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Holistic energy concept

60 percent lower primary energy demand

The project developer maxsolar focuses on holistic energy concepts. In an apartment building in Traunstein, Bavaria, the company succeeded in saving 50 percent of the operating costs and 40 percent of the electricity costs. The biggest challenges were in the design and wiring of the PV system.

The Traunstein real estate developer GreenRock Management built 30 residential units in the "W11 Stadtterrassen Traunstein" project, spread over four residential buildings and an underground car park with 57 parking spaces. The focus of this property is on one- and two-bedroom flats with large terraces and balconies, as well as spacious penthouse flats and four commercial units.

Passive house subsidised by the KfW [investment & development bank]

The building is a KfW40+ efficient house, i.e. it has an annual primary energy demand that is 60 percent lower than the minimum standard. To be eligible for funding from the Kreditanstalt für Wiederaufbau [credit institute for reconstruction], the building must also generate electricity based on renewable energies and have a stationary battery storage system, a ventilation system with heat recovery and a visualisation of electricity generation and consumption.

For electricity generation, the funding guideline stipulates an annual yield of at least 500 kWh per residential unit plus 10 kWh per square metre of building floor space. "However, the roof area alone was not sufficient to generate this yield with solar power modules," explains Simon Heigenhauser, who is responsible for the project at PV project developer maxsolar. This is why maxsolar has installed the solar modules not only on the roofs, but also above the balconies and the terraces of the flats. Because the façade modules were not allowed to influence the external architecture, they were planned facing the inner courtyard.

On the standing seam roofs, maxsolar132 attached monocrystalline half-cell modules from Q Cells with Schletter Rapid 16 clamps. The 330-watt modules face northeast, northwest, southeast and southwest. Above the balconies and terraces, on the other hand, maxsolar mounted 21 monocrystalline solar glasses of the Aleo Elegante type with mounting systems from Gruber Metallbau Industrie GmbH. The 190-watt modules also face northeast, northwest, southeast and southwest.

Complex interconnection

With a 3D simulation using the PV-Sol design tool, the company succeeded in optimally designing the system despite the different inclinations and orientations and avoiding yield losses due to shading. "We took the building plan as a basis and used simple geometric bodies to recreate the building, simulate the shading and generate a yield forecast," explains Heigenhäuser.

In addition, his team equipped the modules with power optimisers from SolarEdge. "This allowed us to interconnect one to two modules at a time and to interconnect the rooftop and façade modules together without any loss of yield." Because the MPP is only generated for one or two modules at a time, maxsolar was able to interconnect differently oriented modules in one string without affecting the total MPP and the total yield.

With success: the forecast resulted in a yield of 46,660 kilowatt hours per year. With the self-generated and stored energy, the house residents can cover their entire energy needs. In addition, the solar system saves 27,996 kilograms of carbon dioxide every year. According to Heigenhuser, the costs for the photovoltaic system, the storage unit and the charging infrastructure will have paid for themselves after seven to ten years.

Protected from fires

The PV experts ensured fire protection with generator junction boxes with several surge protectors on the outer skin of the building. "With the generator junction boxes, we can avoid DC overvoltages entering the building," explains Heigenhauser. This was necessary because the two SolarEdge inverters are located in the basement and the DC distance between the building entrance and the inverter must not exceed ten metres.

Because the roofs are only connected to each other via the lower part of the building, the installers could not connect the strings above the roof cladding, but had to lay the DC cables through the building and secure them separately. "This led to a lot of cabling and many discussions with SolarEdge," reports Heigenhäuser.

The interface to the fire brigade's fire alarm centre ensures that the PV system switches off on the DC side in the event of a fault.

Managing the energy

Solar surpluses are stored in a battery with a capacity of around 50 kilowatt hours. This was built in one of the basement rooms by MaxSolar's sister company Smart Power. The intelligent energy management system ensures that the grid is relieved and peak loads are limited. This can save considerable costs, because electricity prices are based on the highest peak load drawn in a year.

Because the KfW funding guidelines stipulate that grid-connected PV systems feed in a maximum of 60 percent of the installed power, maxsolar has installed a grid analysis device at the grid connection point. The unit outputs the signals to the system controller via the energy management system.

Charging electric cars in the underground car park

In GreenRock Management projects, every flat buyer receives their own wallbox for their electric car in the underground car park if they wish. While the standard package includes three charging stations with two 22 kW charging points each, maxsolar also customises the stations to meet individual customer needs.

Reduce operating costs

Because of the constant interior temperatures, conventional heating is not required in the passive house. The low residual heat demand is instead covered by an air-to-water heat pump. In summer, this can optionally be used to cool the floor because the heat pump's process can be reversed to conserve resources.

The decentralised ventilation systems replace the stale air with fresh air from outside. Heat exchangers store the heat contained in the exhaust air so that around 80 percent of the thermal energy can be recovered. Because the insulation and the energy-optimised substructures meet the highest standards, operating costs are reduced by around 50 percent.

Save electricity costs

The real estate developer GreenRock provides further cost reductions with a tenant electricity model. With tenant electricity, tenants can save around 40 percent of their electricity costs.

 

Author: Iris Krampitz, Krampitz Communications, Cologne

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