DESCRIPTION OF AN AUTONOMOUS AUTOMATIC PHOTOVOLTAIC IRRIGATION SYSTEM

Vourdoubas John

Technological Educational Institute of Crete

Department of Natural resources and environment

Romanou 3, Halepa, 73133, Chania, Greece

E-mail:

ABSTRACT

Photovoltaic energy can find many applications in agriculture, providing electrical energy in various cases, particularly in areas without an electric grid. Today the operation of the solar water pumps or the photovoltaic electric fences is well known. In this paper the description of an autonomous automatic photovoltaic irrigation system, is presented. This system was designed and constructed for the automation of the irrigation system of the Organization of the development of Western Crete based in Chania, Crete, Greece. Since various irrigation points of this organization are located in areas without an electric grid, photovoltaic cells can provide the necessary power for the operation of this automatic irrigation system.

INTRODUCTION

Automatic irrigation systems offer many advantages over the traditional manual systems related with the higher productivity of the agricultural crop and with significant savings of water resources. However many times the automatic irrigation systems are located in areas without power supply. Also in Greece, irrigation is needed during the summer when the solar energy is abundant.

The automatic irrigation system (controller and valves) does not consume a lot of energy. Therefore the necessary power can be provided with photovoltaic cells together with a battery for the energy storage.

DESCRIPTION OF THE IRRIGATION SYSTEM

In Western Crete – Greece, the organization for the management of water resources, is using few thousands remote irrigation points to water the cultivated land and various crops with manual operating valves. The water flows in closed pipes under pressure, and the farmers are using the manual valves to water their crops. The system which is described here, replaces the manual valves with automatic electromagnetic valves and a programmable controller can replace the farmer in opening and closing the watering valves. This system has many advantages over the traditional manual watering system like

a)The farmer can programme from the beginning of the irrigation period, the irrigation time and the irrigation frequency.

b)It is not necessary for the farmer to open and close manually the irrigation valves, therefore this system saves his time

c)Since the irrigation time is programmable, the system obtains water saving, particularly if it is combined with water saving irrigation techniques.

The automatic autonomous photovoltaic irrigation system is consisted of

  1. Photovoltaic cell generating power from the solar energy

A photovoltaic cell 35W, 3A, is generating power from solar energy. The output voltage of this cell is 12-17VDC

  1. Electric battery

An electric battery is used for storing the electrical energy, which can be used over night or during the days with limited sunshine.

  1. Electronic battery charge regulator

This is an electronic device which controls the overcharging of the battery and the excessive discharging of it.

  1. Transformer-inverter 12VDC to 24VAC

This device transforms the power from 12VDC to 24VAC. This is necessary since the controller and the valves are operating in 24VAC.

  1. Programmable controller

The programmable controller obtains the control of various electromagnetic valves in different programmes, covering different irrigation needs. Various valves can be connected with this device.

  1. Electromagnetic valves

These valves open and close automatically in a programmable way. They can also operate manually. The farmer can arrange from the beginning of the irrigation period the irrigation frequency and the time interval. He can also intervene manually if he thinks that he should change the irrigation of the crop.

In table 1 the characteristics of the automatic autonomous photovoltaic irrigation system are shown.

DEVICE

/

CHARACTERISTICS

1. Photovoltaic cell / Power 35 W
Voltage 12VDC
2. Battery / Capacity 100 AH
Voltage 12VDC
3. Battery Charge regulator / 3 Amperes
4. Transformer-Inverter / 12VDC 24VAC
5. Programmable controller / Voltage 24VAC

6. Electromagnetic valve

/

0.3 A

Voltage 24VAC

Table 1: Characteristics of the autonomous automatic photovoltaic irrigation system.

OPERATION OF THE SYSTEM

This system was designed and constructed for the operation of six electromagnetic valves 2’’ and the programmable controller was suitable for their control. Different controllers with various control characteristics, permitting the control of more valves can be used.

The angle of the photovoltaic cell was 300 and the battery was capable to power the system if there were 3 continuous days without sunshine. The battery can be discharged up to 60%. Only one valve was open every day for 8 hours. Solar radiation in Chania – Crete – Greece is

In April 152 KWH/M2, in May 183 KWH/M2, in June 191 KWH/M2 , in July 208 KWH/M2 ,in August 207 KWH/M2, in September 172 KWH/M2 , in October 127 KWH/M2 and in November 107 KWH/M2, in an angle of 300 .

A 25% overdesign for the photovoltaic cell and the battery was considered.

The operation of the constructed system was satisfactory.

RESULTS

The autonomous automatic photovoltaic irrigation system which was described earlier has various advantages over the similar manual operating systems, particularly for the Organization of the development of Western Crete – Greece. These are

  1. The system can be installed in areas without electric grid and the necessary power can be provided with photovoltaic energy.
  2. During the summer when, irrigation is needed there is enough solar energy.
  3. This system permits the irrigation of various crops in a programmable way. The presence of the farmer is not necessary during the irrigation.
  4. The system obtains water savings, since the irrigation time and frequency can be accurately programmed.
  5. The cost of this system is relatively low and its reliability is high.
  6. The use of a battery for energy storage, permits the operation of the system over night or in days with limited sunshine.
REFERENCES

[1] Al-Ali,A.R.,Rechman,S.,Al-Agili,S.,Al-Omari,M.H.,Al-Fayezi,M. ,(2001), Usage of photovoltaics in an automated irrigation system , Renewable energy , (23) , pp. 17-26

[2] Markvart, T. (editor) 1994, Solar Electricity, Unesco series, J. Wiley and Sons.

[3] Kontaxakis, E. (1991), Meteorological data of Chania for 1986-1990, National Agricultrural Research foundation, Chania, Crete,Greece.

[4] Technical bulletin, Station controller, Hardie rain jet.

[5] Technical bulletin, Automatic controller, Toro.

[6] Renewable Energy (2000), Godfrey Boyle (editor), Oxford University press.

Fig. 1. Flow diagram of the autonomous automatic photovoltaic irrigation system.