This is the second part of solar pump systems if you want to know what is a solar pumping system and what are the main components of solar pump stations and the different types of solar pumps go to the first part (How to install a solar pump) of this post which contains some information you need to know.
The following steps are taken to calculate the components of solar water pumping stations:
- .Determine the amount of water required
- Determine the source of water
- Calculate the required water flow rate (l / min)) water flow rate
- Calculation of total dynamic head (TDH)
- Choose the appropriate capacity of the solar energy pump.
- Determine the capacity of the solar panel array.
- Determination of the power of the inverter (in the case of AC motors)
- Determine the water tank capacity.
The following is an explanation of each step
#1.Determine the amount of water required
- For home use.
- On a farm according to the nature of its work, raising animals or planting it.
Tables (1) and (2) show examples of approx daily consumption for some applications (liters / day & m3 / day).
|Application||The approximate daily consumption (liters / day)|
|A person’s home use||190:200|
|The milking cow||76:114|
|Cattle and horses||38:57|
|Sheep and goats||4:7|
|Small body animals||About 1 liter/day for every 11 kg of weight|
|Poultry||(23 – 45.6) liters / day per 100 birds|
|Small Trees||7 in dry weather|
|Trees are medium in size||75|
|Application||Water consumption per acre (m3 / day)|
|Citrus and mango||15:40 depending on the age of the trees|
|Pomegranate and olives||5:13 depending on the age of the trees|
Acres = 4,200 m 2
1 m ³=1000 liters
#2.Determine the source of water
The location of the water source should be suitable for the installation of the used solar water pumping system. The irrigation system depends on the type of water’s source and its location in relation to the place to be supplied with water. Thus the water sources are classified as Irrigation systems: either deep or shallow.
Table (3) shows some of the characteristics of water sources and the requirements for each source
|Deepwater sources||Surface water sources|
Water quality is good and reliable..
Expensive due to drilling.
Requirements for wells:
•Static water level
• Seasonal depth variation
• Water compensation percentage
• Water quality
The quality of the water is taken care of if it is to be used
For human consumption
|Such as: pool – schedule – torrent|
The quantity and quality of water varies seasonally
It is low in the summer
Requirements for surface water:
•Water quality (presence of mud and organic residues)
#3.Water flow rate (litre /minute)
The following data must first be specified:
[A] :Average daily use of water in liters (liters/day).
[B]: Average sunshine period (hour/day)
then the flow rate calculated according to the following equation :
Flow Rate = [A] / [B]* 60
Flow rate = [l/m]
#4. Calculate total manometric height (HMT) or total dynamic pumping height (TDH)
There are two similar methods of choosing water pumps depending on their characteristics. Which method depends We use it on the manufacturer’s data, who can use HMT or use TDH in manual Pump characteristics. The following is the definition of each method:
I.Total manometric head) (HMT)
It is the pressure difference (in meters) between the inlet and outlet points of the pump. This value is always higher than the actual difference in the height between these two points. When the pumping is continuous, the pump needs to overcome the friction losses that occur during the flow of water through the intake and outlet pipes.
HMT = Ha + Hr + PC + Pr
- Ha=The height of the clouds, which represents the distance between the water surface and the axis of the pump), this height is equal to zero in (Case of using submersible pumps).
- Hr=Discharge height which represents the height between the axis of the pump and the highest point of discharge of water with respect to As for the submersible pump, it represents the height between the surface of the water and the highest point of discharge.
- Pc=The average load loss and represent the energy lost in the water pipes, and it is calculated according to the following equation: Pc=Jr +Ja.
- Jr= friction loss in the vacuum tubes.
- Ja= friction loss in draft tubes, zero value in case of submersible pumps due to the absence of tubes Withdraw in this case.
- Pr= The used pressure required when opening the tap is usually between 1 and 3 bar (i.e. between 10 and 30 meters)Figure (1) shows the definitions used to calculate the total manometric height in the case of a surface pump Figure (2) Definitions in the case of a submersible pump Table (4) shows the relationship between water height in feet and pressure Pounds / Inch 2
II.Total Dynamic Head ( TDH)
This is the most common method, and the total dynamic pumping height is defined as the distance that the the solar pump raises the water to it vertically (meters), which is the opposite of the Earth’s gravity, and indicates the required pressure from The pump to raise water from the depth of the well to the highest point in the reservoir(tank).
