HOT|COOL NO. 4/2020 - "Large and Growing Markets"

Benefits of PTES Thermal Energy Storage (TES) is one of the essential components in the future energy sector. It is a crucial element in reaching the global environmental, energy, and climate targets of the next decades. The TES is the component that binds an integrated and flexible energy system together. PTES is the most flexible and cost-efficient TES. Its high flexibility and low cost enable a cost-efficient transition to a renewable and energy-efficient future. The storage can decouple production and demand and thereby stabilize the energy system and minimize expensive peak load production. This means that a higher share of renewable energy or excess energy can be utilized. A PTES can serve as a peak load or reserve capacity in a district heating system. When combined with power-to- heat units, it can also help the electricity system by offering up or down-regulation capacity. It enables flexible and efficient sector coupling of the power and district heating sectors. Moreover, it will be an essential part of Power-to-X (PtX) processes to secure an optimized operation with high total system efficiency. Technical challenges for PTES lids As mentioned, the PTES technology is a crucial enabler for a cost-efficient transition of today’s energy system. Therefore, the PTES must be made robust and large scale with low maintenance requirements. The PTES technology has been developed and refined throughout the past 30 years. In recent years, increased attention has been paid to the design of the insulating lid. Historically, the lid has caused severe technical failures and un-wanted thermal losses.

By: Morten Vang Bobach, Product Manager, Senior Engineer, Aalborg CSP

There are substantial benefits of implementing a Pit Thermal Energy Storage (PTES) in an energy system. Throughout the lastyears, investmentshavebeenmadeintolow-temperature heat storage to develop, optimize, and commercialize the PTES technology. The latest achievements in improving the insulated PTES lid cover have also matured the technology and made it scalable. The technology has now reached a state where utility companies consider the technology bankable and are prepared to invest on a larger scale. PTES projects, with storage capacities of up to 1 million m 3 each, are currently in the planning and tendering phases. Basic PTES design The basics of a PTES are straightforward, as illustrated in figure 1. A large pit, which will act as the storage, is excavated in the ground. The excavated soil is then placed as embankments around the pit. In the end, the result is a water reservoir partly below and partly above terrain level. The reservoir is typically lined with a polymer liner before water filling. The top surface is covered with a floating, insulating lid to minimize heat loss. Heat is transferred to and from the storage through pipes and diffusers in the same principle as a traditional steel tank thermal storage.

Basic PTES design

Pumping well

Insulating floating lid

Ballast layer

Pumping well






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