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Thesis (M.S. - Agricultural Engineering)--University of Arizona, 1988. / Includes bibliographical references (leaves 81-83).

An original low cost modular system which collects excess solar energy entering a conventional cold greenhouse during the day and uses the stored energy at night for heating has been devised and analysed. During the day, fluid absorbs heat as it is pumped through semi-transparent panels mounted immediately inside the greenhouse roof and then returned to an insulated tank forming the thermal store. At night the warm fluid is recirculated through the panels and/or emitters near the plants to provide greenhouse heating. Semi-transparent panels were designed and constructed and their thermal operation analysed in a test rig. Semi-transparent panels not only collect energy from the sun but also, unlike conventional solar collectors, gain up to 70% of heat from adjacent warm air. A semi-empirical mathematical model of the thermal. operation of the panels is presented which predicts panel energy gain with better than 20% accuracy. A prototype system of panels and store was constructed in a small greenhouse which had been partitioned into test and control compartments. Experiments were conducted into the operation of. the system and its effect on the vertical temperature profile and illumination inside the greenhouse both with and without plants. At night, the panels heated plants mainly by restricting radiative losses to the sky, so that leaf temperatures were elevated by up to 2.5 deg. C. Panels reduced light levels to about 65% of those in the control compartment. A detailed computer model was written to predict the illumination and temperatures inside a greenhouse fitted with a panel/store system. This model was validated and can therefore be used for the general analysis of semi-transparent solar panel systems and their effect in greenhouses. Panel/store systems were calculated to supply, for heating at night, about 6% of the annual solar energy incident on the greenhouse.

This thesis considers the long term energy problem and the role which active solar collector systems for building application might play in alleviating this problem. The major part of this thesis describes the derivation and solution of the mathematical model to simulate the principal components in a solar energy collector system. The model is based on an implicit numerical technique which allows the investigation of the simultaneous interaction between system components in liquid and photovoltaic collectors. A simulation progam called FLARE, based on the aforementioned model, has been developed for use as a research and design model. This program forms the central core of a suite of interrelating computer programs which provide sophisticated user participation by means of a high level interactive graphics facility.

A salt gradient solar pond offers an economical means of both collecting summer solar heat, and storing it in water over periods of a few months for use in winter space heating. The vertical gradient of salt density prevents convection in the pond and makes it self-insulating against heat losses. The solar pond project at the university of Sussex aimed to study the design, construction, filling, and operation of a salt gradient solar pond, and to develop inexpensive instrumentation for the harsh environment of hot salt water solution, for monitoring behaviour and performance. A new method of heat extraction, from both the insulation and storage layers of the pond, was tested, and a computer program was developed to model pond behaviour under non-steady techniques. Construction, filling, and operation of indoor and state conditions, using finite difference outdoor pilot solar ponds is described and a simple means of maintaining salt density gradient, as well as work on achieving good pond transparency over the two-year period of operation of the pond. To improve the efficiency of the pond successful experiments were carried out to extract heat from both the convecting storage layer and the non-convecting insulation layer of the pond. This permits interception and extraction of heat flow in the non-convecting layer which would otherwise be lost to the surface. Laboratory and outdoor exper iments were car ried out to test whether this causes unwanted convective mixing and increased upward diffusion of salt in the non-convective zone of the pond. Heat transfer coefficients were measured with the heat exchanger placed in the non-convecting insulation layer. Both steady-state and finite difference model calculations are presented to indicate the improvements in operating efficiency and temperatures that are achievable with the new method of heat extraction. Theoretical results from the finite difference model are in good agreement with observed performance.

The purpose of this thesis is to explore the potential for integrating biomimetic thinking into the design and implementation of photovoltaic energy systems in a way that promotes ecological health, economic feasibility, and equal access to cleaner energy. Photovoltaic energy production is among the most promising renewable energy sources, however, current conventional photovoltaic systems exhibit a number of shortcomings. Steering innovation toward socio-technical systems that are integrated with ecological systems will help support human needs without inhibiting larger ecological function. This investigation began with the construction of a conceptual biomimetic lens from a foundation of literature related to biomimicry in the built environment. Next, the underlying elements, interconnections and functions of both the ecological systems involved in photosynthesis and socio-technical systems related to photovoltaic energy production were defined and examined. The biomimetic lens was then applied to each system to envision biomimetic approaches to address shortcomings of current conventional photovoltaic systems. The suggested approaches aim to address shortcomings in the design, manufacture, and implementation of photovoltaic systems in ways that mimic key principles found in biology and ecology. Since the success of ecological systems is embedded in the nesting of interrelated systems, the biomimetic lens was applied at multiple scales: the chloroplast/solar cell, the leaf/solar panel, the plant/solar array, and the ecosystem/community scale. The results of this study both suggest the direction of further research in the development of biomimetic solar energy systems and provide insight into the effectiveness of biomimetic thinking as a strategy for designing equitable, economical, and ecologically sound systems. / text

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