Design Guide for Solar Water Pumping. Dankoff Solar Products, Inc.

Transcription

1 Special advance-publication for the Advanced PV Course Solar Energy International May 2001 Design Guide for Solar Water Pumping Dankoff Solar Products, Inc. The world s most diverse selection of solar powered water pumps for livestock, irrigation, aquaculture, homes, villages, medical clinics, parks, recreation, water treatment, swimming pools, solar heating and more Since by Dankoff Solar Products, Inc.

2 How to Define Your Pumping Requirements If you need water WITHOUT electric power, START HERE. The cost of a pumping system is directly related to two factors, daily water demand and vertical lift. The following steps will help you to define those needs. STEP 1. DEFINE YOUR TOTAL VERTICAL LIFT surface pump storage tank TOTAL VERTICAL LIFT is the vertical distance from the water surface in the source to the water level in the tank, or the discharge of the outlet pipe. water source OR submersible pump Your total vertical lift requirement: feet or meters If you have a long pipeline, it may be necessary to add lift as a result of pressure drop in the pipe. See our pipe sizing chart on p. XX. To supply pressure (for home or sprinklers) you will need to add to the vertical lift (1 psi = 2.3 feet) (1 bar = 1 kg/cm 2 = 10 m). See our section on pressurizing pumps. STEP 2. DEFINE YOUR DAILY WATER REQUIREMENT METHOD 1 If you already have a water pump in place, you can use your experience: Multiply your pumping rate in gallons (liters) per minute X 60 X average pumping hours per day. METHOD 2 If you have a storage tank, divide the capacity of tank in gallons (liters) by number of days that it will serve your needs. METHOD 3 Estimate your needs based on the application. Human domestic consumption gallons ( liters) per person Cattle & horses gallons ( liters) per head Young trees 15 gallons (55 liters) per tree An agricultural advisor can assist you further. Your average daily water requirement: gallons or liters per day If you plan to expand your water usage in the future, use a larger quantity. If you have other sources of water, you can use a smaller quantity. STEP 3. DEFINE YOUR SOLAR RESOURCE Determine the PEAK SUN HOURS rating for your region from the map on page XX. This refers to the region s average daily solar exposure, measured in equivalent hours of full noon-time sun. Your solar resource: peak sun hours per day. ============================================= Advanced Class Refer to An Advanced Method of Selecting the Optimum Solar Pump. It defines Effective Peak Solar Day which lets you design a system more accurately and economically -- Next Page

3 An Advanced Method of Selecting the Optimum Solar Water Pump Selection of a solar water pump is often made by dividing the daily water requirement by "peak sun hours" derived from climate data, to determine the peak pumping rate. This is an over-simplified method that often results in an under-productive system. It is more accurate to calculate "EFFECTIVE peak sun hours" based on how the system performance varies through the day. This is a function of the type of pump (centrifugal or positive displacement) and the design of the solar array (fixed mount or sun-tracking). The method shown here helps you select a cost-effective pump and array to meet the daily water requirement. It is reasonably accurate for clear summer weather, when water demand is greatest. Pump Mechanisms: Positive Displacement vs. Centrifugal A positive displacement solar pump traps water into sealed cavities (like a piston pump) and forces it upward. It has full lift capacity as soon as it begins to turn. The flow rate varies in proportional to the power it receives. In other words, it utilizes energy efficiently throughout the day. A centrifugal pump spins the water (in one or more impellers) to produce centrifugal force. At low speed, its lift capacity is reduced EXPONENTIALLY. During the early and late hours of the day and during cloudy periods, even with half-power, it is likely that NO water will reach the top of its outlet pipe. Positive displacement pumps are most efficient for pumping less than 10,000 gallons (40,000 liters) per day. In some cases, they do the job at HALF the system cost of a centrifugal pump. For greater water demand, centrifugal pumps gain the advantage, and are are generally the only type available to fit the application. How to Select the Pump and Solar Array for the Required Daily Volume This graph illustrates four ways to obtain THE SAME DAILY VOLUME of water. Curve PT utilizes the most pumping hours. It uses the lowest flow pump at the highest efficiency throughout the day. FLOW RATE Conditions PV-direct pump, clear day in summer 7 AM NOON 7 PM CF PF CT PT DAILY YIELD = AREA UNDER CURVE EACH CURVE INDICATES EQUAL DAILY VOLUME TIME of DAY Curve Pump Array CF Centrifugal Fixed PF Positive Disp. Fixed CT Centrifugal Tracking PT Positive Disp. Tracking How to Estimate "Effective Peak Solar Day" for Clear Weather NET Type of Type of Factor for the Factor for the Factor for MULTIPLICATION Pump Array1 Type of Pump Type of Array Array Oversize2 FACTOR Centrifugal Fixed 0.7 X 1.0 X = Centrifugal Tracking 0.9 X 1.7 X = Positive Disp. Fixed 1.0 X 1.0 X = Positive Disp. Tracking 1.5 X 1.4 X = Note 1: For cloudy weather, oversizing the array is more effective than tracking. Note 2: Array Oversize is another variable that can enhance the effective solar day. Array Oversize = PV Array Watts divided by minimum array size recommended for the pump "Effective Peak Solar Day" = Peak Solar Day hours from data map X Net Multiplication Factor

