Agriculture Solar Powered Irrigation Pump Methods

...the Solar Pumps for Irrigation System Powered Systems Method. Water pumping has a long history with solar power; so many methods have been developed to pump water with a minimum of effort and encorporate solar energy. These have utilized a variety of power sources, namely solar for energy power generation.Solar irrigation pump systems are used principally for three applications:

• Town and City Water Supply
• Livestock Watering
• Irrigation

A solar irrigation pump system methods needs to take account of the fact that demand for irrigation system water will vary throughout the year. Peak demand during the irrigation system seasons is often more than twice the average demand. This means that solar pumps for irrigation are under-utilized for most of the year. Attention should be paid to the system of irrigation water distribution and application to the crops. The irrigation pump system should minimize water losses, without imposing significant additional head on the irrigation pumping system and be of low cost.

Submerged multistage centrifugal motor irrigation pumpset. This type is probably the most common type of solar pump used for town and city water supply. The advantages of this configuration are that it is easy to install, often with lay-flat flexible pipework and the motor irrigation pumpset is submerged away from potential damage. Either ac or dc motors can be incorporated into the irrigation pumpset although an inverter would be needed for ac systems. If a brushed dc motor is used then the equipment will need to be pulled up from the well (approximately every 2 years) to replace brushes. Brushless dc pump motors would require electronic commutation. The most commonly employed system consists of an ac irrigation pump and inverter with a solar pv panel photovoltaic array.

Submerged irrigation pump with surface mounted motor. This configuration was widely installed with turbine pumps. It gives easy access to the pump motor for brush changing and other maintenance. The low efficiency from power losses in the shaft bearings and the high cost of installation has been disadvantages. In general this configuration is largely being replaced by the submersible motor and irrigation pumpset.

Reciprocating positive displacement irrigation pump. The reciprocating positive displacement pump (often known as the jack or nodding donkey) is very suitable for high head, low flow applications. The output is proportional to the speed of the irrigation pump. At high heads the frictional forces are low compared to the hydrostatic forces often making positive displacement pumps more efficient than centrifugal pumps for this situation. Reciprocating positive displacement pumps create a cyclic load on the motor which, for efficient operation, needs to be balanced. Thus, the above ground components of the solar pump are often heavy and robust, and power controllers for impedance matching often used.

Floating motor irrigation pump sets. The versatility of the floating unit set, makes it ideal for irrigation pumping for canals and open wells. The pumpset is easily portable and there is a negligible chance of the irrigation pump running dry. Most of these types use a single stage submersed centrifugal irrigation pump. The most common type utilizes a brushless (electronically commutated) dc motor. Often the solar pv panel array support incorporates a handle or 'wheel barrow' type trolley to enable transportation.

Surface suction irrigation pumpsets. This type of irrigation pumpset is not recommended except where an operator will always be in attendance. Although the use of primary chambers and non-return valves can prevent loss of prime, in practice self-start and priming problems are experienced. It is impractical to have suction heads of more than 8 meters.

Solar pumping technology methods continue to improve. In the early 1980s the typical solar energy to hydraulic (pumped water) energy efficiency was around 2% with the solar pv panel photovoltaic array being 6-8% efficient and the motor pumpset typically 25% efficient. Today, an efficient solar pump system has an average daily solar energy power to hydraulic efficiency of more than 4%. Solar pv panel photovoltaic modules of the monocrystalline type now have efficiencies in excess of 12% and more efficient motor and irrigation pumpsets are available. A good sub-system (that is the motor, pump and any power conditioning) should have an average daily energy throughput efficiency of 30-40%.

The output of a solar pumping system is very dependent on good irrigation system design derived from accurate site and demand data. It is therefore essential that accurate assumptions are made regarding irrigation water demand/pattern of use and irrigation water availability including well yield and expected drawdown. Contact us to start your irrigation system design.

Please call 520-369-AGRI or email if you would like solar irrigation pump system pricing or a more detailed analysis of costs for your particular application.
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