Surface pump. Surface pump is usually installed above the water level which requires a suction lift. It is used to get discharge from an open well, pond or river where high flow and small head (height to which the water needs to be lifted to) are required. There are many different types of pumps available, and DC surface pumps with total lift up to 21m (70 feet) are easily available in India.
Submersible pump. This pump is basically a hermetically sealed motor. The whole assembly of submersible pump is submerged in the water to be pumped up. It is generally used for pumping water from small-bore wells, and is designed to fit inside the drilled bore. The well may be anywhere from a few metres to 550 metres deep. But the deeper the well, the more powerful and expensive would be the system. The 0.25HP to 3HP pumps are easily available in the market. DC submersible pumps with total lift up to 92m are quite common in India.
Submersible pumps have the ability to lift water to a greater height. So these pumps are also used for water transfer applications from a canal to storage tanks or from an underground storage tank to an overhead tank.
Pump to buy
Before buying a pump you should know the depth at which water is available, daily water requirement and type of irrigation system to be installed. You may also need to know the water flow rate and the total head of the pump. You should buy a pump having the best efficiency. The best combination of head and flow rate at the least energy consumption gives the best pump efficiency.
The performance graph of 1.5HP motor pump available from a vendor is shown in Fig. 3 as an example. To interpret the graph and the table, let us say you have an input power of 400 watts from the PV array and you want to lift the water to a height of 40 metres at a flow rate of 12 litres per minute. As per Fig. 3, you would need a 1.5HP pump-set with pressure of 56.88psi or 392 kilopascals (392kPa).
Next step is to decide whether you should go for AC pump or DC pump. Though a DC pump can be run directly from a solar PV array, it has very limited range as compared to AC pump. The DC pump costs more than AC pump with the same category and the same head. But if a DC pump is available in your local market that meets your requirement it can be worth buying. “One should buy AC submersible pump, because the maintenance for submersible is almost nil as compared to DC pump,” says Hitesh Kapuriya, assistant manager, JJ PV Solar Pvt Ltd.
Indian manufacturers of pump-sets for various applications can be found at http://www.pumpsindia.com website. The type of motor pump, the wattage of the solar module, accessories, etc are some of the decisions you have to make. So before buying the system you should check the following:
1. Solar water pump installation site. You should first check whether it is to be installed near a pond, river, well or somewhere else.
2. Pump setting depth. The accessories required for underground installation would be different and add to overall cost.
3. Requirement of daily water. If you need more water per day, you need heavier and powerful equipment.
4. AC or DC pump. For AC pump, you need solar panel, pump controller (inverter), module mounting assembly and accessories like cable, connectors and pipe. For DC pump, pump controller would not be required in case of direct connection with PV panel.
In addition, you may consider installing solar trackers and pump protection units. The complete system should be tested and certified by an authorised test centre to get the best performance and water discharge norms as specified by the ministry.
Various capacities of DC surface and AC submersible pumps available from a vendor are listed in Table III, just for information.
Current scenario in India
Nearly sixty percent of Indians work as farmers in the field of agriculture. But due to non-availability of electricity in remote areas, irrigation becomes difficult even if the land is fertile as it depends majorly on rainfall only. Solar energy can save not only electricity but also save Indian farmers (during drought and scanty rainfall) who are otherwise prone to suicide. Solar water pumping systems can make irrigation possible even in remote areas. The pumps are available for various types of irrigation, including paddy fields, horticulture farms, gardens, etc.
“The present scope of solar irrigation system in India is very good because there is support from nodal agencies in the states like Rajasthan, Bihar, etc. The Ministry of New and Renewable Energy, government of India, gives 30 per cent subsidy for a five horsepower solar water pump set,” says Hitesh. Unfortunately, “Average cost of solar water pumping system is Rs 450,000. Government policy for subsidy is having restriction up to 5HP solar pump only,” adds Hitesh.
Besides the high cost of solar irrigation systems at present, another problem is the lack of awareness of the benefits amongst the farmers and consumers.
The future scope
With advancements in technology, the systems can be made more user-friendly. You can control the motor pump from a remote location using your mobile phone. You can get water level indication of the reservoir and overhead storage tank in your mobile phone. These technologies are already available in the market, though presently they are not so popular.
For further information on this subject you may refer to ‘Irrigation Automation Opportunities in Rural Areas’ article published in January 2012 issue. Also, you may refer to DIY articles on related topics, such as ‘Cellphone-Based Remote Controller for Water Pump’ published in January 2013 and ‘GSM-Based Borewell Water-Level Monitor’ published in May 2012 issues.
The author is a B.Tech (electronics & communication) from Punjab Technical University