A reliable and clean water supply is an essential need but a large number of people currently lack this basic provision. Solar water pumps is a socially and environmentally attractive technology to supply water. Especially if the need for water is in remote locations which are beyond the reach of power lines, solar power is often the economically preferred technology.

Introduction

Solar water pumps can supply water to locations which are beyond the reach of power lines. Commonly, such places relie on human or animal power or on diesel engines for their water supply (Omer, 2001). Solar water pumps can replace the current pump systems and result in both socio-economic benefits as well as climate related benefits. The water supplied by the solar water pump can be used to irrigate crops, water livestock or provide potable drinking water.

A solar water pump system is essentially an electrical pump system in which the electricity is provided by one or several PhotoVoltaic (PV) panels. A typical solar powered pumping system consists of a solar panel array that powers an electric motor, which in turn powers a bore or surface pump. The water is often pumped from the ground or stream into a storage tank that provides a gravity feed, so energy storage is not needed for these systems. A typical installation is illustrated in Figure 1.

Figure 1: A solar water pump system

Feasibility of technology and operational necessities

There are two main types of solar water pump technologies: a) the centrifugal pump, which uses high speed rotation to suck water in through the middle of the pump. Most conventional Alternating Current (AC) pumps use such a centrifugal impeller. However, when operating at low power the performance of the pump drops dramatically. This makes centrifugal pumps less suitable for solar applications, since low power due to cloudy weather is to be expected; and b) the positive displacement pump, which usually uses a piston to transfer water (Short & Thompson, 2003). Many solar water pumpts use the positive displacement pump, which brings water into a chamber and then forces it out using a piston or helical screw. These types generally pump slower than other types of pumps, but have good performance under low power conditions and can achieve high lift. Since PV is expensive and is an intermittent power supplier, solar pumps need to be as efficient as possible. Efficiency of the pump is measured in the amount of water pumped per watt of electricity used.

Two types of pump exist: submersible pumps and surface pumps. It depends on the water source which pump type is more suitable. In the case of a well, the pump needs to be placed underwater. Surface pumps can be placed at the side of a lake or, in the case of a floating pump, on top of the water. Surface pumps are less expensive than submersible pumps, but they are not well suited for suction and can only draw water from about 6.5 vertical meters. Surface pumps are excellent for pushing water over long distances.

Other options for remote watering exist. In Table 1 the option of solar water pumping is compared to several other remote watering options.

Status of the technology and its future market potential

PV water pumping has become a widely adopted solar energy technology in the last two decades (Firatoglu & Yesilata, 2004). Ten thousand PV water pump systems were installed worldwide up to the year 1993 (Barlow et al., 1993). This grew over sixty thousand systems by 1998 (Short and Orlach, 2003)

Rapid expansion over the last two decades of the global solar PV market has occured, with an average annual growth rate of 40 % (IEA, 2010) and 60% between 2004 and 2009 (REN21, 2010). A record 7GW of new grid-connected capacity was added in 2009, bringing total grid-connected capacity to 21GW with off-grid PV accounting for an additional 3 to 4GW. Crystalline silicon and thin film solar systems are in the early phases of rapid market deployment, and third generation and concentrated solar PV are currently in the R&D and demonstration phase.

While solar water pumps are much more small scale applications compared to PV technologies such as concentrated solar PV, the rapid expansion of PV technologies in general will benefit the deployment rate of solar water pumps. Since the main barrier to wide scale deployment of solar water pumps is the high initial capital costs due to the PV array, and the rapid expansion of PV technologies is leading to reduced prices for PV systems, it is expected that the solar water pump technology will reach higher penetration levels.

The IEA (2010) forecasts an average annual market growth rate of 17% in the next decade, leading to a global cumulative installed PV power capacity of 200 GW by 2020 and 3000GW by 2040 (with repowering of older systems). This would represent roughly 11 percent of global energy demand should this scenario play out. In terms of technology, the market share of thin films is expected to grow to 35% by 2013, due to constraints in the availability of high grade silicon.

