Around 438 GWh/a of thermal energy is generated or collected by Frankfurt bridges and forwarded for storage

With the help of the 15,000 columns of the Frankfurt bridges, around 35 GWh of thermal energy can be extracted from the ground each year - a classic use of near-surface geothermal energy.

In addition, 1 million square meters of PVT solar modules on and along the bridges can generate around 303 GWh of thermal energy per year. Another 100 GWh/a can be generated by waste heat from data centers and industrial parks in Frankfurt. Of this total of about 403 GWh/a of thermal "energy harvest," 107 GWh/a can be consumed in winter immediately after generation. The remaining 296 GWh/a can be stored in the ground with the help of several thousand borehole thermal energy storages (BTES), so that at an efficiency factor of about 30% to 35%, about 92 GWh/a can be extracted and used again for space heating in winter.

Chapter content: Natural geothermal heat is extracted from the ground and, in addition, heat collected above ground is stored in the ground

The soil in Frankfurt is comparatively warm near the surface, with a temperature of 14 °C. The columns of the Frankfurt bridges project with their foundation piers 15 to 20 m deep into the ground. Probes in the pillars can realize space heating or cooling for the buildings on the bridges through thermal exchange as required.

The heat that accumulates behind the photovoltaic surfaces - with an environmentally compatible liquid as a carrier - is sent down into the depths through probe fields, stored there and brought back up again as needed. The probe fields can be installed in the course of the bridge construction in the (anyway) torn up ground and project down to a depth of 250 m.

Both systems use de facto solar energy and not geothermal energy from the glowing center of the earth, as ground-source or "classical" geothermal energy does.

Geothermal piles can be used to extract heat available in the ground for heating, or to send solar heat collected above ground down into the ground and store it there until it is extracted

Geothermal piles under Frankfurt's high-rise buildings have both functions

Classic geothermal energy via foundation piles in the ground is already being used in Frankfurt, especially for high-rise buildings: Here, for more than 20 years, it has been considered directly during construction to have the foundation piles go 30 to 100 m deep under a high-rise building and to equip them with line loops (probes) in order to use the so-called "near-surface geothermal energy", but also to transport heat that accumulates - especially through the large window fronts - down into the ground in order to regenerate it or to store the heat there in summer for extraction in winter.

Unfortunately, however, this cannot be transferred to other buildings with a citywide roll-out, as the subsequent installation of deep, geothermally utilized foundation piles in existing buildings is impossible.

Two basic mechanisms for heat transport are used on the Frankfurt bridges:

I) The foundation pillars of the bridge columns are equipped for convective heat transport.

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II) in the immediate vicinity of the bridges, probe fields for conductive heat transport will be created.

Convectiveheattransport

Here, the heat transport is dependent on the groundwater temperature and, above all, the groundwater flow: If the groundwater (and thus the ground in which the probes are located for the purpose of heat extraction) has a temperature of 14 °C, for example, but flows slowly or hardly at all, then the site will cool down over the years because not enough water with the temperature of 14 °C will flow in.

Correspondingly, the effectiveness of convective heat transport depends on the porosity of the soil and the resulting flow velocity of the groundwater: In more porous soil, the water flows faster.

In Frankfurt, large parts of the ground are suitable for convective heat transport: it is estimated that 12,750 of the bridges' 15,000 columns can be designed for this purpose.

Conductiveheattransport

Conductive heat transport occurs along temperature gradients: Depending on the thermal conductivity and heat capacity of the subsurface, heat can be sent into the ground and stored there: The ground environment of the probes stores the heat until it is extracted again at a later time.

How well heat can be stored depends on the rock type and porosity, but also on the water saturation: A certain saturation in itself is not bad for heat absorption, but if the water has too high a flow velocity, too much heat is transported away instead of remaining stored locally.

During the construction of the Frankfurt bridges, probe fields will be installed mainly north of the Main River, where the Frankfurt clay with good storage properties occurs in greater quantities.

The hydraulic permeability of the soil has a decisive influence on heat transport. Frankfurt has relatively sandy soil in the south, while in the north there is often "Frankfurt clay" directly below the surface.

With high hydraulic permeability, the propagation of the so-called "heat plume" is clearly characterized by convective heat transport - which is positive if one is only dependent on ground heat (i.e. on the influx of heat through groundwater). For thermal storage in the subsurface, on the other hand, the high hydraulic permeability of heat collected oberidically is less suitable. Since groundwater can be found almost everywhere in Frankfurt on the first 20 meters in depth, 85% of the piles of the bridge columns can be equipped with probes for convective heat transport.

