Emmanuel Guillot

A 300kW Solar Chemical Pilot Plant for the Carbothermic Production of Zinc

In the framework of the EU-project SOLZINC, a 300-kW solar chemical pilot plant for the production of zinc by carbothermic reduction of ZnO was experimentally demonstrated in a beam-down solar tower concentrating facility of Cassegrain optical configuration. The solar chemical reactor, featuring two cavities, of which the upper one is functioning as the solar absorber and the lower one as the reaction chamber containing a ZnO/C packed bed, was batch-operated in the 1300–1500 K range and yielded 50 kg/h of 95%-purity Zn. The measured energy conversion efficiency, i.e., the ratio of the reaction enthalpy change to the solar power input, was 30%. Zinc finds application as a fuel for Zn/air batteries and fuel cells, and can also react with water to form high-purity hydrogen. In either case, the chemical product is ZnO, which in turn is solar-recycled to Zn. The SOLZINC process provides an efficient thermochemical route for the storage and transportation of solar energy in the form of solar fuels.

A 40 W cw Nd:YAG solar laser pumped through a heliostat: a parabolic mirror system

Solar-pumped solid-state lasers are promising for renewable extreme-temperature material processing. Here, we report a significant improvement in solar laser collection efficiency by pumping the most widely used Nd:YAG single-crystal rod through a heliostat?parabolic mirror system. A conical-shaped fused silica light guide with 3D-CPC output end is used to both transmit and compress the concentrated solar radiation from the focal zone of a 2?m diameter parabolic mirror to a 5?mm diameter Nd:YAG rod within a conical pump cavity, which enables multi-pass pumping through the laser rod. 40?W cw laser power is measured, corresponding to 13.9?W?m?2 record-high collection efficiency for the solar laser pumped through a heliostat?parabolic mirror system. 2.9% slope efficiency is fitted, corresponding to 132% enhancement over that of our previous pumping scheme. A 209% reduction in threshold pump power is also registered.

SOLFAST, a Ray-Tracing Monte-Carlo software for solar concentrating facilities

In this communication, the software SOLFAST is presented. It is a simulation tool based on the Monte-Carlo method and accelerated Ray-Tracing techniques to evaluate efficiently the energy flux in concentrated solar installations.

Experimental Determination of the Extinction Coefficient for a Packed-Bed Particulate Medium

The extinction coefficient of a powder mixture of ZnO and beech charcoal is determined at ambient temperature using two experimental set-ups: (a) radiation in the range 500–1000 nm is captured by a 200 μm-diameter fiber optic and sent to a spectrometer equipped with a Si/PbSe detector; (b) radiation in the range 350–1100 nm is captured by a 5 mm-diameter Si-photodiode. Both set-ups measure the attenuation of intensity from a 3273 K blackbody source. The experimental results are implemented in the numerical solution of the equation of radiative transfer, using the Monte-Carlo ray-tracing technique. The extinction coefficient is determined to be 10103 ± 615 m−1 at 1000 nm using set up (a), and 7850 ± 337 m−1 for the range 350–1100 nm using the more accurate set-up (b).

TRANSMITTANCE ENHANCEMENT OF PACKED-BED PARTICULATE MEDIA

The optical thickness of highly attenuating packed-bed particulate media can be significantly reduced and, consequently, the radiation heat transfer enhanced, by the addition of large (> 100μm) semi-transparent SiO 2 particles. The monochromatic transmittance of packed-bed mixtures of SiO 2, ZnO, and C particles of various relative mass fractions is experimentally measured as a function of the packed-bed thickness using a He-Ne laser/fiber optic/spectrometer system. Two functions, one derived from the general solution of the equation of radiative transfer for an absorbing-scattering-non emitting medium, and a second one derived from Bouguers law, were fitted to the experimental data and used to elucidate the effect of the incoming scattering and optical thickness on the medium transmittance. The augmenting contribution of the incoming scattering diminishes with increasing content of highly absorbing carbon particles, and, when it becomes negligible, the extinction coefficient is directly determined by applying Bouguers law for attenuation of incident radiation along its path.

Highly efficient end-side-pumped Nd:YAG solar laser by a heliostat-parabolic mirror system.