Contribution of the technology to social development

Solar water pumps contribute to social development in several ways. Since other remote water supply systems are less reliable than solar water pumps. The use of solar water pumps therefore provides a reliable, safe and adequate water supply which improves the community's health. Other benefits to social development are the improvement of social cohesion within the community, reduced migration out of the community, and increased community interaction in social events due to increased time availability (Short & Thompson, 2003).

In addition, in many developing countries there is a strong link between gender and water. In many developing countries, women are responsible for the water supply, spending a large portion of their time to gather the water. The use of solar water pumps can have considerable positive effects for women in these communities (Short & Thompson, 2003). The scope of these benefits is very broad. For instance, the adequate water supply improves the personal hygiene of women but also allows them to allocate more of their time to the other activities (Short & Thompson, 2003). After installation of solar water pumps women in these communities might allocate more time to activities such as education or foodgathering (WaterAid, 2001).

Contribution of the technology to protection of the environment

Solar PV systems, once manufactured, are closed systems; during operation and electricity production they require no inputs such as fuels, nor generate any outputs such as solids, liquids, or gases (apart from electricity). They are silent and vibration free and can broadly be considered, particularly when installed on brownfield sites, as environmentally benign during operation. The main environmental impacts of solar cells are related to their production and decommissioning. In regards to pollutants released during manufacturing, IPCC (2010) summarises literature that indicates that solar PV has a very low lifecycle cost of pollution per kilowatt-hour (compared to other technologies). Furthermore they predict that upwards of 80% of the bulk material in solar panels will be recyclable; recycling of solar panels is already economically viable. However, certain steps in the production chain of solar PV systems involve the use of toxic materials, e.g. the production of poly-silicon, and therefore require diligence in following environmental and safety guidelines. Careful decommissioning and recycling of PV system is especially important for cadmium telluride based thin-film solar cells as non-encapsulated Cadmium telluride is toxic if ingested or if its dust is inhaled, or in general the material is handled improperly. In terms of land use, the area required by PV is less than that of traditional fossil fuel cycles and does not involve any disturbance of the ground, fuel transport, or water contamination (IPCC, 2010).

While the use of PV technology provides several environmental benefits compared to traditional technologies, care should be taken that the installation of the solar water pump does not increase the use of groundwater so that supplies are depleted. Especially in the case where the initial capital costs are covered by a grant or other financial arrangement, the water supplied is more economical to the users compared to the original situation. This might increase water use. One approach to reducing this possible problem is to maintain water price for the users on the original level, and invest the extra money into a community development fund. For example, a solar water pump project in Thailand used the community development fund to invest in solar lighting systems.

Climate

When solar water pumps replace either diesel generated electricity or grid based electricity, there are certain climate related benefits. A diesel generator emits CO2 during operation and grid based electricity is usually generated with either coal, oil or natural gas which also emits considerable quantities of CO2. In contrast. a solar based water pump system does not result in greenhouse gas emissions. Extensive use of solar water pumps would therefore lead to substantial greenhouse gas emission reductions.

Financial requirements and costs

Several aspects of a PV pump system are key in determining the system costs:

a) size of the system. The high initial capital costs of the PV array is the major barrier to high penetration rates of the use of solar water pumps (Firatogly & Yesilata, 2004). The PV array is the most expensive part of the system. The size and capacity of the PV array considerably influences the up-front costs of the system. Therefore, it is important to use the smallest system size possible that still meets all the criteria of that particular location. Government or aid agency subsidies which cover the high initial capital costs are required in many locations to realize PV water pump systems (Short and Oldach, 2003). The high reliability of solar water pumps might offset its higher initial costs compared to diesel powered pump systems (Barlow et al., 2003).

b) insolation levels. This is direclty related to the required size of the system. The intensity and number of hours of sunshine determine the capacity requirements and thus the PV array size requirements. The more sunshine, the smaller the system requirements.

c) pumping head. The pumping head is the distance over which the water needs to be moved. The costs of water volume unit are proportional to the pumping head. Odeh et al., outline that a shallow well of only 20 meters depth compared to a deep well of 100 meters depth reduces water volume unit cost by around five times (Odeh, Yohanis, & Norton, 2006).

