Grantee Research Project Results
Final Report: Affordable, Sustainable Solar Energy Heater For The Developing World
EPA Grant Number: SU834331Title: Affordable, Sustainable Solar Energy Heater For The Developing World
Investigators: Bland, Larry , Sesler, Katie , Cordova, Moises , Whittaker, Susanna , Kim, Young-Gurl
Institution: John Brown University
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2009 through August 14, 2010
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2009) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Air Quality , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities
Objective:
The Phase I research project question was: ―What is an optimum, low-cost, and sustainable system for basic home water heating in underdeveloped areas of the planet?‖ In the United States, the availability of hot water is taken for granted. A knob is turned, and hot water appears. Many people in developing countries are not as fortunate. When hot water is needed in some areas of the planet, it must be heated in a pot over a charcoal fire, a wood fire, or a gas flame. Preparing hot water in small batches is time consuming, energy inefficient, and often unaffordable. Therefore the proposed project research goal was to develop a system for heating water that helps people in developing countries save time, money, and energy, while providing adequate amounts of hot water for their household needs. This research project had two goals: 1) evaluate low-cost, easily maintainable, and sustainable coatings for a parabolic reflector that would be efficient and appropriate for developing locations; and 2) develop a simple, innovative, low cost method of tracking the daily movement of the sun that is usable in all latitudes and all seasons.
This research project proposed to create an affordable, sustainable solar water heater that would be easily inserted into developing communities for usage around the world. Current parabolic trough water heaters are too expensive for most underdeveloped communities. The tracking systems are often electronic sensors pointing at the sun and a motor rotating the parabola as the earth rotates. Although these technical solutions are very effective, they are not appropriate in developing communities due to expense and sustainability. The first goal of this research was to find a reflective surface that is cheaper, durable and sustainable for broader usage around the planet. A cost goal was to reduce the cost of the parabolic trough to less than $5 per square foot of reflective surface. The second goal was to develop a simple tracking system that could be implemented with local materials and require no active components for rotation.
This project began with the basic technical premise that zero-cost energy sources (e.g. sunlight and gravity) exist to meet the needs of heating water. New and innovative options are needed to meet the needs of poor, developing people groups. This project pursued those options by looking for the lowest cost outcome that was sustainable around the planet. The primary focus of these options was reducing energy needs while meeting daily needs for hot water.
The project purpose and objective began with an understanding that: 1) many people groups have environmental conditions and ready access to solar energy where a solar heater will provide easily obtainable hot water and improve lifestyles and hygiene; 2) solar energy solutions provide a significant positive impact in reducing carbon footprints and providing safer energy alternatives in homes worldwide; and 3) solar energy provides a zero cost alternative that is economically quantifiable for prosperity improvements.
Summary/Accomplishments (Outputs/Outcomes):
This research project focused on developing a parabolic trough solar water heater with a semi-automatic tracking system that was both economically feasible for and sustainable in developing countries. The first goal of this research was to find a reflective surface that was cheaper, durable and sustainable for broader usage around the world. The second goal was to develop a simple tracking system that could be implemented with local materials that was purely mechanical. A tracking system was developed using gravity as the primary force for turning the trough and tracking the sun
The parabolic solar water heater for this project design is a parabolic trough with a reflective inside surface. A copper pipe, painted black to absorb sunlight, runs through the focus of the parabola so that most of the sun’s rays are reflected to the water pipe, heating the water inside it. This system is angled upwards according to the latitude, and the top of the pipe is attached to an insulated water holding tank. As the water heats from the energy reflected off the parabolic trough, it becomes less dense, therefore, more buoyant. This buoyancy causes the hot water to rise and create a thermosiphon effect that brings cold water from the bottom of the holding tank to the parabolic trough, and then dispenses the hotter water into the top of the tank.
For the tracking device, a rope, attached to the parabola, goes through a pulley and connects to a weighted buoy floating in a full water bucket. A spigot located at the bottom of the tracking bucket is calibrated for slow water flow to create a decrease in water level at a rate according to the Earth’s rotation. As the water level decreases, the buoy falls within the bucket, pulling the parabola and causing it to rotate and follow the sun across the sky. To maintain a constant flow rate, an ancient water clock technique has been implemented. Two five gallon buckets are stacked, one within the other, and there are about four inches of space in the bottom section between the buckets. A small hole was cut in the bottom of the top bucket with a float underneath that also serves as a plug for the hole. The water is placed in the top bucket, and water exits the clock tracking system at the bottom of the bottom bucket. As the water from the top bucket comes through the hole to the bottom bucket, the float rises and eventually plugs the hole to prevent flow from the top bucket. As the water slowly drains from the base, the float falls and lets more water in to maintain a constant height in the bottom bucket and thus maintains a fixed rate of movement. The buoy that pulls the parabola floats on the water in the top bucket.