With low hydraulic permeability, the propagation of the heat plume is predominantly characterized by conductive heat transport: Although this is unsuitable for the extraction of the soil's own heat, since there is no "replenishment" of heat by groundwater. However, it is all the better for thermal storage of heat collected above ground in the subsurface.

In the course of the construction of the Frankfurt bridges, the road surface will be renewed in each case, so that probe fields can be installed in the roadside area along the bridges on this occasion.

Both geothermal concepts are used on the bridges: The columns extract heat from the ground there totaling 35 GWh per year for heating. Independently, about 403 GWh of heat is collected annually: Around 303 GWh is added by PVT modules and another 100 by waste heat from data centers. The portion of this generated in summer is stored in the ground, while the portion generated in winter is consumed directly.

Depending on whether the heat already in the ground is used or the solar heat collected above ground is sent into the ground for storage, different borehole heat exchanger installations must be used.

Heat exchange between the soil and the probes takes place at the Frankfurt bridges using two systems

Case 1: The Frankfurt bridges use ground heat by extracting its heat from the ground via the piles of their columns, in which probes are mounted

The columns of the Frankfurt bridges reach down to a depth of twenty meters to extract a total of 35 GWh/a of energy:

During the construction of the columns, before the reinforcing steel is lowered into the borehole to be filled with concrete, "probes" (black plastic tubes) are inserted into them on the inside. Later, the brine flows through them, transporting heat up from the ground in winter and vice versa down from above in summer.

The energy piles of the Frankfurt bridges have a diameter of 90 cm.

In the uppermost 10-15 meters, the soil temperature is determined by the climate, i.e. atmospheric factors such as solar radiation, air contact and the temperature and amount of rainwater that seeps away (below this, down to a depth of about 50 meters, the temperature is a constant 10 °C throughout the year, according to a rule of thumb for Central Europe). Due to its location in the Upper Rhine Graben, the soil temperature in Frankfurt is about 12 °C or more in many places from a depth of 2 meters.

Near-surface geothermal energy does not use the earth's core heat

The pillars of the Frankfurt bridges are founded about 20 meters deep and are equipped with geothermal probes. Even there, the geothermal heat of the earth's core is far from being reached as it is revealed by the beautiful geysers in Iceland, but only uses the solar heat that penetrates the earth's surface.

How much heat the soil of a region stores depends not only on the climate of the region, but also on the composition of the soil. Everyone is familiar with the effect: some materials heat up quickly in the sun, but also give off the heat again quickly when it gets cold; other materials, on the other hand, take a while to warm up, but then they also retain the heat.

The amount of energy that can be stored in or extracted from the ground near the surface depends on 1) the climate of the region and 2) the geological composition of the subsurface.

As part of the preliminary planning for the Frankfurt bridges, which will take several years, geological surveys must be carried out for each section of the bridge route to determine how it is built up and how warm it is or can become when energy is added. This is because some layers store heat better, others less well.

The soil beneath a city is usually very heterogeneous, and Frankfurt is no exception. In layman's terms and in a generalized way, one can say that south of the Main River it tends to be sandy, while north of the Main River one quickly encounters clay when digging. If a column pile is placed in a sandy environment, it absorbs heat more easily, but also releases it more quickly. Clayey soil, on the other hand, takes longer to heat up, but then also retains the heat longer.

So close to the earth's surface, another important factor for the heat storage capacity of the soil is the groundwater, which is encountered after only a few meters when digging in Frankfurt: If a lot of groundwater seeps through the soil at a relatively high rate (as is the case with very sandy soil), then this can have consequences for the heat supply of the piles upwards in two directions: On the one hand, it means that there is always a certain base temperature "flowing in," because the groundwater under Frankfurt has between 12 and 14 °C - in some cases even more. On the other hand, additional heat that is transported down into the earth by the piles in summer is also transported away again more quickly.

So if you want to calculate how much heat you can get from the ground of Frankfurt or how much you can store there, you need complex geothermal calculation models for different geological sections.

3) Groundwater is the third important factor for the heat storage capacity of a soil.

The groundwater under Frankfurt has an average temperature of 12 to 14 °C, similar to the soil through which it flows. The piles of the columns extract heat from the ground in winter, but also feed large amounts of heat back into it in summer (otherwise ground cools over the years).

