J. Antonio Urbano Castelan*#, Yasuhiro Matsumoto * y Rene Asomoza P.* # #

Alexei Martinez Munoz#, German Escoto Mora, Alfonso Sotelo Trujillo#

Francisco J. Aceves Hernandez y Antonio Jacome Rodriguez#
*Section of the Solid State Electronics, Electric Engineering Department CINVESTAV-IPN
P O Box. 14 -740 Mexico D. F. C. P.07360 Tel (52) 55 5061-3783, Fax (52) 55 5747-7114

e-mail: jurbano@mail. cinvestav. mx

# SEPI-ESIME and ICE-ESIME-IPN Professional Unit "Adolfo Lopez Mateos"
Zacatenco, Lindavista C. P.07738 Mexico D. F.

ABSTRACT

This article shows how 3.6 kWTH solar oven concentrating system is operated by using only 5 watt-peak PV-module for its tracking system. The solar oven is autonomous and designed for Marfas Islands, Mexican rural area for food cooking, sea water distillation and medical instrumental sterilization.

The PV-module charges continuously energy in a capacitive storage to move two 12 DCV motors of 36W each. These electric motors adjusts azimuth and altitude depending of solar position determined by an electronic optical sensor for an optimum concentration position. There have been made two versions for this purpose, the first one consists on digital states (on/off) for light and dark conditions over a “Greek cross”, and the second one provides redundancy because it has two detection elements besides it is possible to have coarse, medium and fine detection.

The solar oven system of 360 mirrors (10X10cm2 each) achieves temperature of about 300°C at its oil-container. This oil-container transmits the heat directly to the commercial kettle, maintaining 120°C at the pressure of »1.05kg/cm2. Maria s Islands has an average of 340 sunny days in a year.

We expect a contribution for forest conservation avoiding firewood consumption in the near future. Foregoing Mexican rural area has great potential in solar resources for their inhabitant needs. Food cooking, water distillations are most important daily-life activities. In Mexico, solar cooking oven has been introduced since 1955, however, this cooking technique was not assimilated due to the local people’s social and cultural aspects.

This development is intended to be applied in those rural areas in Mexican Republic because there are 28 million people that still use firewood leading to diverse problems such as health pulmonary emphysema, body burnings, deforestation, and CO2 emissions. It has been estimated that one individual consumes about 1.2 tons of firewood [5]; an additional reason to promote this use is due to high solar radiation over semi-desertic and desertic areas, which represent about 3/4 of the Mexico’s territory.

INTRODUCTION

In 1955 the Wisconsin University donated 30 solar ovens to the northern states of Coahuila and Nuevo Leon in Mexico, they were parasol inverted type with aluminum painting and parabolic bend, this is shown in the Fig 1, [1]. One week later it was thought that it would be the most important contribution from an American University to the developing countries; one month later the ovens were abandoned. The Rockefeller

Foundation, worried by this result, sent Technicians and Sociologists to find out the possible causes of the failure. They were sent after identical ovens were applied parallely in American Indian communities. They had the following conclusions and detected disadvantages:

1. The social — cultural aspect and feeding habits, were the decisive facts, since the ancestral tradition of cooking inside the house beside the bonfire was broken. Cooking outdoors and under the sunbeams broke the millennial culture of their ancestors. On the other hand, in the indigenous areas it is used to prepare meals at a very early hour of the day so people return by the afternoon or night to have dinner, both conditions are when the solar resource is no longer present.

2. The housewife was forced to become and Astronomer since she had to distract her activities to locate the oven every certain time since the Sun evolves 15° per hour on the sky: she had to check the angles of altitude and azimuth of the Sun’s path.

3. The unwanted gleams of the oven due light beams outside of they focal condition hurted the housewife’s eyes leading an obvious discouragement to continue using the oven.

4. In those countries located within the tropical area (between the tropics of Cancer and Capricorn), the users are forced to use the oven in an horizontal position during certain times of the year, it caused that the bottom of the parasol got dirty by drippings produced while the product was being cooked.

5. The parabolic type solar oven, hinders its own use when the Sun is in the zenith and the diameter of it surpasses 1.5 meters.

6. The fragility of the oven structure (parasol parabolic type) let the wind sweep it easily, so the oven were found in the neighbor’s house damaged by the air.

7. The absence of the Sun, affects directly the cooking process, since this concentration system operates with the direct component of the Sun’s light.

OBJECTIVE

To design, to build and to test a small PV-Module tracking system for a 3.6kWTH stand­alone solar oven. The target objective was to build a simple, economical and robust solar oven for Mexican rural area Here, we will focus attention to its mechanical, thermal efficiency and tracking system aspects. The outcome is shown in FIG 2 and FIG. 3.