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Power - Photovoltaic - Water pumping - 0.05 kW - Off-grid / Canada
Case study assignment
As a medium size photovoltaic system installer, you need to quickly produce system performance and cost estimates for photovoltaic (PV) pumping systems for livestock watering. You are contracted to install a system to provide water to 20 head of cattle.
Site information
In an effort to keep cattle out of a sensitive wetland, water from the wetland will be pumped to a storage tank, from which it will be delivered to a watering trough. The site is located 100 km northeast of Toronto, Ontario, Canada. From the months of May to September, twenty cows will obtain all their water from the PV pumping system.
A 12 VDC diaphragm pump with 13 Lpm maximum flow will be used. The suction head is estimated at 1 metre, the discharge head at 7 m and the friction pressure drop estimated at 10% of the total head. The overall pump efficiency is approximately 10%. The pump requires rebuilding every five years. Plastic pipe 13 mm in diameter runs 100 m from the wetland to the reservoir tank. The main storage tank has a float control valve that creates backpressure at the pump; this in turn activates the pump pressure switch and prevents the tank from overflowing. The main storage tank contains enough water for 3 days of watering. To enable more hours per day of useful pumping, a linear current booster with efficiency of 95% will be installed. The system is a direct pumping type, with no battery storage.
Financial information
Financial figures for the analysis are: inflation of 2.5%, fuel cost escalation rate of 5.0%, debt ratio of 60%, debt interest rate of 8.5%, discount rate of 9%, and debt term of 10 years. The cattle owner does not require a tax analysis. The pump cost is $150; a rebuild costs $50. The linear current booster for the DC pump is $160. In your experience, four hours of engineering time is necessary to specify, order, and prepare the components for installation; the labour and overhead for installation itself is $320. The system should last about 25 years.
There are two alternatives to the PV pumping system: a 1 km grid extension and a gasoline-powered pump. Grid extension would cost $10,000 per km of extension, plus the cost of a transformer. The gasoline-powered pump would have an initial cost of $700. Annual costs for the gasoline pump would then be the cost of fuel (at $0.70 per L) and the cost of one hour of a labourer's time each week of the pump operating season. The same piping and storage tank would be used for all systems.
As part of a wetland protection project, a grant of half the system installed cost is available for any type of pumping system. The cattle owner will pay for the remainder of the project cost.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
Results
Generation Solar installed a photovoltaic (PV) pumping system north of Toronto, Ontario, Canada, to provide water for 20 head of cattle. The system was necessary to prevent the cattle from entering an adjacent wetland, where they would otherwise seek water. The system is in operation five months of the year.
Alternatives to the PV pumping system were a 300 m grid extension from primary pole service to an AC electric pump near the water; cattle nose pumps, which would have been too expensive; or a gasoline powered pump and adequate water storage for intervals between pumping. The PV system provides a low maintenance solution at a competitive cost.
Partial funding for the project was provided by the Wetland Habitat Fund (Wildlife Habitat Canada, the Province of Ontario and the North American Waterfowl Management Plan Partners). Otonabee Conservation administers the fund in the Peterborough, Ontario, Canada area, and up to 50% of a wetland project cost may be funded.
System description
A simple direct pumping system is used with two storage tanks. A large 2,700 litre tank provides primary storage. A float valve regulates water flow, fed by gravity, into a smaller watering trough.
The system uses a Solec International 100 W 12 VDC PV panel. A low cost 12 VDC Shurflow 2088 pump rated at 13 lpm consumes 4 amps and is connected to the panel through a Sun Selector Linear Current Booster (LCB). No batteries are used in this system. The LCB performs DC to DC conversion, permitting the PV module to operate near its peak power point while the pump draws high current at a much lower voltage. This allows the pump to operate during the lower light levels of morning, evening, and overcast conditions, thereby increasing the amount of water pumped. The PV array is tilted at 30° to maximise the energy collected during the summer months.
Water is pumped through 90 m of ½ inch polyethylene pipe to the primary storage tank. The float valve at the primary tank stops the water flow when the tank is full of water; the resulting back-pressure activates the pump's pressure shutoff switch. The total pumping head is 6 m, including the friction head. The Shurflo 2088 is a DC brushed motor diaphragm pump with a rebuildable pumping body. A pump rebuild kit is approximately $50.
Lessons learned
The big picture
Protection of waterways and wetlands from cattle effluent is critical to the prevention of water pollution. PV pumping systems with water storage offer a simple solution to this requirement. The cattle owner benefits, too, since the health of the cattle is affected by water contamination.
Photos
Cattle - Water pumping - Photovoltaic, Ontario, Canada - Photo 1
Cattle - Water pumping - Photovoltaic, Ontario, Canada - Photo 2
References
Case study assignment
As a medium size photovoltaic system installer, you need to quickly produce system performance and cost estimates for photovoltaic (PV) pumping systems for livestock watering. You are contracted to install a system to provide water to 20 head of cattle.
Site information
In an effort to keep cattle out of a sensitive wetland, water from the wetland will be pumped to a storage tank, from which it will be delivered to a watering trough. The site is located 100 km northeast of Toronto, Ontario, Canada. From the months of May to September, twenty cows will obtain all their water from the PV pumping system.
