An Analysis of Solar Powered Irrigation Systems

If you’re reading this, you probably already know that solar powered irrigation systems will change the way farms are irrigated. But it isn’t just a simple change in power source to solar energy.  It’s more akin to revamping the entire irrigation system on the farm.

The two main benefits of installing a solar powered irrigation system are to:

  • Significantly reduce the time required to irrigate crops
  • Simultaneously cut down on water consumption

Solar powered irrigation systems combine clean and cheap solar energy with technology to produce a system that is energy conscious, performance orientated, and creates zero waste. It does this by using solar panels, controllers and water pumps to deliver the exact amount of water, exactly when it is required.

The Parts of a Solar Irrigation System

A solar irrigation system consists of a host of different parts, and some water pumping systems are more complex than others. All solar-powered water pumps consist of the following components.

Solar Panels

The main component in any solar-powered pumping system is the solar panel itself. A solar panel is a collection of photovoltaic cells that absorb the sun’s rays and convert them into direct current, which is then converted to alternating current at the motor. These cells are usually made of crystalline silicon, and mounted on a supporting structure. This combination of photovoltaic cells and supporting panels create a solar PV. These panels are extremely durable, and only see about a 2% drop in effectiveness a year, which can further be reduced if preventative maintenance is done often.

There are three types of solar panels commonly used in solar irrigation systems:

  • Monocrystalline
  • Polycrystalline
  • Thin-film panels

Monocrystalline and polycrystalline panels are use silicon shards, with the difference being that the former is created using a single piece of pure crystal silicon. In contrast, the latter is made up of crystals melted together from different fragments of silicone. Thin-film panels use a combination of materials that enable them to capture sunlight.

Monocrystalline panels are the most expensive, but also perform the best. They can reach efficiency levels of up to 20% and can produce 400+ Watts of power. In comparison, polycrystalline and thin-film panels reach efficiency levels of 15% and 11%, respectively, and can both produce around 300 – 400 Watts.

Solar Water Pump

In solar water pumping, centrifugal pumps are used almost exclusively. These solar irrigation pumps use an impeller to rapidly spin water inside the casing, which pushes the water towards the area of the casing that leads to the outlet.

There are two main types of solar water pumps used in solar irrigation: submersible, and line-shaft pumps. Each has its advantages and disadvantages.

Submersible Pumps

Submersible pumps are centrifugal pumps that contain the pump and motor in a single waterproof unit. As the name suggests, the entire unit is submerged in the water source. Because it’s below ground, these pumps are quiet, which is advantageous for farms that are close to buildings.

Submersible solar pumps have fewer parts than line-shaft pumps, which means they vibrate less. This helps reduce overall wear and tear on the unit. These types of solar water pumps can also be more cost-efficient in certain instances, since they don’t have any line-shafting. The caveat is that they require more intricate power cables, which could render this point obsolete.

Because the motor and the solar pump is encased in a single unit, submersible solar water pumps tend to be smaller and more manageable to handle in terms of transport. And since the solar pump sits underground, it doesn’t need a pump house to protect it from the weather, which can be an eyesore.

Line-Shaft Pumps

A variation of a centrifugal pump, the turbine pump has a pump mounted underwater, while the motor is above the water. These solar pumps are used for large-scale operations where they cannot be submerged inside the source of water, typically because the space is too small for a complete solar pump to be submerged in.

Surface pumps have clear advantages over their submersible counterparts, with the first being efficiency when pumping water. The motors on surface pumps tend to be roughly more efficient than submersible pumps. This can be mitigated, however, as the depth increases since this set-up loses around 2 horsepower per 100 feet due to the friction that affects the shaft.

Line-shaft solar pumps are less likely to fail than submersible pumps and tend to handle fluctuations in electricity well, while submersible pumps are susceptible to low voltage conditions, and overload easier than line-shaft pumps during power surges. One of the main reasons surface solar water pumps have a lower failure rate than submersible pumps is because the latter operates in a harsher environment. The sand and soil, along with the high pressures, wear out the electric motor waterproof seal.

Since they are installed at ground level, line-shaft pumps are much cheaper to install, inspect, repair, and maintain. Any time a line-shaft pump fails, you simply replace or repair the component that failed. With a submersible pump, you need to uproot the entire unit to repair it.

In conclusion, a submersible solar water pump is best suited for more urban areas where noise and aesthetics must be taken into consideration. This type of solar pump can also be used in areas that would cause vibration issues for line-shaft pumps, whereas the main selling point of line-shaft pumps is their high efficiency and reliability, which is more fitting for rural areas.

Battery Array

While it isn’t a necessity and some solar pumps do not have one, including a high-capacity battery array in the irrigation set-up will allow for uninterrupted usage when there’s not enough solar energy due to the weather or other unforeseen circumstances. Battery arrays are fail-safes that are not often used, as solar power is quite reliable. But when crops are on a strict irrigation schedule, having a battery array can be extremely helpful.

Battery arrays are expensive, however, and adding one in a solar water pumping system will increase the price, as well as introduce another potential point of failure. The battery array has a secondary use, however. The excess electrical energy generated by the irrigation system can be stored in the batteries and used for other operations on the farm. This reduces overall operating costs and could potentially even offset the cost of the battery array.