4 STEP 4. DETERMINE THE PUMPING RATE REQUIRED Peak Flow Required (GPM or LPM) = Daily Water Demand X 60 "Effective Peak Solar Day" STEP 5. SELECT A PUMP AND DESIGN A SYSTEM The SELECTION GUIDE on the next page show an overview of Dankoff pumps. By knowing your lift and flow requirements, you can see which pump(s) can be used. The next step is to read the specifications and to select an appropriate model. You will also see the power requirement for the job, and the solar array requirements. The Solar Array The solar array is made up of a number of photovoltaic (PV) modules (solar panels) plus a mounting rack and possibly a tracker to automatically follow the sun. The array is sized to produce the power (watts) and the voltage that the pump requires. This catalog does NOT include PV array components. Ask your Dankoff dealer for additional information. Reference Section Starts on P. XX The Reference section of this catalog includes a glossary of terms used in the water supply and solar industries, and much more useful information. If you have any questions, your dealer or distributor will be happy to help you. Complete Pump Specifications After you have used the Selection Guides to select one or more pumps, refer to its specification pages. First, read the description to determine if the pump will fit the water source. Next, refer to the performance chart to select the most appropriate model for the lift and flow required. The chart will indicate the power requirement and other required components to complete the system. STEP 6. WATER STORAGE REQUIREMENT Storage is essential for a full-time water supply. Your pump will slow down during cloudy weather, and will stop under very cloudy conditions (generally, when shadows disappear). In most cases, it is more economical to store water in a tank, and not to use batteries. Here is our recomendation for typical tank sizing. Livestock, shallow-rooted crops 5 days minimum Deeply rooted crops, trees 3 days minimum Domestic water, indoor uses 10 days minimum Agricultural uses may not require a large amount of storage, because water demand is reduced during cloudy weather and because the soil stores water. THIS PUBLICATION IS BASED ON A DRAFT FOR OUR UPCOMING CATALOG AND DESIGN GUIDE. PLEASE REQUEST IS AFTER SPRING 2001 Windy Dankoff

5 Solar Water Pump Selection Guide LITERS PER MINUTE = positive displacement C = centrifugal 120 SUBMERSIBLE PUMPS VERTICAL FEET TSP TSP 4000 TSP C TSP SunRise Helix to 100 GPM (400 LPM) 90 VERTICAL METERS Submersible pumps are required for most deep wells. They are sometimes used in shallow water because they can tolerate varying water level, cannot freeze in cold weather, and are more protected and secure GALLONS PER MINUTE to 960 Ft.(290m) LITERS PER MINUTE SURFACE PUMPS Surface pumps can be used for water sources in which the water surface is LESS THAN 20 feet (6m) below the pump. This includes shallow wells, springs, ponds, rivers, etc. In some cases, a surface pump can be suspended in a well, as long as it is close to the water and will not get wet. Surface pumps cost less than submersibles. VERTICAL FEET CSlowpump Solar Solaram Solar Force Hot Water Circulation Pumps = positive displacement C = centrifugal SunCentric GALLONS PER MINUTE C VERTICAL METERS