Energy conservation prospects in water intensive Paddy-Wheat cropping system for groundwater pumping in the semi-arid region of Haryana

Study area

Sonipat district lies between latitude of 28°48′15″N to 29°17′10″N and longitude of 76°28′40″E to 77°12′45″E (Fig. 1) covering an area of 2,260.53 km². The Sonipat district is further divided into eight administrative blocks, viz. Sonipat, Rai, Murthal, Ganaur, Kharkhoda, Gohana, Mudlana, and Kathura. The present study was carried out in the Rai and Sonipat blocks of the Sonipat district. The area under the Rai and Sonipat blocks is 280.49 and 397.89 km², respectively, having sandy loam to loamy sand soil. The total number of electric pumping sets in Rai and Sonipat blocks during the year 2018–2019 were 5,136 and 6,897 compared to 3,456 and 4,587 during 2011–2012, respectively, showing that the numbers of electric pumping sets in these blocks are continuously increasing.

Sampling strategy

A total of 65 pumping sets (35 from Rai and 30 from Sonipat block) were selected randomly for the study. All were equipped with submersible pumps and were being operated by electrical power. The selected pumping sets operated at different water table depths using horsepower (HP) motors. The farmers’ irrigation practice was studied in detail at 10 of the selected 65 tube wells.

Energy assessment

The present study is based on data collected from farmers and actual parameters measured at the selected site during the period spanning from 2017 to 2020. All the information related to the pumping set, its owner and their landholding was recorded. For this, a questionnaire was prepared and used as a research tool for data collection per the study’s objectives.

In order to estimate the current level of energy consumption, pumping efficiencies, and potential saving of electricity consumption involved in groundwater pumping for irrigation, information/measurement on the following parameters as required: area of major crops under groundwater irrigation, actual and potential water application efficiency of the prevalent method of irrigation, net and gross irrigation requirement of the crops, actual and minimum expected efficiency of the pumping sets, groundwater depth and head losses in the pumping systems.

Efficiency of pumping sets

The overall efficiency of the tube well was computed as the ratio of estimated power consumption to meet water horsepower & the actual power consumption as under

(1)

All the selected tube wells were owned privately by the farmers, and no reliable record was available regarding the model/make of the pumping set and the design performance characteristics. The design/expected efficiency of the installed tube well, thus, was determined based on Bureau of India Standards (BIS) code IS 8034:2002. Knowing the number of stages for different pump sets (which was obtained from the farmers during the survey), the head per stage was determined by dividing the total head with the number of stages. Then, using the value of head per stage (m) and discharge (l s⁻¹) for pump sets, minimum efficiency was determined from standard charts given in BIS code IS 8034:2002. The efficiency in charts represents efficiency for three or more stages. For single-stage and two-stage pumps, the efficiency was multiplied by a factor of 0.97 and 0.98, respectively, as per instructions contained in the code. The efficiency thus obtained was further multiplied by the motor efficiency factor given in the same code. As per the BIS chart, the overall minimum expected efficiency of the pump set was estimated by multiplying it by the corresponding factor based on the number of stages and the corresponding motor efficiency factor.

(2)

Irrigation water application efficiency

Measurements at 10 farmer’s fields (five in each block) having tube well irrigation were carried out for wheat crops during 2018–2019 to assess the actual water application efficiency in the study area. All the farmers were using the border method of surface irrigation, and the cropping pattern was predominantly Paddy-Wheat. Generally, wheat receives 4–5 post-sowing irrigation in the study area. Knowing the bulk density, field capacity, and actual soil moisture measured in the root zone before irrigation, the required irrigation depth was computed at each selected farmer’s field (Michael, 2008). Applied depth of irrigation was computed for the first and fourth irrigation event based on the area of the border strip (A_b, m²), duration of irrigation (T_i, min), and discharge (Q, LPS) of tube wells, as given below.

Thereafter, the application efficiency was calculated as the ratio of required and applied irrigation depth for respective irrigations.