Now, it is easy to imagine that groundwater flows faster in sandy soil than in clay layers. When it "washes around" the piles, they can absorb the ambient heat, which averages 13 °C, very well - better than from "dry" soil. But if the piles conduct heat down, then this is also partly taken along or washed away by the groundwater.

Therefore, it is important to determine the flow rate per soil layer in order to deduce how capable a soil is of storing water in the long term.

The flow velocity of groundwater near the surface is low in most places in Frankfurt. But there are also isolated rip currents. There is currently no comprehensive groundwater model for Frankfurt.

In Frankfurt, groundwater is encountered after a depth of about 2 to 5 meters, depending on where you dig. These are not yet rushing rivers (there are also, but usually much deeper), but moisture that seeps through the ground.

One energy pile of a column of the Frankfurt bridges can extract an estimated average of 1 kW of heat from the ground

This results from the consideration of how much heat extraction per meter (W/m) is possible: This differs from earth layer to earth layer, therefore it is weighted with the "thickness", the experts speak of "thickness", of the respective earth layer.

- i.e. respective (W/m) x respective thickness (m).

The result of the calculation: The heat extraction (W) of a 20 m pile was between 885 and 1148 W in the scenario calculation for the Frankfurt bridges. Accordingly, an average heat extraction of 1000 W or 1 kW was applied per pile.

It is important in the analysis to estimate the evolution of groundwater temperature downstream of energy piles

Not all sections can be geothermally utilized at the same time, since the energy piles influence each other, especially if they are located in the direction of groundwater flow

The total distance (approx. 60 km) is therefore divided into two simplified sections:

Sections A: Sections in the direction of groundwater flow - these have a reduced energy potential.

Route sections B: all other route sections - these can exploit the geothermal energy potential.

Whether there is a mutual influence of the energy piles depends on the groundwater flow direction

Effect of groundwater flow direction on the totality of the column energy piles of the Frankfurt bridges.

The bridge section, which is about 60 km long, is supported by about 15,000 columns, 12,750 of which are equipped with geothermal piles. Since of the 8,760 hours that the year has, only one third of the time (2,700 hours) the geothermal pile system is in use, almost all of the piles are used with a time lag.

Regeneration: Especially in summer -but also during intense sunny days in winter- excess heat must be sent into the soil so that it does not cool down over the years

Some communities have already made the painful experience: If one permanently only gets heat from the earth through near-surface geothermal energy to heat houses, without also sending heat back down, then the ground cools down over the years.

So, in the first of many winters, heat could be extracted from the ground in Frankfurt: The ground and groundwater in Frankfurt have an average temperature of about 12 - 14 °C. Already in the next winter, however, the soil temperature would be slightly lower at the point of heat extraction. Over several years, the effect adds up to a temperature loss of several degrees Celsius. Therefore, the soil must be "regenerated" every summer, which means that heat must be sent down into the soil again.

In the case of the Frankfurt bridges, two heat sources are used for regeneration: 1) the residential cooling of the bridge buildings in summer and 2) the heat from the PVT (photovoltaic thermal collectors) modules. Through these so-called "coupling systems", the ground temperature is restored as the heated fluid flowing down from above through the probes releases heat to surrounding soil.

Coupling system ensures that the ground temperature remains almost the same despite decades of use - example simulation for Kennedyallee in Frankfurt

As part of the present feasibility study, the development of the probe inlet temperature over 100 years was simulated for a section of the Frankfurt bridges at Kennedy-Allee, using coupling systems that provide for the regeneration of the ground temperature.

The result confirms the effectiveness of coupling systems: The highest probe inlet temperature occurs only in the first year (11.1 °C) and decreases slightly by the 100th year (10.8 °C). The lowest probe inlet temperature is 9.4 °C in the first year and drops to 9.1 °C by the 100th year.

Of the 35 GWh/a of geothermal energy that helps heat the bridge buildings, 40 percent is extracted from the ground in just two months, from December to January

A large part of the regeneration is realized by the heat of the building cooling in summer; only a small part of the regeneration is realized by solar thermal energy on sunny days in winter

Case 2: Heat collected above ground is sent into the ground via grouped geothermal probes, stored there and extracted from there as needed for heating.

Where the Frankfurt bridges are being built, the pavement of the roads beneath them will have to be renewed as part of the construction project. This opportunity will be used to place probe fields in along the roadway.