While system size and insolation levels greatly influence the capital costs of a PV water pump the operational costs of the system are generally very low due to low labor and maintenance costs. In contrast, inexpensive diesel or gas generators have low initial capital costs but require constant maintenance and the parts have shorter lifetimes which increases operating costs. This long-term economic advantage makes solar water pumping more cost-effective to conventional pumping systems, such as diesel powered pumps (NYSERDA, 2004). For example, a study investigating the economics of solar water pumps shows that in seven countries (Argentina, Brazil, Indonesia, Jordan, the Philippines, Tunisia, and Zimbabwe) solar water pump systems had a cost advantage over diesel pumping systems in the power range up to 4 kWp (Posorski & Haars, 1994; Posorski, 1996). A study by the Bureau of Land Management at Battle Mountain, Nevada, USA, showed that certain PV systems cost only 64 % over twenty years compared to a comparable diesel generator system did over ten years (NYSERDA, 2004). Additionally, the PV system required only 14 % of the labor hours that the diesel generator system required. The study by Odeh et al. found that PV water pumping systems are more cost-effective than diesel pumping systems for equivalent hydralic energy below 5750 m⁴ /day and 21.6 MJ/m2 day average insolation. In turn, diesel pumping becomes more economical for larger applications (Odeh, Yohanis, & Norton, 2006). This difference in costs over a long term is clearly illustrated in Table 2.

PV systems are particularly useful in locations to which it is not practical to extend the grid. Even in locations where connection could be made to a grid, utilities have found it more viable to use PV pumps than to extend and maintain the electric grid (Kou et al., 1998).

Clean Development Mechanism market status

Currently, there are no registered CDM projects using solar water pumps. However, two solar water pump projects were in the CDM pipeline. Of these, one got rejected and the other was withdrawn from the process. In both cases, this was because the methodology that was chosen was incompatible with the project description.

Solar water pump projects, however, certainly have the potential to be eligible for CDM registration and funding. The baseline for GHG emissions in the absence of such a project would be based on a diesel powered pump. A solar water powered pump would therefore reduce GHG emissions which would generate CDM credits.

For calculation of these GHG emission reductions, it is recommended to apply the approved methodology for Mechanical energy for the user with or without electrical energy (AMS-I.B. version 10). This methodology helps to determine a baseline for GHG emissions in the absence of the project (i.e. business-as-usual circumstances), how emission reductions below this baseline can be calculated, and how these reductions can be monitored. General information about how to apply CDM methodologies for GHG accounting can be found at: [[1]].

However, close attention should be paid to the project description to ensure compatibility between the project and the methodology. This methodology considers mechanical energy for the direct user, and is therefore not compatible with a project that delivers water to several users. For example, a project that irrigates multiple fields with the same installation should not use this methodology.

References

• Firatoglu, Z., Yesilata, B., (2004). New approaches on the optimization of directly coupled PV pumping systems. Solar Energy 77, pp. 81-93.
• IEA (International Energy Agency) 2010. Technology Roadmap - Solar photovoltaic energy
• IPCC 2010. Special Report on Renewable Energy Sources and Climate Change Mitigation, In Press.
• NYSERDA, (2004). Guide to Solar Powered Water Pumping Systems in New York State. New York State Energy Research and Development Authority. Retrieved from: [[2]]
• Odeh, I., Yohanis, Y., G., & Norton, B., (2006). Economic Viability of Photovoltaic Water Pumping Systems. Solar Energy Vol 80 (2006) pp. 850-860.
• Posorski, R., (1996). Photovoltaic water pumps, an attractive tool for rural drinking water supply. Solar Energy 58, pp. 155 - 163.
• Short, T., Oldach, R., (2003). Solar Powered Water Pumps: the Past, the Present - and the Future. Journal of Solar Energy Engineering 125 (1), pp. 76 -82.
• Short, T.D., & Thompson, P., (2003). Breaking the Mould: Solar Water Pumping - the Challenges and the Reality. Solar Energy 75 (2003) pp 1-9.
• REN21. 2010. Renewables 2010 Global Status Report (Paris: REN21 Secretariat).