Water Pump updated 1/24/96
An Introduction to Solar Water PumpingSolar Electric Uses Diaphram Water Pump
Jet Sub water Pump with Trace Sine Wave Inverter
Hydraulic Rams Use their own Water Pressure to Lift Water
Use a Slow Pump to Lift Water from Spring
Teel / Jetsub Pump Powered by an Inverter
An Introduction to Solar Water Pumping
By Windy Dankoff 1992
Solar-electric (photovoltaic) pumping systems provide a welcome alternative to fuel burning generators, cumbersome windmills and hand pumps. A solar pump is alot like a windmill, which fills a tank when the energy is available. The BIG difference is that solar pumps don't slow down in summer, when winds are low. They provide the most water precisely when it is needed the most - when the sun shines the brightest! Solar pumps are simple to install and maintain. The smallest systems can be installed by one person in a couple hours, with no experience or special equipment required. Solar power differs fundamentally from conventional electric or engine - powered systems, so solar pumps often depart from the conventional. PV arrays produce DC power, rather than the AC from conventional sources. And, the power available varies with the sun's intensity. Since it costs less to store water (in tanks) than energy (in batteries) solar pumps tend to be low in power, pumping slowly through the duration of the solar day. Simple, efficient systems are the key to economical solar pumping. Special, low-power DC pumps are used without batteries or AC conversion. Modern DC motors work well at varying voltage and speed. They are more efficient than small AC motors, too. The better DC motors require maintenance (brush replacement) only after periods of 5 years or more. Most solar pumps used for small scale application (homes, small irrigation, livestock) are "positive displacement" pumps which seal water in cavities and FORCE it upward. This differs from faster, conventional
CENTRIFUGAL type pumps (including jet and submersible pumps) which spin and "blow" the water up. Positive displacement pumps include piston, diaphragm, rotary vane, and pump jacks. They work best for low volumes, particularly where variable running speeds occur. Centrifugal, jet and turbine pumps are used for higher volume systems. Electronic matching devices known as Linear Current Boosters allow solar pumps to start and run under low-light conditions. This permits direct use of the sun's power without bothersome storage batteries. Solar trackers may be used to aim the panels at the sun from morning to sunset, extending the useable period of sunlight. Storage tanks hold a 3-10 day supply of water, to meet demands during cloudy periods. Solar pumps use surprisingly little power. They utilize high efficiency design and the long duration of the solar day, rather than power and speed, to lift the gallons required. Solar pumps are available in the power range from 1/30 to 1 1/2 horsepower. System costs range under $1000 to the tens of thousands, depending on water requirements, lift and climate.
If your well is near your home, and a battery system is present at the home, then it is usually most economical to run the pump FROM THE HOME SYSTEM. That way in summer, when you use less energy for lights, you have more to spare for pumping and need not add much to your generating capacity. A battery system allows you the options of pumping on demand (any time) to charge a pressure tank, and also the option of using a conventional AC submersible pump powered by an inverter - a good option in some circumstances. And, storage tank requirements may be reduced or eliminated.
STORAGE AND DISTRIBUTION: Homes generally require some pressure for proper water delivery. When considering using an elevated tank to provide pressure, be aware that 2.3 feet of elevation is required for every 1 PSI pressure. Conventional "Town Pressure" is 30 to 60 PSI - over 100 feet! In most cases, it is FAR CHEAPER to obtain pressure using a DC PRESSURE (BOOSTER) PUMP charging a conventional pressure tank. The booster pump runs from the home battery system, as usage demands. Energy requirement is generally less than that supplied by one PV panel, for typical family requirements.
IRRIGATION should be satisfied with gravity flow whenever possible, so energy is not spent pressurizing. Drip systems can usually operate from low pressure by gravity. Irrigation water may also be supplemented by RAIN WATER CATCHMENT and storage, to reduce pumping requirements.
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 systemıs 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 Feeze" 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. 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. 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). 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.