These probes reach down to a depth of 250 meters. They are well insulated for the first 20 meters, where they would potentially pass through groundwater-bearing strata and give off their heat prematurely or heat up the groundwater. On the remaining meters, they then release the heat to the surrounding earth for storage.

The heat is collected above ground by hybrid collectors. These generate both: electricity and thermal energy

PVT hybrid collectors (PVT: Photovoltaic-Thermal hybrid solar collector) generate electricity and heat simultaneously. In PVT hybrid collectors, there is a thermal collector on the back of the PV modules, which absorbs the heat from the sun's rays and transfers it to a heat exchanger. Sometimes you can still find both functions - photovoltaic and thermal collectors - mounted separately on roofs.

At the Frankfurt bridges, PVT hybrid collectors are located on roofs, canopies, the sides of the bridge body and on the facades of the bridge buildings. In addition, the parking lots next to the bridges are covered and equipped with PVT hybrid collectors at the expense of the bridge company.

A total of approx. 303 GWh/a of heat is generated by PVT hybrid collectors

Approximately 303 GWh/a of heat is generated with 1 million square meters of PVT hybrid collectors; about half of this is on the bridges and the other half is on the parking lot canopies adjacent to the bridges.

Around 80% of the heat (246 GWh/a) is generated in summer, when there is almost no demand for heat. Therefore, the generated heat is stored underground in BTES (Borehole Thermal Energy Storage) in summer and retrieved in winter for heating with low temperatures.

In winter, the remaining 20% heat (57 GWh/a) is generated. This is passed on directly to the consumer.

Another source of thermal energy: waste heat. The waste heat potential from data centers, industrial parks and also waste water in Frankfurt amounts to around 190 MW or more than 1.66 TWh per year.

According to the Frankfurt waste heat register, the 1,660 GWh per year are divided as follows:

100 MW (876 GWh) heat from wastewater,

40 MW (350 GWh) waste heat from industrial parks,

50 MW (438 GWh) of waste heat from data centers.

This is about one third of the heat consumption of Frankfurt households, but the thermal heat is only available as low-energy waste heat and would therefore only be usable in buildings with heat pump heating.

Until now, however, the waste heat from the data centers or industrial parks in Frankfurt could not be used at all because there was no pipeline system that could transport the heated brine liquid to the heat exchangers of building users. Unfortunately, it cannot be fed into Mainova's district heating pipeline either, as this is designed for 80 to 90 °C hot liquid.

The construction of the Frankfurt bridges will therefore create a pipeline system along the bridges that not only stores heat collected by PVT hybrid collectors in the ground, but also collects and transfers waste heat from data centers and industrial parks, such as those found primarily along Hanauer Landstrasse and in Sossenheim.

For these data centers and industrial parks, the Frankfurt bridges represent the direct link to the use of their waste heat in buildings or by other consumers.

The Frankfurt bridges run past some critical locations where data centers generate an extremely large amount of waste heat - a very useful source of energy, especially on less sunny or warm days in fall or winter

Near the bridge, 30 data centers and the Cassella Industrial Park generate about 200 GWh/a of low-temperature waste heat that currently goes unused. Half of this (100 GWh/a) can be collected and used with the help of the bridges.

Thermal energy is not only available in summer

Approx. 246 GWh/a of low-temperature thermal energy (approx. 35°C) from PVT modules and approx. 50 GWh/a of waste heat from data centers are stored underground from April to September. But also between Jan. and March as well as Oct. and Dec. the generated heat is either fed underground for regeneration or directly transferred to the consumer.

The thermal energy from PBT and RZ collected in summer (approx. 296 GWh/a) is not consumed directly, but stored in long-term storage facilities

Heat from PVT modules and also waste heat from data centers is stored underground in "probe fields

The Frankfurt bridges offer the possibility of installing probe fields, so-called Borehole Thermal Energy Storages (BTES), at strategically favorable locations, e.g. under the supply centers or roadways beneath the bridges, in order to store - as the name suggests - surplus heat. In this way, time can be bridged between supply (summer) and demand (winter).

The storage efficiency of individual geothermal probes is comparatively low. Therefore, one lays so-called "geothermal probe fields", which arranged in a circle or square most efficiently store the heat. It is recommended to place them at a distance of less than 10 m (optimum 3 to 5 m).

