Solar Pumping System
A wide range of pumps are available for most applications. In selecting a pump the following criteria should be considered:
Flow: Rate at which the pump will deliver, measured in gallons/hour (gph), gallons/min (gpm); litres/hour (l/h) or litres/min (l/m).
Head: Maximum height to which the pump will deliver (neglecting piping friction losses). This is also a measure of the pump's pressure. It is measured in metres (m) of water, or lbs/sq in (PSI) in specifications.
Suction Lift: Needed where the water source is lower than the pump. Some pumps are not self-priming and need to be below the water source to be fed by gravity.
Total Head: This is the entire vertical distance from water source to the tank.
Horizontal Distance: Pumps cannot move water very far by suction, even if the lift involved is below it's limit. So if large distances from source to tank are involved the pump is normally located at the supply and the water pressure used. Adequate wiring must then be used to compensate for voltage drop. Large diameter pipes will minimise losses due to pipe friction. For large distances particularly if large volumes of water are required the simplest route may be to use standard 230 Vac pumps run from an inverter.
Power Consumption: Not the least important consideration in a remote power system!
Flow, Head, Pressure & Power Consumption are all related; for the same pump, the greater the lift the lower the flow and the more power used.
Pump performance varies depending on how much water the pump is moving and the pressure it is creating. This is important because it determines whether the pump is suitable for your system and because it is these pump characteristics which allow pump operation to be controlled. The main thing to understand is that at the same time as the flow INCREASES , the pressure DECREASES.
The performance characteristics of the pump are illustrated by pump curves. These show the inverse relationship between pressure and flow. Higher pressure gives lower flow and greater flow is obtained at lower pressure.
- head in ft. = 2.31 x pressure in psi (pounds/sq inch)
- head in metres = 10 x pressure in bar (kg/sq m)
- Typical household water pressure runs at between 10 & 40 psi
- 10 psi = 0.69 bar (kg/sq cm)
- 1 bar = 14.5 psi
- 1 l/m = 0.22 gpm = 13.25 gph
- 1 gpm = 4.45 l/m
- 1 US gallon = 0.83 UK gallon.
Types of Pumping Systems
Two different methods of running pumps from solar PV systems are possible:
These use no batteries and pumping occurs only during the day when there is sufficient daylight. Special pumps must be used together with carefully matched PV modules. Water is typically pumped to fill an elevated storage tank which is sized to hold sufficient water for supply during cloudy weather or at night. A water tank is cheaper and more durable than the equivalent energy storage in batteries. Water is delivered by gravity pressure to points of use below the tank level. Between the PV modules and the pump a controller is normally used. This matches the power from the PV’s to the demands of the pump motor - allowing the pump to start even in weak sunlight.
Another option is to store energy from the PV modules in batteries which has the advantage that the water can be pumped at any time. Matching of PV modules to pump is less critical since the battery can provide sufficient surge power for starting the pump motor. The water system can be pressurised which eliminates the need for a storage tank and water can be supplied to points of use above the source. Many remote home systems use a battery based pumping system run on the same battery bank that is used for lighting and other appliances.
These are installed completely underwater and although usually fitted down well casings many can also be laid on their side on the bottom of a lake or stream. Submersibles don't need to be primed since they are already under water and they tend to be more efficient because they only push the water - they don't need to suck water into them
These are installed on the surface and lift water by pressurising it and then discharging it. The theoretical maximum suction lift possible at sea level is approx. 7.5m.
Choice of pump depends upon:
- Static Suction Lift: The vertical distance from water line to the pump.
- Static Discharge Head: The vertical distance from the pump to the point of discharge.
- Dynamic (or Total) Suction Head: The static suction lift plus the friction in the pipe line.
- Dynamic (or Total) Discharge Head: The static discharge head plus the friction of the discharge line.
- Total Dynamic Head: The dynamic suction head plus the dynamic discharge head.
Solar Garden Pumps and Fountains
Solar powered pumps can be used anywhere. Run directly from solar panels, they will work whenever there is sufficient sunlight, the brighter the sun the greater the flow. Safe and simple, they allow instant water features in even the smallest gardens and ponds.
- They are intrinsically safe and simple to install since they don’t require mains wiring and transformers.
- No extra costly wiring and safety equipment is required.
- Simple plug-and-play installation