Frankfurt needs much more photovoltaic area

Less than 1 percent of the electricity in Frankfurt is currently produced by photovoltaics. Since the energy turnaround, the German government has envisaged covering 80% of Germany's electricity requirements from renewable energies by 2050. For Frankfurt, with its total electricity consumption of around 7,100 GWh/a, this means that around 5,700 GWh/a must come from renewable energies. And since wind cannot be expanded in Frankfurt because of the airport, photovoltaics will have to make the most important contribution.

Why isn't more photovoltaics being installed at the moment?

On the one hand, it should not be underestimated that our power grids were not originally designed to collect and transmit decentralized and highly volatile surplus electricity. However, while control systems for this purpose are being further developed and expanded, property owners, particularly in inner-city locations, are not yet following suit to the same extent.

For one thing, homeowners in existing buildings balk at the expense of tinkering with a working, leak-proof roof or running new lines through rented space.

In addition, the power supply from the central utility Mainova is cheap, convenient and already connected. The interplay between self-use of self-generated electricity and feeding the surplus into the utility grid also represents an additional effort for many homeowners in terms of control technology.

And another important knockout criterion for many building owners: photovoltaic systems usually do not change the appearance of a building in its favor, since they are classically developed primarily with efficiency in mind, not beauty.

 On the bridges, all this is to change: everywhere where citizens can see the surfaces, aesthetically pleasing or inconspicuous photovoltaics will be installed. On the outer arms of the bridges, on the other hand, where hardly anyone looks at them from the side or above, much more efficient and visually less attractive photovoltaics will be used.

On the bridges, there is also no individual billing per building with the supplier Mainova, but there is an internal "netting" within the quarter, and a balancing with Mainova only takes place via internal supply nodes, the "supply centers".

Roofs, facades, walls, stations - on the Frankfurt bridges can be installed on many surfaces aesthetically beautiful photovoltaic modules from the pipeline of research and industrial development

There are different types of areas for mounting photovoltaic. The most important are: (1) building roofs, (2) roofs of stations or canopies over pathways, and (3) the sides of the bridge body along with the columns. PV modules can also be mounted vertically (4), e.g., on the guardrails or privacy screens at the edge of the bridge as well as on facades.

But they all have one thing in common: All photovoltaic modules should blend aesthetically into the cityscape or the "bridge image" in everyday life and not be particularly conspicuous.

On the Frankfurt bridges, a total of 1 million square meters of surface can be equipped with photovoltaics: 475,000 m2 of roof surface, as well as another 525,000 m2 of other special bridge surface.

If all surfaces on the bridges were used, even more square meters would be available for PV modules. But in the city center, where the bridge passes through built-up areas and must therefore be beautiful from all sides, little photovoltaics will be installed on and around the bridges.

Even on the outer arms, where the bridges still pass through residential areas, photovoltaics are installed only aesthetically integrated.

Because it would be a pity if modern art or handicrafts on the sides of the bridges or on the columns would be aesthetically impaired or even covered by technical modules. In addition, many columns are overgrown with climbing plants that would cover the photovoltaics.

But as soon as the bridges lead out of the city and no residents are looking at them from the side (and no tall buildings on the right and left are shading them), all possible surfaces will be equipped with photovoltaics.

Therefore, the equipment of areas with photovoltaics may not be carried out everywhere in the same form, but must be segmented depending on the bridge section.

The entire bridge network was segmented according to the "degree of beauty" of the installable photovoltaics or the degree of inconspicuousness

Photovoltaics on the ring road and along residential buildings are planned to be aesthetically pleasing or extremely inconspicuous, while highly efficient classic solar modules can be installed on the outer arms in some sections

The energy calculations take into account (1) the tilt angle, (2) the direction, as well as (3) the aesthetic effect on the energy yield of the panels, and last but not least (4) the shading effect of the neighboring buildings and trees.

(1) The construction of the bridges will create over 500,000 m2 of roof space on the bridge buildings, all of which could theoretically be used for photovoltaics - but even some of it can already generate 58 GWh/a of electricity

(1) Roofs: Green roofs on the bridges, roofs with large roof terraces or even roofs with special artistic features will not be able to be covered with photovoltaics

In the urban area of Frankfurt, one can "harvest" up to 275 kWh per square meter of photovoltaic surface per year with the most modern technologies, but only if it is an unshaded area on the roof with the appropriate orientation towards the sun.

Overall, however, PV modules with a slate or tile appearance are only installed on 80% of the roofs, which are mainly on the outer arms. Although these modules can be integrated aesthetically to a large extent, they have an efficiency ratio of only 12% (in contrast to high-efficiency conventional modules, where it is over 25.5%).

No PV at all is used on the roofs of downtown buildings, because industrially manufactured photovoltaic components - no matter how beautifully colored or shaped - do not go well with artisan-covered slate, copper, or tile roofs in downtown areas.

Since there are numerous other surfaces on Frankfurt's bridges where PV modules can be installed, it is possible to "afford" not to install photovoltaics on the roofs of the buildings on the inner city ring of bridges. The roofs there are built by the Master Academy of Arts and Crafts in the traditional style and have a cultural-historical function - so they make a valuable contribution to society in a different way.

(2) Canopies: The paths on Frankfurt's bridges are partially covered by canopies that protect pedestrians from the heat of the sun or rain and generate nearly 20 GWh/a of electricity.