Other factors that are decisive for the efficiency are

thermal properties of the subsoil

groundwater flow rate

surface to volume ratio

working temperatures and time control

Numerical models were built to estimate storage potential and utilization rates, and a long-term simulation of storage operation was performed.

The Borehole Thermal Energy Storage (BTES) model calculates the stored and extracted thermal energy as well as outlet temperatures per storage cycle - and thus also the storage efficiency of BTES.

Requirements:

Model with "4 on 8 probes arrangement", i.e. 32 geothermal probes (EWS) with 4 m distance each.

supplied water temperature in summer of 35 °C and in winter of 4 °C

Upper aquifer up to 10 m below ground surface (below ground surface level), then clay

EWS from 20 to 200 m below ground surface (slice 5-23)

Hydraulic gradient of 6.5

EWS implemented as 1D-line element

Geothermal probes of the BTES:

U-probes with standard dimensions

150 mm borehole diameter

32 mm probe diameter

Constant volume flow with 10 m3/d per probe

Simplified approach: without complex interconnection of the EWS, each EWS a single circuit

For the estimation of the probe field performance along the Frankfurt bridges, three scenarios were simulated, each with different geological conditions that occur in the Frankfurt area

1.Scenario 1 (S1): Ideal case for storage with completely continuous clay layer with hydraulic permeability of kf =10-7 m/s, thus hardly any convective heat losses due to flowing groundwater.

2.Scenario 2 (S2): Clay interrupted by two sand layers (kf =2*10-4 m/s) with thicknesses of 2 and 8 m, thus increased convective heat losses on 5% of the section

3.Scenario 3 (S3): Clay interrupted by four sand layers (kf =2*10-4 m/s) with a total thickness of 50 m, thus convective losses increased on 25 % of the section

The model results show the inlet and outlet brine temperatures within the 10-year operation period. The inlet temperature (T-In) is set to 4 °C in winter and 35 °C (outlet temperature of the PVT hybrid collectors) in summer for all scenarios. For all scenarios, it can be seen that the outlet temperature (T-Out) decreases during heat supply (in winter) and increases during storage (in summer).

Why does the simulation show similar outlet temperatures in winter? Although the temperature gradient to the storage volume is higher for S1 (only clay) compared to S3 (a lot of sand) because the stored heat was not transported away from the groundwater, the heat exchange between the borehole heat exchangers and the storage volume is nevertheless lower at the same time because there is hardly any convective heat transport.

In all scenarios for the probe fields along the Frankfurt bridges, the extracted heat increases after the first few years and reaches a plateau, while the amount of stored energy shows a reverse trend

The model results show the stored and extracted thermal energy over an operating period of approximately 30 years.

In the scenarios with groundwater flow, slightly more energy can be extracted, but significantly more is put in as well

Storage utilization rate:

S1: ~ 87 %

S2: ~ 78 %

S3: ~ 63 %

Convective losses have a significant effect on the storage efficiency.

The storage efficiency is significantly lower if circuitry and control etc. are taken into account.

Geothermal probe fields will require 175,000 m2 of space: They will be installed either (I) under each utility center, (II) next to the data centers and industrial park, and (III) along the bridges in the course of bridge construction under the roads

According to the simulated model, 32 borehole heat exchangers (12*28 = 336 m2) store 650 MWh of thermal energy. In order to store 296 GWh/a, approx. 455 groups with 32 borehole heat exchangers or approx. 155,000 m2 area are required.

(I)Geothermal probes can be installed under each supply center. There are 200 supply centers with an average surface area of 100 m2, so that in this way 20,000 m2 of surface area can be equipped with borehole heat exchangers already during the construction of the supply centers.

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(II)In addition to the data centers and the Cassella Industrial Park, another 5,000 m2 of geothermal probes can be installed to store the heat collected from the east arm and the west arm of the Frankfurt bridges.

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(III)The remaining 130,000 m2 of space required will be along the 60 km long route of the Frankfurt bridges: During their construction, the pavement of the overbuilt roads will have to be renewed in large parts anyway. Here, all the necessary geothermal probe fields can be installed on 130,000 m2.

Moreover, the 130,000 m2 area for the probe fields should, if possible, be laid out around the crossing areas of the bridge sections, as this is more favorable from an energy point of view: from there, the heat has shorter distances to the point of origin and also to the point of use.

The two sections A (which are in groundwater flow direction: green lines) divide the bridge landscape into three areas: East, Middle, and West.

