Solar Powered Water Pumping

Solar Powered Water Pumping | Benefits | Constraints | Resource Assessment & System Design | Links to Suppliers and Further Information | Conclusion | References

---

Solar Powered Water Pumping

There are more than 10,000 solar powered water pumps in use in the world today. They are widely used on farms and outback stations in Australia to supply water to livestock. In developing countries they are used extensively to pump water from wells and rivers to villages for domestic consumption and irrigation of crops. A typical PV-powered pumping system consists of a PV array that powers an electric motor, which drives a pump. The water is often pumped from the ground or stream into a storage tank that provides a gravity feed. No energy storage is needed for these systems. PV powered pumping systems are widely available from agricultural equipment suppliers and they are a cost-effective alternative to agricultural wind turbines for remote area water supply.

 

 

Benefits

Photovoltaic (PV) systems are used to pump water for livestock, plants or humans. Since the need for water is greatest on hot sunny days the technology is an obvious choice for this application. Pumping water using PV technology is simple, reliable, and requires almost no maintenance. Agricultural watering needs are usually greatest during sunnier periods when more water can be pumped with a solar system. PV powered pumping systems are excellent for small to medium scale pumping and there are thousands of agricultural PV water pumping systems in the field today throughout the world. For an indication of the global solar resource available for photovoltaic applications, see Figure 2.

PV powered water pumping systems are similar to any other pumping system, only the power source is solar energy. PV pumping systems have, as a minimum, a PV array, a motor, and a pump. PV water pumping arrays are fixed mounted or sometimes placed on passive trackers (which use no motors) to increase pumping time and volume. AC and DC motors with centrifugal or displacement pumps are used with PV pumping systems. The most inexpensive PV pumps cost less than $1,500, while the large systems can run to over $20,000. Most PV water pumps rarely exceed 2 horsepower in size. Well installed quality PV water pumping systems can provide over 20 years of reliable and continuous service (El Paso Solar Energy Association, 2001).

PV modules on the market today are guaranteed by manufacturer's from 10 to 20 years, while many of these should provide over 30 years of useful life. It is important when designing PV systems to be realistic and flexible, and not to over-design the system or overestimate energy requirements (e.g., overestimating water-pumping requirements) so as not to have to spend more money than needed. A well-designed PV system will operate unattended and requires minimum periodic maintenance. PV conversion efficiencies and manufacturing processes will continue to improve, causing prices to gradually decrease, however no dramatic overnight price breakthroughs are expected (El Paso Solar Energy Association, 2001). For the past and future trends in component costs of PV systems see Figure 3.

 

In terms of average unit energy costs calculated using traditional accounting techniques, PV generated electricity cannot yet compete with efficient conventional central generating plants. Accordingly, the vast majority of PV installations to date have been for relatively low-power applications in locations, which do not have ready access to a mains electricity grid. In such cases, PV has been selected because it offers a secure and reliable power supply, and is often the cheapest power option.

Like any such commodity, the total purchase price of a PV system is based on all inherent costs of producing the individual components, transporting these to the site and installing them. There may also be associated costs of designing and engineering the system and purchasing land - particularly for large-scale or one-off projects (IEA, 2002).

For further information on enabling technologies, see the RISE Information Portal Technologies.

 

Constraints

People should be aware of the practical limitations of PV systems and major areas are discussed below.

Assessment of the economic viability of PV pumping systems in comparison to diesel pumping systems indicate that the limit for PV pumping is 5 kWp. Also the high investment cost of PV pumping systems is a major factor to slowed expansion of the market. Although the life cycle cost of PV is often less than diesel or petrol-powered pumps, the investment cost of purchasing a PV pump is usually higher than that of diesel pumps.

PV pumping is a mature technology and problems are largely due to infrastructure and planning. Technicians and buyers are often unfamiliar with PV technology, and when pumps in remote locations do break down, there may be a lack of servicing, spare parts, or trained manpower to administer them. In reality, PV is much less maintenance intensive than diesel pumps. Because PV only supplies water when the sun is shining, there is usually a need to build storage tanks for when the sun is not shining. This adds extra cost to the investment.

