Everyone knows that water is essential for people and the things that we grow. The problem, however, is that access to water resources can be limiting in settings that are far removed from municipal infrastructure.
Think ranches, farms, cabins, and other off-grid dwellings.
Land users in such remote settings usually have a couple of options: use the distant power grid to run an electric-powered well pump, or use fuel-powered pumps to draw from a pond or river.
Tying into the grid can cost a lot when new electrical lines must be run and then there are the recurring costs for usage.
Similarly, gasoline or diesel-powered pump setups can be pricey, require constant refueling, and can be prohibitive to maintain. In our Leaf House Tea garden, we are all too familiar with the downsides of using gasoline pumps to move water from a pond and into our drip irrigation system.
We need a new system for watering our tea and other crops.
Table of Contents
- The Solar Water Pump Alternative
- Benefits of Solar Powered Pumps
- The Nuts and Bolts of Solar Powered Pumps
- The Water Pump
- Energy Demand of Solar Pumps
- How deep can a solar pump work?
- The Cost of Using the Electrical Grid
- The Costs of Solar Pump Technology: How Much Water per Buck?
- Solar Well Pump Kits
- Are Solar Pumps Competitive Over the Long Term?
- Real-World Use of Solar Water Pumps
- Well Digging: the Hidden Cost of Solar Water Pumps?
- Conclusion: Benefits and Trade-offs of Solar Water Pumps
The Solar Water Pump Alternative
This is where the exciting technology of solar-powered water pumps comes in. Solar pumps could offer a solution to remote watering needs that is both cost-effective and energy-efficient.
And with a few simple components, solar pumping can be used in a variety of settings.
Here we discuss the merits of solar pumps, detail how these systems operate, and explore the ideal situations for its application.
We also compare the cost for a solar-powered pump versus grid hookup and look at a couple of insightful case studies.
Benefits of Solar Powered Pumps
What tips the scale towards solar pumps?
In our research of the solar pump market, we have discovered that there are several features inherent to solar water pumps that can make them advantageous:
The Nuts and Bolts of Solar Powered Pumps
There are two main components to a solar-powered pump system: solar panel arrays for collecting energy from the sun, and the mechanical pump for moving water.
To make the most of solar’s potential, it’s important to understand how solar water-pumping systems function. Let’s start with the sun.
Solar Energy Basics
Every solar setup starts with photovoltaic cells. The cells are what produce electricity from solar radiation. Many photovoltaic cells are connected to make a solar panel. These panels can be connected to create a solar array.
Solar panels generate direct current (D/C) as opposed to the alternating current (A/C) that is used in households. The amount of power produced by a system is dependent on the materials of the cells, the size of the panels, and the number of panels in an array.
The power from solar panels is rated in watts. A watt is a unit of power used to describe energy output or demand for electrical fixtures. You might be familiar with this concept for everyday household gadgets such as a 60-watt incandescent lightbulb.
For solar systems, watts refer to supply. Individual panels come in an assortment of wattages, anywhere from tiny 50-watt to whopping 400-watt panels.
The output of each panel is not as important as the total output of all the panels used in an array. For instance, a 300-watt array can be made using three 100-watt panels, two 150-watt panels, or one 300-watt panel.
In short, solar panels are the power supply for pumping water.
The Water Pump
A pump is any device that uses an energy source to move fluids.
In our case, a pump is a tool that mechanically draws water from a source and delivers it to the desired location. There are many types of pumps for just this purpose but some pumps work better with solar power.
In particular, pumps that require less power to operate at peak efficiency are ideal. For deep wells, positive-displacement pumps are recommended. These pumps move a fixed amount of water with every rotation cycle, and they pump proportionally to the amount of power supplied.
Compare these to centrifugal pumps commonly used with A/C power. If you have a deep well supplying your house with water, and you’re on the utility grid, then you are probably using a centrifugal pump.
Centrifugal pumps draw a lot of power to pump as fast as possible. However, at lower power, they underperform. For instance, at half power, a centrifugal pump will pump at only a quarter of its maximum pressure.
