The Path to the Fastest Energy Website: How PageSpeed.ONE's Long-Term Collaboration Improved INP by 38%
In the energy sector, any delay is synonymous with unreliability. Even minor delays cause visitors to lose confidence during interactions. Discover how our long-term collaboration ensured a seamless experience for innogy's website and ultimately conquered the INP metric.
The speed optimization project for innogy (a leading energy provider in the Czech Republic with millions of monthly visits) required a blend of deep technical expertise and the ability to manage changes in a complex environment.
The PageSpeed.ONE team acts as a strategic partner for web speed, aligning the client's business goals with the technical realities of modern browsers.
Situation: When the website “freezes“
For large corporate websites, perceived smoothness is the biggest challenge. For innogy.cz users, instant interactions, such as in energy price calculators or contract forms, are crucial.
Before intensive optimizations, the site struggled with high INP (Interaction to Next Paint) values. This meant a delay after clicking a button, causing the site to “freeze“ momentarily, leaving users unsure if the system was responding.
Even a delay of a few hundred milliseconds in energy price calculators can slow the entire process and lead to user frustration.
For operators, this poses a risk of users abandoning the conversion path, reducing trust in the digital channel, and potentially losing conversions.
Strategy: The power of concept over quick fixes
Our collaboration with innogy is part of long-term care. Instead of firefighting, we focus on:
- Monitoring PLUS, the foundation for ongoing speed solutions.
- SpeedSprint analyses, deep dives into specific issues (GTM, INP…).
- Monthly budgets, regular meetings, and monitoring speed limits when deploying new features.
- Interdisciplinary coordination – we fine-tuned our analysis results in direct collaboration with the client's internal and external developers and analysts, especially for Google Tag Manager.
Technical breakthrough: How we “cracked“ INP
In January 2026, the graphs turned green. It wasn't the result of a single change but a cumulative effect of adjustments from SpeedSprint analyses. Only some are shown in the graph.
INP metric distribution over time for mobile users on innogy.cz. The goal is to have as many users as possible in the green zone.
What did we do in 2025 to optimize the INP metric?
- Efficient CSS: Cleaning complex selectors (especially reducing excessive use of :has), freeing up the browser's rendering engine.
- Visual feedback: Implementing spinners on action elements. Even if background calculations continue, users receive immediate feedback that the site is “working.“
- GTM under control: Together with analysts, we reviewed Google Tag Manager, removing unnecessary scripts that blocked the browser's main thread during user interaction.
- jQuery code tuning: We reviewed code using the jQuery framework and proposed targeted adjustments to event delegation.
As the graph shows, these changes gradually increased the number of users with green INP values.
Result: 38% improvement in INP
Thanks to this meticulous work, innogy.cz (including subdomains) has moved to the top of the market.
Comparison of PageSpeed.ONE Score (SPS) for innogy.cz and competitor sites. Below, you can see the score status for all innogy sites.
The optimization results are excellent:
- INP Improvement: Reduced by 38% – from 290 ms to a green 180 ms.
- SPS Score Increase: The site now scores 88%, making it the fastest Czech site among major energy players.
- Core Web Vitals: The entire domain and subdomains are now “compliant“ across the board, expecting a positive impact on traffic and potentially conversions.
Innovation as proof of leadership and courage
The client's courage is also evident in adopting the latest technologies. As one of the first in the Czech Republic, innogy.cz implemented the Speculation Rules API.
While this technology doesn't directly “fix“ INP, it demonstrates a proactive approach – striving to stay ahead of competitors and user expectations. Both activities stem from the same philosophy: minimizing any user wait, whether during interaction (INP) or page transitions.
What does the client say?
“It's great that we've significantly improved the INP metric! It took considerable effort and fantastic teamwork from everyone involved, as maintaining web performance in a corporate environment is not a sprint but a marathon. Engaging the PageSpeed.ONE team brought us broad expertise that continues to move us forward. Thanks to their regular monitoring and professional approach, they have been a reliable partner for us for four years.”
Honza Bobek from innogy
PageSpeed.ONE's perspective: Long-term commitment is the only way
“Making changes in such a large project is very challenging. Innogy's websites are built on universal and interconnected components, which is another technical challenge. We chose a strategy of gradual changes, and the client supported this with excellent coordination, which is key to successful optimization in a corporate environment.”
Michal Matuška from PageSpeed.ONE