A 12 VDC diaphragm pump with 13 Lpm maximum flow will be used. The suction head is estimated at 1 metre, the discharge head at 7 m and the friction pressure drop estimated at 10% of the total head. The overall pump efficiency is approximately 10%. The pump requires rebuilding every five years. Plastic pipe 13 mm in diameter runs 100 m from the wetland to the reservoir tank. The main storage tank has a float control valve that creates backpressure at the pump; this in turn activates the pump pressure switch and prevents the tank from overflowing. The main storage tank contains enough water for 3 days of watering. To enable more hours per day of useful pumping, a linear current booster with efficiency of 95% will be installed. The system is a direct pumping type, with no battery storage.
Financial information
Financial figures for the analysis are: inflation of 2.5%, fuel cost escalation rate of 5.0%, debt ratio of 60%, debt interest rate of 8.5%, discount rate of 9%, and debt term of 10 years. The cattle owner does not require a tax analysis. The pump cost is $150; a rebuild costs $50. The linear current booster for the DC pump is $160. In your experience, four hours of engineering time is necessary to specify, order, and prepare the components for installation; the labour and overhead for installation itself is $320. The system should last about 25 years.
There are two alternatives to the PV pumping system: a 1 km grid extension and a gasoline-powered pump. Grid extension would cost $10,000 per km of extension, plus the cost of a transformer. The gasoline-powered pump would have an initial cost of $700. Annual costs for the gasoline pump would then be the cost of fuel (at $0.70 per L) and the cost of one hour of a labourer's time each week of the pump operating season. The same piping and storage tank would be used for all systems.
As part of a wetland protection project, a grant of half the system installed cost is available for any type of pumping system. The cattle owner will pay for the remainder of the project cost.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
- A linear current booster is a device that matches the low voltage, high current requirements of a pump to the high voltage, moderate current output of a PV array at its maximum power point.
- The debt ratio in the financial summary page has been set to 30%; this results in a 60% debt ratio for the 50% of the system costs that are not covered by the 50% wetland protection grant.
- Grid extension was not considered here because it was obviously more costly than either PV or gasoline-powered pumping.
- The annual labour costs of the gasoline-powered pump are calculated at one hour per week for five months, at $15/hour.
- The genset efficiency seems low at first glance, but is reasonable given that 1) the genset is small; 2) the energy content of gasoline suggested in the help files (and used in the RETScreen greenhouse gas model) is the higher heating value, whereas the products of combustion are in the gaseous, not liquid, phase.
- The 50% wetland protection grant is not essential to the financial viability of the PV powered pumping system. The internal rate-of-return and simple payback period would still be excellent without any grant.
Results
Generation Solar installed a photovoltaic (PV) pumping system north of Toronto, Ontario, Canada, to provide water for 20 head of cattle. The system was necessary to prevent the cattle from entering an adjacent wetland, where they would otherwise seek water. The system is in operation five months of the year.
Alternatives to the PV pumping system were a 300 m grid extension from primary pole service to an AC electric pump near the water; cattle nose pumps, which would have been too expensive; or a gasoline powered pump and adequate water storage for intervals between pumping. The PV system provides a low maintenance solution at a competitive cost.
Partial funding for the project was provided by the Wetland Habitat Fund (Wildlife Habitat Canada, the Province of Ontario and the North American Waterfowl Management Plan Partners). Otonabee Conservation administers the fund in the Peterborough, Ontario, Canada area, and up to 50% of a wetland project cost may be funded.
System description
A simple direct pumping system is used with two storage tanks. A large 2,700 litre tank provides primary storage. A float valve regulates water flow, fed by gravity, into a smaller watering trough.
The system uses a Solec International 100 W 12 VDC PV panel. A low cost 12 VDC Shurflow 2088 pump rated at 13 lpm consumes 4 amps and is connected to the panel through a Sun Selector Linear Current Booster (LCB). No batteries are used in this system. The LCB performs DC to DC conversion, permitting the PV module to operate near its peak power point while the pump draws high current at a much lower voltage. This allows the pump to operate during the lower light levels of morning, evening, and overcast conditions, thereby increasing the amount of water pumped. The PV array is tilted at 30° to maximise the energy collected during the summer months.
Water is pumped through 90 m of ½ inch polyethylene pipe to the primary storage tank. The float valve at the primary tank stops the water flow when the tank is full of water; the resulting back-pressure activates the pump's pressure shutoff switch. The total pumping head is 6 m, including the friction head. The Shurflo 2088 is a DC brushed motor diaphragm pump with a rebuildable pumping body. A pump rebuild kit is approximately $50.
Lessons learned
- For modest watering requirements of a few hundred litre/day at low head (i.e. a low wattage pump, 30 to 50 watts) PV systems are cost competitive when the grid is more than an "extension cord away".
- Low-cost pumps that are easily repaired or replaced result in low initial and operating costs.
- The supply of solar energy and the demand for water for irrigation or livestock are strongly correlated since the demand for water goes up with the level of insolation.
The big picture
Protection of waterways and wetlands from cattle effluent is critical to the prevention of water pollution. PV pumping systems with water storage offer a simple solution to this requirement. The cattle owner benefits, too, since the health of the cattle is affected by water contamination.
Photos
Cattle - Water pumping - Photovoltaic, Ontario, Canada - Photo 1
Cattle - Water pumping - Photovoltaic, Ontario, Canada - Photo 2
References
- Boone, Simon, "Personal communication," Generation Solar Renewable Energy Systems Inc, 2000.
- Lapp, Steve, "Personal communication," SGA Energy, 2000.
