Case study | Arch Solar maximizes solar ROI atop a partially shaded Wisconsin city hall

Solaredge Wisconsin project

In 2010, the municipality of Wauwatosa, Wisconsin made a commitment to cut emissions in half by 2030 and achieve carbon neutrality by 2050. A government-supervised mission, projects would need to be funded with taxpayer money, and would have to be cost-effective and remain 100% transparent. Taking budgetary risks was not an option.

After over a decade of working toward a cleaner grid, the Wauwatosa Common Council was ready for a larger project that could take its energy savings to the next level and set an example for other communities.

They landed on Wauwatosa’s City Hall complex, which includes the local Civic Center and Public Library, as the proposed site. With a flat roof area of just under an acre, it is ideal for solar modules – giving Wisconsin-based installer, Arch Solar C&I, an opportunity to present their innovative solar PV concept.

To win the project, Arch Solar would need to convince the council that the proposed solar system would (a) provide the right amount of clean energy to help Wauwatosa meet its green goals on time, while (b) offsetting upfront costs through a fast ROI.

“Being able to optimize energy production was essential to making this project financially viable,” stated J. D. Smith, Head of Business Development, Arch Solar C&I. “There are a lot of trees and buildings surrounding the City Hall complex. With a traditional string inverter system, even if just one or two modules are shaded, the performance of the entire string is reduced.”

The Solution | Higher Efficiency + Higher Uptime = Faster Payback

Wisconsin city solar PV project

Installation at a Glance:

  • 389 kW PV system
  • 3 x SE100K Three Phase Inverters with Synergy Technology
  • 518 x P860 SolarEdge Power Optimizers
  • 1036 x 375W Boviet Solar Modules

The winning solution was a 389 kW PV system with SolarEdge P860 Power Optimizers and Boviet Solar Modules. The maximum power point tracking (MPPT) of the system ensures that should one or more modules underperform, due to shading or debris, the other modules on the same string will not be affected.

Because of Wisconsin’s latitude, Arch Solar C&I needed to mount its rooftop modules at a greater angle than the industry standard 10 degrees. Component selection enabled design flexibility so that modules could be placed at different orientations and in uneven strings lengths. The Wauwatosa City Hall modules are mounted at 20 degrees to help the system accommodate lower sun angles and reduce snow accumulation, contributing to greater energy production.

SolarEdge’s Monitoring Platform also provides users with real-time performance data down to the module level. Any drop in energy production, due to shading or faults, is instantly pinpointed and reported to the maintenance team, enabling fast remediation and increasing system uptime.

Results | The City Hall project received a $40,000 Wisconsin Focus on Energy Grant and came in under the Common Council budget. In the last twelve months, the 1036-module array generated 458,011 kWh of clean energy – equivalent to 55% of the site’s total usage in this period – and reduced carbon emissions by 358 tons.

This has put Wauwatosa firmly on track to cut carbon emissions by 50% by 2030. To share its achievement with the local community as well as other stakeholders, the Council has launched a live dashboard where anyone can see how much electricity is being generated.

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