The solar facade unfortunately does not get off the ground

Even from a distance, the facade of the sports and leisure facility in Wallisellen shines out at visitors. The red splash of color on the spacious sports grounds of the Zurich agglomeration municipality has an energy background. With this project, the building owner and the local energy service provider are treading innovative paths to promote renewable electricity production. Two facades are equipped with colored solar cells. Together with photovoltaics (PV) on the roof, the 3800 square meter solar surface provides 600,000 kilowatt hours of electricity annually. This is enough to produce renewable energy for 140 households, according to the local energy service provider die werke.

Treat the ice field with solar power

The solar plant on the sports grounds in Wallisellen is currently one of the top 15 in the canton of Zurich in terms of size. It is the second power-generating façade of this size in the city of around 15,000 inhabitants. With the system, the sports facility can supply itself with electricity over the course of the year. The operators also use solar power in the fall to prepare the 3400-square-meter ice field. In winter, it is cooled in a CO2-friendly way thanks to the PV system. But the financial side is also interesting: According to the energy provider, the solar power is cheaper than that from the grid.

The Wallisell-based energy service provider has taken decarbonization a step further. It wants to increase its PV production tenfold by 2030: "Our goal is ten gigawatt hours of solar power, which would enable us to supply up to 2,500 households," says Louis Krähenbühl, Product Manager Energy Supply. In the contracting process, werke has PV systems installed at the customer's request.

The lighter the color, the greater the power loss

With solar energy, practically all colors and diverse shapes are possible today, says Krähenbühl. But he warns: special requests would drive up costs. Krähenbühl points out an interesting point about colored PV modules: The lighter the color, the more power loss. If, for example, a builder wants a façade with white modules, he would have to reckon with a loss in electricity yield of around 40 percent. With the reddish modules used for the sports facility, the loss is around 20 percent.

It goes without saying that a solar façade is easier and more cost-effective to implement in a new building because it can be planned at a very early stage.

The local energy service provider would like to implement more solar facades, because they are particularly interesting in the winter months when the demand for electricity is high. However, Krähenbühl explains that it is not easy to find suitable surfaces, especially in existing buildings. "Often, the well-sunny sides of a house are already equipped with large windows or balconies."

In addition, the building owner tends to be critical about the aesthetics of his house facade, even though the color palette and the choice of shapes for PV modules are now wide. A solar system on the roof meets with much less resistance from the homeowner.

This is a pity, because the solar cells on the building façade have various advantages over a PV system on the roof: According to experts, the electricity yield is more balanced throughout the year - ergo ideal for the winter half-year with a lower position of the sun. In addition, no snow remains on the vertically installed solar modules.

Building fan-shaped houses Beat Kämpfen (Kämpfen Zinke + Partner Architekten) is also committed to more solar architecture. In 2001, he realized Sunny Woods, Switzerland's first zero-heat energy house with a thin-film PV system on the roof, which met with a great response at the time. But his repertoire also includes buildings with a solar façade, because it is clear to him that nowadays the focus is on promoting winter yield. In 2019, he received the Swiss Solar Prize for his wooden multi-family house realized according to Minergie-P with a brownish photovoltaic building envelope at the Höngg site in the city of Zurich (see photo below). What is special about this building are the glass PV modules, which are printed in color with a small-scale grid. They also contain black, but not visible, squares. Therefore, the power loss of these modules is less than 20 percent.

In order to generate more renewable energy in the winter, Kämpfen basically advocates new architecture: "The optimum would be fan-shaped houses with as large an area as possible with a southeast to southwest orientation." In terms of design, it is often difficult to equip existing buildings with solar modules on the facade.

Planning is complex and costly, which drives up costs, the architect said.

Exemplary renovations with solar facade

Despite all the complexity - one person who does not shy away from renovations and conversions with retrofitted solar facades is Karl Viridén. With his architectural office, he has already shown several times what is possible in this respect and has set corresponding accents: The office building of the insulation manufacturer Flumroc in Flums SG, which was renovated a long time ago and is aesthetically successful, is exemplary; it mutated into a plus-energy building - and once won the Solar Prize: an example of successful PV integration on the facade (see photo above). The architecture firm has also given a new, almost inconspicuous photovoltaic envelope to a 40-year-old apartment building with 28 new apartments in the city of Zurich. A solar dress in a grayish hue, which thus has a power loss of around 39 percent compared to a black solar façade. Nevertheless, this old building was renovated in such a way that it is now a PEB, i.e. a plus-energy building, which produces more electrical energy on an annual average for heating, hot water and electricity than it requires. This renovated building is a lighthouse project supported by the Swiss Federal Office of Energy (SFOE) (see photo below).

