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 supplier 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 web browsers.

Situation: When the web “freezes” under your hands

For large corporate websites, perceived smoothness is the biggest challenge. For innogy.cz users, it's crucial that interactions, such as energy price calculators or contract forms, are immediate.

Before intensive optimizations began, the site struggled with high INP (Interaction to Next Paint) values. In practice, 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 several 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 one-time fixes

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, in-depth probes into specific issues (GTM, INP…).
• Monthly budget, regular meetings, and monitoring speed limits when deploying new features.
• Interdisciplinary coordination—our analysis results were fine-tuned in direct collaboration with the client's internal and external developers and analysts, especially for Google Tag Manager.

Technical breakthrough: How we “broke” INP

In January 2026, the graphs turned green. It wasn't the result of a single change but a composite effect of adjustments from SpeedSprint analyses. The graph shows only some of them.

Development of INP metric distribution over time on mobile for innogy.cz. The goal is to have as many users as possible in the green area.

What did we do in 2025 to optimize the INP metric?

1. Efficient CSS: Cleaning complex selectors (especially eliminating excessive use of :has), freeing up the browser's rendering engine.
2. Visual confirmation: Implementing spinners on action elements. Even if background calculations continue, users receive immediate feedback that the site is “working.”
3. GTM under control: Together with analysts, we reviewed Google Tag Manager. We removed unnecessary scripts that blocked the main browser thread during user interaction.
4. jQuery code tuning: We reviewed code using the jQuery framework and proposed targeted adjustments to event delegation handling.

As seen in the graph, these changes gradually increased the number of users with green INP metric values.

Result: 38% improvement in INP

Thanks to this meticulous work, innogy.cz (including subdomains) moved to the top of the market.

Comparison of PageSpeed.ONE Score (SPS) for innogy.cz and competitor sites. Below is the score status for all innogy sites.

The optimization results are excellent:

• INP improvement: Reduced value by 38%—from the original 290 ms to a green 180 ms.
• Speed score increase (SPS): The site now achieves a score of 88%, making it the fastest Czech site in the larger energy players category.
• Core Web Vitals: The entire domain and subdomains are now in “compliant” mode across all fronts, so we expect 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.

Although this technology isn't directly responsible for “fixing” INP, it demonstrates a proactive approach—striving to stay ahead of competitors and user expectations. Both activities stem from the same philosophy: minimize any user waiting, whether during interaction (INP) or page transitions.

What does the client say?

“It's great that we significantly improved the INP metric! It took considerable effort and fantastic teamwork from everyone involved because maintaining web performance in a corporation isn't a sprint but a marathon. Engaging the PageSpeed.ONE team brought us broad expertise that continues to push us forward. Thanks to their regular monitoring and professional approach, they've been a reliable partner for us for four years.”

Honza Bobek from innogy

PageSpeed.ONE perspective: Long-term commitment as 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 helped with excellent coordination, which is crucial for successful optimization in a corporate environment.”

Michal Matuška from PageSpeed.ONE