# Towards Restaurants Powered by Scheffler Reflectors

Gabriel Guillet, Séverine Barbosa, Thomas Fasquelle, Benjamin Kadoch

► To cite this version:

Gabriel Guillet, Séverine Barbosa, Thomas Fasquelle, Benjamin Kadoch. Towards Restaurants Powered by Scheffler Reflectors. Doctoral School Day of the Doctoral School 353, Jun 2022, Marseille, France. hal-04972780

HAL Id: hal-04972780

https://amu.hal.science/hal-04972780v1

Submitted on 1 Mar 2025

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Distributed under a Creative Commons Attribution 4.0 International License
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Gabriel GUILLET (*), Séverine BARBOSA, Thomas FASQUELLE, Benjamin KADOCH

## CONTEXT

Scheffler reflectors are parabolic dishes with the special feature of being **flexible**. Concentrating-type cookers using a Scheffler reflector seem to be promising among solar cookers because they can **provide sufficiently high power and temperature** for various cooking processes, and they allow to **keep the parabola and the focus point at stationary positions** throughout the year.

The restaurant **Le Présage** has designed and is already using a **new model of Scheffler-type cooker**. The purpose of this study is to evaluate its **performance**, to **position it** in relation to the literature and to estimate its **potential for improvement**. The performance of the cooker was assessed according to the **American standard** (ASAE S580.1 NOV2013).

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Source : lepresage.fr

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Source : lepresage.fr

## METHOD

### Test Bench

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Automatic sun-tracking system

Scheffler primary reflector: 8 m²

Flat secondary reflector: 0.85 m x 0.70 m

Cooking pot: Φ 0.40 m, 30 L max

Cast-iron slab: 1.00 m x 0.60 m x 0.0013 m

Water temperature $T_w$

Ambient temperature $T_a$

Slab temperatures $T_3$ to $T_9$ (evaluation of the heat stored/released by the slab)

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### Experimental Data

Location: lat.: 43.3449°, lon.: 5.4374°, alt.: 120 m

Date: 17/12/2021

Intercept area: $A_{int} = 6.9 \text{ m}^2$ (season dependant)

Standard load: $m_s = 48.2 \text{ kg}$

Real load: $m = 22.0 \text{ kg}$ (time and volume limitations)

Average ambient temperature: $\bar{T}_a = 16.2 \text{ °C}$

Average direct normal irradiance: $\bar{I} = 794 \text{ W/m}^2$

Wind not measured

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## RESULTS AND DISCUSSION

The **instant power** *P* absorbed by the water is computed from the data above. It is **normalised** by a standard irradiance of 700 W/m² to obtain the **standard power** *P*<sub>s</sub> and then, plotted against the **temperature difference** Δ*T* = *T*<sub>w</sub> - *T*<sub>a</sub>

**Standard cooking power:**

* High power for a solar cooker

* Low power density (91 W/m²)

**Regression model:**

* High power at low temperature difference

* Rapid decrease in power with increasing temperature difference

**Possible explanations:**

* Lack of about 25 % of mirrors (a)

* Optical losses (b, d)

* Thermal losses (c)

**Uncertainties due to the protocol:**

* Volume of water required

* Number of pots

* Evaluation of the heat stored/released by the slab

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## CONCLUSION AND PERSPECTIVES

High power but great potential for improvement:

* Reduction of the **optical losses**

* Association of the **plane secondary reflector** with the **Scheffler reflector**

* Reduction of **thermal losses from the bottom** of the slab: window, selective paint, concentration...

* Reduction of **thermal losses from the top** of the slab

Other measuring method: **Infra Red measures** with inverse methods (e)

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