Final Report: Evaluating and Designing Ultra-low-cost Solar Water Heating SystemsEPA Grant Number: SU835499
Title: Evaluating and Designing Ultra-low-cost Solar Water Heating Systems
Investigators: Nelson, Brent , Alsadiq, Saleh , Beckham, Matthew , Cacal, Kaila , Caton, Joseph , Chott, Austin , Griffin, Thomas , Heine, Christopher , Li, Shuo , Ocana, Jesse , Savage, Kathryn , Woodruff, Devin
Institution: Northern Arizona University
EPA Project Officer: Hahn, Intaek
Project Period: August 15, 2013 through August 14, 2014
Project Amount: $14,429
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2013) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Energy , P3 Awards , Sustainability
Utilization of solar water heating remains low, in large part due to high costs of commercial systems. These systems have significant up-front costs that create a barrier to entry for individuals with minimal discretionary funds or shorter payback horizons. As a result, only a fraction of the available solar capacity is being utilized despite tremendous effort and resources being spent on improving the performance of solar water heating systems. The emphasis on performance optimization increases energy savings, but does little to reduce the installed cost of solar water heaters. Low-cost materials can be utilized for reflectors, concentrators, insulation, thermal storage materials, and absorbers. Low-cost supplies for such applications include emergency blankets, scrap lumber and insulation from construction sites, Fresnel lenses from discarded projection televisions, and packing foam. While a low-cost design will incur a decrease in thermal performance compared to commercial systems, the reduced cost of a stillviable system could lower the barrier to entry in using solar water heaters.
The goal of Phase I of this project was to research, evaluate, design and prototype an ultra-lowcost solar water heater system for use both in industrial and residential applications. In particular, optimization was done on absorbed solar energy per area per unit cost. Aim 1 was to evaluate low-cost supplies and approaches for solar water heating and compare their performance. After characterizing the relative performance of various low-cost strategies and evaluating the cost/performance tradeoffs, Aim 2 was to build and test an ultra-low-cost solar water heater prototype based on the evaluation in Aim 1. Aim 3 was to perform financial modeling to evaluate the commercialization potential of low-cost solar water heating systems and to optimize cost savings for potential users.
Aim 1 was to evaluate solar water heat components, but before components could be evaluated, a design concept was first needed. Therefore, the first level of evaluation assessed various design approaches and evaluated them for their predicted solar absorption per area per dollar. Design concepts considered include an insulated storage tank/absorber, a simple flat-plate collector, and a parabolic focusing collector. All designs were required to integrate with existing water heating systems, and so these integration costs were also considered in all analysis. Theoretical analysis was performed to estimate the collectors’ solar absorption per area per cost. Several variations of the key components were modified and analyzed in order to identify which components had a significant effect on the absorption per area per dollar analysis. Thermal analysis was performed by generating thermal resistance networks to estimate thermal losses and energy transfer into the water and basic radiation analysis to estimate solar absorption and radiative loss. The results of this analysis showed that a black painted galvanized pipe would have the best absorption per area per dollar for both an active and a passive circulation system, and the parabolic systems were predicted to have superior performance per cost compared to the other designs.
Aim 2 was to build and test prototypes of ultra-low-cost solar water heaters. Because the parabolic collector was predicted to have the best performance, it was chosen for prototyping and testing. A flat-plate solar collector was also prototyped and tested because it had the second-best theoretical performance and it is the most common commercial system. The collectors were constructed using parts that are available at a standard hardware store, such as lumber, sheet metal, and water piping, and could potentially be obtained for free or reduced cost as scrap materials. Passive circulation proved difficult in the flat-plate system due to pressure loss throughout the piping, and thus active circulation with a pump was required for the flat-plate system. The parabolic collector worked with both active and passive circulation, with passive circulation yielding slightly better performance per cost than active circulation. Depending on the assumptions made about energy costs and integration costs, the flat-plate collector may prove better than the parabolic collector for commercial applications. Both systems yielded performance that would result in a payback period of 1-5 years if offsetting electric water heating, depending on the number of components that can be scavenged or obtained at reduced cost.
Aim 3 was to estimate the commercialization potential of ultra-low-cost-solar water heaters similar to those prototyped and tested. From both primary and secondary market research, it was determined that there is a viable market for a supplemental low-cost solar water heater. Research showed that people are generally supportive of such a device, especially when initial investment cost is below $500 and payback period is 3 years or less. As costs can be decreased significantly by making a do-it-yourself system, there also appears to be adequate demand for a low-cost solar water heater kit. The market would be focused on male homeowners between the ages 25-64 that are capable of completing relatively complex home projects that include plumbing. Using census data to estimate this demographic, and making a reasonable assumption of additional potential buyers, the total market size can be estimated at approximately 1.5 million potential buyers. This market is large enough that even a small market capture rate may prove enough to justify the manufacture and sale of the system or some of its component parts. One promising potential business model would use small businesses for the manufacture and distribution of a do-it-yourself kit that could be used by a homeowner to build the collector used in the system.
The work completed during Phase I demonstrated a viable low-cost solar water heater prototype and a potential market and commercialization plan for such a product. The tested prototype was only a first attempt, however, and opportunity exists for design improvement and refinement. Moreover, the long-term durability and performance of the system is unknown. To assess longterm durability and performance, the prototype should be site-tested at a residential or commercial location, with its performance and maintenance monitored over an extended testing period.