Pond Aeration: Photovoltaic Powered Scott Ely, Tami Schneck, and Ken Olson Pond Aeration is a technology used by ranchers, recreationalists, scientists and entrepenuers for improving water quality and fisheries management. The basic principle involves the pumping of air into the water column to increase the supply of oxygen. We would like to share with you our collective efforts and experiences with PV powered pond aeration systems. Why aerate? Pond aeration allows ranchers the opportunity to keep ponds free from aquatic vegetation which can clog watering and irrigation equipment. Recreationalists can better enjoy their fishing experience in a healthy pond or lake environment. Water treatment facilities utilize pond aeration in waste water lagoons to achieve water quality. Another common application for aeration is the business of aquaculture where aquatic life is cultivated for sale. Although the process has been used for many years, only recently have these systems been powered by photovoltaics. SMALL POND APPLICATIONS For our purposes, we will define a small pond as a body of water ranging up to 1-1/2 acres in size and 10 to 12 feet deep. Some examples of small pond environments which can benefit from aeration include: 1. Ponds that are plagued by algae and aquatic plant growth due to nutrient inputs such as runoff from fertilized lawns and agricultural areas, etc. Excessive vegetative growth can cause water quality problems in terms of high pH levels and fluctuating oxygen levels. Oxygen depletions and fishkills typically occur in the Summer when plant growth and water temperatures are highest. 2. Ponds that are located in areas where ice cover and heavy snowfall occur during the winter months. In such situations, sunlight can not penetrate into the water column thus limiting oxygen production by plants. An oxygen depletion or 'winterkill' will typically result. 3. Ponds that are stagnant and may be low in oxygen because there is no flowing water. 4. Ponds that are affected by eutrification (the natural aging process of a body of water). Such waters are typically high in nutrients which cause an excessive growth of aquatic vegetation. The abundance of growth results in an accumulation of organic material on the pond bottom. This leaves little or no oxygen in the bottom water layers and inhibits the natural decomposition process. If low oxygen conditions prevail, water quality may eventually deteriorate to the point where the pond environment will no longer support aquatic life. Aesthetically, the pond may become an eye-sore if aquatic vegetation is excessive. Low oxygen levels may also limit the natural decomposition process thereby causing odor problems. Pond aeration will improve water quality by: 1. Increasing the circulation of water, preventing stagnation and stratification. 2. Oxidizing or breaking down organic material which tends to accumulate on the bottom of the pond. 3. Increasing oxygen levels to provide a more suitable environment for aquatic life. POND AERATION SYSTEMS The selection of equipment is dependent upon the aeration requirements of the application. An aquatic biologist can determine the oxygen requirements of a particular application by analyzing a water sample. Selection of diffusers and tubing must be compatible with an energy efficient compressor to supply the required air volume and pressure. A small diaphragm compressor is used to pump air through polyethylene tubing and into air diffusers strategically placed on the pond bottom. Air bubbles are released through the diffusers to oxygenate the bottom waters and the entire water column. Aeration efficiency can be increased by placing the diffuser(s) in the deepest water, thereby increasing the time length of the bubbling action. Smaller bubbles have a larger surface area to aerate the water column. Although these two factors of bubble size and depth increase aeration efficiency, consideration must be given to the resulting increase in power requirements. POND AERATION EQUIPMENT Compressors Air compressors on the market today are generally appropriate for large aeration applications utilizing utility grid power. The selection of low voltage compressors for this application is rather limited. Typical pond aeration requires an airflow of .5 CFM at a pressure of 5 to 10 PSI. The compressor is selected to provide the required volume of air at the required pressure to be developed. Choosing a compressor is a rather simple task since we've already established