Off-grid solar water pumps have proved to be the most viable alternatives in areas where there is abundant sunshine and fossil fuels are very costly or un-viable. The proposed model of an off-grid solar water pump utilizes eight solar panels which are modular and can be easily oriented for maximum solar harvesting. The panels power a 0.5 HP D.C water pump to pump water from 5 M depth. The output from the pump is a one inch pipe outlet which can supply 1500 lit/hour of water on average. This means the daily requirement of 10000 litres of water for irrigation can be easily met in a normal sunny day considering seven hours of normal sunshine ( 9 A.M to 4 PM). The model also has an option to store the electrical energy in lead acid batteries which can be utilized to run the pump for a few (one to two) hours or for any D.C application like mobile phone charging, lighting etc. Excess drainage of battery is prevented by a cut-off circuit. The whole structure is mounted on a trolley which permits easy transportation. To conserve water, a micro-irrigation system is included which can be tailored to meet the farmer’s needs.
Description of the project
1. Project design.
The construction of the system is as shown in the attachment. The heart of the system is a set of eight solar panels which generate 24 V, 500 Watts of power in a normal sunny day. The solar radiation in most parts of India is available for 300 days on average. The panels are modular and can be easily assembled and disassembled with ease. The panels can be moved in and around for a few feet with flexible cabling for optimum solar energy harvesting. Solar energy harvested is fed to a maximum power point tracking(MPPT) charge controller which converts the electrical energy harvested from the panels into an usable range of D.C voltage. The charge controller has LED indications to indicate the charging process (viz) Charging ON, Low battery etc. The farmer/user has an option to select the output from the charge controller to be on either of the two modes.
In MODE 1: RUN MODE, the power from the controller is directly fed to the pump and water is pumped out for irrigation. In MODE 2 : CHARGE MODE, the DC power is utilized to charge a 24 V lead acid battery configuration which can be utilized either to run the pump or to power any of the DC appliances like charging mobile phones, DC lighting etc. later.
2. Cost analysis of the project
One of the key requirements of the project is that the total cost should be within Rs.One lakh. . The cost split is as shown below:
( i ) D.C. Pump ---- Rs 20,000
(ii) Solar panels, batteries ------- Rs 50,000
& cut-off circuitary.
(iii) MPPT charge controller --- Rs 10,000
(iv) Cables, irrigation systems
& accessories ---- Rs 10,000
(v) Structures and trolley ----- Rs 9,990
Total cost Rs. 99,990.
The prices mentioned above were calculated for a model assembled in Bangalore where the availability of components is not a constraint and also the place of the designer. However for other locations other factors like transportation, local taxes and other levies (VAT etc.) may add up to the total cost.
3. Irrigation system
Micro-irrigation promises better water utilization compared to conventional irrigation methods like flooding, constructing canals etc. They are also known to conserve water and save operational costs in the long run. However designing micro-irrigation systems to suit one’s(farmer’s) requirements is a major challenge and the systems have to be tailored to one’s needs. The method of irrigation system employed mainly depends on the topography of the plot and the type of plant to be cultivated. While drip irrigation may sound to be a generalized solution, other methods like micro-sprinkler irrigation can also be utilized depending on the nature of the plants. A well designed irrigation system will not only conserve water but in the end will also help to save the energy.
4. Operational aspects and portability:
The whole system can be positioned on any convenient location for maximum energy output. The operation does not require any specific expertise from the farmer’s/user’s side. Panels, batteries and the pump are mounted on a trolley which can be moved to any safe location and thus it prevents theft. Lead acid batteries require topping up with water once in a few months and keeping the equipment clean will make the system perform its best like any other electronic appliance. Good stability is achieved with the four wheels of the trolley.
5. Protection mechanisms
Two protection mechanisms are incorporated to prevent the equipment from wrong usage. The first protection mechanism prevents the excess power generated if any, from entering the motor when in Mode 1(RUN MODE) with an over current limiting circuit. The second mechanism cuts off the battery from draining below a certain voltage level harmful for the life of the life of the battery by incorporating a cut-off circuit.