SOLAR WATER PUMPING
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Technical Information:
Solar Water Pumping
The sun is the natural source of energy for an independent water supply. Solar pumps operate anywhere the sun shines. While energy production from solar pumps is impacted by cloudy weather, having adequate water storage and decreasing well usage during cool or rainy weather mitigates these impacts.
Photovoltaic modules, the power source for solar water pumping, have no moving parts, require no maintenance, and last for decades. Solar water pumping systems operate on direct current (DC). The output of the solar power system varies throughout the day and with changes in weather conditions, requiring specialized pumps and controls that operate within a wider range of voltage and current compared to most AC pumps.
Conventional AC pumps are usually centrifugal pumps that spin at a high speed to pump as many gallons per minute as possible. They also consume a large amount of power and their efficiency suffers at low speeds and when pumping against high pressure. If you run a centrifugal pump at half speed, it pumps one quarter the pressure.
To minimize the size of the solar PV system required, solar pumps generally use more efficient motors and pumping mechanisms. The most efficient pumps are "positive displacement" pumps, which pump a fixed amount of water with each rotation. If it is cloudy or early morning, the pump will receive less energy and run more slowly, but with no loss of efficiency – so at half speed, it simply pumps half the amount of water at the same pressure.
To use solar energy economically, solar pumping systems typically pump more slowly than conventional well pumps (many solar pumps are designed to produce less than 6 gallons per minute) and they don't run at all between sunset and sunrise, so an adequately sized storage tank is often required. Solar powered water pumps can provide an equal volume of water per day without the high and inefficient energy demands of a large capacity AC pump. Instead of pumping a large volume of water in a short time and then turning off, the solar water pump works slowly and efficiently all day. Often a solar pump can be used in a well with a recovery rate too slow for a conventional AC pump.
If your water sources are remote from power lines, compare the cost of a low-maintenance solar pumping system to what you would spend on a generator, with continual fuel and maintenance costs, or on a utility power-line extension. In most cases, a good solar pumping system is far more economical, which is why many non-profits and NGOs use solar pumping to provide clean water to remote villages around the world.
Water Storage
Many conventional AC powered water systems pump from a well or other water source into a pressure tank that stores water and stabilizes the pressure for household use. When you turn on water in the house, an air-filled bladder in the tank forces the water into the pipes. When the pressure drops, a pressure switch turns on the pump, refilling and re-pressurizing the tank. This works because an AC pump delivers high volume and pressure on demand; however, this will not work with pumps operating directly from PV modules because the sun may not be shining when you want to take a long hot shower.
For pumps operating directly from PV modules, a non-pressurized water tank can be located high above the house on a hill or on a tower so gravity can supply the water pressure. Water pressure in psi = head (in feet) times 0.433. For reasonable pressure, the tank needs to be at least 40' above the house. Alternatively, a battery operated pressure booster pump can fill a pressure tank as needed from a storage tank that is filled by a solar pump during the day. You must use a pump that can deliver the maximum flow rate required by the house, or have a pressure tank that is large enough to make up the difference between what the pressure pump can deliver and what is required, for the amount of time it is required. This is called the "draw down volume" of the tank.
Calculation of Solar Power Needs
If you are using a pump driven directly by PV modules, the array's nameplate output should be at least 20% higher than the power required by the pump to achieve the desired head and flow rate. A larger array or a tracking system can maximize the power available to the pump, providing more gallons per day. Since the pump will only draw the power it needs, it will not be damaged by over sizing the array. A larger array will produce the needed power in less light, extending the pumping time and volume delivered in the morning, afternoon, and on cloudy days. For instance, a 1kW array will produce 200 W in 1/5 the amount of sunlight.
Submersible Pumps
All pumps are better at pushing than pulling, since the vacuum a pump can draw is limited to atmospheric pressure (about 14 psi). At sea level, a pump can be placed no higher than 10 or 20 feet above the surface of the water source (subtract one foot per 1000 feet elevation). Most wells are much deeper than this and therefore require a submersible pump, which can push the water up to the surface. If you are pumping from a well, we have solar pumps that can deliver from 1 gallon per minute to over 75 gpm. The low-power diaphragm pumps from SHURflo can be powered by two 50 to 100 W solar modules, depending on the head (vertical distance) they are pumping. They can pump 500 to 1,000 gallons per day and lift water up to 200 feet of vertical distance from well to tank. These pumps require service every 2 to 4 years. For higher lift and flow rates, as well as a service interval in the 10 to 20 year range, we offer the Grundfos SQFlex line of pumps. The SQFlex can lift water over 800' and can pump over 20,000 gallons per day from shallow wells. The SQFlex pump can be powered by solar modules, a wind generator, a fuel powered generator, an inverter, the utility grid, or a combination of several of these.
Submersible Pumps - Grundfos
SQFlex Submersible Pumps
This Grundfos SQFLex is an industry-leading submersible pump for water lifts of up to 800'. With the proper controller, SQFlex pumps can be directly powered by solar or wind or can be run on an inverter, a generator, a battery, the utility grid, or any combination of these sources. Virtually any source of power, 30 to 300 VDC and 90 to 240 VAC, can be used to run this pump. It can operate on a series string of PV modules with a total peak power voltage of at least 30 VDC, but its efficiency will be highest at voltages over 100 VDC (10% less efficient at 60 VDC, and 20% less efficient at 35 VDC). Its motor is designed to draw a maximum of 8.4 A, which means that many types of PV modules can be used with this pump efficiently, including common 60 cell modules. SQFlex models 3SQF through 11SQF will fit into a 3" well and models 16SQF-10 through 60SQF3 will fit into a 4" well.
