Use of encapsulated zinc particles in a eutectic chloride salt to enhance thermal energy storage capacity for concentrated solar power

Abstract

Concentrated Solar Power (CSP) is considered as a viable large-scale renewable energy source to produce electricity. However, current costs to produce electricity from CSP are not cost competitive as compared to the traditional energy generation technologies based on fossil fuels and nuclear. It is envisioned that development of high efficiency and high heat capacity thermal storage fluids will increase system efficiency, reduce structural storage volume, and hence, contribute to reducing costs. Particularly, with respect to CSP, current high temperature energy storage fluids, such as molten salts, are relatively limited in terms of their thermal energy storage capacity and thermal conductivity. The current work explores possibility of boosting the thermal storage capacity of molten salts through latent heat of added phase change materials. We studied the advantage of adding coated Zn micron-sized particles to alkali chloride salt eutectic for enhanced thermal energy storage. Zinc particles (0.6 µm and 5 µm) obtained from commercial source were coated with an organo-phosphorus shell to improve chemical stability and to prevent individual particles from coalescing with one another during melt/freeze cycles. Thermal cycling tests (200 melt/freeze cycles) showed that coated Zn particles have good thermal stability and are chemically inert to alkali chloride salt eutectic in both N 2 and in air atmospheres. Elemental mapping of the cross-sectional view of coated Zn particles from the composite after thermal cycles showed no signs of oxidation, agglomeration or other type of particle degradation. The measured enhancement in volumetric thermal storage capacity of the composite with just ~10 vol% of coated Zn particles over the base chloride salt eutectic varies from 15% to 34% depending on cycling temperature range (∆T = 50°C-100°C).

Thermal energy storage of molten salt –based nanofluid containing nano-encapsulated metal alloy phase change materials

“…In order to further increase the total heat storage capacity of a TES material the use of nanoencapsulated Phase Change Materials (nePCMs) was proposed [27][28][29][30][31]. To introduce these PCMs as the solid phase in a nanofluid, a core-shell structure is needed so the particles do not collapse into each other when in melted state, losing the advantages associated with their nanometric size.…”

Nanofluid based on self-nanoencapsulated metal/metal alloys phase change materials with tuneable crystallisation temperature

“…In most cases, encapsulation is obtained by inserting nanoparticles into a high melting temperature matrix 11 – 17 , or by growing a silica 18 – 23 or trioctyl phosphine oxide TOPO 24 shell around them. Different metal cores have been investigated: indium 11 , 16 , 18 , 19 , bismuth 11 – 13 , 16 , 17 , tin 11 , 16 , 20 – 23 , cadmium 11 , lead 11 , 15 , zinc 24 , and their alloys 14 , 17 , 25 . Generally speaking, if metal cores are lower than 50 nm, lowering melting temperature and melting and crystallisation enthalpy values than those measured in the bulk material are observed due to the substantial contribution of the metal atoms near the shell 26 , 27 .…”

“…Regarding the shells that surround nePCM’s cores, silica and TOPO shells have been previously used in nePCM-based nanofluids, where a wide range of base fluids, such as methanol 18 , molten salt 21 , 24 , poly-alpha-olefin (PAO) 19 and commercial thermal oil (Therminol 66) 22 , have been used.…”

Assessing the 2014 retroactive regulatory framework applied to the concentrating solar power systems in Spain

“…9 As an exception, for i = 2013 Ing i must also include the term SR_Revenue i , since the facilities perceived revenue from the RD 413/2014 framework as well. 10 For the existing CSPP and for j = 1, SB j would be computed over the last 10 years prior to the entry into force of the RDL 9/2013 and Δt j would be set to 300 basis points, resulting t j = 7.395%. For j > 1, SB j would be computed over the last 24 months prior the first month of May previous to the beginning of j.…”