Utility launches tender for pit thermal energy storage design
Tender seeks planning expertise for a pit thermal energy store that shifts surplus summer heat to winter peaks, reflecting wider moves into long-term heat storage.
Tender seeks planning expertise for a pit thermal energy store that shifts surplus summer heat to winter peaks, reflecting wider moves into long-term heat storage.
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Stadtwerke Rostock AG has gone to market for planning services for a pit thermal energy storage facility that will bank surplus summer heat for use in winter. The long-term heat store is intended to shift unused heat to periods of peak demand, placing the project within the growing class of non-battery energy storage schemes. It also marks a new stage in Rostock’s exploration of large earth basin heat storage.
On 16th April 2026, Rostock City Utilities AG published a contract notice for planning services to design a pit thermal energy storage facility. The planned facility is described as a long-term heat store that will shift unused heat from summer to winter to cover peak heating demand.
A pit thermal energy storage (PTES) scheme of this kind functions as an earth basin heat store. By holding heat over several months rather than hours or days, it can smooth large seasonal swings between heat supply and demand and make better use of surplus summer heat.
In November 2025, Hanse- und Universitätsstadt Rostock issued a contract notice for a feasibility study for a large earth basin heat storage project. The study is tasked with assessing the suitability of a site in Rostock, drawing on project management, geological analysis, energy modelling, preliminary design and environmental impact assessment.
The new utility-led planning tender now focuses on preparing the construction of a pit thermal energy storage facility. Taken together, the two procurements show that long-term heat storage has become a defined strand in Rostock’s energy planning.
The Rostock notice sits within a broader wave of tenders for large thermal stores. In March 2026, Warendorfer Energieversorgung GmbH went to market for the construction of a heat storage facility at the new Ems heating plant in Warendorf. The store is planned to operate autonomously while integrating with the district heating network, balancing thermal energy from large heat pumps and gas boilers.
Also in March 2026, Stadtwerke Kiel AG published a contract for the planning, construction and commissioning of a heat storage facility as part of its CALOR project. The CALOR scheme aims to enhance district heating production by using environmental heat from the Kiel Fjord, with the new store acting as a central buffer for that low-temperature source.
Earlier, in November 2025, Gothaer Stadtwerke ENERGIE GmbH set out plans to build a large-scale atmospheric thermal storage system at the HKW Gotha West site. With a capacity of 60 MWh and peripheral facilities included, the store is intended to improve CHP operation. In December 2025, Stadtwerke Flensburg GmbH tendered for the construction of a new non-pressurised heat storage facility to replace an outdated unit, matching the specifications of an existing store while restoring capacity and operational flexibility.
Storage capacity is also being added to existing sites. In March 2026, Stadtwerke Augsburg Holding GmbH sought planning services for a thermal storage facility at its HKW-Franziskanergasse site, with commissioning to be phased. That same month, UEM METZ launched a contract for the design and realisation of a production and storage facility combining a 17 MW electric boiler with high-capacity hot water storage, spanning design, assembly and civil engineering works.
Research institutions are pushing storage concepts into higher temperature ranges. In March 2026, Deutsches Zentrum für Luft- und Raumfahrt issued a notice for planning support for a high-temperature geothermal storage project. The aim is to develop a seasonal heat storage system for temperatures above 100°C, using concentrating solar thermal technology and other renewable energy sources, with companies assisting in planning and feasibility work.
Municipal utilities are pairing such storage ideas with new low-carbon heat sources. In February 2026, Stadtwerke Rheinsberg GmbH sought general planning services for a geothermal project that combines a hydrothermal doublet with a photovoltaic system, based on a recent feasibility study and aligned with district heating transformation plans. Energie und Wasser Potsdam GmbH’s November 2025 tender for a geothermal energy centre at the Süd power plant links building design, three heat pump modules and the decarbonisation of the district heating network. In April 2026, Stadtwerke Prenzlau GmbH followed with a contract for construction of a geothermal heating centre and associated plant, using geothermal energy and heat pumps at two locations to supply district heating.
Wastewater and surface water are also being drawn into the heat transition. SWE Energie GmbH’s October 2025 notice sets out general planning services for waste heat utilisation from the Kühnhausen wastewater treatment plant into its district heating network, including various engineering and technical assessments. In March 2026, Ecowerk Solar GmbH & Co. KG tendered for planning a heat pump system at a wastewater treatment plant, covering technical buildings, a source line and an extraction pump station. Stadtwerke Lübeck Energie GmbH, in November 2025, advertised planning services for a wastewater heat pump installation using treated wastewater heat for district heating networks, split into two lots that span planning phases from February to December 2026. In February 2026, Stadtwerke Cottbus GmbH went to market for planning a lake water heat pump system, integrating it with existing facilities at the HKW Cottbus site.
Ancillary infrastructure is a recurring theme. In March 2026, FairNetz GmbH sought planning services for a pump building to support a large heat storage facility as part of the district heating decarbonisation project in Reutlingen. The notice underlines how civil structures and hydraulics around a store are procured alongside the storage asset itself.
Heat networks themselves are undergoing redesign. In October 2025, Stadtwerke Konstanz GmbH issued a contract for planning a heat network in the Hafner area, focusing on plant technology and building structures to support air-water heat pumps. Around the same time, Stadtwerke Ludwigsburg-Kornwestheim GmbH tendered for planning services for a power-to-heat plant at Fuchshof, including TGA planning, engineering structure planning and control technology integration. In March 2026, Stadtwerke Stuttgart GmbH launched a procurement for planning a heating network in Obertürkheim to provide renewable heat from the Green Hydrogen Hub’s waste heat and other local renewable sources.
Hydrogen adds another layer to non-battery storage. In November 2025, Land Baden-Württemberg, represented by Technische Hochschule Ulm, advertised the delivery of a 50 MW hydrogen storage system to increase energy flexibility and link electricity, heat and mobility sectors at the university. In March 2026, Forschungszentrum Energiespeichertechnologien der Technischen Universität Clausthal followed with a tender for the delivery of a hydrogen storage unit and a hydrogen CHP plant, strengthening hydrogen research infrastructure based on local renewable generation. And in January 2026, Deutsches Zentrum für Luft- und Raumfahrt e.V. sought suppliers for pipeline construction under its Store2REPower project, expanding the TESIS facility with liquid salt heaters through prefabricated, insulated piping and associated system adaptations.
Across these notices, planning contracts play a central role in turning concepts into buildable projects. Feasibility studies, general planning tenders and detailed design work span disciplines from geology and energy modelling to structural engineering, plant design and network control.
The Rostock pit storage planning tender fits squarely into this pattern. By concentrating on a long-duration, pit-based heat store rather than on electricity batteries, the utility is adding another option to the portfolio of thermal storage solutions being developed alongside district and local heating systems.
The Rostock contract notice currently sets out only the objective of designing a pit thermal energy storage facility to shift surplus summer heat into winter peaks; technical parameters and construction details will follow in later stages. In comparable schemes, such as those in Warendorf, Kiel and Metz, planning and feasibility work has been followed by discrete contracts for construction and integration. Observers will be watching how quickly the Rostock project moves along a similar path, and how seasonal heat storage contributes in practice to securing low-carbon heat supply.
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