• Energy Research

Contains fulltext : 282475.pdf (Publisher’s version ) (Open Access)

Contains fulltext : 315014.pdf (Publisher’s version ) (Open Access)

We have experimentally determined the main thermodynamic properties of SrCl2, a potentially promising salt for thermochemical heat storage. We found a high energy density of 2.4 ± 0.1 GJ/m3 and proved full cyclability for at least 10 cycles going from the anhydrate to the hexahydrate without chemical degradation. We have experimentally determined the thermodynamic equilibria for each individual transition and the corresponding metastable zones. We find that the metastable zone is widest for the anhydrate to monohydrate transition and decreases with each subsequent hydration step. We have also established that the observed nucleation kinetics are highly dependent on the preparation of the sample. Depending on the preparation conditions, some seeds of the precursor phase can remain in the sample thereby influencing the induction times for the transition. In heat storage applications we recommend selecting conditions well away from the phase transition lines (at least outside the metastable zone) and to leave some seeds of the phase to be transferred in order to increase the transition speed.

In this work, we evaluate 454 salt hydrates and 1073 unique hydration reactions in search of suitable materials for domestic heat storage. The salts and reactions are evaluated based on their scarcity, toxicity, (chemical) stability and energy density (>1 GJ/m3) and alignment with 3 use case scenarios. These scenarios are based on space heating (T > 30 °C) and hot water (T > 55 °C) to be provided by discharge as well as on heat sources available in the built environment (T < 160 °C) for charging. From all evaluated materials, only 8 salts and 9 reactions (K2CO3 0–1.5, LiCl 0–1, NaI 0–2, NaCH3COO 0–3, (NH4)2Zn(SO4)2 0–6, SrBr2 1–6, CaC2O4 0–1, SrCl2 0–1 and 0–2) fulfil all of the criteria. Provided a suitable stabilisation method is found additional 4 salts and 13 reactions (CaBr2 6-0, CaCl2 6-0, 6-1, 6-2, 4-0, 4-1, 4-2, LiBr 2-0, 2-1, 2-0, LiCl 2-0, 2-1, ZnBr2 2-0) From this selection, only 2 salts/reactions (NaI and (NH4)2Zn(SO4)2) have not been extensively studied in the literature. Moreover, many well-investigated salt hydrates, such as MgSO4 and LiOH, did not pass our screening. This work underlines the scarcity of materials suitable for domestic applications and the need to broaden the scope of future evaluations.

Contains fulltext : 252352.pdf (Publisher’s version ) (Open Access)

AbstractA thin, lightweight, flexible solar cell is developed that maximizes the power‐to‐mass ratio under AM0 illumination and has a competitive efficiency after typical high energy electron irradiation. The inverted metamorphic triple junction (IMM3J) solar cells with Ga0.51In0.49P/GaAs/Ga0.73In0.27As subcells are grown on GaAs substrates and have a total epitaxy thickness of about 10 μm. After epitaxial growth, the inverted layer stack is metallized, with the metal serving as back‐contact, back reflector and support layer for the ultra‐thin solar cells before the GaAs substrate is separated by an epitaxial lift‐off (ELO) process. The nondestructive nature of the ELO process makes multiple reuses of the GaAs substrate possible. The solar cell structure is optimized for maximum EOL efficiency, that is, after 1‐MeV electron irradiation with a fluence of 1 × 1015 cm−2, by means of simulations that include the irradiation induced defects in the various semiconductor alloys. Assuming realistic charge carrier lifetime in the materials, we predict a near‐term efficiency potential for the IMM3J ELO of 30.9% under AM0 illumination before and 26.7% after irradiation. Several IMM3J ELO solar cells with an area of approximately 20 cm2 from different development stages were tested under AM0 illumination. The newest solar cells (generation III) with a mass density of only 13.2 mg/cm2 reach conversion efficiencies of 30.2% at 25°C. The resulting power‐to‐mass ratio of 3.0 W/g for the bare solar cell is one of the highest published ratios. After irradiation, a conversion efficiency of 25.4% was measured for “generation II” devices under AM0 illumination, which corresponds to a power‐to‐mass ratio of 2.6 W/g. IMM3J ELO solar cells from “generation I” were also tested for mechanical stability as “de‐risking” test of this new cell technology. No degradation of the cell performance was found after dipping the cell in liquid N2 and then heating up to 25°C for five times, despite of strong deformation of the flexible cell during the temperature cycle.

Contains fulltext : 313545.pdf (Publisher’s version ) (Open Access)