Abstract. Agricultural efforts are normally carried out in remote areas where electricity from national electric grid may not exist or grid connection is very expensive. Greenhouses industry is one of the most important agricultural practices in remote areas. Greenhouses help in extending the gardening activities and allows us to cultivate certain plants all over the year; by controlling air temperature and relative humidity inside greenhouse. In greenhouses, cooling and pumping equipments dominate the demand for electricity. Therefore, a stand-alone photovoltaic (PV) system is necessary to feed that demand. Medicinal herbs, for example are the most suitable plants to be cultivated in the greenhouses. They often need a temperature range of 15 -21 oC and about 70% relative humidity to grow. As the climate in Egypt is not suitable all over the year to cultivate these medicinal herbs, it is preferable and necessary to use PV-based control greenhouse to cultivate these medicinal herbs in Egyptian remote areas. This paper presents a proposed greenhouse cooling system, which uses a stand-alone PV system to feed the electrical loads of the greenhouse. At the same time, it introduces the complete sizing procedure of the greenhouse stand-alone PV system

A A Nafeh

F H Fahmy

H M Farghally

N M Ahmed

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European Association for the 
Development of Renewable Energies, 
Environment and Power Quality (EA4EPQ) 
 
 
International Conference on Renewable Energies and Power Quality  
(ICREPQ’11) 
Las Palmas de Gran Canaria (Spain), 13th to 15th April, 2011 
 
 
A Modified Cooling System for Stand Alone PV Greenhouse in Remote 
Areas 
 
F. H. Fahmy and A. A. Nafeh N. M. Ahmed, H. M. Farghally,  
Electronics Research Institute, 
El-Tahrir St., El-Dokki, Giza, Egypt 
 
 
 
Abstract. Agricultural efforts are normally carried 
out in remote areas where electricity from national 
electric grid may not exist or grid connection is very 
expensive. Greenhouses industry is one of the most 
important agricultural practices in remote areas. 
Greenhouses help in extending the gardening activities 
and allows us to cultivate certain plants all over the 
year; by controlling air temperature and relative 
humidity inside greenhouse. In greenhouses, cooling 
and pumping equipments dominate the demand for 
electricity. Therefore, a stand-alone photovoltaic (PV) 
system is necessary to feed that demand. Medicinal 
herbs, for example are the most suitable plants to be 
cultivated in the greenhouses. They often need a 
temperature range of 15 - 21 oC and about 70% 
relative humidity to grow. As the climate in Egypt is 
not suitable all over the year to cultivate these 
medicinal herbs, it is preferable and necessary to use 
PV-based control greenhouse to cultivate these 
medicinal herbs in Egyptian remote areas. This paper 
presents a proposed greenhouse cooling system, which 
uses a stand-alone PV system to feed the electrical 
loads of the greenhouse.  At the same time, it 
introduces the complete sizing procedure of the 
greenhouse stand-alone PV system. 
 
Key words 
 
 Greenhouse, cooling system, pump, 
sump, PV system, battery. 
 
1. Introduction 
 
The main purpose of a greenhouse is to improve 
the environmental conditions in which plants are 
grown.  Greenhouses are usually equipped with 
some environmental modification devices such 
as cooling, ventilation and heating systems. 
Ventilation can remove excess heat, increase air 
mixing, and reduce temperature stratification in 
the greenhouse [1]. During summer, in Egypt, 
ventilation alone is not enough to maintain 
optimum interior temperature. Therefore, water 
evaporative cooling systems are usually used to 
reduce the interior air temperature to an 
acceptable level. The cooling of these systems is 
commonly accomplished by using an electrically 
driven fan, pad and a certain shading technique 
[2]. The function of the fan and pad is to prevent 
greenhouse overheating and cool the plants 
during hot weather. Whereas, the function of the 
shading technique is to absorb the solar thermal 
radiation and penetrates only the sunlight that is 
necessary for growing of plants. Therefore, to 
electrify the previously mentioned cooling 
equipments, that are used in remote area 
greenhouses, it is necessary to use a well 
designed stand-alone photovoltaic (PV) systems. 
The main objective of this paper is to introduce a 
proposed greenhouse cooling system, which uses 
a stand-alone PV system to feed the electrical 
load of the greenhouse.  At the same time, it 
introduces the complete sizing procedure of the 
greenhouse PV system. 
 
