Solar Powered Water Pumping Windy Dankoff and Steve McCarney Aquiet revolution is taking place in the way water is pumped beyond the electric power lines. Solar power provides a welcome alternative to fuel-burning generators, cumbersome windmills and tedious handpumps. Over 20,000 solar pumps are in use throughout the world. Most of them are small systems for remote homes, livestock and village drinking water. Solar pumps are gaining in popularity because they are reliable, require no fuel, are easy to install and require little maintenance. They are now economical at locations not served by electrical utilities. Solar pumps move the most water during dry, sunny weather when the most water is needed. These and other advantages add up to satisfied users willing to tell their story. "Never had a minute's worth of trouble" says Arizona farmer Gary Scott of his solar pump. Echoing Scott's report is Gary Richards, electrician at the Philmont Boy Scout Ranch in New Mexico, where 13 solar pumps are operational and another 7 are planned. "We were looking at a $5,000. repair bill for our generator-driven pump and a new solar pump was selected because it was the same cost" says Richards. Philmont administrators already knew about the high reliability and low maintenance of solar power. Solar Technology At the heart of the technology is solar electricity, also known as PHOTOVOLTAICS or simply "PV". Photovoltaics directly convert light (not heat) into electricity. The generator in a solar electric system is the PV MODULE. When sunlight strikes a PV module direct current (DC) electricity is produced. A typical PV module in full sunlight will produce over 3 Amperes of current at 16 Volts (50 Watts). Modules are easily assembled into a larger array that produces the desired voltage and current. While the current varies with the intensity of sunlight, usable power may be derived from a properly designed system even during moderately cloudy weather. The most common uses of PV power are for small electrical requirements in remote areas. PV systems are already in use for a variety of applications including offshore navigational aids, mountain top radio repeaters, environmental monitoring, billboard and sign lighting and homes. Most of these systems use batteries to store electrical power for nights and cloudy periods. PV pumping systems are often simpler, using water tanks for storage instead of batteries. Pumping with PV Power PV powered well pumping differs fundamentally from conventional pumping methods, particularly where water requirements are modest. To work reliably, solar pumps must work well at reduced speeds during low-light conditions. On sunny days the system must pump more than the daily requirement in order to refill the system's water tank. Five to ten days storage may be required, depending on climate, pattern of water usage and whether there is a back-up source of water or energy. Most well pumps are too fast and powerful for direct solar power. It is a fact of physics that the larger a pump is, the more efficient it tends to be in terms of energy ($) per gallon pumped. Utility or engine power is usually used to pump at a high rate over short periods of time, thus gaining efficiency as well as minimizing running time, wear and noise. Solar pumping is opposite in nature. It is most economically applied at low power levels over the course of the day using pumps designed for the purpose. Where water requirements are less than 3,000 gallons per day, a solar pump should be low in flow rate (5 GPM or less) without sacrificing efficiency. Many homes require only 100 gallons per day for luxury living. At such low flow rates ordinary well pumps are not energy-efficient. Conventional pumps (including the popular submersibles) use CENTRIFUGAL FORCE to push water. They don't work efficiently below 5 GPM, but their performance drops off disproportionately at reduced speeds (under low light conditions). Also, conventional pumps use ac motors that don't work at reduced voltage. One solution to these problems involves the use of storage batteries and a conventional ac pump. Energy accumulates over time in the batteries and is discharged quickly to run the pump for short periods. A battery system complicates the installation, operation and maintenance of a system (unless it is needed for other home applications) and loses 20% of the stored energy. Operation of ac pumps with DC power requires an inverter. The inverter adds cost and complexity and increases energy