The aesthetics of the PV modules, as everywhere on the bridges, depends on whether or not the PV modules can be seen from buildings along the bridges. In certain places where the bridges are very high (e.g. at the IT college), the sides are equipped with PV modules up to a height of 4.5 meters.

(5) To supplement the power supply, highway canopies may be continued at the ends of the bridges

To minimize the expense of these PV installations, the "highway extensions" will only be installed where the highway runs straight, otherwise the expense of custom fabrication of the curved PV roof modules would be added. All seven arms of the Framkfurt bridges terminate over federal highways: A total of 30,000 m2 of trunk road can be covered with such "extensions" and equipped with PV modules in the direction of the sun and at the optimal angle. This will generate a total of 7 GWh/a of electricity.

(6) Parking spaces next to bridges: Along the Frankfurt bridges, 380,000 m2 of parking spaces can also be equipped with PV modules.

380,000 m2 of photovoltaically activatable parking lot canopies are to be built on the right and left over the parking lots of DIY stores, commercial units or offices in the course of bridge construction - at no cost to the property owners. These have the advantage that their customers can get out and in of their vehicles protected in all weathers: dry feet in the rain and not in an overheated car in the summer. In addition, their employees or customers can charge the increasing number of e-vehicles during parking time via charging options at the stand columns.

(6) Roofs next to the bridges: PV modules can be gently placed on 725,000 m2 of roof space of companies and institutions along Frankfurt's bridges

Along the Frankfurt bridges are flat roofs of large corporate buildings or institutions, many of which are suitable for PV modules. For most property owners, rail systems and modules resting on load-distributing building protection mats are the most attractive, as they do not damage the thermal insulation and roof cladding.

By cooperating with the bridge company, property owners have a competent partner in the installation, operation, usage distribution and storage for the PV systems on their roofs - making the installation of PV modules on the roof convenient and advantageous for them.

In total, 417 GWh of electricity per year can be generated with PV modules on and along the bridges

The largest contribution to this on the bridges is made by the roofs of the bridge buildings with 58 GWh/a, as they can be aligned at an optimal angle of 37 degrees to the sun on flat roofs that cannot be seen. In second place are PV modules mounted on the sides of the bridges with 31 GWh/a. These are vertically integrated, i.e. are only "splayed" from the bridge side to a limited extent or in some places at the optimal angle towards the sun.

However, large parking lots and buildings next to the bridges offer the greatest potential: Since most of them are located along the outer arms of the Frankfurt bridges and can hardly be looked down on from residential buildings, large parts of their surface are covered with highly efficient PV modules that are optimally oriented towards the sun and produce a total of 277 GWh/a, almost twice as much as the PV modules directly on and next to the bridges.

The concept of energy bands is easy to implement, comparatively inexpensive, and not invasive to nature or humans

Approximately every 15 meters, a pole made of iron trusses is erected, similar to conventional electricity poles, only much smaller: the truss construction saves material and ensures that motorists maintain a clear view along the road.

At a height of about 5 m, the masts are connected to each other and photovoltaic modules are mounted on the connecting webs in a row (like a ribbon) between the masts.  A second row is placed about 2 m above the first, so that the shading of the lower row remains slight.

The PV modules have a width of 1.50 m and are aligned at the optimum angle to the sun. They are highly efficient black PV modules. Since they are installed over the edge of roads that are already dark gray, they can be installed for kilometers without causing a negative albedo effect or heating up the small-scale climate around them.

However, the actual optimal use of these enormous amounts of additional electricity must be determined by the local supplier, Mainova: 140 GWh/a of this is consumed by the Frankfurt Bridges neighborhood itself. A large part of the remaining 377 GWh/a flows into green hydrogen production and vehicle supply along the bridges.

No increased health hazards are to be expected from a photovoltaic system if it is installed professionally

The zoologist and researcher on the magnetic sense of animals, Professor Dr. Hynek Burda (Duisburg), investigated in a study the influence of low-frequency fields on melatonin secretion in the body and came to the conclusion that calves exposed to alternating electromagnetic fields produce less of the sleep hormone melatonin in winter than in summer - with the effect reversing in summer.

The causes of this are unclear and not yet researched, but from some effect of magnetic fields on the human organism can not be excluded.

Therefore, it is crucial to professionally reduce the effects of magnetic fields to a completely harmless level when planning integrated photovoltaics: Laying DC lines of the PV system as close as possible to each other to reduce alternating magnetic fields, paying attention to low line loop formation, maintaining distances to the inverter - if available, professional grounding, etc. are among the rules that specialist companies all apply.

The additional electrosmog pollution caused by a PV system is also correspondingly low from a building biology point of view and harmless to health if executed correctly.

With the expansion of wind and solar power, there will be an increasing abundance of energy at peak times

On an annual average, wind and photovoltaic systems are so effective that Germany will not only have enough electricity, but in the future, after the generous expansion of these technologies, even more than enough. The problem: Depending on the wind and sun, the electricity is not necessarily produced at the time it is also consumed. Whenever more electricity is produced than is consumed, plants that produce green electricity must either be shut down, or the electricity must be sold abroad or to surrounding areas, or sold at negative prices. Especially because electricity storage options such as batteries and pumped storage power plants are currently only available to a very limited extent, there is then too much electricity at certain times that cannot be usefully used anywhere without storage. Because of this "surplus" of electricity, the number of hours when electricity is sold at negative prices has increased significantly in recent years: Anyone who wants to sell electricity still has to pay the buyers money in this case. This is because there must not be too much electricity in the grid, as the power grid should not be overloaded, otherwise there is a risk of outages.