New SIA leaflet coming

If you ask the solar architect Viridén why things are not moving faster with the facades, he speaks plainly: "Only a few architects are sufficiently versed in this area. There is a lack of support and standards, and people are probably afraid to take risks." His hopes rest on the Swiss Society of Engineers and Architects (SIA), among others. Currently, the new SIA data sheet 2062 is being prepared, which deals with the integration of photovoltaics on buildings. This could pave the way for his professional colleagues to increasingly approach the topic, Viridén says. The hesitancy of builders and architects is unlikely to be due to the cost issue. "Within 15 years, a builder has recouped the extra cost of a solar façade over conventional cladding with the electricity yield." But perhaps many would not know that.

The solar potential would be great

It is well known that Switzerland's electricity consumption is significantly higher in winter than in summer. This is why there is an import surplus of four terawatt hours (TWh) on average during the cold season. This is likely to increase with the closure of further nuclear power plants. The rapid expansion of renewable energies is particularly important for security of supply, according to the Federal Council's report "Electricity generation in winter thanks to photovoltaics", published in June 2021. The study, which goes back to a postulate by former SP National Council member Mathias Reynard, shows how photovoltaics on and on buildings could increase electricity for the winter half-year: The solar registers of sonnendach.ch and sonnenfassade.ch show an annual energy yield of 50 TWh for buildings in Switzerland and 17 TWh for the most suitable roof and facade surfaces, i.e. a total of 67 TWh.

Increased use of winter-optimized PV systems

According to the Swiss Federal Office of Energy, annual electricity production from PV systems could be around 34 TWh in 2050. The fact is that the systems installed in this country produced around 2.5 TWh of solar power annually at the end of 2019, of which just 0.7 TWh, or around 27 percent, was produced in the winter half-year.

In the aforementioned report, one has worked with several scenarios: In the "Maximum winter electricity potential" scenario, the paper concludes that winter production could be increased to 35 percent - at least in purely theoretical terms. Because to achieve this, the most suitable building facades would have to be fully utilized. But that is hardly realistic, as the federal government writes. The costs of this scenario would also be disproportionately high.

With the scenario "Incentives Winter Power", a share of 30 percent could be targeted. This would mean that more emphasis would have to be placed on winter-optimized PV systems. In concrete terms, this would mean that more PV systems would be installed on south-facing facades. However, according to the SFOE, such façade systems are hardly ever built today. The report therefore suggests that the addition of façade systems could be promoted, for example, by means of a higher one-off payment, similar to that for integrated systems. Of the 34 TWh of solar power in 2050, around 10 TWh could be produced in winter, and at reasonable cost.

Notes:

- The detailed report "Electricity generation in winter thanks to photovoltaics" can be found here: www.newsd.admin.ch/newsd/message/attachments/67326.pdf

- Anyone who would like more information on the economic efficiency of PV systems, also at Facades, would like, will find under: https://pubdb.bfe.admin.ch/de/publication/download/10325

Strong growth - facade remains niche

The latest figures for the SFOE's Solar Energy 2020 statistics were recently published. According to these, the addition of photovoltaics (PV) in Switzerland increased by 48 percent year-on-year to a new record of 493 megawatts. In total, solar panels with a capacity of nearly three gigawatts were installed as of the end of 2020, covering 4.7% (2019: 3.8%) of Switzerland's electricity demand, the trade association Swissolar writes. An increase compared to the previous year was noted in all size categories and application areas. The increase is particularly high for systems on industrial, commercial and service buildings and for systems over 100 kilowatts.

The solar facade still ekes out a niche existence, as the figures from Swissolar clearly show: Of the 19410 grid-connected systems installed in 2020, only 70 are PV systems (tilt angle of 75° to 90°) on facades.

Info: www.swissolar.ch