Application Guide

How to Apply for Principal Software Engineer (m/f/d)

at 1KOMMA5°

🏢 About 1KOMMA5°

1KOMMA5° is at the forefront of the energy transition, aiming to make every building CO2-neutral through integrated clean energy solutions. Their holistic approach combines solar, heat pumps, energy management, and e-mobility, offering a unique opportunity to work on impactful technology that directly fights climate change.

About This Role

As Principal Software Engineer, you will define the technical vision and architecture for scalable, state-of-the-art systems that power decentralized energy solutions. Your decisions will directly impact the reliability and scalability of products used by thousands of customers, making this a high-leverage role in a mission-driven company.

💡 A Day in the Life

Your day might start with a sync with product managers to align on upcoming features, then dive into an architecture review for a new API that enables real-time energy trading. After lunch, you could mentor a team on designing for fault tolerance, and end the day by writing an architectural decision record (ADR) for a critical system component.

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Interview Prep

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🎯 Who 1KOMMA5° Is Looking For

  • A seasoned engineer with 5+ years of hands-on development in multiple general-purpose languages (e.g., Python, Go, Java, TypeScript) and a deep understanding of system design trade-offs.
  • Proven experience architecting large-scale, secure, and distributed systems, ideally in IoT, energy, or real-time data platforms.
  • Strong API design skills (REST, GraphQL, or gRPC) with a focus on developer experience and backward compatibility.
  • Excellent communicator who can align engineering teams with product goals and explain complex technical decisions to non-technical stakeholders; German is a plus but not required.

📝 Tips for Applying to 1KOMMA5°

1

In your resume, highlight specific systems you architected that scaled to handle high loads or had strict security requirements (e.g., handling sensitive user data or controlling hardware).

2

Tailor your cover letter to mention your passion for sustainability and how your technical decisions have contributed to reducing carbon footprint or improving energy efficiency.

3

Include a link to your GitHub or a portfolio that demonstrates clean, well-documented code and API design patterns.

4

If you have experience with IoT protocols (MQTT, OCPP) or energy management systems, emphasize that explicitly.

5

Use concrete metrics: e.g., 'Designed an API handling 10M requests/day with 99.99% uptime' or 'Reduced latency by 40% through architecture refactoring.'

✉️ What to Emphasize in Your Cover Letter

['Express genuine interest in the mission of decarbonizing buildings and how your technical vision can accelerate that.', 'Describe a specific architectural challenge you solved that involved cross-team alignment and trade-offs between scalability, maintainability, and cost.', 'Mention your experience with agile development and holding teams accountable for technical decisions through code reviews, ADRs, or architecture guilds.', "If you have experience with cloud infrastructure (AWS, Azure, GCP) and containerization (Kubernetes), highlight how you've used them to build resilient systems."]

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🔍 Research Before Applying

To stand out, make sure you've researched:

  • → Read about 1KOMMA5°'s product lineup: Heartbeat energy management, smart meters, and their integration with solar and heat pumps.
  • → Understand the regulatory landscape for energy in Germany (e.g., EEG, Smart Meter Gateway) and how it impacts system design.
  • → Look at their tech blog or open-source contributions (if any) to understand their tech stack and engineering culture.
  • → Check recent news about their expansion and funding rounds to grasp the company's growth trajectory.

💬 Prepare for These Interview Topics

Based on this role, you may be asked about:

1 Design a system for real-time monitoring and control of thousands of distributed energy devices (heat pumps, solar inverters, chargers).
2 How would you ensure data consistency and security across a fleet of IoT devices with intermittent connectivity?
3 Describe a time you drove a major architectural change across multiple teams. How did you gain buy-in and manage migration?
4 How do you balance short-term product needs with long-term technical strategy? Give a concrete example.
5 What is your experience with API versioning and deprecation strategies for external and internal consumers?
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⚠️ Common Mistakes to Avoid

  • Don't focus solely on frontend or mobile development; this role is about backend architecture and systems thinking.
  • Avoid generic statements like 'I am a team player' without concrete examples of leading technical decisions.
  • Don't neglect the mission aspect – failing to show enthusiasm for clean energy can signal a misalignment with company values.

📅 Application Timeline

This position is open until filled. However, we recommend applying as soon as possible as roles at mission-driven organizations tend to fill quickly.

Typical hiring timeline:

1

Application Review

1-2 weeks

2

Initial Screening

Phone call or written assessment

3

Interviews

1-2 rounds, usually virtual

✓

Offer

Congratulations!

Ready to Apply?

Good luck with your application to 1KOMMA5°!

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