Germany shopping center incorporates 2.2 MW rooftop PV system

In the early spring of 2016, the owner of the Nordhorn shopping center faced a problem that many other owners with older commercial buildings encounter. The commercial site, which houses a major supermarket and many smaller shops, was plagued with a leaky and asbestos-laden roof. The enormous surface area of the rooftop meant that the renovation work would be very costly. To offset this huge outlay, the owner came upon the obvious idea to combine renovation of the roof structure with the installation of a solar PV system. The solar energy generated by the rooftop PV plant could be sold back to the grid and the FiT revenue would help to pay off this large investment.  

An important requirement of the supermarket tenant was that their business operations were not hindered by the roof renovation measures. To connect a new solar system to the existing grid connection point at the site, would mean the exchange of old electrical equipment and a minimum of two weeks emergency power supply would be needed for this to happen. Constructing a completely new grid connection for the new photovoltaic rooftop system was determined to be the best way to avoid interruption of business.

Two firms were selected to complete the project. Prinz Solartechnik, with 25 years in renewable energy, was selected to plan the complete solar system up to the grid connection point. Wopereis Group, with expertise in steel rooftop systems, was selected for the planning and construction of the roof and solar system.

In March 2016, the project construction began. The original gable roof was replaced with similarly designed steel structure which could be erected quickly. The building rooftop consists of 7 saddle roofs positioned in rows that are orientated to the northwest and southeast, respectively, and the tilt angle set at 11 degrees. Due to the different orientation of the two halves of the gable roof, the optimum solar irradiation for energy harvest is reached at different times of day.

It was therefore, ideal to use solar inverters with 2 maximum power point trackers (MPPT’s), whereby each MPPT could work independently at different times of day to provide optimized power from each roof surface. When compared to a flat rooftop, the saddle roof has the added advantage that additional solar modules could be incorporated in the design due to the larger surface area of the gable roofs.