# Revision history [back]

From: Neil Noble Sent: 24 August 2015 12:20 To: 'jfslevi@gmail.com' Subject: FW: Solar powered pumps enquiry

Dear John,

This subject was popular many years go in the 1970s but seemed to drop off, possibly because of improvements in technical aspects of photovoltaic systems although, solar PV water pumps have taken a long time to become viable in development environment in Africa rather than larger commercial applications.

It has only been over the last few years that the cost of PV systems has reduced to an extent that it is now viable to introduce these systems, although there will still be an issue on the supply chain and maintenance. Practical Action is currently installing solar PV water pumping systems in a number of African locations along with developing the supply side of things.

For non PV designs of water pumping I think there were a few different options looked into. External heat engines, such as Stirling Engines, steam engines would be able to use solar thermal energy. The extract from the old VITA document outlines the situation a little better.

History

The history of thermodynamic solar water pumping technology goes back nearly four hundred years, when Solomon de Caux in France raised water for a fountain by the expansion of solar-heated air. By the beginning of this century, many of the currently competing design concepts had already been explored, and several promising attempts at commercialization were under way when activity subsided due to the advent of the internal combustion engine and cheap commercial fuels. Much of this development had been aimed at relatively large-scale applications. It was not until the resurgence of interest in solar energy caused by the 1973-1974 oil embargo that greater attention began to be directed at small-scale rural applications in developing countries.

Of particular interest to the serious reader in this field is the definitive and comprehensive work done in conjunction with the United Nations Development Programme/World Bank Small-Scale Solar-powered Irrigation Pumping Systems Project by Sir William Halcrow & Partners and the Intermediate Technology Development Group, Ltd. The most important reference for the prospective solar pump user is Handbook on Solar Water Pumping.

In contrast, the development of photovoltaic water pumps has heavily emphasized small-scale rural applications since the 1960s. While both of these technical approaches continue to mature, neither can yet be judged inherently superior. Most of the recent efforts, however, have concentrated on photovoltaic systems and a majority of solar pump field operating experience has been with photovoltaic installations.

Thermodynamic Systems

All thermodynamic systems use a solar collector to convert solar radiation to heat and a heat engine to convert the heat to mechanical power for pumping. In heat engines a fluid or gas absorbs heat at a higher temperature, which causes it to expand; it then contracts upon removal of the heat at a lower temperature. This expansion and contraction is harnessed to move a reciprocating piston in a cylinder, or it can expand against a turbine wheel.

The necessary temperature differential across the heat engine and the unavoidable losses associated with each stage of the process. Of the two indicated temperatures, the lower one cannot be lower than that of the pumped water to which the unusable degraded heat is typically rejected, while the upper one is largely controlled by the type of collector. Increasing the upper temperature (within practical limits) raises the overall system efficiency and reduces the required collector size, but usually at the cost of greater complexity or more expensive materials. This broadly characterized conceptual approach can have many different embodiments, with various types and combinations of collectors, working fluids, heat engine cycles, engines, and pumps.

Most of the small-scale systems that have been developed beyond the prototype stage use Rankine cycles, with organic working fluids such as Freon 11 and slow-speed reciprocating engines that directly drive piston pumps. Many developing regions are familiar with Rankine systems because of experience with steam engines. Organic working fluids can produce higher heat-to-work conversion efficiencies than steam at temperatures up to their stability limit of about 150ºC, but extreme care must be taken to ensure zero leakage since very small amounts incapacitate the system and recharging is difficult in the field. A reciprocating engine is virtually the only choice, since turbines and rotary expanders are excessively expensive in the small sizes of interest. Slow-speed reciprocating (piston) pumps tend to be more efficient than conventional high-speed centrifugal pumps at heads greater than about 10 meters, although single stage centrifugal pumps (which are easy to make) are well suited for very low-head irrigation.

Many other technically intriguing and potentially useful systems have been or are being developed, including:

 1.   smaller organic Rankine systems;
2.   very small (about 25 watts) steam Rankine systems;
3.   an organic vapour liquid piston pump;
4.   a heated air liquid piston pump;
5.   a fluid overbalancing rocking beam engine pump; and
6.   various solid state systems based on "memory metals,"
polymers, and the differential expansion of bimetal
strips.


Some of these systems have become commercially available, but it must be emphasized that none of them (or of the other concepts described above) is known to have successfully undergone the extensive testing under field conditions that characterize a mature product.

Unfortunately, Practical Action does not have anyone that is knowledgeable of solar thermal technologies or able to take on the development of a new design of solar thermal technology. Sorry that I can’t be of further help on this subject.