2. Proposed cooling system 
 
This system is responsible for reducing the air 
temperature inside the greenhouse that affects 
the greenhouse environment and consequently 
the growing of cultivated plants. The proposed 
cooling system consists mainly, of four 
components, as shown in Fig. 1.  These 
components are aluminum pad, cool air fan, 
pump and sump. The pad-fan system requires 
sufficient makeup water to replenish the water 
evaporated from the pad into the incoming air. 
https://doi.org/10.24084/repqj09.240 95 RE&PQJ, Vol.1, No.9, May 2011
When large quantities of air are pulled through 
the evaporative cooling pads that are saturated 
with water, a substantial cooling effect is 
realized due to the evaporation of that water. 
This makeup water is supplied by a reliable 
pump, which pumps the water from sump and 
delivers it to the pad. Therefore, the pad can be 
kept wetly during the cooling system operation. 
This cooling technique can insure a reduction of 
greenhouse interior temperature to about 10-25 
oC. Greenhouse shading is an auxiliary cooling 
technique which is used in this work, to absorb 
the solar thermal radiation and to penetrate only 
the sunlight that is necessary for growing of 
plants. Another auxiliary cooling technique is 
used in the proposed greenhouse sides. This 
technique is based on using the polyethylene 
white coating material layer, which can reflect 
about 50% of the incident solar thermal 
radiation. It is to be noted, that the water 
impermeable plastic material cover is used in the 
proposed greenhouse to protect the interior of the 
greenhouse from the surrounding weather 
conditions. 
 
 
 
Fig.1 The proposed greenhouse cooling system. 
 
1 polyethylene white coating reflects 50%of radiation 
2 water impermeable plastic material cover 
3 greenhouse shading (woven water-porous shade curtain 
material) 
4 aluminum pad 
5 cool air fan 
6 sumps 
7 pump 
8 soil 
 
3. The proposed electrical system 
The proposed greenhouse electrical system 
shown in Fig. 2 is the source of the electrical 
energy required to DC power to the cooling 
system electrical loads. Therefore, the PV array 
and battery subsystems must be sized to provide 
continuous DC power to valves, pumps and fans. 
 
Fig . 2 The proposed greenhouse electrical system. 
 
4. Cooling System Design 
 
A. Cooling Pad  
 
The needed pad area depends upon several 
factors including the type of pad material used. 
The pads should be continuous along the entire 
length of the greenhouse wall.  There are several 
pad materials on the market. Among these are 
pads fabricated from aluminum, from plastic and 
fibers. The used type of pad material in this work 
is aluminum. Aluminum pads have minimum 
maintenance, weather resistant and more 
compatible lightweight. It is recommended that 
one square foot of pad be provided for each 250 
cubic feet per minute (CFM) of air moved by the 
fans [3]. 
 
B.  Pump and Sump  
 
The pumps are sized for the system to supply at 
least 0.5 gallon of water per minute per linear 
foot of pad system. The sump should have a 
capacity of 1 to 1.25 gallons for each linear foot 
of pad in order to hold the water that drains back 
to the sump when the system stops [3]. 
 
C.  Fans 
 
Regardless of the type of pad material used, the 
fans should have the capacity to provide a 
minimum of one air change per minute in the 
greenhouse. The fan capacity should be based on 
total CFM delivered at 1/8 inch static water 
pressure. Standard measurement of airflow 
indicates how many cubic feet of air passes by a 
stationary point in one minute. The higher the 
number, the more air is being forced through the 
system. In controlled environment where a 
precise temperature of air is critical to plant 
growing, power tube fan is required, which 
constructed from heavy gauge steel. The power 
https://doi.org/10.24084/repqj09.240 96 RE&PQJ, Vol.1, No.9, May 2011
tube fan is available in sizes from 12 to 30 
inches. The 12 and 18 inch fans are direct drive 
units. The 24 and 30 inch fans are belt driven.  
The Performance ratings of power tube fans are 
shown in Table 1 [4]. 
 
Table 1:  Performance ratings of fans. 
 