requirements by an additional 10%. The most efficient low volume, non-battery systems use a POSITIVE DISPLACEMENT DC PUMP. Positive displacement pumps seal water into cavities and "squeeze" it upward, rather than "blowing" it up the way centrifugal type pumps do. These pumps work efficiently even at crawling speeds. DC motors also work well at varying voltages and speeds. Overall efficiency of today's DC solar pumps may exceed 3 times that of a conventional pump with battery storage and inverter. A number of companies make specialized DC pumps for deep wells. Choices include diaphragm, rotary vane piston and jack pumps (all positive displacement types). They are available in a wide range of sizes from 1HP down to an incredible 1/10HP. The low power pumps offer cost savings due to smaller PV arrays, reduced pipe and wire size. And they can still lift 200 feet or more! Low pumping rates allow the development of low yield wells and springs. Specialized PV/pumps make it economical to develop a marginal water source a long distance from the point of use. Long wire runs are eliminated by site produced electricity and pipe size is minimized by low rate pumping. The smallest "Micro-Submersible" solar pump system (priced under $2,000, complete and delivered) can pump 1/2GPM from 200 feet. That's 100 to 300 gallons per day with a solar power system. With a 1,000 gallon storage tank, that's plenty of water for a small family. It's inconspicuous solar array measures only 10 square feet. The pump weighs only 14 lbs. and may be installed and pulled by hand. Systems requiring over 1/2HP to pump over 3,000 gallons per day (roughly speaking) may use more conventional pumps (centrifugal, submersible or turbine) fitted with special DC motors. The shallower the well, the more likely this type of pump may be used. To determine the best pump for your requirements, determine your lift and volume requirements and compare specifications of the various types available -- OR, contact a PV or solar pump dealer. System Configuration Solar pump systems can be set up in a variety of ways to match your water needs and your water source. Technology allows a choice of either ac to DC power, purely solar or integrated with other sources of power. Array-Direct Non/Battery The simplest solar pumping systems use a DC pump wired directly to the PV array (a group of modules). This works with centrifugal DC pumps because DC motors start easily when lightly loaded. Positive displacement pumps however require higher starting torque (current) and are usually coupled to the PV array through a special controller. Solar pump controllers deliver high current even in low light conditions by increasing the current at the expense of lower voltage (the electronic equivalent of low gear). This "automatic transmission" allows pump operation throughout the solar day, however slowly, even in moderately cloudy conditions. These controllers are known as "maximum power point trackers" or "linear current boosters". A system designed for reliable output in cloudy climates may have an oversized array to assure a more constant water supply. Battery Systems for Domestic Water Battery storage and ac/inverter pumping systems sometimes are appropriate. As more and more remote homeowners use PVs for their electrical needs, we find battery storage and inverters already in place or planned for. The conventional ac submersible powered by inverter is a viable option for domestic water requirements. The storage battery system allows pressure pumping on demand, day or night. A water conserving home using low-water toilets (1 to 1 1/2 gallons per flush) may use well under 50 gallons per person per day. Where water usage is minimal, efficiency is less crucial. As a rule, if the right DC pump is available and economical for the job, use it. If not, consider using inverter/ac power. Sunnyside Solar is a PV supplier in West Brattleboro, Vermont. Their main market is remote home owners. Regarding solar pumping, owner Richard Gottleib reports, "What people want here is pressurized water on demand, tied in with the home battery system. The most successful systems are in a dug well or a 6" well casing with fairly stable water level, using the Flowlight Booster Pump suspended above the water." The Flowlight Booster is a non-submersible DC (12 or 24 Volt) rotary vane pump resembling a hydraulic pump. It is used to feed the same conventional pressure tank system that ac pumps use. How much solar power is required to provide a small