|CLARK, R. NOLAN - Retired ARS Employee|
Submitted to: Solar Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2011
Publication Date: 5/1/2011
Citation: Vick, B.D., Clark, R. 2011. Experimental investigation of solar powered diaphragm and helical pumps. Solar Energy. 85:945-954.
Interpretive Summary: For rural locations in developed countries like the United States and Europe, stand-alone water pumping systems are needed for livestock watering, small scale irrigation, and for domestic water usage if utility grid electricity is not available. In less developed countries with a semi-arid to desert climate, stand-alone water pumping systems are normally a necessity since utility grid supplied electricity is usually not available. Frequently the best alternative for powering the pumps at these rural locations is solar (due to high cost and maintenance of diesel powered pumps), but which pump is the best one for specific requirements is not usually known. Data were collected from 2006 to 2010 at the USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas, on different solar powered pumps for different pumping depths (65 to 500 feet) and different daily water volumes (250 to 1350 gallons per day). There are four types of pumps which have been used in solar water pumping (piston, centrifugal, diaphragm, and helical), and the two types analyzed in this paper were diaphragm and helical. Two of the diaphragm pumps were designed at a pumping depth of 230 feet, and for the same solar input power (160 Watts), the daily water volume of one diaphragm pump was 5 to 100% better than the other pump depending on the pumping depth (65 to 230 feet) – highest improvement occurred at lowest pumping depth. The daily water volume of the more efficient diaphragm pump performed better for two reasons: the controller allowed the pump motor to operate at a higher power level and this pump used three chambers instead of two. The more efficient diaphragm pump was made predominantly of plastic and required servicing every year to prevent pump failure while the other pump was made predominantly of metal and required servicing every two years to prevent failure (this assumes pumping depth is 230 feet; pumps will last longer in shallower pumping depths). The other two diaphragm pumps (both using four chambers) were designed for a lower pumping depth (100 feet), but were capable of 35 to 100% more daily water volume than the other two diaphragm pumps at a 100 feet pumping depth. Both these diaphragm pumps were also tested at a solar power rating of 160 Watts. One of these diaphragm pumps was tested with a controller and the other was tested without a controller. The diaphragm pump tested with a controller pumped about 10% more water than the diaphragm pump without a controller, but both likely would have had similar performance if the same controller had been used on both. The diaphragm pump tested without a controller was made mostly of plastic, and failure occurred after less than one year of testing. The other diaphragm pump which was tested with a controller and was made predominantly of metal, lasted more than 1.95 years. The helical pump we analyzed had daily water volumes of 400 to 1050 gallons per day (similar to diaphragm pump daily water volumes), but was capable of pumping at much deeper pumping depths (250 to 500 feet). However, the power required (depending on pumping depth and daily water volume required) varied from 320 to 640 Watts. The helical pump had a peak pump efficiency of 60% compared to 48% for the best diaphragm pump efficiency. The helical pump testing demonstrated less maintenance was required than three of the diaphragm pumps (one diaphragm pump may have had similar reliability, but testing was discontinued after 1.95 years of testing). This paper should help solar water pumping installers decide which solar pump to select, and also should also help diaphragm solar pump manufacturers make improvements to their pump designs.
Technical Abstract: For several years, many types of solar powered water pumping systems were evaluated, and in this paper, diaphragm and helical solar photovoltaic (PV) powered water pumping systems are discussed. Data were collected on diaphragm and helical pumps which were powered by different solar PV arrays at multiple pumping depths to determine the pumping performance, efficiency, and reliability of the different systems. The highest diaphragm pump hydraulic efficiency measured was 48%, and the highest helical pump hydraulic efficiency measured was 60%. The peak total system efficiency (e.g. solar radiation to pumped water) measured for the diaphragm and helical pumps were 5% and 7%, respectively (based on PV modules with 12% efficiency). The daily water volume of the three-chamber high head diaphragm pump performed better than the dual-chamber high head diaphragm pump (5 to 100% depending on PV array input power and pumping depth). Use of a controller was shown to improve the quad diaphragm pump performance below a solar irradiance of 600 W/m**2 (20 m head) to 800 W/m**2 (30 m head). While diaphragm pumps made mostly of plastic demonstrated similar to much better pumping performance than diaphragm pumps made with a high proportion of metal, the metal pumps demonstrated a longer service life (greater than 2 years) than the plastic pumps service life (<2 years). Helical pumps analyzed in this paper were capable of deeper pumping depths and usually demonstrated a longer service life than the diaphragm pumps that were analyzed.