Appropriate Solar Technology
Linked Table of Contents: Click links or scroll down to navigate.
- Introduction
- Direct Current PV Systems
- Solar Thermosiphons
- Solar Thermal Delta Ovens
- Integrated Food Dehydrators
- Solar Parabolic Furnaces
- High Temperature Thermal Storage
- Integrated Pyrolizer Retorts
- Greenwall Shade Systems
- When Will There Be Published Designs?
- Potential Technologies
- SMART Schools
Introduction: Our campus designs include several solar & hybrid technologies appropriate to the developing world. Our design goal of elegant simplicity focuses on reliable, low cost, low maintenance systems. We minimize the use of battery storage and power electronics so these systems are less dependent on global supply chains and repair specialists.
In the course of our basecamp SRB development we will create small scale or mobile versions of these technologies that billions of people around the world can build DIY. All SMART school designs and research data are shared free open source. These are systems for you!
Direct Current PV Systems: Photovoltaic solar panels, for solar electric power, are now inexpensive and efficient. The costly and often unreliable components of a solar power system are electronics and storage bank batteries. Panels generate a direct current (DC), like that of a battery. We use this power directly for heating elements, driving electrochemical reactions, power tools, charging low voltage electronic devices, etc. We will have small battery banks and inverters for standard AC (wall plug) devices but using as much DC power as we can keeps capital costs low and increases reliability.
Solar Thermosiphons: This is an elegant, efficient way to heat hot water up to 95 degrees C, just short of boiling. Hot water rises, so this system circulates without the use of a pump. With low cost insulated storage tanks water can be kept at temperature for days. The thermosiphon effect can even be used to move hot water from the storage tanks to appliances above tank level. The components of a typical system are as follows:
- Hot Water Supply (line out to ground tanks or appliances – shown with valve)
- Insulated Storage Tank (small short term storage)
- Collector Line (hot water rises through this line to #2)
- Collector / Absorber (coiled or grid pipes with a black absorber behind them and a glass surface in front lets light in and retain heat – water rises through the system as it is heated)
- Cold Water Supply (line in for water at ambient temperature)
Solar Thermal Delta Ovens: With an ample supply of hot water we can easily pasteurize and cook (sous-vide, slow cook). Using energy from a hybrid source (direct solar PV, biomass heating, gas burners) we can raise the temperature further, only inputting the difference in energy (the delta). If we heat the water directly it will boil, which can be used to pressure cook or produce steam. If we use the solar hot water to pre-heat a dry, solid thermal mass then we can raise the temperature of that dry mass as high as we like.
In typical oven used for baking often exceed 140 to 165 °C (280 to 330 °F) because food browns rapidly at those temperatures. This is due to the Maillard reaction, resulting in the crispy texture and distinct flavors of bread, pizza, etc. To achieve these high temperatures we must heat the dry thermal mass as heating water would only result in the energy escaping as steam exited the system. Pre-heat water is thus drained back into storage before high heating begins.
Integrated Food Dehydrators: With liquid or solid thermal mass well above the temperatures required to dehydrate food, large volume processing unit can be integrated into our ovens, storage system, etc. Given our system can stay at temperature for days, we can properly preserve large batches of sliced produce. This allows shelf stable storage and reduces shipping costs by removing water weight.
Solar Parabolic Furnaces: Though our other hybrid systems work for most applications a concentrator system using parabolic mirrors can achieve extremely high temperatures. This could be useful for heating solid thermal mass, iron or gravel for example, to red-hot temps. We could melt metal, cure materials and make use of high temperature chemical reactions in our research.
High Temperature Thermal Storage: An insulated thermal mass slowly bleeds energy over time. A solid thermal mass brought to extremely high temp and stored in a well insulated system can provide a useful thermal curve overnight and perhaps longer.
Integrated Pyrolizer Retorts: Pyrolysis is a process that decomposes substances such as biomass at high temperatures. A biochar reactor is easily integrated into our designs to provide useful products such as high quality charcoal and high heat during periods of overcast weather (low solar incidence).
Greenwall Shade Systems: We need to use every part of our small farm campus as efficiently as possible. Growing plants to shade the southern exposures of our structures is a great way of keeping the buildings cool and growing small container or trellised crops that love direct sun. We are excited about the hundreds of tomato varieties there are to experiment with.
When will there be published designs? Full schematics for everything we develop on campus will be published at the late prototype stage. These will be free open source files. If the Champions’ Club really wants to see early plans that might happen… but expect videos first.
Potential Technologies: We are evaluating a number of other potential technologies from bio-gas reactors to solar chimneys for passive cooling. We even have a design for a floating parabolic solar furnace that rests on the surface of a pond. These are all at early design stages and are not likely at the SRB development stage.
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