Data pertaining to irrigation practices at ten selected farmer fields are given in Table 1. Based on these observations, the actual water application efficiency of irrigation in the study area was found to be 62.6%.

Energy requirement

Knowing the water requirement of different crops and pumping efficiency (existing as well as the minimum expected), the energy requirement was estimated by using the following relationship:

(5)

Net irrigation requirements for wheat (325 mm) and paddy (975 mm) were adopted as per the recommendations of Dhindwal, Phogat & Hooda (2008). As indicated earlier, the water application efficiency was taken as 62.6% (Singh, 2021).

Overall and minimum expected efficiency

Electrical energy requirements for groundwater pumping in major crops grown in the Sonipat & Rai blocks were computed at the existing level of overall efficiency and based on minimum expected efficiency. The overall efficiencies of selected tube wells, as computed (Eq. (1)) based on actual measured power consumption, varied from 10.1% to 56.6% in the Sonipat block and 15.3% to 52.8% in the Rai block (Fig. 3). The difference between overall efficiency based on actual power consumption and expected minimum efficiency for different tube wells is also shown in Fig. 4. It can be seen that the actual overall efficiency of only two of the selected tube wells (TW-17 & TW-48) was higher than the minimum expected overall efficiency in the study area. The actual overall efficiency of TW-17 was noted as 56.6% against the minimum expected overall efficiency of 49.3% (i.e., 7.4% higher than the minimum expected efficiency). In comparison, the actual overall efficiency of TW-48 was noted as 52.8% against the minimum expected overall efficiency of 50.2%. The possible reason for the good efficiency of these tube wells may be that both the tubewells were newly installed at the time of observation, i.e., TW-17 (8-month-old) and TW-48 (3-month-old). For all other selected tube wells in the study area, the actual overall efficiency was lower by 4.5% to 38.7% from the respective minimum expected efficiency. It may be stated that most pump sets working in the study area are inefficient due to improper selection and poor maintenance of the pumps. The tubewell pumping sets in the study area were found to be working at an overall average actual efficiency of 26.1% & 32.5% against the minimum expected average efficiency of 47.6% & 49.7% in the Sonipat & Rai block, respectively. Further, it was also observed that some of the tube wells (e.g., 17 & 48) were found to be working at reasonably good efficiency, indicating that it is possible to bridge the gap between actual and expected minimum efficiency. Therefore, there is a lot of scope for energy conservation in the study area. Declining groundwater depth in the Rai block has resulted in increased energy demand over the years, and there is a need to improve water application efficiency and groundwater status in the study area.

Pump sets in the study area were found to be working at an overall average actual efficiency of 26.1% & 32.5% in the Sonipat & Rai blocks, respectively. These results are inline with previous studies conducted in the region. World bank in an energy audit of electrical pump sets in Haryana found that average overall efficiency of pump sets varied between 21–24% and only 2% of the pump sets had average overall efficiency above 40% (World Bank, 2001). National productivity council (NPC) reported average overall efficiency of pumps in Haryana to be between 25% to 35% (National Productivity Council (NPC), Government of India (NPC), 2009). Another study suggested that average efficiency of pump sets in Haryana is 34.7% (Sood, 2010). Pilot studies conducted under the Agriculture Demand Side Management (Ag-DSM) scheme suggested that efficiencies can be increased from the existing level of 35% to 50% by advocating replacement of existing pump sets to Bureau of Energy Efficiency (BEE) labelled pump sets (Tyagi & Joshi, 2019).

Energy use and savings

The energy requirement for groundwater pumping in wheat and paddy crop at different farmers’ fields according to their irrigated area (Fig. 5) was computed using Eq. (5) and is given in Tables 2 and 3. Irrigated area cropped by selected farmers varies between 0.81–7.69 ha and 1.21–4.86 ha in Sonipat and Rai blocks, respectively. Energy requirement at the current efficiency level was 1,162.8–12,976.1 kWh and 3,490.7–38,953.3 kWh for wheat and paddy crops, respectively, in tube wells from the Sonipat block, while it was 1,469.5–6,975.8 kWh and 4,411.5–20,940.7 kWh for wheat and paddy crop, respectively in Rai block. The average energy requirement at the current efficiency level for both wheat (4,354.0 kWh) and paddy crop (13,100.4 kWh) in the Sonipat block were recorded higher than the corresponding value for wheat (3,424.8 kWh), and paddy (10,280.9 kWh) crop in Rai block as the average overall efficiency of tube wells working in Sonipat block (26.1%) was lower than Rai block (32.5%), while the average irrigated area cropped in both the blocks was almost equal (i.e., 2.56 and 2.57 ha) in the Sonipat and Rai blocks, respectively. Further, it may be noted that the energy requirement for paddy crop is higher than that for wheat crop due to its high-water requirement. Similar observations were realized by Khan, Khan & Latif (2010).

One of the possible interventions to reduce the pumping energy requirement for the existing cropping pattern and irrigation practice is to improve the efficiency of the pumping sets. As can be noted from Tables 2 and 3, the average energy requirement can be reduced by improving overall efficiency to the minimum expected efficiency level resulting in 566.4–7,004.6 kWh and 1,700.3–21,027.4 kWh energy use for wheat and paddy crops, respectively, in Sonipat block (Table 2) and 909.2–4,577.4 kWh and 2,729.4–13,741.1 kWh for wheat and paddy crop, respectively in the Rai block (Table 3). Energy saving potential for different tubewells in Sonipat and Rai blocks through improved efficiency of pump sets for wheat and paddy crops is given in Fig. 6. Energy saving by improving overall efficiency from current level to minimum expected level varied between 30.2–79.3% and 8.9–70.8% in Sonipat and Rai block, respectively (Fig. 7).

Average energy use per hectare was 1,761.9 and 5,288.9 kWh/ha for wheat and paddy crops, respectively, in the Sonipat block. Similarly, this was 1,370.2 kWh/ha and 4,113.1 kWh/ha for wheat and paddy crops, respectively, in Rai block (Fig. 8). Energy savings of 913.3 and 2,741.5 kWh/ha can be realized in wheat and paddy crop, respectively by improving the overall efficiency of pumps from current level to the minimum expected level in Sonipat block. Similarly, for the Rai block, 518.0 kWh/ha and 1,555.1 kWh/ha energy savings can be realized in wheat and paddy crop, respectively.

Pump sets in the study area were working at lower overall efficiency of 26.1% & 32.5% against the minimum expected average efficiency of 47.6% & 49.7% in the Sonipat & Rai block, respectively. This suggests that replacement of exiting pumps with more efficiency pumps can be a viable option in the study area, leading to average energy savings of 48.3% and 35.9% in the Sonipat and Rai blocks, respectively. Replacement of existing irrigation pump sets with BEE/BIS approved ones resulted in energy saving of 23–37% during a pilot scale study conducted in Karnataka (Ravindranath, 2016). Similarly, 25% energy saving was realised by replacing about 2,209 inefficient pump sets from Mangalwedha subdivision of Solapur circle in Maharashtra (Nargundkar, 2017).

Efficiency can further be increased by proper design and installation of pump set according to pump characteristics curves, reducing other losses such as hydraulic losses, leakage losses, mechanical losses and disc friction losses in submersible pump set. Along with that other measures like improving cropping pattern by reallocation of crops and introduction of new less water intensive high yielding crops, accompanied by introducing water and energy saving technologies (like zero tillage, laser land levelling, and micro-irrigation, etc.) and ground water recharge can lead to substantial water and energy saving in the region.