family with pressurized water in the New England states? Gottlieb says that two 50 Watt PV modules (Å $350 each) will power a shallow well booster pump year round. In the sunnier western states less than one module's output will suffice. Energy is stored in deep cycle "golf cart", electric vehicle or marine batteries. A PV powered pressurizing system is far cheaper (and less freeze-prone) than an elevated tank. Conventional "town pressure" averages 40 PSI and that requires a tank 100 feet high! A water system with a very deep well or one that's distant from the house will often use a low-flow solar pump at the water source. This fills a storage tank placed closer to the house. A DC booster pump then draws from this tank to charge a pressure tank using power from the home's battery system. If it is too costly to install solar pumping on a domestic well, one may compromise by using a generator and an ac pump to fill the storage tank. Once the tank is full, the generator need not be run for several days. The DC booster takes over the job of frequent pressurizing. If irrigation is required around the house, try to place a storage tank high enough to allow gravity flow. FOR MORE INFORMATION ON WATER SYSTEM DESIGN refer to Windy Dankoff's previous article "AN INTRODUCTION TO SOLAR WATER PUMPING" in HP#5 (back issues still available). Solar Tracking Where peak water needs occur during the sunny summer months, consider a solar tracker. A tracker is a special PV mounting rack that follows the path of the sun. Trackers increase daily output by up to 50% in the summer (less in winter). This increase matches the increased need for water in the summer by lengthening the effective solar day. A longer daily pumping period reduces the number of PV modules required while also reducing pump, wire and control sizes (cost). Zomeworks Corp. builds a "Passive Solar Track Rack" that uses only the sun's heat and the motion of fluid to tilt it toward the sun. It is reliable (10 year warranty) and as simple to install as a fixed array. Back-Up Power Generators are sometimes used as a back-up power source during prolonged cloudy periods. This may be done in any of several ways. An ac submersible may be mounted to the bottom of a pump jack cylinder and will push water up through the same drop pipe. In a 6" or larger well casing, a submersible may be mounted underneath the solar pump on the same or a separate drop pipe. Or, a generator may supplement a DC solar pump using a simple ac/DC power supply. Case Study: Philmont Scout Ranch New Mexico's Philmont Scout Ranch is a shining example of successful solar water pumping. The ranch is used as a summertime Boy Scout camp and cattle ranch. The ranch has a wide variety of wells requiring various solutions. In the past, windmills and propane fired generators were used. Now, water is pumped quietly by 13 solar pumps. All 13 systems use solar trackers to maximize summertime water production. Another 7 solar pumps are slated for installation this season. Fifteen other PV systems are being used to power radio communication, lights and refrigerators for remote cabins. In 1986, after favorable experiences with PV powered two-way radios, Philmont Ranch opted to try a low cost PV pumping system. Gary Richards, staff electrician, was frustrated by the high cost of solar pumping until he ran across an ad for Flowlight Solar Power in New Mexico's rural electric co-op newspaper. Flowlight had the expertise and equipment he was looking for. Now Gary does all the design work himself, attesting to how quickly solar pumping can be learned. To ease remote-site installation, Gary will pre-assemble and wire most of the system in his shop. Then he transports it to the site where he drops the pump in by hand. "Helpers couldn't believe that after they got the old windmill down I was pumping water within 15 minutes. To date, all the pumps are 12 or 24 volt DC (1/8 to 1/4 HP). None of the systems require battery storage since several day's supply of water can be stored in sealed tanks for human consumption or in stock tanks for cattle and horses. A typical system consists of between two and six 55 Watt ARCO Solar PV modules on a pole-mounted tracker. Summer days are often cloudy in Northern New Mexico. Richards uses "Linear Current Booster" controllers to increase efficiency in low light conditions. Richards Says "I love the PV pumping systems because they replace the old windmills and generators that require so much maintenance". A maintenance trip on the