An important “building block” of the energy concept is the PV system on the roof (9.4 kWp). This system can generate ca. 7500 kWh electricity per year. It is assumed that about one third of this electricity is used for the building itself and two thirds can be fed into the public power grid. Based on the economic feasibility analysis, a payback period of nine to ten years is expected. This payback period may even be shortened when the charging station for electric vehicles and bikes, which is already in place, will increase their own electricity consumption.
You can find more information about the PV system, its output and performance at https://www.piko-solar-portal.com/PlantViewCharts.aspx.
On the seams of the stainless steel roof (Uginox 0.5 mm / 0.02 in with double standing seam and Solitex roof underlay), a supporting structure to hold the 36 solar modules was mounted. Because of the circular shape of the roof, both installing the roof (cone-shaped roofing sections and joints) and installing the supporting structure for the solar modules (aligned at an angle of 15 degrees and attached to the cone-shaped standing seams) were a technical challenge.
From a building biology perspective, inverters, which are needed to convert DC electricity into AC electricity, can pose a problem due to the emission of major electromagnetic fields. The following strategies were implemented to virtually eliminate any associated risks for the occupants of the IBN building as well as the neighbors:
- Selection of a low-EMF inverter
- Proper grounding
- Placing inverter far away (> 3 m / > 10 ft) from areas where people spend considerable amounts of time such as at the desk or in bed
- Running wiring between PV modules and inverter in metal conduits that are connected to the equipotential bonding bar
- Shielded cable between inverter and meter in the utility room (ground floor)
At a distance of 1 m (3.3 ft), the following EMF levels were measured at a time of high solar exposure with 700 to 800 W/m at 11:15 a.m. on 26 June 2014 (AC electric field in V/m and AC magnetic field in nT; testing equipment = NFA 1000 broadband meter by Gigahertz Solutions, frequency range 5 Hz to 1000 kHz):
- Inverter on: 36 nT, 0.4 V/m
- Inverter off: 6 nT, 0.0 V/m
- Continuous control measurements in indoor spaces with broadband meter and RF spectrum analyzer
The inverter is tied into the computer network. Thus the electricity output can be looked up on the computer screen at all times.