Institutions in Hamburg are proposing to build a large underground thermal heat storage system that could supply roughly a quarter of the city’s heating needs with waste heat from industrial and power plants. If successful, it would make Vattenfall’s plans to realise a CO2-neutral district heating network superfluous. It could also serve as an example for other cities.
German climate policy tends to focus on the electricity sector, but electricity constitutes only about one-fifth of total energy services. The residential and industrial heating sectors not only demand nearly half of all energy used, but solutions for their decarbonization are harder to come by due to over 40 million households as well as commercial buildings that rely on locally available energies.
A good deal of this demand can be interlinked in cities by district heating networks, which account for around 5% of total German energy consumption. They can use waste heat from industrial processes and geothermal sources as well. The Netherlands, for example, has recently announced it wants to go down this route, gradually replacing its natural gas heating system with district heating networks supplied with waste heat.
In Hamburg, a proposal has now been presented for a large heat storage system under the city. Heat produced in the summer from industry, waste incineration, renewable energies and seasonally heated river water could be captured for use during the winter.
Hamburg to be climate neutral in 2050
Hamburg is a city in transition. In November 2015, Vattenfall’s new Moorburg coal-power station – Germany’s second largest coal power plant – entered service on the southern bank of the Elbe River after many years of delays over technical and environmental conflicts. One of the problems with Moorburg, as I explained in an article for Energy Post back in 2014, is that this new plant is poorly located for delivering heat in addition to generating power. In order to serve the existing heating network, a 4.4 km pipe tunneled underneath the river would have been required.
Vattenfall, which already supplies district heat to parts of Hamburg from its 321/955 MW coal-fired CHP plant at Tiefstack and the 260/433 MW installation in Wedel west of the city, is now planning a €83.5 million refurbishment of Wedel to prolong existing heat supplies in compliance with more stringent environmental standards.
With Continental Europe’s oldest modern water supply system dating back to 1842, Hamburg has catalogued a quarter million drill holes
At the same time, the city has said it wants to achieve “climate neutrality in Hamburg heat operations by 2050”. In response to this, Vattenfall is considering configurations using “heat storage, power-to-heat, industrial heat, decentral solutions and possibly gas-CHP that will replace the existing plant”.
However, the Hamburg Institut, a local ecological planning office, and Consulaqua, a subsidiary of the municipal waterworks Hamburg Wasser, see a more immediate path toward reducing the CO2 footprint of district heating.
Hamburg is situated on the Elbe River above two expansive sand aquifers for fresh and salt water with an intervening, nearly impervious clay layer. Similar geological prerequisites already permit heat energy to be stored below the Bundestag parliamentary building in Berlin. In Hamburg, a far greater amount of thermal energy could be sequestered underground sufficient for supplying one-quarter million homes and an equivalent additional amount for commercial buildings. This is approximately one-fourth of all structures in Hamburg, which extends over a land area equivalent to that of New York City.
During the warm months, cold saltwater from beneath the city could be pumped to the surface and heated by factories, waste incinerators, gas plants, and surplus renewable energy. It would subsequently be injected at a different location below the clay strata for heat storage. As the winter approached, pumping the heated saltwater up from storage to the surface would enable the thermal energy to be withdrawn for heating distribution. The cooled saline solution could then be pumped back into the aquifer from which it had been originally taken.
Favourable geological conditions exist throughout the Germanic Basin between South England and the eastern border of Poland
The achievable heat storage capacity is practically infinite, since layers of sand awash in saltwater lie below the entire city. Due to incident solar energy along its course, the Elbe River is warmed excessively during the summer months. Bathing is therefore prohibited to preclude communicable diseases, but the river becomes a ready source of thermal energy for storage.
The waste heat that Hamburg produces in its industrial facilities – notably the Aurubis copper smelter and ArcelorMittal steelworks – as well as in electronic data centers and refrigerated warehouses could be added as needed.
Local warming as response to global warming
The heat storage concept is exemplary for Germany’s innovative energy transition. The dissipated heat of gas-fired combined heat and power is produced in alternation with renewable energies. That is, whenever solar or wind power is insufficient, more gas can be burned. The excess renewable grid power available at other times, however, may be efficiently converted by heat pumps into warm water and stored for the winter.