We report a large improvement in the collection and slope efficiency of an Nd:YAG solar laser pumped by a heliostat-parabolic mirror system. A conical fused silica lens was used to further concentrate the solar radiation from the focal zone of a 2 m diameter primary concentrator to a Nd:YAG single-crystal rod within a conical pump cavity, which enabled multipass pumping to the active medium. A 56 W cw laser power was measured, corresponding to 21.1  W/m2 record-high solar laser collection efficiency with the heliostat-parabolic mirror system. 4.9% slope efficiency was calculated, corresponding to 175% enhancement over our previous result.

An adaptive temperature control law for a solar furnace

This paper describes the development of an adaptive control law based on exact feedback linearization and Lyapunov adaptation of the process dynamics applied to a solar furnace. The controller is tested on a 6kW solar furnace model that represents a plant installed at the Odeillo Processes Materials and Solar Energy Laboratory (Oriental Pyrenees in the South of France). The adaptive features allow to tackle the problems posed by knowledge uncertainty about furnace dynamics. It is concluded that the specifications related to material testing are met.

Control of a solar furnace using active cooling

This paper explores a control architecture for a solar furnace that uses active cooling to improve the temperature reference tracking during the decreasing phase of the reference. This is done in conjunction with the command of the shutter that adjusts the incident power and compensates sun power variability due to weather conditions. The controller uses exact linerization coupled with a PI controller to handle model parameter uncertainty. Off-line identification is employed to characterize the temperature dynamics, this is used to avoid online adaptation mechanisms that may cause stability problems during the controller startup, that may melt the material sample. Experimental results obtained from the plant in closed loop control using active cooling are presented.

On-sun first operation of a 150 kWth pilot solar receiver using dense particle suspension as heat transfer fluid

A 50-150 kWth pilot solar rig comprising the key equipments of a real plant and that uses silicon carbide Dense Particles Suspension as the heat transfer fluid has been tested at the 1 MW solar furnace at Odeillo-Font Romeu, France. The tests were carried out under large ranges of operating parameters and controlling the mass flow rate when higher temperature was required and when changes on DNI (direct normal irradiation) occurred. This paper presents experimental results on particle outlet temperature, dynamic response of the system to solid mass flow rate and solar power variations, and receiver thermal efficiency (η). Mean and maximum particles’ temperature up to 585°C and 720°C respectively was reached. The receiver thermal efficiency was measured in the range 50-90%.

Solar Carbothermic Production of Zinc From Zinc Oxide: Solzinc

In late 2004, the pilot Solzinc solar reactor was commissioned. The European Union and the Swiss Federal Office of Science and Education are funding this project to demonstrate the technical feasibility and the economical potential of producing Zn by reducing zinc oxide with the aid of concentrated solar energy and a small amount of carbon at a close to industrial scale. The zinc can be used as a means to store solar energy in a chemical way, e.g. suited to release electricity in Zinc-air fuel cells. This allows on demand use, boosting the availability of solar energy. Furthermore, as the Zinc-air fuel cells’ waste is ZnO, we get a cyclic process by reducing this ZnO in the Solzinc solar reactor. Numerous lab tests and numerical studies of the chemical and thermal behavior of the solar carbothermic ZnO reduction process were conducted by the Swiss Paul Scherrer Institute, the Swiss Federal Institute of Technology, the Israeli Weizmann Institute and the French CNRS Processes, Materials and Solar Energy laboratory. An indirectly heated beam-down reactor concept was chosen and influencing parameters, such as the type of carbon, the stoichiometry of the ZnO-C mix and the process temperature were explored. Based on these findings the technology was scaled up for the pilot plant for about 0.25 MW solar input leading to a designed zinc production rate of 50kg/h. The Swedish company ScanArc Plasma Systems AB developed a special quench system to produce zinc dust directly from the gaseous zinc exhausted from the solar reactor. The dust’s characteristics were adapted to the requirements of the Zn-air fuel cells developed by the German company ZOXY Energy System AG. The resulting zinc can be easily stored and transported for generating electricity as needed. In 2004, the pilot reactor, the quench system and extensive instrumentation were installed at the Weizmann Institute’s solar facilities to process batches of up to 500 kg of ZnO-C mixture. After cold testing of the installation and fulfilling all safety requirements, the first batches were processed. This paper explores the results of the commissioning to show the technical feasibility of this process to produce zinc and to store solar energy.Copyright