One of the largest single users of energy is agriculture, and within this field, the energy used for irrigation is quite significant. Approximate estimates indicate that ground water pumping requires more than 16x109 kwh of electricity and about 2,000 million liters of diesel oil annually.
The requirement of energy for pumping groundwater, can be reduced if the power for this purpose is used most efficiently, which implies designing an efficient well assembly and having an efficient pumping unit and using the pumped water in the most efficient manner in the field. A preliminary analysis of energy used in irrigation suggests that 30 to 50 % of the total energy used could be saved through improved technology. i.e. more efficient valves pumps, proper design and construction of well and by better use of the water that is applied. Improper selection of pump, prime mover and well assembly, inadequate maintenance and faulty operation of the unit and other factors also contribute to the low efficiency of the system.
Causes of Low Efficiencies
Undersized PipesIf pipes of smaller diameter are used, the initial cost will be less but the frictional head loss and the operational cost will be more. On the other hand, if pipes of larger diameter are used, the initial cost will be more but the frictional head loss and thereby the operational cost will be less. The optimum diameter of the pipe will have minimum total cost i.e. the initial and the operational cost. The farmers, while selecting the pipe size, give consideration to the initial cost only without bothering about the extra operational cost which they have to pay every year by way of increased energy bill. It is a general practice that with 100x100 mm pump, the suction and delivery pipes of 100 mm diameter are used. The velocities in the suction and delivery pipes should generally be lower than that at the entry and exit of the pump.
High Delivery Point
Large number of pumping units have extra-ordinary high delivery point. This is especially true for diesel units. Excessive height of delivery pipe causes extra energy consumption.
The fittings provided by most of the farmers are very poor resulting in large losses and leakage. Head losses in a poor quality foot valves are high. Similarly the head loss in the sharp bends are also high. The farmers are mostly ignorant about the operational quality of the components.
Field study has indicated that average efficiency of the pumps operated by electric Motors is 47% and about two third of the pumps are operating at efficiencies less than 50%. Similarly the average efficiency of the pumps with diesel engines is 56% and more than half have efficiency less than 60%. Some of the pumps are operating at efficiencies less than the optimum efficiency because the units are not operating in the high efficiency range of Q and H. This is due to improper selection of pumps and mismatching prime movers and due to inferior quality of the pumps being marketed. The selection of the pumps should be governed by the characteristic curves i.e. the efficiencies in the various ranges of Q and H valves. At the normal operating condition, the efficiency should be maximum.
Faulty Prime Movers
The prime movers of the pumps should be of proper size. Generally farmers go in for higher capacity motors and diesel engines. Generally the foundations and the belt transmissions are in poor shape. The farmers should be properly guided to choose the suitable sized prime mover, provide proper foundation and belt transmission, and to select the pump so as to take advantage of high efficiency of the pump.