Underground storage realized for this purpose becomes more economical in relation to size. The volume of a large reservoir increases by the cube of the radius while radiated heat is lost only over the squared outer surface area. About a third of the stored energy is ultimately dissipated underground, a tolerable margin according to Consulaqua.
Standard drilling equipment is used to tap into aquifer reservoirs. Hamburg already has hundreds of drinking water wells. With Continental Europe’s oldest modern water supply system dating back to 1842, Hamburg has catalogued a quarter million drill holes. Heated salt water can be pumped into the ground at many places as is done for drying large building sites.
With 1,800 km of heating pipes already installed beneath the city, heat could be readily transported from producers to central storage
Parts of the district heating network are maintained at over one hundred degrees, while temperatures in aquifer storage would lie between 70 and 80°C. The water in the transport pipes would therefore require additional heat, which is why experts from the Hamburg Institut prefer a storage site under a planned trash and biomass incineration plant in Stellingen that could provide auxiliary heating.
Consulaqua estimates that aquifer storage functionality could be achieved for only about €1 million, compared with Vattenfall’s long-range project costs approaching half a billion euros for the CO2-neutral replacement of the Wedel power plant.
Hamburg Institut has calculated storage expenses of one cent per thermal kWh including storage losses, with another cent covering unaccountable inaccuracies. Industrial waste heat is available for 1–2 c/kWh, resulting in maximally four cents altogether. District heating customers are currently paying double that price in Hamburg.
Additional heat exchanger costs are said to be marginal. With 1,800 km of heating pipes already installed beneath the city, heat could be readily transported from producers to central storage.
While no timetable has been set, early implementation in Hamburg could subsequently be emulated by other cities. Favourable geological conditions exist throughout the Germanic Basin between South England and the eastern border of Poland. Time will tell how successful this concept could become.
Jeffrey Michel (firstname.lastname@example.org) is an independent energy expert based in Hamburg. See his author’s archive on Energy Post.
Helmut Frik says
If it would be my project, I would porpose to slowly reduce temperature in the heating network, by e.g. 1-2°C per year. This allows everybody to adopt. In fact the existing heat distribution systems in the buildings should already come along with significant lower temperatures, since alsmost all buildings have received some improvements in insulaion during the last decades, resulting in lower heating needs, and this process will go on in the following decades. Alos within the building temperatures above 90° will not be used, too dangerous. If improvements of buildings will go on al planned, it will be possible to heat a district with temperatures below 60°C, which originally needed 110°C in e.g. 1970. Which would remove the necessity to heat the water further, and allow a higher efificeincy of the storage, and the use of waste heat. Customers who never ever changed anythings at their buildings might need to change their heat distribution system, or have a big incentive to insulate their building. Which I would see as a benefit, not as a problem.
S. Herb says
Indeed interesting (I live a few km from the proposed site). A report ‘HH-Heating-BUE’ is available on the Hamburg Institute website. From my reading of it, the number that underground storage could cover 25% of Hamburg’s heating needs should be compared to the proposal at hand. The report is based on the need to replace the 1.5 GWh/a contribution to the district heating system of a coal-fired plant which is to be retired. Hamburg’s total heat energy use is listed as 23 TWh/a, of which about 5 TWh/a is supplied via the district heat piping.
At report end six variant proposals are compared, one of which includes the proposed underground storage in Stellingen, which is stated as contributing 270 GWh/a to the district heating. This is about 1% of the total Hamburg heating energy. So apparently 25 such plants would be required for 25% coverage (and one must also ask whence comes the energy used for heating the water during the summer).
The report also notes that although the economics look attractive this is a first and approximate try at costing a system of this size. I hope that the plans will be further developed and discussed, but I suspect that a smaller test project should be attempted before going full out.
S. Herb says
oops, one wrong number in the above. ‘1.5 GWh/a contribution’ makes no sense, should be 1.5 TWh/a,
Nigel West says
Astonishing that Hamburg has just commissioned a new huge coal-fired power station in a country that already burns far too much coal.
Jeffrey Michel says
The city of Hamburg entered an agreement for construction of the Moorburg power station in 2007 under the condition that an application for CCS would be submitted by 2013. By that time, however, Vattenfall was able to demonstrate that no adequate prerequisites existed for geological CO2 storage. Furthermore, it had never been possible to secure an adjacent plot of land for the required carbon dioxide separation and compression equipment, which would have been as expansive as an airplane hanger.