In order for us to help you design your water system the following information is neded:
WELL DEPTH (or description of water source)
DEPTH TO WATER SURFACE - Does it vary? Describe
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
APPLICATION for water: Home? Livestock? Irrigation (what kind of system)?
Is PRESSURE required (home, sprinkling)?
Can 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? Include map or diagram
DESCRIBE EXISTING EQUIPMENT for pumping, distribution, storage etc.
Compressed Air to Pump Water
© Copyright 1994 By Charlie Collins From "Ask Mr. Solar" Column Published March 27, 1994 Daily Spectrum
Question:I am planning to move to Montana and would like to install some type of electric pump water for household use. My well has water standing at 85 feet. Is it possible to generate electricity with a small wind turbine and then use this electricity to pump water or what other pump options do I have?
Vance Covington, Hurricane Ut
Mr. Solar: Vance, As we are sure you are aware the old method of pumping water using standard windmill and there are ranchers that have been using this method for years. This method still works, however it does have a several draw backs, being that the owner must regularly pull the pump and change the leathers as well as service the mill. With this type of pump the farmer or rancher can only get about 3 gallons per minute from his well. You have three basic choices to pump water from a well. They are the old fashion wind mill, the compressor type pump, a solar electric or a wind turbine to generate electricity to operate an electric pump. We will discuss in the next few weeks each of the different pumps available to you. We will point out to you the advantages as well as the limitations of each. You can now get small solar electric pumps that will pump approximately 2 gallons per minute to a large system that will lift 50 gallons per minute from 50 feet.
This week we are going to explain how you can use compressed air to pump water from your well. The Bowjon International Company has been manufacturing an air compressed type pump for many years. The air is compressed with a five blade wind mill that is mounted atop a tower located near the well head. This is one major advantage of this type of pump is that it doesn't need to be located directly over the well. It can be located where the wind may be stronger up to a quarter of a mile away from the well.
The Bowjon pump will deliver water to the service from water levels up to 300 feet below ground. It's maximum delivery is seven gallons per minute. Normally the pump must be placed approximately two thirds the distance below the static water level. In other words if your water is 225 feet below the surface then you would need to place your pump at 330 feet below ground or 105 feet below the static water level. However now their is a special pump head that can be used on the compressor type pump that allows the pump to be placed only three feet below the water level. As the wind compresses the air it is forced down a pipe and mixed with the water. This mixture then raises to the surface. These pumps should be serviced approximately six months to check all the above ground fittings, wind mill and compressor. These pumps cost about $1,600.00.
Also there is a compressor pump which operates directly from compressed air. They come with a low voltage motor to operate an air compressor which in turns operates your air pump. The cost of this system is only about $800.00 plus your battery bank and charge system which you would normally have to operate your remote home.
If you would let us know of your daily water requirements, well depth and static water level, we will be more than happy to give you an approximate quote on this as well as other pumps that you may want to consider. There many of these pumps through out the country and would be happy for you to see one in operation. If you would like information on these larger pumps or have friends that would be interested we will be glad to explain them to them.
Solar Electric Uses Diaphram Water Pump
© Copyright 1994 By Charlie Collins From "Ask Mr. Solar" Column Published March 27, 1994 Daily Spectrum
Question: I am planning to move to Montana and would like to install some type of electric pump water for household use. My well has water standing at 85 feet. I know that there are many people in this area that use a couple of solar electric panels connected to a submersible pump which pumps water for them. I am wondering how this will work in a northern location where there is less sunlight. Is it possible to generate electricity with a small wind turbine and then use this electricity to pump water or what other pump options do I have?
Vance Covington, Hurricane Ut
Mr. Solar: Vance, This week to continue our discussion on the various types of pumps available to farmers and ranchers we will explain the use of a small diaphram pump. This pump is on a low voltage pump which generates its electricity from solar electric panels or a electric wind mill. There is a small wind mill on the market which produces approximately the same power that two solar electric panels produce in a 10 mile wind. The cost of this wind mill is less than the cost of 2 solar electric panels. Of course the advantage of using wind to generate power to operate your pump is that in a windy location you can pump around that clock rather than only when the sun shines. Another major advantage of using the wind to pump is that as the wind increases your electric power will also be increased. This increase of power will give you an increase of water pumped. The diaphram pump works good on wells up to a couple of hundred feet deep and will deliver up to 2 gallons per minuet during the middle of the day in shallow wells. The diaphram pump will lift water from a depth of approximately 300 feet. The main advantage of this pump is that it can easily be moved from well to well with only one man and therefore a rancher can use the same pump for several wells. You will need a special automatic attachment to the small wind mill so that it is able to get up to speed and power before your pump starts pumping. This will reduce the drag created by your pump lifting water thus enabling your wind turbine to get up to full power.
The main disadvantage of this type of pump is that it must be pulled from the well when it needs servicing approximately every 6 months or so to replace the rubber diaphram. Originally this maintenance was only done at the factory. Now there is an improved pump that can easily be serviced by the rancher in the field with a repair kit. This saves the rancher down time.
The major advantage of this pump system is this low cost which is about $1500.00. Therefore it is considerably less than the old fashion wind mill with the pump rod. Another advantage of this type of pump is that one man can service the system and he doesn't need any help.
Water Pump - Spinning Shaft
© Copyright 1994 By Charlie Collins From "Ask Mr. Solar" Column Published April 3, 1994 Daily Spectrum
Question: I am planning to move to Montana and would like to install some type of electric pump water for household use. Is it possible to generate electricity with a small wind turbine and then use this electricity to pump water or what other pump options do I have?
Vance Covington, Hurricane Ut
Mr. Solar: Vance, We have discussed in detail during the last few weeks the advantage as well as the disadvantages of each. This week to continue our discussion on the various types of pumps available to farmers and ranchers. We are going to discuss the newest type of pump, one that uses the sun or wind to generate electricity and stores it in batteries. Then when there is ample electricity it pumps water by means of a surface DC motor connected to a cyntrifical pump to deliver large amounts of water to the surface.
This pump is manufactured by Appolo Manufacturing Company. This pump consists of a DC motor mounted on top of the well and connected to a cyntrifical pump in the well via a spinning rod. These pumps operate either from a wind mill or solar panels which generate electricity. The power is stored in batteries and when needed it automatically starts pumping. This pump is designed for large amounts of water such as irrigation. It will pump up to 50 gallons per minute from shallow wells. It will also operate quite successfully from wells up to 300 feet deep, however the gallons per minute is less. This can pump enough water to irrigate or water a large numbers of cattle. A system using this pump works quite well with a stand alone home system. The reason for this is that we can design your system so that when there is excess power from your solar electric panels or wind mill then this power is used to pump water.
Burgey Wind Pump
© Copyright 1994 By Charlie Collins From "Ask Mr. Solar" Column Published April 10, 1994 Daily Spectrum
Question: I am planning to move to Montana and would like to install some type of electric pump water for household use. My well has water standing at 85 feet. I know that there are many people in this area that use a couple of solar electric panels connected to a submersible pump which pumps water for them. I am wondering how this will work in a northern location where there is less sunlight. Is it possible to generate electricity with a small wind turbine and then use this electricity to pump water or what other pump options do I have?
Vance Covington, Hurricane Ut
Mr. Solar: Vance, We have discussed in detail during the last few weeks the advantage as well as the disadvantages of each. This week to continue our discussion on the various types of pumps available to farmers and ranchers. Now there is a wind mill manufacturer that has connected his pump directly to a four inch submersible pump end with a Franklin 230 VAC motor.