The 11 different pump models available can deliver from 82 gpm at 6' of head to 4 gpm at 800' with a 1.6 kW or smaller solar array. Use the helical rotor pumps (models 3, 6 and 11) for high head applications and centrifugal pumps (models 16, 25, 40, and 60) for low head applications for best efficiency. The SQFlex has built-in protection from dry-running, overloading, and overheating.
The Whisper 200-120 V wind generator can be connected directly to a SQFlex pump. Use the Grundfos IO-102 Wind interface in place of the Whisper 200 Controller.
SQFlex pumps have a 2-year warranty from the date of purchase. A 5-year extended warranty is available.
Grundfos SQFlex Optional Controls
SQFlex controls can be combined if you need more features than one control can provide. The CU200 interface box communicates with the pump and monitors operating conditions. Built-in diagnostics indicate faults and dry-running, as well as display operating status, power consumption and water level switch input. The Water Level Switch interfaces with the CU200 control to turn off the pump when the
tank is full. Since the CU200 control circuit uses only 15 mA, the water level switch can be located in a tank as far away as 1,640' from the pump, using a minimum #18 AWG 2-conductor wire. (see Wire and Cable.) The CU200 is covered by a standard 2-year warranty.
The IO50 control box includes cable terminations and a manual on/off switch that interfaces between a solar array and the pump to allow you to turn off the high voltage array when servicing the pump or plumbing.
The IO101 AC interface box is for using AC backup on a solar pump. An automatic transfer switch disconnects the solar array when AC power from a generator (120 VAC only), utility connection, or inverter is present. When AC power stops, it automatically reconnects the array to let the sun continue pumping. The SQFlex pumps will not function with a GFCI in the supply circuit, and should not be used
where a GFCI is required.
The IO102 interface unit is used for systems powered exclusively by a wind turbine or by a combination
of wind and PV.
Grundfos Pump and Array Sizing
To choose a pump and array size appropriate to your project, consult the table on the next page. The left column shows total head in feet and meters, the top row shows array wattage/number and suggested type of modules, and the boxes show seasonal pump performance and maximum flow. Select the row with the head (total lift) that most closely matches your application then move across the row to the column that contains the desired daily volume or peak flow rate. Note the pump model in that block and wattage of the PV array in that column.
NOTE: Daily volume and flow calculations are based on Fresno, CA data at a 36° fixed tilt. Daily summer volume assumes 7.8 kWh/m2/day of insolation and winter volume assumes 5.3 kWh/m2/day. Most solar pumping systems will provide significantly more output in the summer than in the winter. The typical flow rate is calculated at 800 W/m2 and can be up to 25% greater under bright conditions. Also, up to 40% more water can be pumped in the summer if the array is on a tracking mount. The output can vary by location and weather patterns, and is not guaranteed. Contact the AEE Tech Team if you need help sizing your specific system.
SHURflo
9300 Submersible Pump
The SHURflo 9300 is a positive displacement diaphragm type pump with very high efficiency; however, it does have a much shorter life than centrifugal or helical rotor pumps. Its diaphragm should be replaced every 2 to 4 years, depending on the pumping volume. The SHURflo 9300 can be operated on a 12 or 24 VDC battery, or with the use of one of the SHURflo pump controls directly with a PV array. The pump can lift 1.3 gpm to 230' and can pump nearly 2 gpm from very shallow wells. It measures only 3.75" diameter and 12" long. Performance on a 12 VDC battery or solar array will be less than half the flow shown on the table below. The 9300 carries a 1-year warranty and the pump should be pulled up out of the well every 2 years to replace the brushes, diaphragm, and valves. Occasionally, the cable plug, which is the connection between the cable and the pump, also needs to be replaced due to corrosion or abrasion. To reduce current loss and plug corrosion in SHURflo 9300 installations, always use a #10 AWG, 2 conductor, no ground, solid core submersible pump cable. The selected pump cable needs to have a smooth outer jacket with no "valleys" in the shape (round or oval) in order to properly seal out water. The sub pump cable 10-2C listed in the table below would work with the SHURflo 9300.
SHURflo 9300 Solar Pump Controllers
These solid-state controllers will protect the 9300 pump from over-voltage and over-current conditions and will provide current boosting in low sunlight conditions, providing both protection and maximum water delivery. SHURflo 9300 Pump Controllers optimize your solar water pumping system by translating the current and voltage available from your photovoltaic panels into a combination better matched to the pump requirements. With an optional float switch installed, the controller will automatically stop pumping when the storage reservoir is full. One of these controllers is required for PV array-direct pumping systems with the SHURflo 9300 submersible pump.
The SHURflo 902-100 controller is not waterproof so it must be mounted in a dry location or an appropriate weather-tight enclosure. For use with a 24 VDC nominal PV array (two 36-cell 12 VDC nominal modules wired in series – see Solar Modules). Maximum input voltage is 45 VDC, and max output is 28 VDC and 5 A. The SHURflo 902-200 controller has all the features of the 902-100 and more. This controller is switch selectable for 12 or 24 VDC operation and includes a manual on/off switch for easy pump maintenance. The 902-200 controller comes complete with three high / low water level sensors and sensor wire. Water sensors hang in the well and are used to prevent dry-running in low yield wells. Maximum input voltage is 45 VDC, and max output is 28 VDC and 7 A. Use a single 36-cell 12 VDC module (reduced water delivery) or two in series for 24 VDC nominal operation. The 902-200 includes a weatherproof enclosure suitable for outdoor mounting. A single common 60-cell module can also be used with either controller, and will produce the 4 A max current that the pump draws with only about 50% of full sunlight. This will increase the amount of water delivered per day by increasing water output early and late in the day or in cloudy weather.