Yours sincerely, Neil

Neil Noble Knowledge Services Developer T +44 (0)1926 634418 Skype neilpnoble Twitter @PracticalAnswer @KP_TSS

Practical Answers is now part of KnowledgePoint, a new question and answer service that brings together Practical Action, IRC, WaterAid, REDR, and EngineeringAid to provide a broader range of expertise on water, sanitation and hygiene as well as humanitarian issues. http://knowledgepoint.org/en/questions/

From: Gerry Corkhill Sent: 24 August 2015 09:55 To: Neil Noble Subject: Solar powered pumps enquiry

From: Neil Noble Sent: 24 August 2015 12:20 To: 'jfslevi@gmail.com' Subject: FW: Solar powered pumps enquiry

Dear John,

This subject was popular many years go in the 1970s but seemed to drop off, possibly because of improvements in technical aspects of photovoltaic systems although, solar PV water pumps have taken a long time to become viable in development environment in Africa rather than larger commercial applications.

It has only been over the last few years that the cost of PV systems has reduced to an extent that it is now viable to introduce these systems, although there will still be an issue on the supply chain and maintenance. Practical Action is currently installing solar PV water pumping systems in a number of African locations along with developing the supply side of things.

For non PV designs of water pumping I think there were a few different options looked into. External heat engines, such as Stirling Engines, steam engines would be able to use solar thermal energy. The extract from the old VITA document outlines the situation a little better.

History

The history of thermodynamic solar water pumping technology goes back nearly four hundred years, when Solomon de Caux in France raised water for a fountain by the expansion of solar-heated air. By the beginning of this century, many of the currently competing design concepts had already been explored, and several promising attempts at commercialization were under way when activity subsided due to the advent of the internal combustion engine and cheap commercial fuels. Much of this development had been aimed at relatively large-scale applications. It was not until the resurgence of interest in solar energy caused by the 1973-1974 oil embargo that greater attention began to be directed at small-scale rural applications in developing countries.

Of particular interest to the serious reader in this field is the definitive and comprehensive work done in conjunction with the United Nations Development Programme/World Bank Small-Scale Solar-powered Irrigation Pumping Systems Project by Sir William Halcrow & Partners and the Intermediate Technology Development Group, Ltd. The most important reference for the prospective solar pump user is Handbook on Solar Water Pumping.

In contrast, the development of photovoltaic water pumps has heavily emphasized small-scale rural applications since the 1960s. While both of these technical approaches continue to mature, neither can yet be judged inherently superior. Most of the recent efforts, however, have concentrated on photovoltaic systems and a majority of solar pump field operating experience has been with photovoltaic installations.

Thermodynamic Systems

All thermodynamic systems use a solar collector to convert solar radiation to heat and a heat engine to convert the heat to mechanical power for pumping. In heat engines a fluid or gas absorbs heat at a higher temperature, which causes it to expand; it then contracts upon removal of the heat at a lower temperature. This expansion and contraction is harnessed to move a reciprocating piston in a cylinder, or it can expand against a turbine wheel.

The necessary temperature differential across the heat engine and the unavoidable losses associated with each stage of the process. Of the two indicated temperatures, the lower one cannot be lower than that of the pumped water to which the unusable degraded heat is typically rejected, while the upper one is largely controlled by the type of collector. Increasing the upper temperature (within practical limits) raises the overall system efficiency and reduces the required collector size, but usually at the cost of greater complexity or more expensive materials. This broadly characterized conceptual approach can have many different embodiments, with various types and combinations of collectors, working fluids, heat engine cycles, engines, and pumps.

Most of the small-scale systems that have been developed beyond the prototype stage use Rankine cycles, with organic working fluids such as Freon 11 and slow-speed reciprocating engines that directly drive piston pumps. Many developing regions are familiar with Rankine systems because of experience with steam engines. Organic working fluids can produce higher heat-to-work conversion efficiencies than steam at temperatures up to their stability limit of about 150ºC, but extreme care must be taken to ensure zero leakage since very small amounts incapacitate the system and recharging is difficult in the field. A reciprocating engine is virtually the only choice, since turbines and rotary expanders are excessively expensive in the small sizes of interest. Slow-speed reciprocating (piston) pumps tend to be more efficient than conventional high-speed centrifugal pumps at heads greater than about 10 meters, although single stage centrifugal pumps (which are easy to make) are well suited for very low-head irrigation.

Many other technically intriguing and potentially useful systems have been or are being developed, including:

 1.   smaller organic Rankine systems;
2.   very small (about 25 watts) steam Rankine systems;
3.   an organic vapour liquid piston pump;
4.   a heated air liquid piston pump;
5.   a fluid overbalancing rocking beam engine pump; and
6.   various solid state systems based on "memory metals,"
polymers, and the differential expansion of bimetal
strips.


Some of these systems have become commercially available, but it must be emphasized that none of them (or of the other concepts described above) is known to have successfully undergone the extensive testing under field conditions that characterize a mature product.

Unfortunately, Practical Action does not have anyone that is knowledgeable of solar thermal technologies or able to take on the development of a new design of solar thermal technology. Sorry that I can’t be of further help on this subject.

Yours sincerely, Neil