India’s government has encouraged the use of solar powered pumps in irrigation for more than 20 years, but this requires high subsidies. However, one Australian company's pump design could cut the cost of supplying India’s farmers with solar pumping power.
The Solar Pumping Programme was first started by India’s Ministry of New and Renewable Energy (MNRE) in 1992. However, by 2014, fewer than 14,000 solar pumping systems had been installed, a tiny proportion of the 18 million pumps connected to grid power and the 7 million pumps running on diesel in the Indian agricultural sector. Renewed efforts This low initial take-up of solar pumping systems was attributed to high start-up costs and lack of awareness among farmers. Since 2014, prices have come down and the programme has become more viable, so the Indian government has renewed its efforts to persuade farmers to use solar power. It launched the Solar Pumping Programme for Irrigation and Drinking Water in 2014 with the intention that, by 2021, one million solar pumps will be in use.
According to the MNRE, the agricultural sector consumes nearly 20% of installed power generation capacity in India. More than 4 billion litres of diesel and 85 million tons of coal are consumed every year to support water pumping for irrigation. An increased take-up of solar powered pumps would ensure a significant decrease in the country’s CO2 emissions, and provide reliable and affordable energy for irrigation. If one million diesel pumps are replaced with solar pumps, diesel savings could be as much as 9.4 billion litres of diesel over the life cycle of solar pumps.
Capital subsidies The government remains committed to increasing awareness and continues to support farmers with considerable capital subsidies, which consist of 30% from central government (MNRE), between 30-60% from state government and farmers contribute the rest. The Indian Renewable Energy Development Agency (IREDA), State Nodal Agencies (SNAs), and some private sector organisations also offer solar pumping support services and farmers can buy systems from certified manufacturers, through state governments, or non-governmental organizations (NGOs).
One of India's largest solar pump and power drive manufacturers, Rotomag Powerdrives India, works closely with the government to supply solar-powered irrigation pumps for agriculture. The company has recently signed an agreement with Brisbane-based New Fluid Technology (NFT) guarantying the use of its Supa-Stelth solar pump technology in Rotomag’s future generation of solar agriculture pumps.
Extensive evaluation The agreement came after Rotomag had carried out extensive testing and evaluation of the Supa-Stelth pumps and their related technology at its Vadadora labs. Rotomag concluded that it could cut the number of solar panels required for any given solar pump project by around 30% and so the amount of water pumped on a litres per hour of sunlight basis could be increased by over 30%. India works on an average ‘Solar Day’ for water pumping of 7.15 sunlight hours and by incorporating Supa-Stelth pumping technology, Rotomag can more economically supply the 75 million rural households in India who are off grid.
Wet-end focus Rotomag uses the latest Italian motor technology in its manufacturing process, building its own motors from scratch under licence. The company has been working closely with NFT to improve pump technology with the focus on the wet-end – the part that pumps the water. The Supa-Stelth pump technology has a wide efficiency curve and, in some cases, where the head height is not so great, the company says that it can cut down on the number of solar panels required by up to 50%. The Supa-Stelth works particularly well when farmers are using back-up power, such as during the night. Not only is the solar hardware cost reduced by 30-50%, but the back-up power also comes down by the same percentage.
Energy efficient The reason that Supa-Stelth pumps are more energy efficient is that NFT has improved and replaced the wet-ends. The motors used are standard motors and it is only a simple internal geometric shape change to the wet-end that achieves the performance advantages. The principle of operation is called a solid body rotation of fluids (or solid body vortex). The cost of pumping is directly related to the number of litres (or gallons) pumped per watt of power per hour (litres per watt hour.) It took NFT around ten years to develop this technology and the company says that, on average, Supa-Stelth pumps save over one third of running costs, but often much more. Test pumps are from 400 watts up to 2.2 kw, the legal global maximum for single phase input powered pumps.
Solid body vortex The water is accelerated via a high efficiency impeller, which draws the water into the casing, and starts to form a vortex. The water increases peripheral velocity until it “snaps” into a solid body vortex. Each molecule of water aligns radially with each other. NFT has also added a large diameter drum (spigot) integral to the impeller which assists in anchoring the vortex to the impeller so that the impeller becomes integrated into the vortex.
The Supa-Stelth pump develops its pressure by centrifugal force at the solid body vortex periphery inside the casing wall. The diameter of the water vortex is greater than the diameter of the impeller. The result is higher pressures and also greater efficiency than conventional centrifugal water pumps. In addition, the water undergoes less momentum and direction changes than with onventional water pumps. Pumps operating on the scientific principle of solid body vorticity outperform centrifugal pumps for efficiency, on average by 30%, but often more. The pumps do not require a diffuser or volute to realise a pressure gain. NFT says these in fact restrict normal pumps by acting as self-limiting valves between the pump outlet and the periphery of the impeller.
In addition, with conventional variable speed pumps, because rpm is varied, the diffusers or volutes, as physical devices. can only be optimised for one speed. Usually they are tuned for either 3000rpm 50hz or 3600rpm 60hz. If standard pumps then try to increase their rpm above, for example, 4000 rpm the water simply can’t pass through these restrictions. For similar reasons, if conventional pumps reduce their rpm, the hydraulic efficiency for the wet-ends is reduced. Any efficiency advantages usually come from the system itself.
However, the impeller in the Supa-Stelth pumps is, actually, a solid body of water that simply cannot change its shape because of the speed it repeatedly travels through the small vortex-shaping surface. This is the only hard surface that comes into contact with the solid body vortex impeller. The primary function of the physical impeller in Supa-Stelth pumps is to introduce the original priming water to create the impeller in the first place and it then continues to “feed the vortex” with new water. The impeller made of water can spin at much higher rpm than standard pumps.
VSD benefit Supa-Stelth pumps can and do use conventional induction motors. The greatest benefit though, is with variable speed drives, operating at much higher rpm than conventional pumps, efficiency increases as the rpm increases. Supa-Stelth pumps have been built and tested with an impeller diameter of 77 mm (3 in) and at 4516 rpm, can deliver a hydraulic efficiency of 75% at 267 litres per minute at a head of 157 kPA. With a 93 mm (3.66 in) impeller it can deliver 370 litres per minute at 455 kPA. This enables a one-stage Supa-Stelth pump to replace up to a seven- stage conventional pump for rural and irrigation purposes, simply by continually increasing its rpm. Supa-Stelth pumps naturally follow the same affinity rules of conventional pumps.
Using NFT’s technology on the high quality Rotomag motors gives the company and the Indian government an opportunity to cut the enormous cost of supplying India’s small plot farmers with off grid pumping power. The Indian government’s programme is likely to be a work-in-progress for many years to come but already, many parts of India are seeing the benefits. Solar irrigation pumping has enabled small-plot farmers to increase their productivity and crop intensity, without a huge amount of personal financial outlay and using a greener, cleaner, more sustainable method. Indian farmers are now able to grow more crops, increase their income and improve and protect food security into the future.
