Leading solar manufacturer: Solar management app rebuilt for 125,000+ active users, UX redesigned, custom hardware integrations added, Kotlin Multiplatform migration in progress.

The Challenge

In the residential solar market, hardware quality is table stakes. The differentiator is the digital experience that surrounds it: how easily homeowners can see what their system is doing, act on that information, and feel confident that their investment is performing as expected. The client recognized that its existing digital offering was falling behind those expectations. The original solution was a web-based interface that had not been designed for mobile-first use. On smartphones, it was clunky, hard to navigate, and increasingly out of step with what users expected from smart energy products in 2024. Customers who owned premium hardware were managing it through a substandard digital experience, a gap that posed both a customer satisfaction risk and a competitive exposure. The technical problem behind the user-facing issue was significant. The client’s solar hardware ecosystem spans multiple product generations, inverter types, battery storage units, and increasingly, EV chargers and smart home integrations. Many of these devices were never designed to communicate through a unified app. Building a reliable integration layer required custom development work for each hardware category, and a flexible architecture capable of handling the diversity without creating an unmaintainable tangle of device-specific code. Timing added pressure. The client was simultaneously rebuilding its backend infrastructure. The redesigned app needed to be designed for and integrated with a brand-new backend from day one not retrofitted to it later.

The Approach

Gradion has been the client’s mobile engineering partner since 2018. The long-term relationship provided the deep system knowledge and integration context that made the 2024 full redesign and relaunch feasible at the pace and quality level required. The redesign was comprehensive. Gradion developed a new native smartphone app that replaced the web-based interface, giving users direct control of their solar systems from live data tracking to system configuration adjustments. The user experience was rebuilt from the ground up around a clean, modern interface designed to be immediately accessible to non-technical homeowners while still offering the depth of insight that more engaged users require. On the integration side, Gradion mapped all backend requirements and designed an API framework capable of handling the full range of the client hardware types - legacy and new - with stable, secure connections. The architecture was built to accommodate the new backend infrastructure from the start, avoiding the integration debt that comes from designing to a moving target. German regulatory requirements shaped the integration context. Section 14a of the German Energy Industry Act (EnWG) and Section 9 of the Renewable Energy Sources Act (EEG) mandate real-time grid response and controllable load management for solar and storage systems, requiring the app and its integration layer to support compliance-ready data exchange with energy grid operators. From 2025, Gradion is rolling out Kotlin Multiplatform across the app, consolidating the Android and iOS codebases into a shared cross-platform architecture. This reduces duplication, simplifies future feature delivery, and provides a more maintainable foundation for the ongoing development of the the client solar app ecosystem.