Elsevier

Energy Procedia

Volume 99, November 2016, Pages 314-320
Energy Procedia

High Temperature Latent Heat Storage with Direct Electrical Charging – Second Generation Design

https://doi.org/10.1016/j.egypro.2016.10.121Get rights and content
Under a Creative Commons license
open access

Abstract

The increasing share of renewables in today's generation mix and the accompanying fluctuation in generation requires large scale as well as decentralized storage capacities to secure grid stability. In the described power-to-heat concept, electricity, produced from PV-plants or small scale wind farms, is used to heat up high temperature latent heat storages. The heat can be used in industrial processes. The storage is equipped with electrical heating elements, directly immerged into the phase change material to achieve best conversion efficiency. Discharging takes place by an oil cooled plate heat exchanger. For heat transfer enhancement during discharging, a concept, using moving blades to scrape off the solidifying material, was developed. With this method, the solidified layer of phase change material on the heat exchanger surface is kept at constant thickness, allowing for constant heat flux during the major period of the discharging process. Feasibility of the concept with moving scrapers was demonstrated, proving the advantages over the passive concept. Various aspects have been identified for improvement of the concept. In the second generation design it is intended to combine the electrical heating with the cooling plate to minimize the amount of components and material inside the storage and to maximize the available heat exchanger surface. With this solution, the same heat exchanger surface can be used for charging or discharging. Flat heat exchanger surfaces will allow a very narrow gap between scraper and heat exchanger plate. The mounting of the scraper mechanism is changed from a central slide to a portal frame, supported by four ball bearings. Two bearings each are guided in a track on each sides of the storage. For exact positioning in relation to the cooling plates, two bearings each are mounted in the middle of the traversal trusses, and guided along the middle track. The scraper is re-designed to also be able to scrape off solidifying salt at the bottom of the storage. In addition investigation are under way, to reduce the adhesion between PCM and heat exchanger surface by nanotechnology or any other means.

Keywords

Thermal energy storage
Latent heat
Power-to-heat
High temperature
Electrical heating

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Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy.