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Water Pumping and Groundwater Depletion - Comparison of Different Energy Sources for Water Pumps: Grid, Solar and Diesel

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Introduction

When comparing grid connected, diesel powered and solar water pumps different parameters have to be taken into account.

For the decision which energy source the water pumping system should run on, externalities, which are mainly of ecological nature (see this energypedia article), are almost never taken into account. Therefore ecological benefits are commonly not decision-relevant for farmers. The reason could be that external effects and environmental consequences of groundwater pumping are harder to observe than private economic costs and benefits. Even though monetization of external costs could be a valuable step, farmers in developing countries – where by far the highest share of irrigated area is located [1] – do very often not have the freedom to care about environmental arguments which is a plausible reaction when struggling with the non-availability of sufficient food.


Advantages and Disadvantages of Grid Connected Systems

Disadvantages

Economic Aspects

Under economic aspects the grid connected solution is an alternative which can be taken into account only under the precondition that a grid connection is already available before the water pumping project is planned. If that is not the case, like in large parts of the world, then the grid connected water pumping system won’t be feasible. In Sub-Saharan Africa, more than 600 million people across almost 50 countries have no access to electricity and in India this number is around 300 million [2]. Also in remote areas in rich countries like the US, an extension of the power supply is either too expensive or not feasible because of natural conditions. Meah et al. [3] state that the cost of extending a distribution line run from 10,000 USD to 16,000 USD per km. This is clearly too much to pay for a farmer or any other end-user especially considering that not only the building costs have to be covered but also the maintenance of the line has to be ensured. People who benefit from remote water pumping could not pay for these costs either [4].


In addition to the costs of setting up and maintaining a distribution line, comes the problem of an unreliable grid in many countries. In western and southern India for instance – the country with the largest irrigated area (39 million hectares) [5] – the government has subsidized electricity for irrigation purposes. It is available at very low (one or two cents per kWh) to no cost and therefore provided irregularly during off-peak periods. This provision of heavily subsidized electricity leads to groundwater over-pumping [6][7]. The off-peak periods are usually during night time, when it is dangerous and unproductive to be outside on the fields. The irregular access to energy forces the farmers to grow low value crops that can tolerate infrequent water supplies keeping them financially dependent on the subsidy. Besides, the utilities make no money in this distorted market and have no incentive to approve electric water pumping applications leading to a pent-up demand. Also no incentive to increase the efficiency of electric pumps is given with the effect that electric pumps show an efficiency range of 15-20%. This is highly wasteful knowing that 75% efficiency is attainable [7].


Environmental and Social Aspects

From an environmental point of view, grid driven water pumps can only be sustainable, if the electricity is produced with as little as possible emissions because the emissions of various gasses emitted by combustion of fossil energy sources like coal is related to climate change as well as health hazards [8]. Staying with the example of India, this is not the case. The largest share of electricity production is covered by coal (60%) and only 15% by hydropower [9]. In the International Energy Outlook 2016, coal has also worldwide the largest share of electricity production (40% in 2012). In the report’s reference projection it won’t be until 2040 that renewable generation surpasses coal as the source of electricity generation with the highest share [10].


Advantages

On the other hand grid connection allows for the possibility to sell excess energy produced by stand-alone systems back to the grid. This is a very effective method to minimise water pumping and use energy efficiently. Combining a solar pump with grid connection would be an ideal concept to counteract groundwater over-exploitation [6]. The precondition of an already existing grid connection is of important because of the above mentioned high costs of extending the distribution line.


Conclusion

In conclusion it can be stated that grid connected water pumps are only a suitable option if first, a grid connection already exists at the water pumping installation side, second, the electricity supply via the grid is stable and third the energy supplying the grid is mainly if not entirely produced out of renewables. As outlined these conditions won’t be met either easily or soon and therefore alternative systems of power generation are needed.


Comparison of Solar Powered and Diesel Powered Water Pumping Systems

Stand-alone systems like solar and diesel can improve rural electrification [8] and in the following these two systems are compared.

The only difference between a diesel and a solar powered system is the source of energy that is utilized. Diesel pumping systems use an electric generator and a PV system includes solar panels. The other system components stay the same: pump, controller/inverter, power cables, draw down pipes and accessories [3]. For that reason the source of power generation is decisive when comparing both options.


The following table gives an overview of advantages and disadvantages of both, solar powered and diesel driven systems. Except for the disadvantage of noise and air pollution from diesel pumps, the other factors are of certain economic nature.

Type
Advantages Disadvantages
PV pump Unattended operation High investment costs
Low maintenance costs Water storage is required (cloudy periods, night)
Long lifetime (low average yearly costs) Repair often requires skilled technicians
Diesel pump Fast and easy installation Fuel supplies erratic and expensive (high operational costs)
Low investment costs
High maintenance costs

Short life expectancy

Noise and air pollution

Source: Author based on Abu-Aligah (2011)[11]

It becomes clear that the advantages of the PV pump are the disadvantages of the diesel pump and vice versa. Diesel pumps require low initial investment costs but have high operation and maintenance costs. The investment costs of solar pumps are high but these pumps do not require a lot of maintenance and operational costs are zero as PV runs on solar.


Private Economic Costs

The private economic costs (external costs and benefits are not included) of solar water pumping systems can compete with diesel powered systems when the solar system is adequately designed and operational and maintenance costs are considered [12]. According to Al-Smairan (2012) [4] the total life cycle cost of a solar pumping system is almost three times less than the life cycle cost of a diesel pumping system. The life cycle costs include investment costs, operation and maintenance costs along the system’s life time. And Chandel et al. (2015) [13] state that “The overall upfront cost, operation and maintenance cost, and replacement of a diesel pump are 2–4 times higher than a solar photovoltaic (PV) pump”.


The decisive cost factor of a solar water pumping system remains the high investment cost of the panels [4] even though the price of solar panels is declining in recent years [4][14]. Apart from pump or controller failures solar modules normally only need cleaning, which can be done by unskilled labour. This keeps the maintenance costs low or even for free [11][3]. Diesel based systems on the other hand require fuel and despite short-term fluctuations fuel prices are increasing in the long term [11] and so do operational costs for diesel pumps. Also maintenance costs of diesel engines are significantly bigger resulting in the fact that solar water pumping systems are cheaper in the long run [4].


Reliability and Efficiency

According to Abu-Aligah (2011) [11] solar powered systems are more reliable than diesel engines, which is evident in field where thousands of rusting diesel engines lie unused. The reliability of solar systems requires sunlight and a solar water pump is hence not working during cloudy and foggy days [15].


Abu-Aligah (2011) [11] provides two solutions to counteract this problem:

First, batteries can be coupled to the system. These systems are called battery-coupled systems. The electricity produced during daylight hours charges the batteries and the pump can be used whenever water is needed. The downside of this solution is that the efficiency of the overall system can be reduced. The voltage supplied by the PV panels during maximum sunlight conditions can be higher by one to four volts than the voltage supplied by the batteries and because the operating voltage is determined by the batteries, the system’s efficiency is reduced in this situation. An appropriate pump controller which boosts the battery voltage supplied to the pump can minimize this reduced efficiency.

Second, water storage possibilities can be attached to the system. These systems are direct-coupled and they are designed to only pump during the day. Water can be stored in tanks which can be elevated in order to gravity-feed the irrigation system. During sunny days the storage tanks are filled with water which can then be used during the night or cloudy days. The capacity of the water storage depends on climate and pattern of water usage. Drawbacks of this solution are evaporation losses, if the storage tanks are open, the additional costs of the water tanks and the possibility that the water in the tanks might freeze during cold weather. Nevertheless most PV pumping systems use this solution of storing water in tanks or reservoirs.


The amount of water pumped with a direct-coupled solar pumping system totally depends on the amount of sunlight and the type of pump. The efficiency of a solar pump is not steady and changes throughout the day with the intensity of the sun and the angle the sunlight hits the PV panels. During low-light periods (in the morning and late afternoon) the efficiency can drop by 25% or more and during cloudy days the pump efficiency will be even less. Under optimum sunlight conditions (on sunny days during midday) the solar powered pump works near 100% of efficiency [11]. Diesel powered pumps on the other hand can work continuously at certain efficiency if the diesel fuel supply is ensured. In most circumstances an efficiency of 70% to 80% should be achievable for diesel pumps [16].


Environmental and Human Health Impacts

When comparing the environmental impact of a PV and a diesel powered pumping system, one has to take into account a product’s whole life cycle – from production to recycling. The Life Cycle Assessment by Armanuos et al. (2016) [17] shows that PV pumping systems have a way smaller negative impact on natural resources depletion, human health, climate change and ecosystem quality that diesel powered ones. Nevertheless solar powered irrigation systems do still have a negative impact on these four categories.


The negative impacts of solar systems depend on the kind of solar panels that are used and on the recycling infrastructure. Silicon based photovoltaic solar panels have a very much higher negative environmental impact than organic ones. Organic solar photovoltaic (OPV) panels are on the other hand less efficient and have a shorter life time than silicon PVs. The potential of increasing the ecological advantage of solar pumping systems compared to diesel powered pumping systems even further lies in increasing the efficiency and lifetime of OPVs and in the implementing of full-scale silicon recycling processes, which are right now not existing [18].


Summary

When comparing solar pumps with other sources of energy one has to keep several factors in mind. Depending on for instance the location but also e.g. market distortions like subsidies on electricity and diesel which would decrease the costs of these options, the following advantages and disadvantages of SPIS can be summarised.


Advantages of Solar Powered Irrigation Systems (SPIS)

In remote areas with high solar radiation solar pumps have proven to be cost effective and a dependable method for water pumping [4][19]. At the end of remote supply chains grid connection is not available and an extension of the power supply system would be too expensive. The world’s poorest might also not be able to afford diesel as world demand increases and so do fuel prices [11][4]. In addition the mere availability of fuel could already be a problem in remote areas. In addition of providing water, SPIS also increase rural electrification rates in general which is a major challenge in large parts of the world [2].

To reduce the dependency on fossil fuels or coal based electricity is also beneficiary in less remote areas. First, for environmental and health reasons as solar panels are less environmental unfriendly and do not create noise and create air pollution [13].

The cost effectiveness of SPIS is given when considering the whole (and longer) life span of the solar pumping system with a higher reliability than diesel based ones [4][13][12].

High solar radiation and the need to irrigate crops very often go together which can be derived from the fact that developing countries have the highest share in irrigated areas [1].


Disadvantages of Solar Powered Irrigation Systems (SPIS)

Solar radiation strongly depends on the latitude and climate [4]. There are ways (battery, water tank) to counteract the problem of reduced efficiency when insulation decreases but they come with reduced system efficiency and higher costs [11].

The increasing costs of the system are a problem when considering the already high investment costs which are very often the relevant obstacle of investing in SPIS [11][4][19].


Conclusion

Solar powered irrigation systems show several advantages over electric and diesel based systems as outlined above and their utilisation is a valuablestep towards more sustainability in irrigation practices. Nevertheless, the problem ofgroundwater depletion cannot be overcome by SPIS. As outlined in this energypedia article, groundwater preserving water pumping obligatory requires regulation, enforcement of the rules and monitoring.

Further Information

References

  1. 1.0 1.1 FAO, 2012. World Agriculture Towards 2013/2050: The 2012 Revision (No. 12–3), ESA Working Paper. Global Perspective Studies Team. http://www.fao.org/docrep/016/ap106e/ap106e.pdf. Cite error: Invalid <ref> tag; name "FAO, 2012" defined multiple times with different content
  2. 2.0 2.1 Brent, W., 2017. India: Ground zero for scaling electricity access and SDG7. http://www.powerforall.org/blog/2017/8/8/india-ground-zero-for-scaling-electricity-access-and-sdg7. Cite error: Invalid <ref> tag; name "Brent, 2017" defined multiple times with different content
  3. 3.0 3.1 3.2 Meah, K., Fletcher, S., Ula, S., 2008. Solar photovoltaic water pumping for remote locations. Renew. Sustain. Energy Rev. 12, 472–487. doi:10.1016/j.rser.2006.10.008. https://www.researchgate.net/publication/222015334_Solar_photovoltaic_water_pumping_for_remote_locations. Cite error: Invalid <ref> tag; name "Meah, 2008" defined multiple times with different content Cite error: Invalid <ref> tag; name "Meah, 2008" defined multiple times with different content
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Al-Smairan, M., 2012. Application of photovoltaic array for pumping water as an alternative to diesel engines in Jordan Badia, Tall Hassan station: Case study. Renew. Sustain. Energy Rev. 16, 4500–4507. doi:10.1016/j.rser.2012.04.033. http://bit.ly/2hdsIjM. Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content Cite error: Invalid <ref> tag; name "Al-Smairan, 2012" defined multiple times with different content
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