Impact of groundwater level on energy use

It is evident from these results that there is great potential for energy saving in the study area by replacing the existing pump sets with suitable, efficient pump sets. However, the above intervention will be difficult to implement in the Rai block, where the water table is declining at a relatively rapid rate as compared to that in the Sonipat block (Fig. 9). Under declining groundwater conditions, properly selected pumps according to the groundwater depth at the time of installation may soon become less efficient due to the more rapidly changing groundwater depth with time. Therefore, in Rai block, until and unless suitable measures to control the decline in groundwater depth are undertaken (such as groundwater recharge and crop diversification towards less water-demanding crops), it may be very expensive to frequently replace the pumping sets to suit the resulting head on the pump due to declining groundwater depth. However, in the Sonipat block, where groundwater is not declining very rapidly, immediate replacement of inefficient pump sets with properly selected and efficient pump sets may be attempted to achieve the potential energy saving in groundwater pumping.

The estimated energy requirement in the Rai block for wheat and paddy crops considering the water table depth in 1990 and 2020, while other aspects kept the same, is shown in Fig. 10. The decline in groundwater depth has led to a considerable increase in energy demand in the Rai block. It can be clearly seen that if suitable groundwater recharge interventions can restore the groundwater level, the energy demand for different crops can be reduced considerably in the Rai block. For instance, the current energy demand for wheat crops in the Rai block based on a groundwater depth of 15.97 m is 11,059.1 MWh (Megawatt hour) and this would reduce to 6,696.6 MWh if groundwater depth can be restored to 1,990 level, i.e., 6.49 m depth. Similarly, the energy requirement for paddy crops can be reduced from 35,220.4 to 21,327.0 MWh by improving groundwater depth.

The groundwater table is an important factor affecting irrigation energy consumption. Most irrigated regions in the world are facing the problem of a continuous decline in groundwater, leading to an increase in irrigation energy consumption. The decline in groundwater level has increased the energy required for pumping the groundwater in many parts of India (Shah, 2009; Dhillon et al., 2018). Zhao et al. (2020) also attributed the decline of the groundwater table to an increase in energy consumption for pumping groundwater. It was also found that the decline of the groundwater table not only offset the effect of energy and water-saving measures but also consumed an additional 98.8 billion kWh of electric energy in the Hebei Province of China.

Most of the tube wells in the study area are already using low-friction HDPE pipes (High-Density Poly-Ethylene). However, in some of the tube wells, it was observed that head loss due to friction was quite high due to the use of a relatively small diameter column pipe. Therefore, in such tube wells, replacement of existing column pipe with large diameter column pipe may help to reduce the energy consumption. Likewise, the height of the delivery pipe may also be reduced to save energy consumption to a certain extent in the study area. Consumption of excessively higher energy by most of the pump sets compared to expected energy consumptions based on installed pump HP in the study area indicates that poor selection/maintenance of pump sets contributes a lot towards wasteful use of energy for the purpose of groundwater pumping. Non-availability of any authorized service centre for submersible motor and pumping sets was another major reason behind the lower efficiency of the tube wells. Farmers generally get repair work from local mechanics like rewinding & bush maintenance. The local mechanic has many limitations, like lack of proper training, machines, and tools. Also, they do not use authorized parts from reputed manufacturers and good quality materials for repairing these motors and pumps, which adversely affects the performance and efficiency of pumps.

This study has clearly indicated the need and scope of enhanced pumping efficiency of the existing tube wells in the study area. However, due to limited observation/information available under field conditions, it was not possible to identify the most effective strategy to be implemented to realise enhanced pumping efficiency of the tub wells. For instance, it was not possible to point out, on case to case basis, the actual rectification strategy to be adopted to achieve the desired level of pumping efficiency. For instance, in some of the cases it might be possible to achieved improved pumping efficiency through improved quality of pump repair and maintenance. On the other hand, in some of the cases, it might require the replacement of poorly selected pump set with a properly selected new pump set. Further there is need to implement suitable rectification measures on a pilot scale to demonstrate the actual energy saving potential for groundwater pumping.