sprawling 137,000 acre ranch takes at least a half day's travel over rugged roads "if the weather is good". When asked about the maintenance requirements of PV pumping systems Richards replied "there is very little". Soon all Philmont's remote wells will be solar pumped. New wells are also being drilled in areas so remote that they were considered unusable in the past. Specifications of a typical Philmont Ranch system USE: domestic drinking water TOTAL HEAD: 30 feet VOLUME REQUIRED: 2000 gallons per day VOLUME PUMPED: (summer) 2400 gallons per day PUMP: Flowlight Slowpump model 2507-15 PV ARRAY: 4 ARCO Solar M-55 modules wired for 24 volt MOUNTING: Zomeworks Track Rack solar tracker CONTROL: Sun Selector Linear Current Booster STORAGE: 2000 gallon tank MATERIAL COST, PUMP & FILTER: $490 SOLAR PV ARRAY, INSTALLED: $1,925 CURRENT BOOSTER CONTROLS: $110 SYSTEM INSTALLATION COST: $150 TOTAL SYSTEM COST (less tank): $2675 Case Study: Oregon SolarJack To see a SolarJack in action is to experience perfection and balance. The dedicated engineering of Jim Allen, drilling contractor and founder of SolarJack, has transformed the old-fashioned pump jack into a finely tuned machine. Behind the action sits an array of PV modules silently providing the power. Allen's earliest prototypes are still working after 5 years (some with no maintenance). Today, SolarJack is the most energy efficient low-volume deep well pump on the market. Every detail contributes to its performance. Allen's patented variable stroke mechanism makes the downstroke take less time than the upstroke. This contributes to high efficiency, which means more water per watt of solar power. The White family of Jacksonville, Oregon is one enthusiastic SolarJack user. Their mountainside homestead is far from the nearest powerline. A 512 foot deep well is 75 vertical feet downhill from their storage tank. After considering a windmill (winds are fickle) or a generator (fuel, noise, maintenance) the Whites chose a SolarJack system. The pump runs quietly without human attention. Installation was performed by the solar system supplier, Electron Connection Ltd., POB 442, Medford, OR 97501 ¥ 916-475-3179. SPECIFICATIONS: Oregon SolarJack USE: Domestic, home and garden TOTAL HEAD: 475 feet VOLUME REQUIRED: 1000 gallons per day max. VOLUME PUMPED: 1,170 gallons per day max. PUMP: SolarJack pump jack at 90 Volts DC PV ARRAY: 8 Kyocera 48 watt modules MOUNTING: Non-tracking CONTROL: SunSelector Linear Current Booster STORAGE: 3,600 gallon tank MATERIAL COST, PUMP: $6,451 (including freight, concrete) SOLAR PV ARRAY, INSTALLED: $3,088 PUMP INSTALLATION COST: $658 TOTAL SYSTEM INSTALLED COST (less tank): $10,197 Solar Pump Manufacturers A.Y. McDonald (medium to high volume DC submersible & jet pumps) POB 508 Dubuque, IA 52004 (319) 583-7311 Flowlight Solar Power (low volume surface and submersibles, booster pumps) POB 548 Santa Cruz, NM 87567 (505) 753-9699 Grundfos (high volume submersible pumps) 2555 Clovis Ave. Clovis, CA 93612 SolarJack (jack pumps, centrifugal and low volume submersibles) 325 E. Main Safford, AZ 85546 (602) 428-1092 Contact your favorite PV dealer for advice and pricing. About the Authors Windy Dankoff is owner of Flowlight Solar Power, a manufacturer of PV pump systems and a supplier of remote home photovoltaic systems. He began working with wind generators in 1975 and has been installing solar pumps since 1980. Steve McCarney teaches at the Colorado Mountain College PV program and is with Appropriate Technology Associates (ATA), offering PV design, installation, and training services. ATA is located at 410 Garfield Ave., Carbondale, CO 81623. Phone (303) 963-2682. Get yer ducks in a rowÉ Before you can specify a PV/Pump system you should know the following: ¥ WELL DEPTH (or description of water source) ¥ DEPTH TO WATER SURFACE -- Does it vary? If so, how much? ¥ YIELD OF WELL, estimate in gallons per minute ¥ TOTAL VERTICAL LIFT from water surface to storage tank/pipe outlet ¥ SIZE OF CASING (inside diameter) ¥ QUALITY OF WATER (silty, mineralized) ¥ WATER REQUIREMENTS in gallons PER DAY, according to season ¥ APPLICATION for water: Home? Livestock? Irrigation? ¥ Is PRESSURE required (home, sprinkling)? ¥ Can a STORAGE TANK be located higher than point of use (easily)? ¥ Is system to be located near a home/battery? Distance? ¥ Elevation above sea level (determines suction limitations) ¥ Complex terrain? draw map or diagram ¥ DESCRIBE EXISTING EQUIPMENT for pumping, distribution, storage etc.