The total dynamic headroom consists of the sum of the following distances:
- The vertical distance from the surface of the earth to the water level in the well or the river or the canal (that is, it is deep water from the surface of the earth ) known as the static water level( per meter).
- The vertical distance from the ground surface to the highest point in the reservoir, which is known as the vector rise.
- The value of the friction loss in the pipes. (This value is in meters and is obtained from tables that Contain the diameter and length of pipes and the shape of the connections used in the line )
Friction loss is defined as the resistance of the inner surface of the pipes against the flow of water. For pipes of smaller diameter and higher pumping value, they have a higher resistance.
The dynamic pressure rise is calculated from the following equation:
TDH = Hh + Ja + Jr
Hh = hydraulic load (static height)
Ja and Jr = friction loss inside tubes
Figure (5) shows an example of calculating dynamic height in case:
(1) The intake water level is higher than the axis line of the pump
(2) The intake water level is lower than the axis line of the pump.
The manufacturers’ tables can be used to calculate the friction loss, which is explained in the attachment (3).
The diameter of the discharge pipe is usually smaller than the pipe diameters used in horizontal lines because it is in Extraction pipes use the entire section of the pipe to deliver water to the surface (Table 5) can also be used. To help determine pipe diameter by knowing the maximum flow rate.
and you can find an example on how to calculate the friction loss using this table.
#5- Determine the suitable solar energy pump
Figure 6 show the steps you do to select the suitable solar pump .
In hydraulic pump catalogs, there are curves for the relationship between flow rate and dynamic height
Kidney (or total manometric height) for different types of manufacturer pumps from which one can choose the right pump
Figure (7) illustrates an example of these curves
To Calculate the approximate initial value of the required pump capacity ( K. Watt ) according to either of the following two equations depending on the unit water flow rate as follows:
- Pump capacity =[Q(l/m)*TDH(m)*0.0001635]/[(Iinverterefficiency*Pumpefficiency)]
- Pump capacity =[Q(l/m)*TDH(m)*0.002725]/[(Iinverterefficiency*Pumpefficiency)]
Note: Pump capacity (HP) =Pump capacity(Kw)*0.745
#6- Determine the appropriate solar array capacity
After determining the pump capacity, the technical data of the suitable solar panel array is determined to provide the electrical energy needed to run the solar pump.
Solar array power = pump capacity (K. Wat )*1.5
A safety factor (1.5) has been added to compensate for losses in the inverter and circuit components, as well as for compatibility With the fluctuations of weather conditions.
After determining the capacity of the array, the number of appropriate modules is chosen, whose total capabilities are equivalent to that of the array.
There are many photovoltaic (PV) models with different capacities. Figure (9) illustrates some of the modules that It is useful for determining the number of necessary modules by dividing the capacity of the array by the capacity of the selected module.
Read also : Solar Panels Qualities and Costs
#7.The Solar pump inverter
This inverter is used in the event of an AC power requirement, as it is installed to convert the DC current generated from the Photovoltaic station to AC. And the power of the inverter is determined as follows:
Inverter power( k. Watt )= pump power (k. Watt )
There are inverters with multiple capacities available ranging from 1 to 300 kW, which cover water flow rates
Up to 450 cubic meters per hour.
#8.Determine the capacity of the water tank
All solar water pumping systems use water tanks, to store water for several days instead of storing electrical energy generated from solar panel array. (batteries) .
The general experimental method for determining the reservoir (tank) volume recommends that a minimum of 3 to 5 days of water use be sufficient.
Figure (10) shows a pressure tank and its accessories with a submersible pump. The idea of the pump work is summarized in: Figure (10) is as follows:
- The pump is controlled by a pressure switch.
- Typically, the pressure switch is set in order for the pump to operate at a pressure as low as 30 to 40 ISP.
- The pump disconnects at a pressure of 50 to 70ISP.
- Common to set the pump: Plugged at 40 ISP and Disconnected at 60 ISP.