Submersible D/C water pumps, in contrast, use only 20 to 50% of the energy required by A/C centrifugal pumps to move the same amount of water. This is why solar energy works so well with D/C pumps.
Energy Demand of Solar Pumps
Several factors determine the energy demands of solar water pumps.
The head, or the vertical distance that the water must be pulled or pushed from the source, largely determines power need. For instance, the head on a water draw from a surface pond is generally much smaller than the head on a deep well.
Additional considerations are the horizontal distance that water must travel from the pump to the application and the dimensions of water supply lines.
Another obvious factor is the water demand itself which is often reported in gallons per day.
An important thing to note here is that higher energy demands translate to more solar panels. More panels mean more cost and more infrastructure.
The Solar Pump Advantage
But don’t despair over your investment in solar-powered pumps!
While it is true that pumps rated for solar use may take longer each day to satisfy water demand, they will pump just as much water over an entire day of solar exposure as standard A/C pumps do but at a portion of the cost.
The reason for the solar advantage is that A/C pumps, in comparison, draw a lot of power to pump quickly and then shut off. But solar pumps work at the same rate that solar energy is being converted.
In other words, water is pumped as long as the sun shines and the good news is the cost of a solar pump balances out by the end of the day.
A setup like this doesn’t require batteries, and when sunshine is abundant, a solar pumping system can fill an auxiliary tank to be drawn from on days when the sun is hiding behind clouds.
How deep can a solar pump work?
Solar pumping systems can be scaled to fulfill most water needs but can be limited by the depth of the water source.
As discussed, the energy and cost advantage of pumps for solar applications is due to lower power demand. Although lower power translates to lower overall output, most pumps can provide between 75 and 350 feet of vertical lift.
Some solar pumps are rated for greater depth, but the increased cost of these products quickly offsets the benefit of solar pumping.
The Cost of Using the Electrical Grid
For sites that are not connected to the grid, the cost of stretching power lines can be substantial.
According to an article by the University of Iowa, in many rural parts of the US, the average rate for adding power lines beyond 1000 feet from the nearest grid-tie is $5 per foot, which totals greater than $25,000 per mile.
And it can get worse than that.
Additional costs may be incurred if accessibility is reduced by dense vegetation, unfavorable soil conditions, or changes in elevation.
Unless participation in a rural power co-op is an option, the landowner will eat these costs directly. Running utilities to sites more than one-quarter mile from the connection is therefore quite expensive.
And though rates for electricity differ by utility provider and by region, there is nevertheless a recurring payment for usage after installation.
Add it all up, and the costs of tapping into a utility grid make solar pumps are much more attractive option.
The Costs of Solar Pump Technology: How Much Water per Buck?
In my research of the market, I found that a solar-powered water pump for irrigation ranges from $2000 to $5000 for a solar array and pump kit, along with all connections.
The kit price includes a pump for $1200 to $2500 with a balance of no more than $2 per watt for the solar panels.
The total cost largely depends on water demand in terms of flow rate, volume per day, and where it is being delivered.
Costs also depend on the water source. Surface water systems, such as those that draw from a pond or river, will tend to be cheaper due to less energy demand than water pumps submerged deep into a well.
I also found, however, that seasonal discounts are often quite deep, with up to 25% off the retail price. Keep your eyes open for sales and use price-trackers for instant alerts.
Solar Well Pump Kits
Below are some examples to illustrate how water output from a well is related to cost. The figures given here from RPS Solar Pumps are merely for demonstration purposes and not intended as an endorsement.
According to RPS, three of their solar well pump kits serve about 90% of their client’s pumping needs. In my assessment, these products represent typical costs, components, and output now available on the market.
