Electrical design and installation of solar pumps

TYPE OF PUMP
VOLUMETRIC
CENTRIFUGAL (< 2 HP)
CENTRIFUGAL (> 2 HP)
Performance ratio
0,6
0,4
0,6
Formula for calculating the daily electrical energy in Watt hours per day (Wh/day):
Daily Electrical Energy (E1) = 
Water Volume (m
3
/day) × TH (m) × 2,725
Pump performance ratio
To fill a tank of 30 m3 disposed at 10 m of height, with a 3 HP water pump, located in a borehole of 50m depth. Pressure 
loss in the pipe is estimated to 1 bar (voluntary overestimation).
Daily Electrical Energy (E1) = 
= 9 536 Wh/day
30 (m
3
/day) × (10 m + 50 m + 10 m) × 2,725
0,6
In this example, the solar system will have to produce 9 536 Watt.hour (Wh) per day to power the water pump.
EXAMPLE_STEP_2_CALCULATION_OF_PUMP_RATED_POWER'>EXAMPLE
STEP
2 
CALCULATION OF PUMP RATED POWER
Generally speaking, the rated water flow of the installed pump is equal to 20% (1/5th) of the daily energy need. We can 
calculate the pump power with the following formula: 
Rated Power of the pump (P1) = 
Daily Electrical Energy E1 (Wh/day)
5
To equip the borehole from previous example (step 1), the rated power of the pump will be:
Rated Power of the pump (P1) = 
= 1 907 W 
9 536 Wh
5
EXAMPLE

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29
SOLAR PUMPING
Guidelines - Electrical design and installation of solar pumps
STEP
3 
CALCULATION OF DIESEL GENERATOR POWER
When powered by a variable energy source, such as solar panels that produce more or less depending on sun power, pump 
start-ups are progressive. This is not the case when pumps are powered by a generator.
After the generator starts, when the output circuit breaker of the genset is switched on, the pump is powered suddenly and 
reaches its full power in some milliseconds. This sudden increase of power of the electric motor generates strong magnetic 
fields, which the generator must overcome before the electric motor can start. This phenomenon is called a «load impact at 
start-up».
If you choose a generator with the same power as the pump (eg 2.2 kVA for a 2kW pump), it will be unable to start the pump. 
Concretely the engine of the generator set will stall brutally. 
To avoid it, we apply the following calculation formula: