About the Role We are looking for an experienced Senior Back-End Engineer to help build and scale the infrastructure behind Scenario Builder, our electricity grid modelling platform. Scenario Builder is an in-browser platform that currently provides capacity expansion and dispatch modelling through an accessible no-code interface. The vision for Scenario Builder is to expand into power flow modelling to create a fully integrated grid modelling platform with the features and functionality needed to enable users to develop bankable scenarios that support energy investment decisions. You will work closely with the wider product and engineering team to design, develop, and maintain the back-end services that power our platform. You will also be expected to mentor and guide more junior engineers on best practices and system design. This hybrid role is based out of our London office near Waterloo Station and reports to the Head of Platform. Responsibilities Back-end development & architecture Design, develop, and maintain scalable back-end services and APIs using Python and modern frameworks (FastAPI). Design and build high-performance API endpoints to handle complex hierarchical data queries and multi-dimensional aggregations for grid modelling computations Ensure system reliability, performance, and security through best practices in code quality, testing, and monitoring. Collaborate with front-end engineers to design and implement RESTful APIs that support our web application. Infrastructure & DevOps Manage and optimise cloud infrastructure (GCP) to support our computational workloads. Implement and maintain CI/CD pipelines to enable rapid, reliable deployments. Monitor system health and performance, proactively identifying and resolving issues. Implement and maintain infrastructure-as-code Technical leadership & collaboration Participate and lead in code reviews, architectural discussions, and technical planning sessions. Collaborate with cross-functional teams, including product, data engineering, and modelling, to deliver impactful features. Stay current with industry trends and best practices, bringing new ideas and technologies to the team. Mentor junior engineers and contribute to a culture of technical excellence and continuous improvement. About You We are looking for an experienced Senior Back-End Engineer to help build and scale the infrastructure behind Scenario Builder, our electricity grid modelling platform. Scenario Builder is an in-browser platform that currently provides capacity expansion and dispatch modelling through an accessible no-code interface. The vision for Scenario Builder is to expand into power flow modelling to create a fully integrated grid modelling platform with the features and functionality needed to enable users to develop bankable scenarios that support energy investment decisions. You will work closely with the wider product and engineering team to design, develop, and maintain the back-end services that power our platform. You will also be expected to mentor and guide more junior engineers on best practices and system design. This hybrid role is based out of our London office near Waterloo Station and reports to the Head of Platform. Skills & Experience Essential 5 years of experience in back-end software development, with strong proficiency in Python. Experience designing and building RESTful APIs and microservices architectures. Strong understanding of database technologies (PostgreSQL, Redis, Firestore), ORMs and data modelling principles. Experience with cloud platforms (preferably GCP) and containerisation technologies (Docker). Solid understanding of software engineering best practices, including testing, code review, and documentation. Excellent problem-solving skills and ability to work independently on complex technical challenges. Desirable Experience with AGILE/Scrum based ways-of-working Experience in the energy sector or with computational modelling/simulation software. Understanding of OAuth and web security best practices Familiarity with scientific computing libraries (NumPy, Pandas) and optimisation frameworks. Experience with generative AI/LLMs in applied engineering contexts Experience with infrastructure-as-code tools (Terraform, Terragrunt) and GitOps practices. Salary & Benefits Benefits Enhanced competitive pension scheme - auto-enrollment from day 1 25 days annual leave (excluding UK public holidays) and an additional discretionary days off such as over the festive period 20 days of annual allowance to work from anywhere in the world Hybrid working and core working hours model Allowance to set up your home office Annual budget and dedicated leave time for relevant training courses Enhanced gender-neutral parental leave (16 weeks fully paid) Private healthcare following the successful completion of the probation period Yearly team offsites Our Commitment to Diversity, Equity, & Inclusion Our commitment to diversity, equity, and inclusion Studies have shown that some people from marginalised or underrepresented groups are less likely to apply to a role unless they meet all of the hiring guidelines or qualifications. Whoever you are, even if you don't meet all of the criteria, if you can demonstrate a variety of skills and experience relevant to this role, we encourage you to apply as you might just be the candidate we hire! At TransitionZero, we're looking for people who are genuinely passionate about what they do, and we welcome all people, regardless of their background. If you would like to discuss any reasonable adjustments to the application or hiring process that may better facilitate your participation, please contact our People Team (people@transitionzero.org) for an informal chat. We will make every effort to respond to your request for assistance as soon as possible. About us We are a climate-tech startup established in 2021. We provide electricity grid modelling software to accelerate energy planning in emerging markets and developing economies. Today’s tools are costly, closed, and hard to use, with modelling studies taking months or years when they should take weeks or days. We designed Scenario Builder to meet this challenge, so energy planners and investors can make better decisions, faster. Our funding currently comes from a range of US and EU foundations, including the Quadrature Climate Foundation, Google.org, the Sequoia Climate Foundation, Bloomberg Philanthropies, and the European Climate Foundation. At TransitionZero, we understand that diversity is an essential component of a successful team, whether that be diverse ways of thinking, personal or professional backgrounds, or skills. We aim to be the most talented non-profit in our vertical through our culture of ownership and adaptability.