21 avril 2017

3 Post-Doctoral positions available at Ben-Gurion University (Israel)/PROMES-CNRS (France)

Novel utility-scale solar electricity generation strategy 

In the framework of a collaborative research project between Ben Gurion University and PROMES-CNRS, we offer 3 post-doctoral positions at Ben-Gurion University (1 year). One of these 3 post-doctoral position will be extended for a one-year supplementary contract at PROMES (Odeillo, France).

Motivation: The proposed project aims at a novel utility-scale solar electricity generation strategy, with day-night storage and unprecedented efficiency, via an innovative conflation of high-efficiency photovoltaics (for direct conversion of sunlight to electricity), high-temperature solar thermal (for conversion via Rankine cycles), and a new genre of innovative concentrator optics that facilitates these ambitious objectives.

The system design is predicated on new unprecedented 3D concentrator optics - to wit, aplanatic solar tower systems - where a completely static secondary mirror atop the tower can be used to actually increase flux concentration (in contrast to conventional Cassegrain beam-down solar tower optics), while simultaneously permitting a receiver (focus) at or below ground level, with prodigious practical advantages. This core concept can also be implementated as part of a multi-tower system, where a given heliostat can be aimed at more than one tower, depending on solar geometry, thereby substantially reducing shading and blocking losses, as well as markedly increasing system ground-cover ratio.

Multi-junction photovoltaics currently lack the affordable, efficient storage capability of solar thermal. Hence the paramount importance of storage skews the system optimization toward a limited fraction of photovoltaic direct conversion.

The importance of operating at high concentration (e.g., exceeding 1,000 suns) is multi-fold. First, solar cell efficiency can increase as the logarithm of concentration. Second, high concentration basically removes the per-cell cost of expensive multi-junction solar cells from the cost equation. Third, system heat loss need not exceed more than a few percent of the the collected solar beam radiation, even at these high temperatures, simply for geometric reasons, also obviating the need for selective coatings used extensively in line-focus solar thermal power systems. And fourth, the high collection temperature needed for high-efficiency turbines is readily achieved at high concentration.

The project divides into three linked scientific realms: photovoltaic materials, optics, and thermal design, as follows.

Position N°1: Photovoltaics tailored to the new high-temperature hybrid concept:


• Identify and simulate solar cell materials and architectures that can operate efficiently and robustly at temperatures upward of 400°C and flux densities above 1,000 suns (> 1 W/mm2).
• Develop several candidate designs for a tandem stack of sub-cells.
• Evaluate sensitivity to irradiance, sub-cell temperature, and spectrum.
• Model the 3D temperature distribution within the tandem stack.
• Optimization studies for the part of the solar spectrum to be exploited by each sub-cell, sub-cell operating conditions, and suitable tunnel diodes between the sub-cells.
• Design and perform bench-top experiments toward validating and informing the modeling studies, most notably at irradiance values up to thousands of suns, and temperatures above 400°C.

Position N°2: New advanced optical designs:


• Formulate and fully solve the new concept of aplanatic optics for solar tower (3D Fresnel) concentrators.
• Include options from uniform-height to étendue-matched heliostat fields.
• Focus on high-concentration solutions that permit the receiver (focus) to be at or below ground level.
• Simulate how collectible solar beam radiation will vary with sun-earth geometry.
• Evaluate the sensitivity of concentrator performance to mirror and tracking inaccuracies.
• Explore the practicality and consequences of mini-tower heights of no more than a few meters.
• Formulate solutions for the multi-tower problem, with the aim of markedly increasing system ground-cover ratio and significantly lessening shading and blocking losses.
• Build and conduct small-scale optical experiments for one such aplanatic mini-tower and heliostat field.

Position N°3:Thermal design for high-temperature collection and storage:


• Design and evaluate the thermal receiver and the interface between the photovoltaic cells and the high-temperature coolant, including 3D temperature distributions and sensitivity to coolant flow rate.
• Identify fluids suitable both as coolants for the hybrid receiver, and as a sensible-heat storage medium (from a broad assortment of molten salts), with an eye toward long-term chemical stability, non-toxicity and safety.
• Evaluate the impact of concentration on system thermal and flow operation.
• Determine insulation materials and geometries that can maintain acceptably low heat loss.
• Conduct bench-top calorimetric and component-durability experiments for selected thermal receiver designs and molten salt coolants.

Context: This research work will be carried-out at Ben Gurion University (Midreshet Sede Boker, in the Negev Desert http://in.bgu.ac.il ), under the supervision of Pr. Jeffrey Gordon, a world-renowned expert in the field of solar concentrators and ultra-efficient photovoltaics (http://www.bgu.ac.il/~jeff/).
There is a possibility for a 1-year extension at PROMES-CNRS laboratory in Odeillo (France) funded by SOLSTICE laboratory of Excellence (http://www.labex-solstice.fr/), for one the 3 positions, under the supervision of Dr. Alexis Vossier. Interested candidates should mention in their file whether they are interested in pursuing the research work initiated at Ben-Gurion University for an additional year at PROMES (http://www.promes.cnrs.fr/ ).

Salary: ~1300-2000€ + affordable housing options

Application terms: Highly-motivated candidates with a Ph.D. in Optics, Photovoltaics, Thermal engineering or a related field are strongly encouraged to apply. Applicants should possess a strong expertise in their field, an excellent English level, as well as an excellent track record.
Interested candidates should email a brief cover letter indicating their research interests and career goals, CV, and contact information for 3 references to:

Contact: Additional details can be provided upon request (email: phone: +33 4 68 30 77 52)