These pumps are available in a two versions. The medium one uses a 1.5 HP motor and with an average wind speed of 12 miles per hour will lift approximately 2,000 gallons a day from 225 feet. This medium pump will also deliver approximately 10,000 gallons a day from 50 feet. This pump is powered by a 1500 watt wind turbine. The cost of this including a 60 foot guyed lattice tower, pump, wind turbine, and all necessary controls is approximately $8,000.00.
The large one uses a 7.5 HP motor and with an average wind speed of 12 miles per hour will lift approximately 2,000 gallons a day from 800 feet. This medium pump will also deliver approximately 85,000 gallons a day from 50 feet. This pump is powered by a 10,000 watt wind turbine. The cost of this including a 80 foot guyed lattice tower, pump, wind turbine, and all necessary controls is approximately $26,000.00.
The manufacturer is also working on a pump to be operated by their new 850 watt wind mill and will have these available shortly. If you would let us know of your daily water requirements, well depth and static water level, we will be more than happy to give you an approximate quote on this as well as other pumps that you may want to consider. There many of these pumps through out the country and would be happy for you to see one in operation. If you would like information on these larger pumps or have friends that would be interested we will be glad to explain them to them.
Jet Sub water Pump with Trace Sine Wave Inverter
© Copyright 1994 By Charlie Collins From "Ask Mr. Solar" Column Published April 17, 1994 Daily Spectrum
Question: I am planning to move to Montana and would like to install some type of electric pump water for household use. My well has water standing at 85 feet. Is it possible to generate electricity with a small wind turbine and then use this electricity to pump water or what other pump options do I have?
Vance Covington, Hurricane Ut
Mr. Solar: Vance, We have discussed in detail during the last few weeks the advantage as well as the disadvantages of each. This week we will complete our discussion on the various types of pumps available to farmers and ranchers.
This week we are going to explain the newest pump on the market. As you may have been aware there has been a problem starting deep well pumps because of the pressure created from the column of water in the well. This is referred to as the surge needed to start a deep well pump. This surge would amount to up to seven times the running power needed by the pump. What this means is that you would need a much larger inverter or generator just to start the pump. Now the new Grundfos JetSub has recently come out with a pump that requires no surge power to start it. This is because of their slow start up which they have built into their pumps. It actually takes many seconds to reach full power, but it doesn't take any excess power to start it. These pumps will only operate off of pure sine wave 220 VAC electricity. Now there is an inverter from Trace which produces a pure sine wave at 4000 watts which will easily operate this pump. The pump is reasonably priced at approximately $500.00. These pumps will deliver up to 16 gallons per minute and will lift water up to 450 feet with less per minute. The main disadvantage of this type of pump is that it requires a pure sine wave power and therefore you must have this available at your well sight. You cannot use the old fashioned modified square wave inverter.
Hydraulic Rams Use their own Water Pressure to Lift Water
© Copyright 1993 By Charlie Collins From "Ask Mr. Solar" Column Published 4/18/93 Daily Spectrum
Question: Steve Hicks, Cederville, CA Can I use the water pressure to lift water? I understand that there are several pumps available to pump water. Would you please explain the differences in them and advantages of each?
Mr. Solar: Steve, we are going to explain how you can use water to move water without the use of any power other than water itself. This type of knowledge is actually very old and has been used for centuries world wide. These types of pumps are called hydraulic rams. Today these rams are very light weight and they can easily be carried in to a remote location by one person. This ram type pump works on the pressure created by falling water. In other words you will need to place the pump several feet below the water source. Then have the water enter the pump through a pipe, thus creating pressure. This pressure will force the pump to lift the water up as high as 1,000 feet above the ram pump. This pump can operate on as little as quart a minuet and pump over 1500 gallons a day.
You will find that this ram pump works extremely well in mountain areas where there is a large fall and therefore plenty of pressure. Due to the light weight this pump can easily be installed by one man and give him years of trouble free service. The reason for the low maintenance is that it is self lubricating using the water and also is self primming. Another major advantage of the ram pump is the cost as it is under $1,000.00. Of course the major disadvantage of this type of pump is that it must be located below the water source.