PV pumps are best suited for households, small communities or remote livestock needs. PV pump outputs are normally too low for high volume irrigation requirements. For example, the Grundfos solar pump, designed for domestic water supply, pumping in an area with average insolation of 6 kWh/m² day, will deliver approximately 6m3/day at 15 m head from a 0.25 kWp PV array. Such a system would cost approximately $ 4,500 for hardware excluding storage tank and pedestal.

Experiences show that solar pumps should be installed in secure environments. In remote unguarded locations, there is a small risk of the modules being stolen or vandalised (IGAD’s Household Energy Regional Programme , 2006).

 

Resource Assessment & System Design

Through the Information Portal, RISE provides networking services to assist people researching various renewable energy Applications. There are many excellent decision-making and capacity building tools and software freely available for download provided by other quality institutions.

In this section, some of these programs are summarised below;

“The RETScreen International Clean Energy Decision Support Centre seeks to build the capacity of planners, decision-makers and industry to implement renewable energy and energy efficiency projects. This objective is achieved by: developing decision-making tools that reduce the cost of pre-feasibility studies; disseminating knowledge to help people make better decisions; and by training people to better analyse the technical and financial viability of possible projects.”

Visit the RETScreen International Clean Energy Decision Support Centre

These RETScreen files contain a collection of project case studies, including assignments, worked-out solutions (RETScreen Software Analysis) and information about how the projects fared in the real world. This document includes a background of energy technology and it provides algorithms for Project Models. In addition there are many case studies that provide succinct details on various renewable installations including system descriptions, lessons learned and many other important and useful information.

Areas that are included are;

 

HOMER

“HOMER is a computer model that simplifies the task of evaluating design options for both off-grid and grid-connected power systems for remote, stand-alone, and distributed generation (DG) applications. HOMER's optimization and sensitivity analysis algorithms allow you to evaluate the economic and technical feasibility of a large number of technology options and to account for variation in technology costs and energy resource availability. HOMER models both conventional and renewable energy technologies.”

Visit the HOMER Optimisation Model for Distributed Power Page

HOMER allows up to three independent generation technologies to be included in the simulation model. Each generation technology can be a different size, cost, and fuel, or they can all be alike. HOMER dispatches the generators in an economically optimal way, meaning that each hour it chooses the generator (or combination of generators) that can meet the load and operating reserve requirements at least cost. It considers replacement, O&M, and fuel cost when making its dispatch decisions, as well as the value (if any) of the waste heat recovered from each generator. Homer allows an extremely large range of system configurations to be simulated. You can download and use the full version of HOMER for free. You must be a registered user to download the software. When you install HOMER, you automatically receive a free six-month license, which you can renew for free an unlimited number of times.

Sources/Systems incorporated in HOMER are:

          

Links to Suppliers and Further Information

RISE Resources - Information regarding available renewable energy resources.

RISE Technologies - An extensive collection of information regarding renewable energy technologies.

RISE Applications & System Design - Renewable energy application information and system designs.

RISE System Displays - Case studies and information on installed renewable energy systems & performance data.

Solar Water Pumping Online Course - RISE Information Portal

For a comprehensive list of Australian PV suppliers, manufacturers, consultants and associations see Solarbuzz

IEA WEB PV Resources

Renewable Energy Pages from Oregon Department of Energy

IEA Australian PV Information

IEA PV Building Integrated

IEA Australia’s Cumulative Installed PV Power by Sub-Market

IEA Grid Connected Systems Case Studies

ITDG Solar Water Pumping Technical Brief (pdf)

Solar-Powered Livestock Watering Systems (University of Tennessee) (pdf)

Conclusion

Currently photovoltaic technology is suitable for remote site applications that have small power needs, or small power consuming applications even where the grid exists. However the falling prices of PV's over time will make many more applications of photovoltaics economically competitive in the future.

 

References

IEA, 2002. "Stand-alone PV power systems (off-grid)" (Online) http://www.iea-pvps.org/pv/sa_syst.htm (Accessed 28 February 2007).

IGAD, 2006. "Household Energy Regional Programme - PV Pumps" (Online) http://igadrhep.energyprojects.net/Links/Profiles/PVPumps/PVPumps.htm (Accessed 28 February 2007).

El Paso Solar Energy Association, 2001. "Photovoltaics - Solar Electricity" (Online) http://www.epsea.org/pv.html (Accessed 28 February 2007).