Pit Thermal Energy Storage (PTES)

A Pit Thermal Energy Storage (PTES) allows for district heating plants and utility companies to collect and utilize excess energy and heat that would otherwise go to waste. By utilizing the excess heat, the energy utilization is optimized significantly, while the system-flexibility is likewise improved. 

Aalborg CSP offers supply and installation of key PTES components as well as turnkey PTES solutions customized to fit individual energy needs and requirements for the most efficient and reliable heat production. Aalborg CSP also offers pre-studies and analysis, e.g. feasibility studies, pre-engineering and detailed engineering service for systems and solutions around the PTES.

Optimum energy utilization

A Pit Thermal Energy storage is a large water reservoir used for storing thermal energy. The reservoir is lined with a water-proof plastic lining to retain heat and prevent water from leaking out into the surrounding soil. The top of the storage is covered by a floating insulating cover used for retaining the heat and keeping rainwater from entering the storage.

Excess heat from solar heating- and biomass plants and industrial processes as well as energy from wind turbines and PV-panels can be used for heating up the water inside the PTES to approx. 80-90 °C. When the heat demand increases, cooled return-water from the district heating network is lead into the bottom of the storage, while the heated water from the top is sent out to the consumers. Heat is thus stored, when the production price is low and supplied to the consumers, when it is expensive to produce. Hereby, an optimal utilization of the energy is achieved.

A significant optimization of the energy utilization can be achieved by combining a PTES system with other energy technologies. PTES systems are therefore ideal in co-operation with other renewable heat sources such as solar heating plants, biomass boilers and heat pumps.

Certified lid solution ensures a minimum of heat loss

With a PTES solution from Aalborg CSP, district heating plants and utility companies will furthermore benefit from a durable and operationally stable lid technology, which ensures a minimum of heat loss. Aalborg CSP's unique lid technology is certified by Lloyd's Register and addresses and solves problems and challenges while minimizing the risks typically experienced during the installation and operation of a PTES.

The durable and operationally stable lid technology prevents accumulation of air, water and moisture inside the insulation in an efficient way. 

PTX and energy storage for efficient sector coupling

The Pit Thermal Energy Storage (PTES) technology is an ideal technology, when it comes to Power-to-X (PTX). PTX with sector coupling of e.g. electricity and district heating by means of energy storage is considered one of the keys to the sustainable energy system of the future.

PTES system can with great benefit be integrated with energy systems already containing an electric boiler. The boiler uses excess electricity from wind turbines and PV-panels to heat up water for district heating purposes and the heated water is stored in a PTES. When the electricity price is low, cooled water is extracted from the storage and heated by means of the electric boiler. Afterwards, the water is stored in the PTES once again for later use, when the demand increases. It is hereby possible to convert excess electricity to district heating - PTXHEAT – and thus utilize the fluctuations in electricity prices to achieve optimum system flexibility.


Andreas Zourellis
VP Sales - International
District heating / industrial solar technologies
Phone: +45 50 30 00 25