Eng. Fagulha Pereira

Sustainable Process & Energy Systems, TNO


Talk Title
A High Energy Density Heat Battery
Talk Abstract

The targets for reducing the global warming as set forward in the 2016 Paris agreement require a generalized effort, particularly in the energy intensive industrial, transportation and built environment sectors, to switch their main energy source from fossil to renewable. The result has been the ongoing development of several innovative technologies focused on an efficient, safe and reliable transformation and storage of energy from natural intermittent sources, as the sun and wind.
A dominant part of the total energy consumption in Europe - 50% - consists of heat. Specifically in the European residential sector, heat corresponds to roughly 70% of the total energy consumption, associated to domestic space heating and hot tap water generation. For the latter applications, thermal energy storage in either the forms of sensible (e.g. solar water boilers), latent (e.g. phase change materials) or sorption heat (e.g. thermochemical salts) can be a solution to fulfill the goal of increased self-consuption of renewable energy and potential zero-energy dwellings.
Unlike sensible and latent heat storage technologies suffering from heat losses, long-term cycles throughout the year can be obtained by thermochemical storage, a process dependent on a stable chemical reaction allowing a virtually loss-free system. Salt hydrates have been extensively researched in the past, and they can be directly powered using solar heat in the range of 60-140°C, feeding an endothermic reaction of dehydration; on the other hand, when heat is required, these salts are rehydrated and carry an exothermic reaction from which heat can be applied to household needs.
A heat battery technology is investigated based on the most promising salt hydrate for the application of long term heat storage in dwellings: sodium sulphide (Na2S). This salt hydrate exhibits a large energy density under relevant solar collector conditions (2.7 GJ/m3) associated with its transition from pentahydrate to the hemihydrate:
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Absorption of water vapor can take place at sufficiently high temperatures (40-60°C), while desorption can occur at relatively low temperatures (70-83 ºC), under vacuum conditions.
In our labs, studying the properties and performance of Na2S in a heat battery started back in 2012 with the FP7 MERITS project, where a demonstration container with 8 heat battery modules reached 0.18 GJ/m3 at a system level. Following the first successes with MERITS, material and system design improvements were implemented to increase the energy density. The main disadvantage associated with Na2S is its potential chemical decomposition. During a follow-up project, undesired formation of non-condensible gases was suppressed by improving the Na2S material.
With this contribution, we share a milestone in thermal energy storage: 1.15 GJ/m3 at a 1 kg heat battery level was reached using improved Na2S in a vacuum heat battery, corresponding to an extrapolated energy storage of 0.44 GJ/m3 for a total battery volume of 380 L - a 2.5 times more compact heat battery than sensible storage with water. Energy storage density is expected to further increase with additional improvements at the design level, moving us closer to the ground-breaking goal of 1 GJ/m3 for a two-module battery by 2020.

Short Biography

Fagulha Pereira, alumna from Faculdade de Ciências e Tecnologia (Universidade Nova de Lisboa, Portugal) completed her chemical engineering master degree studies at the Technical University of Delft (the Netherlands), in 2015. For the following years, she persued her career in the specialty chemicals industry, developing her knowledge and skills in varied fields, such as process improvement, manufacturing and engineering. Filled by the drive of having a positive impact in the world and aspiring to develop as a scientist in the energy transition movement, Sara is since June 2018 a researcher at TNO. She and her enthusiastic Energy Conversion and Storage group work today on several different concepts of compact energy storage, including compact heat storage (thermochemical and redox) and electricity storage (organic redox-flow batteries) for applications in the built environment, industry and energy grid.

Talk Keywords
Heat battery; compact thermal energy storage; dwellings; reactor development.
Target Audience
Students, Post doctoral, Industry, Doctors and professors
Speaker-intro video

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