One of the popular and widespread applications of solar photovoltaic technology is in pumping application. The beauty of this application is that it allows anyone located in any corner of the world to be able to pump water either from ground or rivers, dams, other sources.
Solar pumping may be used for
- drinking water,
- water supply in rural areas,
The biggest advantage of solar powered pumps are that they allow the capability to use them at any place which receives sunshine. Hence, it removes the difficulty and high costs of installing and bringing a grid transmission and distribution infrastructure to that location . In fact in many developing and even developed economies, sometimes the cost of bringing the transmission and distribution line to the final user location is far higher than even putting up the relevant capacity of solar pumping system. Further the solar system saves the additional running costs, maintenance costs and difficulty, etc.
The solar pumping system typically consists of following components ;
- Solar Photovoltaic modules
- Mounting structure for above solar modules
- Protection systems for DC and AC side so as to protect the pump, solar modules, controller, etc
- Other minor accessories
The rest of the components are similar to other solar systems. But the pump and the controller are different. In fact a normal solar inverter is usually not the ideal choice for solar pumping systems.
Further it is to be noted is that most solar pumping systems today do not use any kind of battery. This helps in avoiding the cost of battery and also improves the system efficiency and performance. Further the associated replacement costs of batteries are also avoided in future.
Presented here is a general overview of the types of pumping systems and their applications, suitability
Types of solar pumping systems
Solar pumping systems can be classified first of all based on the type of pump.
Usually the pumps used fall under following classiciations :
- DC pumps.
Of course it goes without saying that the DC ones used a DC motor which are permanent magnet based. Nowadays many pump-motor manufacturers are offering BLDC (Brushless DC) motors to improve the system reliability, performance and to reduce the maintenance costs.
Some manufacturers have an in-built controller for the solar photovoltaic input, whereas other manufacturers have a separate solar pumping controller. The DC pumps have the advantage of avoiding the conversion losses of Solar PV DC input to AC. But they have the disadvantage of having a higher cost and also the inability to get it repaired easily due to limited knowhow available in markets about DC motors.
- AC pumps.
Asyncronous induction AC motors are very widely used in solar pumping systems . However, a special controller is needed between the solar modules and the pump so as to first of all convert the DC power from the solar panels into AC 3 phase or single phase supply. And secondly to regulate the power coming from solar panels so as to ensure that the AC motor does not get damaged. Since AC technology is very well spread and widely used, hence these pumps are more cost effective. Further they have the advantage of being easier to repair since the knowhow is widely available. Even AC pumps are available in very high efficiency versions.
Apart from the classification of solar pumping systems based on the types of motor. There is also a classification of pumping systems based on the pump category type.
- Borewell submersible pumps
This is one of the most widespread application of solar pumps. It is very similar to using a normal submersible borewell pump , but rather it is powered by solar instead of Grid supply or DG supply.
These pumps are inserted in the borewell and remain submerged in water.
The size of the pump and motor is chosen so as to match the borewell Diameter. So in case a borewell dia is 150mm, then one may choose a pump which can fit inside this dia. However in some cases the dia may be smaller, eg. 110mm. In such cases the pump must be selected accordingly.
Both AC and DC pumps are used for this application.
DC pumps are typically available in power ratings ranging from 0.5HP upto 3HP. Few manufacturers also offer 5HP models. The DC pumps require a solar controller to ensure proper regulated solar DC input voltage is fed to the motor.
AC pumps are also used here in ratings from 2HP going onwards upto even as high as 40HP and in some cases even higher.
Howerver, it is preferable to use higher energy efficiency AC pumps so as to make a better utilization of the solar system (which is in fact the costlier part of the whole system).
These types of solar pumps are available with the capability to lift water from depths as high as 500 meters.
- Openwell submersible pumps
For sites where there is an openwell, in such cases it is not very ideal to choose a borewell pump. Hence, in such cases it is better to choose an openwell submersible pump. Usually these pumps are monobloc.
They are available in DC and AC versions.
Power ratings can range from 0.5HP upto as high as 20HP or even higher.
- Surface monobloc pumps
Another very widespread and common usage of solar pumps is for low head applications or other applications where the water is being lifted from a river or a dam. In such cases it is ideal to choose a surface monobloc pump. They offer a better discharge and can be easily repaired or checked in case of any problems.
These pumps are available in DC and AC variants.
DC models are available in power ratings from 0.5HP going upto 3HP.
However, AC models are available from as low as 1HP and can go as high as 100HP or even higher.
As has been discussed above there are a wide variety of options for solar pumping. It is very important to wisely choose the right model at the time of purchase itself. In case of doubts, it is always better to contact the vendor or the manufacturer and take their help in choosing the right pump model to best meet your site conditions and requirements. One of the important factors in choosing the pumps is also the solar radiation conditions of the site, pattern of usage (eg. Only few months in a year or round the year, etc) , water flow requirements (in terms or Liters per day), the Head of water and discharge head, etc.
DC and AC pumps have got their own advantages – disadvantages. However as per currently available models DC pumps are available upto limited power ratings by most manufacturers. Whereas AC pumps are available for a very wide and even for very large power ratings. Further AC pumps have the advantage of being much more easily serviceable in the future. However, DC pumps have the advantage of being more appropriate for smaller power ratings such as 0.5HP , 1HP , etc.