If you would let us know of your daily water requirements, we will be more than happy to give you an approximate quote on this as well as other pumps that you may want to consider. There many of these pumps through out the country and would be happy for you to see one in operation. If you would like information on these larger pumps or have friends that would be interested we will be glad to explain them to them.
Use a Slow Pump to lift water from Spring
© Copyright 1992 By Charlie Collins From "Ask Mr. Solar" Column Published 8/9/92 Daily Spectrum
Question:
Larry B., St George, Ut.
Mr. Solar: Larry, we can use one of several slow pumps to lift your water from your spring to your storage tank at different pump rates. You will need a small tank at your spring to hold the spring runoff for a total of 3 days accumulation.
The reason that you will need this small tank is that in the event that there are cloudy days then you will not be pumping the maxiumn amount of your pump and therefore you can accumulate the water to be pumped at a later date. In the small tank we would recommend that you install a mercury float cut off switch so that it will automatically start your pump when the water reached a preset level and cut of when the water level dropped below the point that you would want to pump. We would then sell you a 5 micro replaceable filter screen to filter the water from your spring to your pump. This screen will serve two purposes, one that it will keep your pump clean and therefore last longer and the other reason is to filter out all the trash as well as sand from your spring and thus give you clean water. The pump we could supply you would pump from 27 gallons per hour using two solar electric solar panels to one that would pump 219 gallons per hour using eight solar electric panels. You see you have range of pumps and several in between. We would need to know how much water you will be needing at your home and how much water that your spring is making and then we can be more specific on the pump that we would recommend.
We would also include a Linear Current Booster (LCB) which is a thing that automatically matches the voltage from your solar electric panels with the pump and reduces the current so that your pump will run in even cloudy weather as well as early in the mornings and late in the evenings when there is low sun light.
As you know we only sell and use UL approved electric solar panels and other UL approved equipment where it is now available. In the installation you will find that it is done to comply with all electrical standards and code.
Larry we have helped install several of these type pumps here in Southern Utah and the owners will be more than happy to show them to you, should you be interested in seeing them operate please contact me and we will be happy to arrange a visit with a local satisfied solar pump user.
Teel / Jetsub Pump Powered by an Inverter
© Copyright 1995 By Charlie Collins From "Ask Mr. Solar" Column Published 3/27/95 Daily Spectrum
Question:I have a well that is 150' deep and would like to pump water using a solar system to so it. I am planning on installing a complete solar electric system for my home. I do not want to use the diaphragm solar pump as I understand there is a lot of maintenance on this type as yearly the diaphragm has to be chnged. Is that possible using an inverter to use regular submersible pump?
Walter Josey, Apple Valley UT
Mr. Solar: Walter, yes it is quite possible and actually the best approach when you have an inverter. You have a couple of choices. You can use the new large 4000 Watt "smart" inverter which can be automatically set to pump whenever your batteries are full from the sun or you storage tank is low. This system consists of a 24 VDC set of batteries to operate the true sine wave "smart" inverter. The pump that I would recommend would be the new Jet Sub manufactured by Grundfos Pumps Co. This is a very unique pump that it does not have a electrical surge on start up and therefore the need for a oversized inverter to start is not necessary, however the inverter must produce a true sine wave. You would also need a transformer to increase your voltage to 220VAC to your pump. The other choice would be to use a 12 VDC system with the normal 2500 watt inverter producing a modified sine wave and a smaller horse power submersible Teel pump which would operate at 110VAC. This system would require a smaller investment, however you would not have the automatic features built into the inverter. The features to start your pump automatically could be added to your system by the use of additional switches. The total watts required to lift the water from your well to a storage tank is the same with either system. Both systems would require the same number of solar electric panels to charge your batteries. The major difference in cost is the use of the "smart" sine wave inverter vs. the standard modified inverter.
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