that there is a limited selection of low voltage compressors on the market. The challenge to the designer becomes selection of the proper diffuser and pipe to match the compressor's capacity. Pressure is determined by the type and depth of diffusers, and size and length of polyethylene tubing being used. Tubing For small pond applications, tubing size is normally limited to 1/2" to 3/4". The tubing is a lead-weighted polyethylene which is buried from the compressor to just below shoreline. From there it runs to the diffuser which should be located near the center of the pond where the depth is greatest. Diffusers There are basically three types of diffusers manufactured for pond aeration: airstone, venturi and perforated diffusion tubing. The airstone and perforated tubing are more efficient in terms of oxygen transfer because they generate a smaller bubble size. They also have correspondingly larger power requirements. The venturi is the simplest type of diffuser although it produces large, coarse bubbles which do not allow for very efficient oxygen transfer. INSTALLATION OF AERATION EQUIPMENT The installation of pond aeration equipment is fairly simple. The compressor is generally located near the body of water in order to minimize length of tubing runs. The polyethylene tubing should be buried and enter the water below the water's surface. This will protect it from sunlight, animals and people. Consideration must be given to fluctuations in water level so as not to expose the buried pipe. To install the diffuser, attach it firmly to the polyethylene tubing using hose barbs, hose clamps or other appropriate fittings. The installer floats out to the desired location and lowers the diffuser allowing it to settle on the bottom. POWER BY PHOTOVOLTAICS PV powered pond aeration is appropriate for small ponds where utility or generator power are impractical. Although maximum benefits can be expected from continuous operation, adequate results may be derived from a shorter duty cycle. An aeration system powered by photovoltaics is typically designed to provide a minimum of 4 to 6 hours of operation daily. The particular hours and length of operation will depend upon the site specific needs of the water body as determined by an aquatic biologist. The photovoltaic components for a small pond aeration systems are very straight forward. Photovoltaic panels charge batteries through a controller which prevents overcharging. The controller should be set for proper charge termination corresponding to the battery type used. Temperature compensation is advisable for cold or very warm climates. Sealed, deep cycle, maintenance free batteries are suggested for most pond applications where access to the system for maintenance is a problem. A reliable, low voltage timer allows the compressor operating time to be set according to seasonal requirements. As with most photovoltaic systems, the modules require proper orientation and seasonal angle adjustments for maximum performance. CASE STUDY: THE OJO CABIN Located just southwest of Cimmarron, New Mexico is the 500,000 acre UU Bar Ranch. The ranch is a privately owned hunting and fishing retreat. Fish kills are a common problem in high mountain lakes and ponds. The need to sustain large, healthy trout populations in these waters was the basis for this project. The numerous small bodies of water and remote location made this application ideal for photovoltaic pond aeration. The small hunting and fishing cabins are located on the water and house the pond aeration equipment. The original system was installed in 1983. It was recently upgraded in the Fall of 1990 to take advantage of current technology. The pond aeration system at the Ojo Cabin consists of two 35 Watt modules on a stationary mount attached to the roof of the cabin. Sunlight resistant cable is run down to an exterior, well insulated `power box' which houses the batteries, charge controller, metering, compressor, timer, fuses and disconnects. There are 150 feet of 1/2" polyethylene tubing running to a single Venturi diffuser located at a depth of 10 feet at the bottom of the pond. Two Johnson Controls GC12V100, maintenance free batteries are wired in parallel for battery storage of 180 Amp-hours at 12 Volts. A Trace C30 charge control is set to 14.2 volts charge termination. Battery voltage and charge current meters indicate system status. The timer is a 20 amp, 12VDC, 24-hour timer manufactured by the Lumenite Electronic Company, Inc., Franklin