 
 
5. The Electrical System Sizing 
  
A relatively simple sizing procedure [5] can be 
adopted to size the stand-alone PV system of the 
greenhouse. Where, the system sizing in this case 
is based on the yearly energy balance between 
the radiation and the load and is implemented for 
an array with a fixed panel orientation.  
 
A.  Radiation and Load Data  
 
The chosen zone is a remote area of Sinai (Saint 
Cathrine) was selected as the site under 
consideration. The area is located approximately 
in the middle of Sinai Peninsula of Latitude 27
•
 
17
'
, north and Longitude. 33
•
 46
'
, east [6]. 
Fig. 3 shows the monthly averaged daily 
irradiation data. Temperature data are usually 
given in the form of minimum and maximum 
ambient temperatures as indicated in Fig.4.  
 
 
Fig. .3 Solar radiation of Saint Catherine. 
 
Fig. 4. Maximum and minimum temperatures of 
Saint Catherine. 
The electrical load data gives detailed 
information about the equipments to be powered: 
their number, nominal power, nominal operating 
voltage and the number of hours of operation in a 
typical day. Table 2 shows these data for a 
typical greenhouse cooling system.  
 
Table 2: Data for the greenhouse electrical loads. 
 
 
B.  The Sizing Procedure  
 
1)  The number of series-connected modules  
The DC operating voltage VS of the system is 
specified to be 24 V. The number of modules Ns 
[7], which are to be connected in a series string, 
is directly determined by the DC operating 
voltage, as  
 m
S
S V
V
N =
      (1)                                                    
  Where mV is the nominal voltage of the module 
at STC. = 9.6 V( obtained from the PV system 
located in the PV Dept., Electronic Research 
Institute ,Giza, Egypt) . 
 
2)   The number Np of parallel strings  
 
This number is directly related to the current 
requirement of the load. 
The equivalent load current [7] is calculated 
from the equation 
  
 ( )
S
L
L V24
E
AI =                   (2)                                               
 Where EL (Wh/day) is the typical energy 
requirement of the load.  
Now defining the nominal current IP which is 
required from the photovoltaic generator when 
working at its maximum power point and 
irradiated by the standard spectral distribution 
AM1.5 radiation at 1 kW/m2.The energy balance 
[7] for a typical day can then be written as: 
  
 ( ) VsIPSHWh/dayE PL =       (3)                                                         
Where, in Eq. (3) the radiation incident on the 
panel is expressed in peak solar hours (PSH). 
https://doi.org/10.24084/repqj09.240 97 RE&PQJ, Vol.1, No.9, May 2011
Clearly, PSH is numerically equal to the 
irradiation in kWh/m
2
day [6]. Using Eq.(2) and  
Eq.(3) the nominal current IP can be obtained 
according to the following equation: 
  
 PSH
I24
I LP =
   (4)                                                                                       
The number of modules to be connected in 
parallel is then calculated using the following 
equation [7]: 
 
 
m
P
P I
I
N =        (5)                                                                                                          
Where Im is the nominal current supplied by the 
individual photovoltaic module when illuminated 
under standard conditions = 2.4167 A ( obtained 
from the PV system located in the PV Dept., 
Electronic Research Institute, Giza, Egypt) 
 
3)  The Storage Battery Capacity  
 
The storage battery capacity can be regarded as 
serving two purposes. One is to provide a reserve 
capacity to cover an exceptionally long period 
without sunshine, (or system failure). The other 
purpose is to provide seasonal storage [8]. 
The amount of reserve capacity CR required 
depends on several factors. Climate is the most 
effective factor; where sunny arid regions require 
less than foggy coastal regions. The accessibility 
of the site, the regularity of system monitoring, 
and the consequences of system failure are other 
important considerations. Normally, reserve 
capacity of 4 days is adequate for St. Catherine 
site [6].   
Thus CR [8] will be given in terms of the ampere 
hour required per day (Ahr =
s
L
V
E ) and the 
number of the storage day SD,as  
 
 CR =Ahr×SD           (6) 
                                                                        
Having selected the reserve capacity, the next 
step in determining the total capacity Ct is to 
determine the required battery capacity that is 
required to provide seasonal storage Css.  
Where, Css [8] can be given as a function of the 
battery discharge d, as 
  
