Accurately designed solar based water pumping system – a way to cost effective and sustainable farming
11000 agricultural workers are dying due to electrocution in India every year. On average 30 persons are dying every day. The reasons are attributed to standards not being followed in wiring, cutting, and fallen transmission lines due to aging, corrosion, and formation of the conductive path on the motor casing and control box under damp conditions.
The unavailability of electrical power leaves the rural farmers at the mercy of other sources of water generation to irrigate their farmland and the use of human power to carry the water source to the field. To obtain optimum yield on such land efficient, sustainable water supply and management exerts a crucial role in supplemental irrigation of farmland
Type of Mounting Structure – Fixed Tilt or Auto-Rotating Tilt
For maximum solar input at latitudes higher than 10 degrees, the fixed ground-mounted array frame usually should be orientated towards the equator. This means that in the southern hemisphere the modules usually should point north while in the northern hemisphere they usually should point south. For latitudes less than 10 degrees the orientation is not an issue. Also, the tilt should never be less than 10 degrees because that much tilt is needed to allow rainwater runoff fast enough to help clean the modules.
If the water resource requirement varies throughout the year, the designer will need to select a tilt angle and array size such that the solar water pumping system can provide the water required for all months.
It has been observed that generally, 4-8 Modules are installed on a single structure which makes it heavy and also increases the height of the system hence becomes difficult to rotate manually. In such a case, the farmer will always need two additional people to do the needful which is practically impossible and not feasible.
The solution to this is the use of an auto-rotating system but as that can increase the cost of the system, fixed-tilt is always a preferable option. In these farmers won’t need to do an extra effort and would be able to focus on farming more.
In some cases having half the modules tilted toward the east and half toward the west may result in more water being pumped through the availability of the irradiation level.
Pump Sizing Calculations
To get the proper solar system, analysis of pipe sizing and Pump sizing is crucial. Depending on the irrigation the pump sizing and pipe sizing are finalized. Generally, while selecting pump sizing, total head & water requirement are the factors that are being considered but we fail to pay attention to pressure drop calculations.
In this, the total dynamic head is calculated based on the vertical height (static head) that the water must be pumped and the effective head caused by having to pump the design volume of water per unit time (gallons/minute or liters/minute) through the actual length and diameter of the pipe (frictional head) that is used to transport the water from the source to the final destination, often a water tank.
The thickness of the water pipe wall mainly determines the water pressure that the pipe can withstand. The pressure that will affect the pipe comes from the water pump itself, that is it generates a water pressure sufficient to move the water from one location to another at the needed rate. This pressure can be determined from the dynamic head that the water pump must overcome. Water pipe specifications include the pressure rating for the pipes.
The selection process for the most appropriate water pipe will involve balancing the additional costs incurred against the increased system efficiency. However, with a solar water pumping system, the solar array and its mounting is usually the costliest component so the objective is to select the smallest solar water pumping system that can provide the daily required water.
The process for selecting the size of the water pipe is an iterative process. The overall dynamic head is estimated based on the static head and a predicted total frictional head loss so that the designer can then select a solar water pumping system that provides the required water volume with the solar irradiation available at the site.
While designing, one should consider all these factors while deciding the pipe size, pump size, and overall system specifications.
The smaller the pump size the cost of the system will be low. Hence to get the right system accurate pump and pipe calculations are necessary.
Training and Development
Normally, these kinds of systems are installed at remote locations where there is not enough electricity. So, if any problem occurs after the installation of the system farmer will have to reach out to the contractor/ vendor to get it resolved. But due to far distances, they will not get the service when required. This is a time-consuming process and results in losses. Hence to get it done the easy way we should train and develop them so that they can resolve the issues effectively.
As an engineering consultant, we have designed 1000+ and have audited 300+ solar-based water pumping systems till now. We have had an increase in the number of installations of Solar Based Water Pumping System in recent years. Following are the factors are considered to design an effective solar-based water pumping system.
1. To identify the water requirement per day/month/year (Seasonwise will be better in case of farming)
2. When the required daily flow (volume of water) Devaries from month to month then the system will need to be designed on the worst month. The worst month will be when the ratio between solar energy available and the flow required is the smallest. The solar energy available during that worst month and the required flow of the worst months should be chosen as the design basis for selecting the solar water pumping system.
3. Design the network – piping from source to destination (exclusive of pipe sizing)
4. Calculate the water pump and pipe sizing with engineering calculations
5. Based on the calculations the specifications of the solar system needed can be identified like kWp, DC capacity of the module, Controllers (DC to AC & DC to DC)
In India, the cost of the water pump is more than the per capita income of the farmer. Hence to optimize the cost as per the requirement and get the right system hiring the right people is necessary. The right team will always provide a solution and will not just sell their product.