Park, IL, (Model DT 112-SR). The compressor is manufactured by the Gast Manufacturing Company. of Benton Harbor MI, phone 616-926-6171. Maximum power draw is 6.2 Amps at 12VDC, .1 CFM at 50 psi. By designing the system to operate at a lower air pressure, the air volume increases to our desired .5 CFM. Actual current draw under these conditions is 4.8 amps. The pond at the Ojo Cabin requires two hours of aeration per day in the Winter and three hours/day in Summer. Winter run-time is best at midday when ice and snow are weakest. Summer run-time is best during early morning hours when oxygen levels are lowest. The 15 amp-hour/day compressor load along with four 30 Watt (sparingly used) Thinlites comprises the entire system power requirements. The system has done a wonderful job of oxygenating the water and preventing snow and ice build-up. System Costs The following list shows the typical costs of an up-to-date photovoltaic powered aeration system operating three hours per day, year-round for a one acre pond in a southwestern, high altitude climate. 2 - 40 Watt Photovoltaic Modules - $700. 2 - 12 Volt, 100 AH Deep Cycle batteries - $400. 1 - Two Panel Mount - $80. 1 - PV Charge Control - $100. 1 - Metering Package - $40. 1 - 12 Volt timer - $100. 1 - Wire Package - $100. 1 - Diaphragm Air Compressor - $200. 1 - Venturi Diffuser - $90. 1 - Poly tubing/fittings package - $200. TOTAL - $2010. CASE STUDY: DANCIGER RANCH TROUT POND The Ty-Bar Ranch, Carbondale, Colorado, owned by Dave and Emma Danciger has two adjacent trout ponds totaling approximately 1-1/2 acres. Cold Colorado winters make it nearly impossible to keep trout from one year to the next. Ice and snow build-up over the winter deplete the pond's oxygen supply, killing the fish stock. Students from the Colorado Mountain College's Solar Program installed a photovoltaic powered pond aeration system (see photos) in April 1990 under the close guidance of Johnny Weiss and Steve McCarney, two of the Program's instructors. The Danciger system has larger oxygen requirements than the Ojo Cabin system for a number of reasons: There are two ponds and two venturi diffusers. The location is at a lower altitude (6300 Ft elevation) and warmer climate than the Ojo Cabin (9200 Ft). Seasonal drought conditions and lesser water inflow often contribute to warmer water temperatures. Each of the two ponds has one venturi type diffuser located at the pond's bottom/center. One 12 Volt compressor supplies air to both of the diffusers. Aeration operation is set to operate from 6 AM tm 8 AM and Noon - 4PM during the Winter months (Nov - Apr) and 5 AM - 11 AM during the Summer months (May - Oct). The system specifications and equipment costs are as follows. 2 - Venturi diffusers, Lead-weighted polyethylene tubing 1 - Compressor, Gast Model AG 244, 12 Volt, 14 Amp max 1 - 12V, 24 Hr Timer, Lumenite, Model DT 112-SR 6 - ARCO M-75 Modules 6 - Trojan T-105, Lead-acid batteries, 660 AH @12 Volts 1 - 30 Amp Safety Switch 2 - Trace C-30 Controls (One set to terminate battery charging at 14.5 Volts and one set to terminate battery discharge at 11.2 Volts) 1 - Photocomm Metering package, Array Current and Battery Voltage Misc. Wiring, fuses and connectors Total equipment cost approximately $ 4500. Additional information of small pond aeration is difficult to find. There are resources in the waste water engineering field but are very complex and do not translate well into the small pond aeration systems. The application of photovoltaics in the aeration of ponds is a new technology and requires experienced biological input as well as qualified PV design assistance. Access for Authors: Scott Ely, Sunsense Design, 2640 Juniper #3, Boulder, Colorado 80304, 303-440-4786. Scott owns and operates a solar design, consulting and construction business. He is a graduate of the former Colorado Mountain College Solar Program and is an instructor in the Solar Home Program at the Solar Technology Institute, Carbondale Colorado. Tami Schneck, Aquatics Associates, 749 S.Lemay, Ste. A3-125, Fort Collins, Colorado 80524, 303-493-2626. Tami is an accomplished aquatic biologist. She has designed and installed pond aeration systems throughout the Rocky Mountain Region. Ken Olson is a founding Board member of the Solar Technology Institute, P.O. Box 1115, Carbondale Colorado 81623, 303-963-0715. The Solar Technology Institute is offering numerous practical applications workshops in renewable energy technologies. See Ad pg. XXXXXXX. for schedule.