Each model of solar water pump kit is driven by a brushless motor which eliminates the need to replace worn-out brushes. Also included are a pump controller, various connectors and fittings, shut-off sensors for tanks and wells, and a two-year “comprehensive” warranty.
|Pump Model||RPS 200||RPS 400||RPS 800|
|Number of Solar Panels||2 x 100-Watts||4 x 100-Watts||8 x 100-Watts|
|Maximum Output GPM, GPD (no head)||5.1, 1836||7.6, 2736||8.9, 3204|
|Output at Max Depth GPM, GPD (max head in feet)||1.5, 540 at 150′||1.2, 432 at 250′||4.1, 1,400 at 325′|
|Total Kit Cost||$2,150||$2,550||$3,500|
Of course, there are other options available such as dewatering pumps which are often designed to grind up the debris that may be drawn up from a pond, creek, or ditch.
Keep in mind, however, that the more specialized the application the more costly the components. If your needs are on the less complex end of the scale, then you can easily realize the cost benefits of solar water pumps.
And don’t forget to factor in the costs of water tanks, water lines, and the parts for connecting to the solar-powered pump. These pieces are seldom included in kit prices.
Are Solar Pumps Competitive Over the Long Term?
In the scenarios given above, installing solar pumps can be much cheaper than extending power lines. There are many conditions where this holds true.
For any instances where electric company infrastructure must be extended more than one-quarter of a mile, solar pumps have a clear cost advantage.
However, one must also consider the longevity of such projects.
A downside with many solar pump setups is that they may need to be serviced and components periodically replaced. For instance, smaller well pumps may have to be serviced every two to four years while larger well pumps and surface pumps require service about every 15 years.
In addition, most solar panels these days have life spans between 20 and 30 years.
Making sure that things are adequately installed and maintained for the intended use will offset some of these issues. However, the replacement of solar cells and pump components is inevitable.
Real-World Use of Solar Water Pumps
Now that we understand the basics of solar water pumps, we will look at a couple of applications that demonstrate the potential as well as the constraints of using solar systems
Case 1: Solar Pumps in Senegal
In rural Senegal where I worked as a Peace Corps Volunteer, water is the most limiting factor for vegetable productivity. Water use is also the largest consumer of time and labor for gardens where the watering is done by hand.
In this setting, tapping into the electrical grid is usually not an option, and once gardens are above a certain scale, hand-drawing water is not an option either.
When international aid organizations partner with these communities to build sustainable food practices, it is solar pumping systems that local farmers want.
A standard setup for a Senegalese community garden is to have a centralized well that feeds several cisterns located through the garden. Solar pumps draw water from a shallow, sand point well, and fill an elevated reservoir. This reservoir then gravity feeds water to waist-height cisterns located throughout the garden. From here, the gardeners fill up buckets at the cisterns closest to their vegetable plot.
Drip Irrigation Is Gravity-Fed
On many private farms in Senegal, solar-powered pumps are an integral part of drip irrigation systems.
In drip systems, solar pumps are used to transfer water from shallow wells and up into elevated water tanks. Gravity-fed irrigation lines that feed off the tanks then rely on the height of the water to provide adequate pressure for water flow.
Determining the height needed to achieve a certain water pressure is straightforward.
The rule of thumb is that 2.31 feet of vertical elevation at the outlet of the water tank are required for each pound per square inch (psi) of water pressure needed at drip emitters.
Most towers are from 15 to 30 feet above the ground and from there water is gravity fed back down through irrigation piping. Most often, such elevations are adequate to operate drip lines that require between 10 and 15 psi pressure.
There is no shortage of sunlight during the vegetable-growing season in Senegal, and there is enough solar energy to supply all the water demand. And with an efficient flow rate, there is less risk of drying up the well through over-pumping and drawdown.
The application of solar pump technology in Senegal has proven to have a significant impact on the productivity of farms and gardens.
Case 2: Off-Grid Solar Powered Water Pumps for Iowa Cattle Ranchers
Refilling livestock water reservoirs is perhaps one of the most appropriate uses for solar water pumping.
Ranches with large tracts of land, far away from municipal utilities, and plenty of thirsty animals are great candidates for solar-powered technology.
In Cherokee County, Iowa, cattle rancher Dick Lester found that solar was the best solution for his watering needs on a 650-acre pasture.
Prior to installing a solar pump system, the only available water source on Lester’s property was a small creek that ran through the pasture.
