Design of Photovoltaic (PV) Pumping

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Overview

In order to implement cost effective photovoltaic (PV) pumping system, it is necessary to follow some basic guidelines to design and size every system component. This page will explain about detailed calculation needed for sizing every system component.

The basic step to design photovoltaic (PV) pumping system is:

  1. Determination of water supply need
  2. Calculation of pumping head
  3. Estimation of solar resource
  4. Finding appropriate solar pump and inverter
  5. Calculation of PV panel required


Determination of Water Supply Need

There are two distinct application for photovoltaic (PV) pumping system[1]:

  1. Drinking water supply (domestic water supply)
  2. Irrigation water supply


Domestic Water Supply

For domestic water supply, the first data needed is to estimate the water requirement for one person/day.

A good estimate can be found in "Basic Water Requirements for Human Activities: Meeting Basic Needs" , that relate how much water required to sustain particular activities. Here is the estimate[2]:

Purpose

Recommended minimum

(liter/person/day)


Drinking water

5

Sanitary services

20

Bathing

15

Cooking and Kitchen

10

Total

50

For example:

  • if there are a village with basic need of drinking water, bathing and sanitary services but no need for cooking; then it will require 5+20+15=40 liter/person/day.
  • If the population is 300 persons, then the entire village will require 300 x 40 = 12 000 liter/day.
  • Normally to compensate for water leakage on piping or distribution, 20% additional water will be required then the village will require 14 400 liter/day or 14.4 m3/day.


Calculation of Pumping Head

Pumping head is normally measured in meter (m), so sometimes there are misconception that pumping head is equal to pumping elevation. In actual, pumping head is divided into three components: elevation head, major losses head, and minor losses head.

Pumping Head (m) = Elevation Head (m) + Major Losses Head (m) + Minor Losses Head (m)

  1. Elevation head is measured from the water source surface level to the point of outlet pipe level.
  2. Major losses head is influenced by water flow rate, diameter of pipe, length of pipe, and type of pipe (PVC, HDPE etc)
  3. Minor losses head is influenced by piping accessories including valve, elbow, inlet pipe etc

The detailed explanation can be found on "The Mathematics of Pumping Water, AECOM Design Build Civil, Mechanical Engineering".

Estimation of Solar Resource

Ideally, a ground based solar radiation measurement in location to be installed with solar water pumping system, is required in order to measure accurately the solar resource available for every part of the year. However, due to expensive equipment required, alternative data can be obtained from "Surface meteorology and Solar Energy" (NASA) for every part of the world freely or other solar resource data website available in the internet. 

Solar resources available per day is cited on unit of kWh/m2/day or PSH (peak sun hour) with 1 kWh/m2/day = 1 PSH. Common confusion of solar resource data understanding is usually with solar data cited on unit of W/m2 that describe power.

What is needed on solar pumping design is data cited on energy:

  1. Solar Energy / Day ► cited on unit of kWh/m2/day or PSH     (commonly used for solar pumping design)
  2. Instantaneous Solar Power ► cited on unit of W/m2               (only used for complex modelling)


Finding Appropriate Solar Pump and Inverter

The most important criteria on determining the optimum solar pump is by finding the pump that can satisfy both of daily water flow and pumping head requirement. Normally a solar pump can operate on wide range of water flow rate in response to variation of solar radiation. Generally there are three kinds of pump normally used as solar pump:

1. Centrifugal pump

2. Helical rotor pump

3. Piston (diapraghm) pump

Here is the table that explain the different characteristic of solar pump [3]:

Type

Pumping Head (m)

Flow Rate (m3/day)

Mechanism

Centrifugal pump


0 to 80

6 to 20

Similar to conventional pump

Helical rotor pump


50 to 150 

> 20

Robust, only one turning part

Piston (diapraghm) pump


0 to 150

2 to 5

Complex, lot of moving parts, require oil lubrication

Further Information


References

  1. ↑ https://energypedia.info/index.php/Photovoltaic_(PV)_Pumping
  2. ↑ http://www.pacinst.org/reports/basic_water_needs/basic_water_needs.pdf
  3. ↑ http://www.drfn.info/docs/cbend/energy_factsheets/solar_water_pumps.pdf
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