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International audience; Hybrid solar photovoltaic/thermal power systems offer the possibility of dispatchable, low-cost, efficient and reliable solar electricity production. A key design strategy capable of fully exploiting the heat generation stemming from both solar cell thermalization and sub-bandgap photons involves an integrated photovoltaic/thermal absorber operated under concentrated sunlight, at temperatures conducive to efficient turbine operation, to wit, hundreds of degrees C. A pivotal aim is attaining the highest efficiency possible while ensuring a substantial fraction of the total power derives from the turbines, with gas-fired backup heating and/or thermal storage mitigating the ephemeral character of solar availability. However, the performance of solar cells at unprecedented elevated temperatures remains an open question. Key issues include (a) whether the efficiency loss stemming from high-temperature solar cell operation can be maintained acceptably small, as well as how optical concentration affects it, and (b) whether the solar thermal contribution can constitute a significant fraction of total electricity production. Here, we try to establish upper bounds on photovoltaic and system performance, covering a broad range of cell temperature and concentration levels, for single- and multi-junction cells operating at the radiative limit. We demonstrate that (1) the use of highly concentrated sunlight markedly diminishes photovoltaic - as well as thermal - efficiency losses at high temperature, and (2) the extent to which high operating temperature affects cell efficiency strongly depends on cell architecture. The implications for future generations of high-temperature/high-concentration solar cells are also addressed.

International audience; Hybrid solar photovoltaic (PV)/thermal power systems offer the possibility of dispatchable, affordable and efficient solar electricity production – the type of transformative innovation needed for solar cell devices to realize high grid penetration. The PV sub-system enjoys high efficiency, and the thermal sub-system can ensure uninterrupted power delivery via backup gas heating and/or multi-hour thermal storage. However, elucidation of the basic performance bounds, and the quantitative perspective required for judging the leading hybrid strategies relative to one another, as well as relative to the existing alternative of autonomous photovoltaic and solar thermal power systems, have remained incomplete. A more thorough and basic evaluation of the performance of the assorted combinations of PV and solar thermal sub-systems over a wider range of possible operating conditions than regarded previously is presented here. This involves analysis of the most fundamental processes limiting system efficiency, tempered by the realities of current and foreseeable PV and thermal technologies. The 3 leading hybrid strategies are: (1) concentrated solar beam radiation irradiating an integrated PV–thermal receiver, with the unique advantage of recuperating PV thermalization losses as heat delivered to the thermal receiver, thereby contributing to driving the turbine, (2) the spectral splitting of concentrated solar beam radiation, with sub-bandgap photons directed to a thermal receiver and the rest to concentrator PV cells, and (3) nominally 1 sun PV cells performing double duty as both a direct converter and as a spectrum-splitting reflector that concentrates sub-bandgap photons onto a thermal receiver. The two figures of merit appraised are: (a) the solar-to-electricity conversion efficiency, and (b) the share between thermal and PV electricity production

The development of high temperature CPV/thermal (CSP) hybrid systems appears to be a promising route to improve the overall solar to electricity conversion efficiency. Moreover, such systems would not only use the residual heat stemming from the unconverted fraction of the incident solar radiation in PV cells, but they would also provide the advantage of storing energy as heat. However, the performances of such hybrid systems depend strongly on the temperature of the thermal receivers which are only effective at high temperatures (typically above 250°C) while solar cells typically operate at temperatures close to ambient. An appropriate strategy is to make PV cells efficiently operate at temperature levels significantly exceeding the normal range of temperatures for which they are commonly designed. The degradation of electrical performance associated with high working temperature is less pronounced when the cell is submitted to high sunlight concentrations. An efficient photovoltaic conversion at tempera...

The present work aims at better understanding the effects of the different limiting mechanisms, such as resistive losses and external radiative efficiency, on the performance of single junction solar cells simultaneously submitted to concentrated sunlight and angular restriction of the radiation emitted by the cells. It particularly tries to identify the optimal combination of the angles of absorption and emission leading to the highest conversion efficiency, for different values of series resistances and external radiative efficiencies. It also assesses the extent to which these parameters affect the efficiency of the proposed strategy.

Cardiac tissue damage due to myocardial infarction (MI) is one of the leading causes of mortality worldwide. The available treatments of MI include pharmaceutical therapy, medical device implants, and organ transplants, all of which have severe limitations including high invasiveness, scarcity of donor organs, thrombosis or stenosis of devices, immune rejection, and prolonged hospitalization time. Injectable hydrogels have emerged as a promising solution for in situ cardiac tissue repair in infarcted hearts after MI. In this review, an overview of various natural and synthetic hydrogels for potential application as injectable hydrogels in cardiac tissue repair and regeneration is presented. The review starts with brief discussions about the pathology of MI, its current clinical treatments and their limitations, and the emergence of injectable hydrogels as a potential solution for post MI cardiac regeneration. It then summarizes various hydrogels, their compositions, structures and properties for potential application in post MI cardiac repair, and recent advancements in the application of injectable hydrogels in treatment of MI. Finally, the current challenges associated with the clinical application of injectable hydrogels to MI and their potential solutions are discussed to help guide the future research on injectable hydrogels for translational therapeutic applications in regeneration of cardiac tissue after MI.

The present work aims at better understanding the effects of the different limiting mechanisms on the performance of multi-junction stacks comprising up to 5 subcells, and to assess the extent to which the iso-efficiency curves derived with the detailed balance model are affected by these non-ideal losses. In light of these results, further discussions and analysis will be carried out in order to understand which arrangements of bandgaps could potentially achieve practical conversion efficiency approaching the theoretical limit.