaborative, product-focused and practical, giving you the opportunity to work on technically interesting SaaS products while contributing to the transition towards a greener energy world. There is also scope to apply broader engineering experience across data engineering, data mesh, ML-enabled applications, IoT, embedded systems and cloud-native platform development as the product evolves. You do not need to tick every box. We are looking for talented, enthusiastic full stack engineers who want to make a difference and bring fresh perspectives to a growing team. Opus Resourcing acts as an employment agency with respect to permanent employment. Apply now or message us for more details. Referrals always welcome! FullStackEngineer JavaJobs GreenTech SaaSJobs