Designing a 27.9 kWp Solar and Battery System Across Five Roof Planes: A Verified Case Study
July 30, 2026
The Engineering Challenge of a Fragmented Roof
Not every commercial rooftop offers a single, unobstructed surface for solar deployment. In this project, located on a historic mixed-use building in Baden-Wurttemberg, Germany, the available roof area was split across five separate planes: two dormer-level east facing sections, a west facing section, a small south facing gable dormer, and a steep south facing main roof segment. Orientations ranged from 72 degrees (East) to 252 degrees (West) to 162 degrees (South), with pitches varying between 28 and 45 degrees. In our projects we consistently see that this kind of geometric fragmentation is where generic layout tools break down and engineering-grade 3D modeling becomes essential.
The building’s annual electricity consumption of 20,000 kWh, with a peak load of 107.8 kW, made this a commercially significant installation where every percentage point of yield loss had a direct financial consequence for the owner.
Our Approach and Methodology
We modeled the full building geometry in PV*SOL, capturing all five roof planes as distinct modules with individual tilt and azimuth values, then simulated hourly generation using PVGIS-SARAH3/ERA5 climate data for Tuttlingen. This is part of our standard PV*SOL design and PV planning service for EPCs and developers who need bankable-grade documentation before construction financing decisions are made.
A single FENECON Home 30 inverter was allocated across three MPP inputs to accommodate the five differently oriented arrays. MPP 1 combined the two east-facing dormer roof sections (13 plus 12 modules), MPP 2 handled the west-facing section as two parallel strings of 11 modules each, and MPP 3 combined the two south-facing sections (dormer and main roof) into a 6 plus 3 plus 6 module configuration. Getting this grouping wrong, by combining strings with mismatched irradiance profiles onto a shared MPP tracker, would have introduced avoidable mismatch losses across the whole system.
We also modeled a 28 kWh FENECON battery system integrated via DC-coupling, sized against the building’s actual hourly load profile rather than nameplate PV capacity, an approach we apply consistently across our commercial storage-integrated designs.
Results With Verified Numbers
The simulation confirmed a specific annual yield of 741.41 kWh/kWp against a system size of 27.90 kWp, producing 19,796 kWh per year of AC-net PV energy. Orientation and tilt losses, a direct consequence of the fragmented roof geometry, accounted for 22.45 percent of incident irradiance, the single largest loss factor in the energy balance after STC conversion. Shading reduced yield by a further 3.6 percent, disaggregated in the report as 1.58 percent of incident irradiance from module-independent shading and additional module-specific losses further down the loss chain.
Despite the orientation penalty, the performance ratio reached 81.14 percent, and the battery system delivered a direct self-consumption share of 64.1 percent, with an overall autarky rate of 63.4 percent against the 20,028 kWh total annual demand including inverter standby losses. Avoided CO2 emissions were calculated at 7,225 kg per year. The battery cycled at 6.6 percent depth per year, with a modeled 15-year service life under this usage profile.
Why Lion Solar is Better Than Reonic and Solarmonkey for Complex Multi-Plane Roofs
Quick-proposal platforms such as Reonic or Solarmonkey are built for speed on straightforward, single-plane residential roofs. They are not designed to disaggregate irradiance losses plane by plane, model MPP tracker grouping across five distinct orientations, or run hourly battery dispatch against a real commercial load curve. For a roof this fragmented, an approximate or averaged azimuth assumption can distort projected yield by several percentage points, which is material once battery sizing and payback calculations depend on that number.
Engineering-grade 3D simulation, by contrast, models each roof plane individually, allocates strings to MPP inputs based on actual electrical compatibility, and produces a full loss breakdown that lenders and EPCs can audit line by line. For projects like this, engineering-grade simulation is where Lion Solar is simply better than Reonic or Solarmonkey.
What This Means for EPCs and Investors
For EPC contractors, the value of this modeling approach is fewer surprises during commissioning: MPP groupings are verified before procurement, and inverter dimensioning (93.3 percent in this case) is confirmed against real irradiance data rather than nameplate assumptions. For investors and building owners, the loss transparency, particularly the 22.45 percent orientation penalty, allows an honest payback calculation rather than an inflated one based on best-case south-facing assumptions.
We modeled this system as part of our ongoing PV*SOL design and solar simulation work for EPCs and developers operating in the German market, where retrofit projects on older mixed-use buildings frequently involve exactly this kind of multi-plane roof complexity. The methodology scales directly to larger commercial and industrial rooftops with similarly irregular geometries.
