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Solar Cooking & Heating

by David A. Nuttle, Inventor

PROBLEMS: To help avoid problems with insects, livestock, and wildlife --and as a matter of tradition-- many tribal and rural villagers cook inside their huts. Such indoor cooking fires are then used during cold nights as needed to provide some warmth. The problem is that fuels are in short supply in many areas of the Third World that follow such cooking and heating practices. Most of the fuels used are dried livestock manures and locally available brush, both causing a smoke that is high in very harmful materials. According to data from the United Nations, some 1.6 million women and children die annually as a result of exposure to this type of severe indoor air pollution (from smoke). Currently available solar cookers and ovens must be used outdoors, in direct sunlight, and they are not popular with most villagers. With millions of people cutting brush, for fuel, desertification is dramatically increasing in many areas.

SOLUTION: A simple solar hot water collector may be made using metal pipes, with attached metal fins (see drawings). When placed outside of a hut, facing the sun, this type of heat collector is very efficient. Pipes are used to thermo-cycle the hot water to a slow-cook solar oven, and then back again to the solar collector. The indoor solar oven is a double-walled metal box, with lid, designed to allow a water-coil to be located in sand placed between the two boxes. The sand, heated by hot water in the coil, facilitates heat transfer to the solar oven. This indoor oven is located in the center of a large insulated metal box containing rocks used to store surplus heat. To access the oven, or provide interior heating, the lid to the rock-box is removed. (The oven cooks at some 200 degrees F.) Basic design, for this innovation, has been simplified to make local villager construction possible in remote, rural areas.

ADDITIONS TO SOLUTION: 1) By attaching a typical bimetal thermoelectric device with one end fixed to a hot water pipe, and the other end fixed to a cool water pipe (or buried in cool soil), sufficient electrical power may be generated for a light (and/or other electrical devices). 2) If supplemental electrical power is needed ---for items such as a radio or electric grill--- a small (flexible) photovoltaic array may be located outside of a hut, in a place with good solar access (sunlight). Most tribal and rural villagers will need technical help when making these additions. Please contact NPI for any technical support needed (email:

ACQUIRING THE SOLUTION: As noted above, the basic oven design is simple enough to facilitate local construction of this basic solar cooking and heating system. Otherwise, NPI plans to contract with local manufacturers to make this invention easily available to all who have a need for solar cooking and heating. NPI’s barter trade system will be used to help many poor villagers acquire the basic components of solar cooking and heating systems, solar water stills, nutrient production kits, and other unique self-help items ---all developed by the subject inventor (Nuttle). Barter trade, as employed by NPI, is explained on NPI’s website.


by Needful Provision, Inc. (NPI)

The solar refrigerator, developed by NPI, is a simplified and improved version of prior solar adsorption-desorption refrigerators ---refrigerators developed in recent years in Germany, France, and the U.S. All of these solar refrigerators have no moving parts. Water is used as the working fluid. The naturally occurring, highly porous silicon compounds (zeolites) are used as adsorbers. NPI’s unique solar powered refrigerator produces about 5 lbs. of ice daily per cu. ft. of storage space.

NPI’s seeks to help meet food storage needs for Third World families, with locally constructed solar refrigerators having the following parts:
1. An insulated, open-top solar collector box, about 7 ft. x 7 ft. (painted black), with
two-layers of glass (or other glazing) attached to the open-top. This box is used to collect solar heat via exposure to direct sunlight. A single 2 1/16-inch hole is drilled, on one side, to allow the exit of a 2-inch PVC pipe (see drawing).
2. A container, for zeolites, made of 6-inch PVC pipe generally forming a square
that fits inside the above collector box ---with four added cross-sections as shown on the drawing to follow. (Pipe should be black PVC, or paint the outside black.) Locate 2-inch PVC pipe in the center of the above 6-inch pipe, after drilling the 2-inch pipe to provide numerous, scattered 3/16-inch holes. Fill around this smaller pipe with ¼ to ½ -inch zeolite gravel (some 300 cubic inches per lineal foot).
This gravel is to hold smaller pipes in the center of the 6-inch pipes, and to help perform an adsorption-desorption function. All the holes in the 2-inch pipe must be drilled so they fit inside the 6-inch PVC pipe. Cap the opening of the 6-inch pipe joint using a 2 1/16-inch hole to allow the 2-inch pipe to pass through. Use PVC glue to seal the crack between the cap and the 2-inch PVC pipe. (The overall pipe system is of a size to fit within the above solar collector box.)
3. A vacuum hand-pump is used to help maintain a partial vacuum in the above
Described pipe container system sealed with PVC glue to prevent air leaks. (A good hand-operated vacuum pump, with gauge, is available from Triple Helix for US $39.95 --tel. 1-803-360-7872 or see website:
4. An attached heat exchanger, made from copper or brass tubing, also acts as a
condenser to convert hot water vapor into water, or water droplets.
5. An insulated cooler (refrigerator) box of at least 4 cu. ft. may be located in the
ground or partly below ground to improve insulation (also use an insulated top door). This size is suggested to meet the food cooling needs of a family of four.
6. A one (1) cu. ft. sealed container to be located inside the above cooler box. At the
various stages of operation, this container holds a combination of water, water vapor, and ice. There is an airtight cap, over a 2-inch hole, that may be opened to add water as needed to keep this container at least 2/3rds full of water and/or ice. A sealed, attached float-gauge indicates the level of the water/ice without opening this container. (Loss of water vapor, and loss of the partial vacuum, may occur if any of the above components develop a leak.)
7. An adapter and appropriate glue or sealing materials are used to connect the 2-inch PVC pipe to the copper or brass tubing used for the condenser (item 4 above). Use solder, or similar means, to fix (and seal) the tube-end to the sealed container (item 6 above). Air leaks will greatly reduce the cooling efficiency of this refrigerator.