The placement of the geothermal probe fields is most sensibly done around the intersections of the bridge courses (indicated by black circles):

This is because if heat only ever needs to be routed to the next intersection for storage (and vice versa for extraction), then the route length for energy transport is shortened, heat losses are lower, and the efficiency of heat storage is thus higher.

Of the 15,000 columns on the bridges, the piles on 12,750 are fitted with probes. Like the probe fields under the roads, these are connected to an underground ring main so that heat can be passed on when it is not needed on site

Approximately one to two meters below ground, i.e. in the frost-free zone, a ring line runs to which both the probes in the column piles and the geothermal probe fields under the roads are connected. These particularly well-insulated connecting lines allow the heated probe fluid to flow wherever it is needed. The customers are the buildings on the bridges, greenhouses and swimming pools next to the bridges and, in the more distant future, residential and office buildings next to the bridges.

When heat is extracted from the storage tanks, the temperature-controlled probe fluid is piped up from the ground when heating is required and -just like the brine from the PVT modules- is piped underground to the basement of the nearest supply center.

The brine from the solar thermal energy of the photovoltaic modules runs through pipes along the columns down to the ground, where it continues to flow in a common connecting pipe to the supply center.

Either it is used there (in winter) for heating or it is transferred to the ground for storage, to be brought up again when needed and directed to the supply centers. There, the heat is transferred through a heat exchanger to the pipes that continue to the bridge buildings and other consumers for heating.

Also, the probe fluid from the ground, which was heated by the ground temperature there of about 14 °C in the bridge pier probes, comes up in the bridge piers to the geothermal ring main, which is about 2 m below ground level, so that it is frost-free and comes out at the level of the basement of the utility center to be used there.

Both the pillars that will be equipped with probes ("geothermal pillars") and the probe fields (BTES) are connected to the common heat conduction network of the Frankfurt bridges, which requires a good control and regulation system

If one day fewer lanes are needed and buildings are constructed under the Frankfurt bridges, these can also be supplied geothermally

Since almost all supports of the bridges are geothermally activated, any additional "buildings" that may be constructed in the future next to or under the bridges can also be heated in an energy-efficient manner. Due to the supply centers connected to the system, which are planned every few hundred meters along the bridge, the connection of these additional buildings is unproblematic.

Frankfurt's bridges not only create green and humane living spaces above ground, but their columns also open up the possibility of using the ground beneath the city as an energy store underground

Almost 1 million m2 of solar thermal area is being created on Frankfurt's bridges, not only on the roofs of the bridge buildings, but also on the body of the bridge and on the parking lots along the bridges. With the heat from this, as well as the waste heat from many data centers, the ground under the bridges can not only be regenerated after the winter season with its heat extraction; in fact, far more heat could be sent down than taken out. Theoretically.

Because there is one limiting factor: the groundwater must not get too warm. In some places in downtown Frankfurt, it is already 18 °C or more due to the geothermal energy from the high-rise buildings. These are already problematic values: Too much warming of the groundwater can be harmful to several hundred animal species that inhabit this area and to the ecosystem of groundwater organisms that make an enormous contribution to purifying the groundwater.

Accordingly, during the preliminary planning phase of the Frankfurt Bridges, it must be examined in detail together with the Hessian State Office for Nature Conservation, Environment and Geology to what extent and at which points the Frankfurt Bridges geothermal system may store heat in the ground.

Experts on the topic

Fraunhofer-Einrichtung für Energieinfrastrukturen und Geothermie - Universität Bern - Institut für Geologie - National Renewable Energy Laboratory - Laboratório Nacional de Energia e Geologia - International Geothermal Association

Conclusion: The bridge structure and bridge construction can be used to extract heat from the ground or store it there

At present, infrastructure projects are usually still considered to be environmentally harmful and, due to the CO2 emissions of concrete buildings, also to be harmful to the climate.

This contrast between structure and nature can be eliminated if the structure itself is used for energy generation and storage or if environmentally friendly renewable energy generation is installed at the same time as the infrastructure is built.

In the case of the Frankfurt bridges, the pillars can be used for energy generation from the ground; furthermore, the construction project itself can be used to install probe fields for energy storage along the bridges in the course of bridge construction.

The urban energy transition

Electricity demand on the Frankfurt bridges

Heating and cooling requirements of the bridges

Near-surface geothermal energy

The energy infrastructure of the future

The bridge world

Sustainability through technology

The Co2 balance of bridges