 Css = Ct ×d     (7)                                                                                 
The excessive depth of discharge will shorten the 
battery life .Therefore, the suitable value of d is 
chosen, in this case, as 0.7. 
Once the value of d is chosen, the total battery 
capacity can be calculated, as 
                      Ct = Css + CR = 
d
CR
−1
       (8)                                                                 
6. Results and Discussion 
 
The complete results of the sizing the greenhouse 
electrical system are illustrated in Table 3 
.Where, the DC operating voltage of the system 
is specified to be 24 V and the  nominal max-
power voltage and current of  the used  module 
at STC are:  9.6 V and 2.4167 A , respectively. 
The Specifications of different components of 
the greenhouse are shown in Table 4. Fig. 5 
presents the hourly data for PV stand alone 
system. As cleared, the PV stand alone system 
with battery bank is able to provide energy 
approximately all time of the day without excess 
electricity to dissipate. The load could be met; 
and the battery state of charge is shown in fig 6, 
ranges between 96 and 99.5 %.  
 
Table 3 The sizing procedure results. 
 
 
 
Fig. 5 Hourly data for stand-alone PV system. 
 
Fig. 6 Battery state of charge. 
https://doi.org/10.24084/repqj09.240 98 RE&PQJ, Vol.1, No.9, May 2011
Table 4  Specifications of different components of the  
proposed greenhouse cooling system. 
 
7. Conclusion 
The PV   powered greenhouse is the best and 
clean method to grow Medicinal herbs in remote 
areas. This method helps to cultivate plants, all 
over the year, that might otherwise be impossible 
to be cultivated during certain seasons, and also 
it helps to protect the plants at a good quality.  
The proposed greenhouse cooling system is 
designed. The design parameters and 
specifications of each component in the cooling 
system are illustrated. The greenhouse volume is 
13762 ft3. Two aluminium pads are  used; each 
has area of 35.75 ft2.  Two pumps are used to 
provide sufficient water to keep the pads wet 
during operation. The pump power is 1/10 hp 
and the mass flow rate of water is 3.25 gallon 
/min. The fan capacity is 3650 ft3 /min. The 
complete sizing procedure of the stand-alone PV 
system is presented. The number of series-
connected PV modules is 3. While, the number 
of parallel strings is 69. Five batteries are used in 
parallel, each has 3000 Ah. 
 
References   
[1] K.S. Kumar *, K.N. Tiwari, Madan K. Jha,” 
Design and technology for greenhouse cooling in 
tropical and subtropical regions: A review”,J. Energy 
and Building, issue 41, pp. 1269–1275 , 2009 . 
[2] Marcel Fuchs , Ehud Dayan, Eugene Presnov,” 
Evaporative cooling of a ventilated greenhouse rose 
crop”, J. Agricultural and Forest Meteorology,issue 
138, pp. 203–215, 2006.  
[3] Dr. Gene A. Giacomelli, "Considerations for 
Energy Management of Greenhouse Heating and 
Cooling", Southern Greenhouse Vegetable Growers 
Association Conference, Shreveport, LA July 19 - 20, 
2002. 
[4] Greenhouse Ventilation Systems, American Cool 
air Corporation. 
[5] T. Markvart, "PV System Sizing Using Observed 
Time Series of Solar Radiation", under published, 
Solar Energy, 2005. 
[6] New and Renewable Energy Authority, Minisstry 
of Electricity and Energy, Egyptian Solar Radiation 
Atlas, Cairo, Egypt, 1998 
[7] D. Mukherjee, and S. chakrabarti, "Fundamentals 
of Renewable Energy Systems",   New Delhi, first 
edition, 2004. 
[8] K.C. Divya, and Jacob stergaard., "Battery energy 
storage technology for power systems—An 
overview", Electric Power Systems Research 
2009,vol. 79, pp. 511–520. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
https://doi.org/10.24084/repqj09.240 99 RE&PQJ, Vol.1, No.9, May 2011


A Modified Cooling System for Stand Alone PV Greenhouse in Remote Areas

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A Modified Cooling System for Stand Alone PV Greenhouse in Remote Areas

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