Controller

Solar-powered irrigation systems are designed to manage power consumption and water consumption. To achieve this, the system is built around a controller. The controller serves as the brain of a solar powered irrigation system, and has functions that can be configured to the end users unique requirements. For example, the following are 2 common configurations:

  • The point at which the panels should stop charging the battery and focus solely on the irrigation process
  • Below what power level the battery should kick in

One of the most important features of a solar powered irrigation system is that it can be operated automatically and without supervision. The caveat is that additional components are needed in order to do so.

The more basic version of automation is to use a timer, where the user manually schedules at what time the system discharges the water, as well as for how long. This scenario works well for most systems and crops. If crops are more sensitive or water has to be conserved, however, it can also be equipped with sensors that detect the level of moisture in crops. What this means is that the system will turn on the sprinkler system and pump water when that value drops below a predetermined level. A moisture sensor automates the solar water pumping and irrigation process, so that crops are watered efficiently.

Irrigation System

 

There are a variety of irrigation systems that can be solar powered:

Localized Irrigation systems

use low-pressure water distributed over a system of pipes, and are best used in small-scale operations.

Sprinkler Systems

Deliver water by spraying it over the top of the field, which results in more coverage. A more advanced version of a sprinkler irrigation system is a center pivot system, where multiple sprinklers are positioned on wheeled towers. Sprinkler irrigation systems can cover large areas, but are susceptible to overspray and evaporation, which makes them much more inefficient in comparison to some localized systems since evaporation and overspray mean more water waste.

A Drip Irrigation System

Is one of the most efficient, and pumps water by delivering droplets to the roots of plants via quite a bit of plumbing. Since the water is distributed close to the plant, evaporation is kept to a minimum. There is also no overspray, which can result in up to a 90% increase in efficiency in comparison to sprinkler systems.

Supporting Components

Supporting components must be used for an irrigation system to function, whether they are solar-powered or not. For example, storage tanks are used to temporarily store the water that is pumped up from the source, as well as water from sources like rain, until its use in the next irrigation cycle.

The plumbing that is used must be of high quality when setting up a solar-powered irrigation system. This reduces maintenance costs, as leaks can cause substantial amounts of damage. The same holds true for electrical systems.

How to Choose the Right Equipment

Water and power requirements differ from farm to farm, and must be calculated when trying to determine what equipment will be best for the job, while still maintaining cost-efficiency. The key thing to keep in mind is that the main components of a solar irrigation system that affect performance and cost are the water pump and the solar panels. While most systems come standard with a combination of the two that will work, there could potentially be a solar panel setup that works better with a specific water pump that is a better option depending on end-user needs.

There are two main metrics to consider when deciding which type of water pump will be needed on a farm: gallons per minute and required pressure. Whatever water pump is used must meet – and exceed – the requirements to ensure that the pump will not be damaged if there is a failure elsewhere. The two types of pumps, submersible and line-shaft (surface), come in two configurations:

  • Flow pumps are useful for low-pressure irrigation systems like drip systems, have a massive maximum flow rate, and take up less power than pressure pumps. This lack of pressure, however, prevents the water from being pushed through filters. If the water source is clean and does not require much force, flow pumps are the way to go.
  • Pressure pumps, on the other hand, have high pressure and a low rate of flow. They are used for sprinkler-type irrigation systems, or in situations where water must be moved large distances or through a filtration system.

When choosing a solar panel for the system, if:

  • Saving space and energy costs is important, monocrystalline panels are the way to go since they produce the most power
  • Weight must be taken into account and costs must be restricted, a thin-film panel can be used
  • Space is not an issue, and initial costs need to be kept down, polycrystalline panels are the best option

Surveying The Location

When attempting to install an irrigation system, solar or otherwise, the farm must be surveyed to determine what options will be best for how the system is set up. For example, in farms that use diesel pumps, there’s a very real possibility that the entire system will need to be uprooted, which might not be feasible. Other factors like power draw could also be an issue, since solar pumping isn’t the most powerful method of pumping water, and the system might struggle to pull irrigation water from the water supply.

If land in southern Asia is to be surveyed for solar-powered pumps, keeping the dry season in mind is important, since a solar water pump might not be powerful enough due to such a low water table. The flip side is that the sun shines there for longer, which means the system can capture a large quantity of the sun’s energy and operate at maximum capacity, allowing the system to be built larger than it normally would be.

If a solar irrigation system is going to be installed, further choices have to be made. For instance, will the water pump be land-based or submerged, and what type of irrigation system will be used? Sprinkler systems that cost less are good for larger areas, but they waste water. Drip style systems, on the other hand, require more plumbing and are therefore more costly, but most effective for smaller areas.

The Bottom Line

Solar-powered pumping systems are environmentally friendly, growing in popularity across the entire world, and starting to replace both diesel-powered and grid-powered systems, particularly in areas that lack a regular supply of water. They also help farmers reduce costs and revamp their outdated systems, which require more maintenance and are less efficient.

Over the last two decades, the average cost of solar panels and other components in solar powered water pump systems has become cheaper and easier to attain, especially with the assistance of government subsidies. These systems do have limitations, but they can be circumvented with little effort, and using them is the perfect solution to the persistent irrigation problems.