This idea comes from our experience of working on small-scale solar solutions in India and of setting up small-scale pumping in Africa where this has been in use for 2 years irrigating a farm in Malawi during the dry season. The idea has also benefitted from our experience of working with solar pumping in the UK and Mozambique.
Each pumping kit, consists of 2 x 60W Solar panels, cables and a 24V DC50B-24130 centrifugal electric pump. Each pump also needs ¾ inch plastic tubing to extend from the pump in the water source to the field. Each pump, including solar panels, costs around 11,000 rupees.
The video shows a single pump being put in place in Africa. The outlet of the pipe coming from the pump can be moved manually to sprinkle water or can be placed in a stationary position with the water distributed by channels dug in the ground. It is possible to pipe the water over 100m from the source (in the video where the water is piped up to 150m from the source through ¾ inch tubing). The tubing for the pump can be buried for semi-permanent installation for part of the system.
The diagram shows multiple pumps being used in the same water source. Each pump is a fully working system, capable of working alone or alongside other pumps. Each pump is capable of raising at least an average of 7200 litres of water to 5m head per day in Bihar's drier months.
The drier months in Bihar are particularly November to April. During these months, a panel tilted at around 35 degrees to the south will receive insolation of an average of over 6 hours a day, rising to 7 hours a day in March and April.
The DC50B-24130 pump has a conservative estimate of flow when powered by 2 x 60W panels in direct sunlight of over 20l of water a minute at 5m head or 15l / minute at 9m head.
In Bihar you would therefore expect an average flow of a least 20 x 60 x 6 = 7200 litres from each pump per day during the drier months.
Each pump is therefore capable of covering 1440m2 to an average depth of 0.5cm per day. This gives an indication of what is possible with one pump. With 7 pumps you could irrigate 7 x 1350 = 10,080m2 to a depth of ½ cm. This is equivalent to half a cm of rainfall on a hectare each day.
Depending on the type of crops (and their requirements for irrigation) you could use between 1 and 9 pumps per hectare for a price of below 100,000 rupees.
Total cost 11,000 rupees for each pump or 99,000 rupees for 9 pumps
The cost of each pump including solar panels and cables is about 11,000 rupees (4000 rupees for each panel and 3,000 rupees for the pump). Added to this would be the cost of digging the well and of the ¾ inch plastic tubing to lead from the pump to the field. This should be very cheap although the expense will vary depending on where the water sources are situated in relation to the fields.
You could therefore use just one pump to produce 7200 litres of water per day, 7 pumps to produce enough water to cover a hectare with 0.5cm depth of water per day or even up to 9 pumps for below 100,000 rupees.
Furthermore, it is not necessary to pay all the money up-front. It is possible to start with one pump for 11,000 rupees and then add another a year later and slowly scale up. This presents much less of a cost barrier and much less financial risk than paying larger amounts up front for a single large system.
(The reason each pump is so cheap is that for just 5-10m head it is possible to use centrifugal pumps rather than more expensive screw pumps. Centrifugal pumps are both cheaper in themselves and also cheaper in their requirements for solar panels as they do not need as many solar panels to run.)
Each pump, including solar panels weighs a little under 15 kg. This would be easily capable of being transported on a bullock cart or even simply by a person. The installation also does not require any specific in situ apparatus except for a nearby water source. It is therefore both easy to transport and easy to move from one water source to another.
Robust, easy to maintain and flexible
The pump is easy to maintain with the electronics completely enclosed in a watertight plastic casing and with the pump mechanism easy to clean using just a screwdriver to take it apart into its three key components. Also, if you have multiple pumps supporting an area there is little impact if one is out of action whilst undergoing any maintenance. The multiple pumps also give significant flexibility in terms of where to irrigate and what size to irrigate at optimal cost.
Why we do not suggest using more complicated set up for the pump or for the irrigation method
This solution is very simple. One of the problems we found in prototypes is that using complicated systems is often too big a step for farmers that are not used to the technology. It appears people need something that is robust, simple and clear and easy to use. In particular, it appears that the more complicated a solution is, the longer it takes for farmers to use it optimally, if at all.
This is also why we are not suggesting to use water storage and drip irrigation as the added complexity makes success less likely and also increases up-front costs.
Further ancillary benefits
It would be possible to use these solar panels to charge a 12V car battery (preferably via a charge regulator costing about 600 rupees). We could have easily added this to the system above. However, this simple battery charging technology appears to spread very quickly once solar panels are available. So we suggest not designing a more complicated system to start with. Once the technology is available we would expect rapid uptake of solar panels for also charging 12V battery systems to provide power for lighting, phones and other electronic devices.