Grantee Research Project Results
Final Report: Solar Powered Water Collection, Containment, and Self Regulating Distribution System
EPA Grant Number: SU834784Title: Solar Powered Water Collection, Containment, and Self Regulating Distribution System
Investigators: Lilly, Brian , Polk, Ross , Ward, Thomas
Institution: University of Illinois Urbana-Champaign
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2010 through August 14, 2011
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2010) 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:
According to the EPA, “Light-duty vehicles in the U.S. produced 1152.6 Tg CO2 Eq. in 2003, representing 77 percent of on-road vehicle GHG emissions and 62 percent of total transportation emissions.” Among these vehicles are municipal and privately owned trucks which travel up to four times weekly to water large planters scattered throughout cities, towns, hotels, airports, stadiums, office buildings, universities, etc. However, the vast majority of these planters are designed for aesthetic appeal as opposed to efficiency. In order to achieve proper growth, potted plants need to be placed over only six inches of soil, yet one would be hard-pressed to find a planter with such a depth. As a result, most horticulturists use cheap soil or even Styrofoam to fill in the additional space inside of the planter (below the six inches of premium soil). By implementing a system in this “additional space” which allows for onsite water storage with efficiently regulated on site watering, we are working to reduce planter maintenance costs and associated vehicles emissions by up to 90 percent, and reduce the amount of water used to maintain healthy plants.
Our research is focused on coming up with a cost effective system to install within the planters. More recently, the scope of our work has increased to regulating off the grid rain collection containers. This can be accomplished with solar panels, custom circuitry, moisture sensors, and a pump. Pending the success of prototypes installed throughout the University of Illinois campus, we hope to move forward towards commercialization of this product.
Summary/Accomplishments (Outputs/Outcomes):
One of our main objectives was designing a circuit which could support numerous applications. The circuit needed to be able to operate in a large municipal setting with high powered solar panels (15 Watts or more), batteries (40 Ampere-hour or more), and pumps (2000 gallon per hour or more) as well as low power settings for planters (.25 Watts, 1 Ampere-hour, 50 gallon per hour). In addition to operating many different components, we also allowed for use of several different moisture sensors (the reasoning of why will be explained later). Our design also gave the circuit the ability to independently operate multiple pumps controlled by multiple moisture sensors. To prevent complete power loss, our circuit set to stop pump activity once a predetermined amount of battery life remains.
There was also a large amount of calibration necessary in regards to the placement of the moisture probe. The most obvious factors were the horizontal distance of the probe to the water source as well as the depth of a buried probe. The closer the probe was to the source (if flow is even in all directions), the quicker the pump would turn off. However, how tightly packed the soil was around the probe also made a significant difference. The volumetric water content of the soil which triggered the sensor to read either “wet” or “dry” had to be tested. Initially, research was conducted to relate the volumetric water content to a output voltage (in a controlled environment of Miracle Grow potting soil). For example, if the volumetric water content of the soil is 0 percent, the output voltage is .5 Volts. If the volumetric water content of the soil is 15 percent, the output voltage is 2.4 Volts. From these reading, “wetness” and “dryness” voltages were established and tested. If, for example, the user wanted the soil to be very moist after watering, you might tell the sensor to turn off when the soil moisture reached 9 out of a possible 10 (this is a theoretical scale). However, depending on how tightly the soil is packed around the moisture sensor, it could be sitting in completely soaked soil (essentially a puddle of water) and an 8 could be the output. The pump would then continue to run until either the water ran out or the battery was dead. Numerous experiments and adjustments were necessary to safeguard against an occurrence like this flooding your garden or planter.
Throughout the entire process it was very clear that in order to have significant “positive impacts…toward sustainability” this system must be commercially viable. If the system is not sold in the marketplace, it will never have an impact on the planet. It is for this reason that maintaining low costs was a critical element of the design. As a result, every element of the system was called into question. The following conclusions were drawn. The pump, battery, solar panel, water container, and related components are all going to be bought “off the shelf” so to speak. None of these elements will be custom made, and as a result their prices will be reduced in two ways. First is receiving discounts by purchasing in volume. Second, purchasing directly from the manufacturer will also provide discounts. However the moisture sensor and the circuit both provided more immediate opportunities to reduce costs.
Depending on the accuracy necessary from a moisture sensor, prices can range anywhere from $300 or more to about $9 per sensor. For our application, it did not make sense to use an expensive sensor to get extremely accurate results. In reality, the system should begin to water when the soil is relatively dry, and it should shut off when the soil has become moist; exact measurements are unnecessary. The first sensor was chosen for two reasons. First, it was extremely precise for the low cost of $30 per sensor. This allowed data to be collected and analyzed for use in our second design. Second, it had already been calibrated and could be operated with an off the shelf mechanical relay. Because our initial prototype was to be created in a short period of time (so measurements could be made during the growing season) and with a small budget the first sensor was a great success. However in a commercial setting $30 per sensor is not reasonable. Once the Phase I grant had been received, our team began testing three different sensors (two of each type of sensor) priced at $8, $9, and $12. Through a design of experiment, we systematically tested several factors including: how quickly each type of sensor reacted to a change in volumetric water content, if the sensors were able to maintain accurate readings over large periods of time (days and weeks), how close the readings of the specific types of sensors were (both initially and over time), how the sensors reacted at different depths, how they reacted in different types of soil, and how the density of soil around the sensors affected the readings. In the end, the $12 sensor was chosen.
As with the moisture sensor, the circuit was chosen so an initial prototype could be up and running for the summer. As expected, the majority of the Phase I budget was dedicated to adding functionality to the circuit and reducing the cost. Both were a success. The mechanical relay purchased for the first prototype cost $50 per circuit. Through months of price hunting, and countless hours of rethinking and redesigning, the price per circuit (when producing over 300) came out to be just over $5 (excluding labor). In terms of cost, we were able to reduce the circuit and moisture probe combination from $80 to less than $18, which was a tremendous success.
Conclusions:
We believe this venture will be a success for several reasons. First, similar products have enjoyed success. One such example is the BigBelly Solar who makes an on-site solar powered trash compactor. By reducing trash collections, the BigBelly solar reduces labor costs and vehicle emissions. BigBelly Solar explains that all started with “a mission to reduce fossil fuel consumption through innovative cost-saving approaches.” Second, this product makes fiscal sense. Based on research conducted on the watering habits of the Village of Hinsdale, the addition of four the units would save the village over $400 (conservatively), or 100 dollars per unit. The unit currently figures to cost approximately $150 which would result in a one and a half year payback. Finally, and perhaps most importantly, people within industry have expressed demand for the product. Our initial concept was validated through conversations with Village of Hinsdale horticulturist Dan Hopkins, who expressed that if such a design was feasible it would be a great asset to municipalities. This was confirmed when the City of Urbana placed the first order to be installed in Meadowbrook Park (the first unit ended up being donated for legal reasons). Most recently, the Grounds Department at the University of Illinois supported the installation of three more units on Campus for the year of 2011.
Supplemental Keywords:
cost benefit, water, carbon dioxide, design for environment, moisture probe, resource recovery, solar powerP3 Phase II:
Water Collection, Containment, and Self Regulating Distribution System | 2012 Progress Report | Final ReportThe 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.