Concept of operation is based on the fact that when cool (at night) the zeolite acts somewhat like a sponge soaking up or adsorbing the water vapor ---then when heated during the solar day, this water vapor is desorbed or released. Operating under a partial vacuum, the water vapor moves with high efficiency under low pressures. At about 100F, water vapor begins to desorb from the zeolite. This water vapor is condensed into water droplets as heat is given off by the heat exchanger. The resulting water runs down, using gravity, into a sealed storage tank inside the cooler.

During the night, zeolite is cooled close to ambient temperature and starts adsorbing water vapor. Two sides of the solar collector box are opened to allow night air to help cool the zeolite inside the PVC pipes. Liquid water, in the storage tank (a tank also operating as an evaporator) adsorbs heat from the space to be cooled and is converted into water vapor. Since the system is sealed under very low pressure, any water remaining in the storage tank is then frozen into ice. This ice then melts slowly during the next day providing sustained cooling at reasonably constant temperatures.

The Zeopower Company, and EG Solar, both manufacture commercial versions of solar adsorption cooling (or refrigeration) systems. Other companies, like SunDanzer, manufacture solar coolers (or refrigerators) that use conventional compression-type refrigeration achieved by electrical systems based upon photovoltaics. NPI’s cooler (as
above described) was developed to provide food storage for the poorest of the poor, and is not intended to be a commercial system. The NPI cooler has been designed to allow village users to easily obtain their own inexpensive means of local food preservation, with no power other than solar. Every effort has been made to avoid any possible patent infringement related to existing, somewhat similar, commercial solar powered refrigerators.

Zeolite deposits may be found worldwide, and the abundance of zeolite is part of the successful application of solar refrigeration. In many areas, zeolite is sold commercially for use in odor control. An example commercial source is USA Zeolite (with zeolite products shown on the company website:

Earth-Cylinder Construction Technique for Passive Solar Homes, by David A. Nuttle,
Use clay or sandy clay containing about 10 percent moisture so the clay or sandy
clay forms a ball when squeezed in your hand. If too wet, partly dry in the sun. If too dry, add an appropriate amount of water and mix. Allow 12 to 24 hours for the moisture to equalize throughout the clay or clay-sand.

Clay may be modified as needed to improve texture and bonding ability. Options
include 30 percent sand, 20 percent dried cow manure (if zoning allows), and 05 percent construction lime. Use a garden tiller, small cement mixer, or other means to mix very completely. Adjust for moisture as indicated above.

Concrete foundations should be prepared as desired for 12-inch or 24-inch thick
walls formed by earth-cylinders. The wall exposed to direct sunlight should always be 24-inches thick so it thermocycles to heat or cool the interior as needed. Other walls may be 12-inches thick with insulation attached to improve the desired heating or cooling. The basic frame, doorframes, and window frames should be formed using post-and-beam, steel, bamboo, earth-cylinders, or similar construction.

Earth-Cylinders are formed under pressure using 6-inch or 8-inch diameter steel
pipe to form the earth mix when pressure is applied using a hand-operated hydraulic device (see drawings). A wire saw is used to cut the newly pressed earth-cylinder into the desired length(s). The earth-cylinder blocks are then stacked to form walls, and a cob mix is used to fill in the cavities (between these blocks) to strengthen the walls.

A good cob mix is 50 percent clay, 30 percent sand, 05 percent construction lime,
and 15 percent chopped straw. Use a concrete mixer to make a uniform earth-type mix having about 25 percent moisture. Dump this mix on a tarp, and add the straw on top to facilitate a “Cob Dance” to trample the straw into the mix. Add the cob to cavity areas as the walls are being formed by the earth-cylinders. Use a wet, short board to help shape or form the cob.

In areas with high rainfall, earth-type walls need to be sealed to help keep the
walls from becoming too moist or structurally weakened by rain. Where tung oil is easily available and inexpensive, this may be used to seal the outside of walls. In other areas, it may be necessary to stucco the outside of walls with a good waterproof material. If the
indoor air is often high in moisture content, it may be necessary to seal wall surfaces that are inside the house.

Wood, metal, bamboo, thatch, and other materials may be used to form a roof
over the house made of earth-cylinders. A good overhang may be needed to help protect the exterior of walls from heavy rains. If a solar collection attic is desired, truss materials need to be metal, and both the roof and ceiling must be made using PVC, or other similar glazing materials, to allow entry of sunlight. (See NPI’s “zero net-energy” housing for more details.)