Pump capacity calculation

Question

I have a borewell dug in my farm and the depth of the borewell is around 195 feet. I have applied for a Solar pump subsidy and I am about to get the equipment with following details:

1. 4.7kW solar panels
2. Controller
3. 5 HP 12 stage submersible water pump
4. Borewell diameter - 6 inch

As I understand from the technician, this is just sufficient lift the water from the borewell. But what I plan is to lift to the highest elevation in the farm so that the water can be fed by gravity in the farm as and when needed.

In the snapshot from Google maps I have calculated the distance to 'push' the water:

So now the details are as follows:

1. Depth of borewell = 195 feet ≈ 200 feet
2. Horizontal distance to push water = 333 mtr = 1092 feet ≈ 1200 feet
3. Number of pipe joints = Around 8 to 10
4. Altitude difference between borewell point and highest elevation land = 68 feet ≈ 70 feet
5. Planned elevated tank construction's highest elevation point = 20 feet
6. Desired flow rate - I do not know it exactly in litres per minute but I do know that 5 HP 12 stage output is around 1 lakh litres per day, so I am ok to forgo around 50% of this to push the water to my desired location.

So the pump should vertically lift a total of 290 feet and should horizontally push a distance of 1200 feet along with around 3 joints in between.

I would like to know if the provided equipment is capable of handling lift and push of water for these distances and elevation, if not, what is the capacity I should be looking at.

Please let me know if the above details are sufficient enough. I need some scientific guidance and best practices as against the technicians guidance because they recommend out of their experience and not out of precise calculation as such.

Edit: I received the pump and solar PV specifications from technician, attached are the details:

Kindly guide me with the maximum lift for the water to higher altitudes.

Answer 1

To determine if the provided solar pump system is capable of meeting your requirements, we need to consider a few factors, including the total dynamic head (TDH) and the pump's performance curve.

The TDH is the total equivalent height that a fluid is to be pumped, taking into account friction losses in the pipe. It includes the vertical lift, the friction loss due to the horizontal distance, and any additional pressure needed for the system to function.

Here are the components of the TDH in your case:

Vertical lift from the borewell: 200 feet Elevation difference to the highest point: 70 feet Height of the elevated tank: 20 feet Friction loss due to pipe length and joints: This will depend on the type and diameter of the pipe, as well as the flow rate. The approximate total vertical lift needed is the sum of the vertical lift from the borewell, the elevation difference, and the height of the elevated tank:

Total Vertical Lift = 290 feet  

(Total Vertical Lift=200feet+70feet+20feet=290feet)

The friction loss in the piping due to the horizontal distance and joints can be estimated using the Hazen-Williams equation or other similar hydraulic calculations, but you'll need to know the type of pipe, the diameter, and the flow rate.

To ensure the pump can handle the TDH, you would typically look at the pump's performance curve, which shows the relationship between the flow rate (in gallons per minute or liters per minute) and the height it can pump to at that flow rate. You mentioned that the 5 HP 12 stage pump can pump approximately 1 lakh liters per day. Assuming continuous operation over 24 hours, that's about:

100000 liters / (24 hours × 60 minutes) ≈ 69.44 liters per minute

However, you also mentioned you are willing to forgo around 50% of this flow rate to achieve the desired lift, which would be around 34.72 liters per minute.

Without the specific pump curve, it's impossible to give a definitive answer. If you can provide the make and model of the pump or the pump curve, it would be easier to evaluate.

In the absence of a pump curve, as a general rule, each stage of a submersible pump can raise water by a certain number of feet depending on the design. You would need to know how many feet each stage can lift and then check if 12 stages are sufficient for 290 feet. If not, you might need a pump with more stages or higher horsepower.

Additionally, it's crucial to consider the efficiency of the solar panel system and whether it can consistently provide the required power for the pump, especially during peak usage times.

Answer 2

Having done a google search for a product with a similar spec as what you have stated here, You can see underneath head size it says 113m. From what you described you need a total head size of 290ft which is 88m. So to answer your question in the first stage is the answer is the pump of the type in capable of fulfilling your requirements. As far as the flow rate is concerned it is difficult to say what it would be without a pump curve but you do have a 25m margin which is a good sign, Pump curves are usually supplied by the manufacturer like this one here.

I used omnicalculator to check my calculations, find a link here