The amount of water needed in the top bucket depends on the starting time each day, but it is easy to calibrate for the starting angular position. A focusing device is incorporated into the design to visually determine when the sun is pointing directly at the parabolic surface. This focusing device consists of a small section of pipe mounted vertically at the base of the reflective surface at the side of the parabola. Whenever the sun and parabola are properly aligned, the sunlight will go through the pipe and form a circle on a surface held perpendicular under the pipe.
The design of the tracking device is simple and accurate when properly calibrated. It will track the movement of the sun from horizon to horizon in the cloudiest conditions. Once alignment is established, the movement is based on parameters other than light, providing consistent movement in the most difficult conditions.
Another key element of the design is the ability to adjust the rotating angle of the trough to maximize seasonal solar energy capture at multiple latitudes. As seasons shift, the angle of the earth’s axis changes the required angle of the trough to track the sun. This angle is also different for different latitudes. The system has a simple, effective adjustment to account for both of these needs.
An obvious required outcome from Phase I is the transfer of energy from the sun to the water to heat the water. This was accomplished. Energy transfer of 2,522 BTUs was measured. With the up-scaling planned in Phase II this level can be easily increased for larger quantities of water. This result allows the calculation of economic savings from the solar energy heater. A heat input of about 1,680 BTUs is required to heat five gallons (42 lbs) of water from 60°F to 100°F (adequate for bathing or taking a shower). The energy required is equivalent to about 0.5 Kw-hr of electrical energy. While, the conventional heat value of dry (20% moisture) wood is about 6,000 Btu/lb. at 50% efficiency, in the developing world, the average efficiency achieved is often no higher than 10%. At 10% efficiency, it requires 1.4 lbs. of firewood, to heat 5 gallons of water from 60°F to 100°F. If this is repeated 365 days per year, the firewood used is 511 lbs. per household. Multiply this by the millions of households relying on firewood, and it is clear that the amount of firewood consumed for water heating is truly enormous.
There is the additional impact on global warming and climate change. Fully dried wood used for combustion has a 50% carbon content. Calculations show 949 lbs. of CO2 is produced per year per household. Expanding these figures to the millions of households relying upon firewood for water heating, and one can see that using solar energy for water heating can potentially have a significant beneficial impact on the planet by contributing to reduce carbon footprints.
The second economic element of the Phase I economic outcome analysis was to determine the construction costs of the solar heater. Student teams built two solar water heaters that depended on different products to create the reflective surface of the parabola—one using silver Mylar film and one with aluminized polyester. Both surfaces adequately heated the water, which was the project’s first objective. And both surfaces cost less than the goal of $5 per square foot.
The goal for Phase I was to develop a working model that cost under $100 each. The units ultimately built by student teams cost $130 each. During the build and test phase, students identified problems with rotation of the reflective surface and kinks in the hoses. The initial solution was to insert a quick disconnect. This resulted in a leaky connection due to the low-pressure conditions of this application. This is also a relatively expensive part that may not be readily available in some countries. An early goal for Phase II is to design this part out of the system. To correct issues of kinking hoses, the design team added multiple elbows, barb connectors and clamps to the system. Although the system now works without significant mechanical issues, the result was that the unit required too many parts, driving up its cost and complexity. In Phase II, the design team will re-evaluate all of the parts to determine what may be eliminated or replaced to reduce costs while maintaining operational integrity.
Conclusions:
Phase I proved that a low cost solar heater could be developed economically with an innovative solar tracking system. Initial data were collected but due to a harsher than normal winter, additional data are required before making informed decisions for the next version of the system. Additional efforts are needed to reduce the system costs, improve efficiencies, and up-scale the system for greater energy transfer for larger water storage tanks. The economic and environmental impacts have been shown to be sizable. Further improvements will only make these impacts greater. For this system to be sustainable, educational and technology transfer activities must be developed with the final producers and users in mind. This includes simple production tooling and training programs to equip local people groups. Building solar heating units and shipping them into another country or community will not produce a sustainable model. Therefore, training programs must be developed and implemented for target communities. The next critical steps are to create effective community development strategies, moving the prototypes to a final product, developing production processes and tooling, and developing training and hygiene programs for both economic and lifestyle improvement. The Phase II project goals will address these recommendations. The outcome of Phase II will be to put in place the required elements for a sustainable transfer to the target communities. As products, processes and training move into the communities, people will participate in further refinements for particular cultural needs. Tailoring the Phase II outcomes by and for local people groups will develop local ownership, buy-in and a passion that is sustainable. The next critical step is to proceed with Phase II.
Supplemental Keywords:
solar heating, solar energy source, energy conservation, carbon footprint reductionThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.