With over 300 head of cattle, this riparian system was constantly being gouged away by herd traffic, and the creek’s banks were left bare of grasses and susceptible to erosion.
Lester deduced that giving his herd multiple water sources would break up the group and would result in more even grazing. The need to pump water was therefore quite apparent, and the decision to go solar was a no-brainer in Lester’s case.
When pricing out his pumping needs, Lester was quoted a price of $4.75 per foot, totaling $20,000, to run electricity out to his water pump. On top of that, he would pay $30 a month in fees, not including the cost to power the pump.
The company that installed the solar pump system estimates that a full setup for ranchers is usually between $5,000 and $7,000 including installation.
Factor in sizable cost-share initiatives offered by the Natural Resources Conservation Service for solar pump installation, and there is nothing that comes close to being as effective and affordable.
After considering the alternatives, Lester installed an array of eight 175-watt solar panels. These panels power a pump that draws water from the creek and then delivers it through 4,600 feet of pipe and up to 150 feet to fill each of three large tanks. Fill valves switch the pump on and off based on the water level in the tanks.
This is a great example of how solar power can be used to supply water on demand. Also, by storing plenty of water in the tanks, there is no need to have batteries for times when there is a lack of solar power.
Systems like this one have picked up a lot of traction at ranches across the US. And with cost-share programs like those offered by the NRCS and other rural resource organizations, this is the best deal for livestock watering.
Well Digging: the Hidden Cost of Solar Water Pumps?
As previously mentioned, solar pumps come in two main categories: surface and submersible.
Surface pumps are straightforward in application. In any body of water, these pumps can deliver flow rates between four and ten gallons per minute, on average, and without drawing much power.
In addition to pumping from natural water bodies, this is a good option for cisterns and other water catchments.
For deep wells, submersible pumps are required.
Submersible pumps designed for solar power are built to be more energetically conservative so that the supply of power coming from the panels can maintain the pumping load.
The questions are, how deep into the earth do you need to go and how much water do you need? The deeper it goes, the more it costs, a fact that holds true for all wells and not only solar pump wells.
As previously noted, however, there is a limit to the vertical height that a solar powered pump can move water. The maximum lift for most pumps is between 75 and 350 feet, and though some can go deeper, the increased requirement on design brings the pump prices up and the cost-savings down.
In most applications, it will not be necessary to sink wells any deeper than the upper edge of the water table. Safety concerns for domestic water use aren’t necessary for plants and livestock, so shallow wells are usually sufficient. The lower flow rate of these pumps complements shallow and slow-restore wells.
Conclusion: Benefits and Trade-offs of Solar Water Pumps
Solar water pumps are energy-efficient solutions for many off-grid watering applications.
The technology is suited for a range of water needs but is optimized for systems with low flow.
Solar pumps are also well suited for areas where other power sources are either unavailable or too costly to access. The most relevant applications include crop irrigation, refilling of livestock water basins, and regulation of water levels in ponds and lakes.
Solar-powered pumps are useful for supplying gravity-fed systems and distributing stored water. Pumps can be used in surface water or groundwater sources.
Many retailers offer self-contained solar well pump kits that include solar panels and all the other components needed to make installation a straightforward process.
The biggest trade-offs are in power and unit lifespan.
Solar pumps sacrifice lift power for pumping efficiency, and there are limits to the rate at which solar energy can be converted to electricity even under peak solar intensity.
For very deep water or high flow rate requirements, solar water pumps are no longer economically competitive. Even if functional, using the systems closer to their upward limit increases wear and tear on pump components, which only hastens the need to service or replace the system.
Regardless of the power load, the solar array and pump will need regular attention and will need to be periodically upgraded.
Although the longevity of such systems may be limited, there are plenty of practical, cost-effective applications to justify the investment.
As interest in solar pumping systems increase, improvements in existing designs will advance this technology even further.
Inside the lab and out, at home and abroad, Ethan is a student of sustainable farming. With a B.S. in environmental agriculture from the University of Florida, he has had his hands in farming at multiple climes, including Senegal with the Peace Corps.