Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and a Tourism Motel in Egypt

doi:10.4236/sgre.2012.31006

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Smart Grid and Renewable Energy, 2012, 3, 43-50

http://dx.doi.org/10.4236/sgre.2012.31006 Published Online February 2012 (http://www.SciRP.org/journal/sgre)

Optimization of Renewable Energy Power System for

Small Scale Brackish Reverse Osmosis Desalination Unit

and a Tourism Motel in Egypt

Faten Hosney Fahmy, Ninet Mohamed Ahmed, Hanaa Mohamed Farghally

Electronics Research Institute, Giza, Egypt.

Email: [email protected]

Received December 4th, 2011; revised January 30th, 2012; accepted February 7th, 2012

ABSTRACT

The main objective of this work is to design an optimal—efficient economic power renewable energy system that feeds

the required electric load of a small scale brackish reverse osmosis desalination unit and a tourism motel located in

Hurghada, Egypt. Four renewable energy power systems are presented in this paper to select the most optimum one of

them. These suggested renewable energy systems are PV-wind hybrid system, stand-alone wind system, stand-alone

photovoltaic system and PV-wind-fuel cell hybrid system. The sizing, optimization and economic estimation of the

proposed systems were performed using HOMER software. HOMER solves the optimization problem to minimize the

global cost and provides the optimum wind turbine, PV, battery and fuel cell ratings. In addition, a comparison between

the four different suggested power system configurations is illustrated in details. PV-wind hybrid system realized the

lowest net present cost and levelized cost of energy. Also, this system was able to provide energy approximately all the

day. The battery state of charge varies between 83% and 99% and it was found that, the PV-wind hybrid system is more

suitable than the others for the selected site and the suggested electrical load.

Keywords: PV; Wind Turbine; Fuel Cell; Hybrid System; Net Present Cost; HOMER

1. Introduction

As the energy demands around the world increase, the

need to alternative energy sources is increased. In addi-

tion to, the rapid depletion of conventional energy (fossil

fuel) resources on a worldwide basis has necessitated an

urgent search for alternative energy sources to cater to

the present day demands. The clean green renewable

sources of energy are expected to play more significant

role in the global energy future. Also, with the increasing

concerns on air pollution and global warming, the clean

renewable energy sources that are environmentally

friendly, unexhausted e.g. solar energy, wind, hydrogen,

geothermal etc. have attracted energy sectors to generate

power on a large scale. Wind and solar energy technolo-

gies are the forerunners amongst various types of re-

newable sources [1,2]. The vast and continuous devel-

opment of the Red Sea zone has led to extensive and in-

creasing potable water demands to match the tourist, in-

dustrial and urban settlements. Given the worsening wa-

ter situation in Egypt due to the massive and increasing

demand by the agricultural sector, supplementary non-

conventional sources including desalination of sea and

brackish water, and reuse of waste water, represent very

important sources to ensure maximum water allocation

for its uses [3]. Also, water demand in a vastly growing

and developing Egyptian community was analyzed as

characterized by a rising standard of living, expansion of

industrialization in mining and petroleum sectors and the

vast expansion of tourist development [4]. There are dif-

ferent methods of seawater and brackish desalination

appropriate for Egyptian environment and recommended

the method of selection of the technology to be used in

each particular site where the possible energy sources are

screened. A small scale reverse osmosis (RO) desalina-

tion system powered by renewable energy sources pre-

sents an ideal solution to provide freshwater to small

communities isolated at remote areas [5]. In the last dec-

ade, desalination, especially by RO, has become one of

the principal safe sources of supply of potable water, and

even water for agricultural use, it is in the Mediterranean,

Africa, the Middle East, and so on, where the potable

water supply is a high priority problem. All this leads to

the need to identify new sources of supply such as the

desalination of brackish or sea water [6,7]. Coupling of

renewable energy and desalination systems holds great

promise for increasing water supplies in water scarce

Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and

a Tourism Motel in Egypt

regions. An effective integration of these technologies

will allow Egypt to address water shortage problems with

a domestic energy source that does not produce air pollu-

tion or contribute to the global problem of climate

change. Meanwhile the costs of desalination and renew-

able energy systems are steadily decreasing [8], while

fuel prices are rising and fuel supplies are decreasing. In

addition, the desalination units powered by renewable

energy systems are uniquely suited to provide water and

electricity in remote areas where water and electricity

infrastructure is currently lacking [9-11]. As the energy

cost is one of the most important elements in determining

water costs where the water is produced from desalina-

tion plants. The aim of this work is to design an optimum

—efficient cost power renewable energy system for po-

wering brackish water reverse—osmosis desalination

system to deliver in the order of 5 m3 of fresh drinking

water per day required for feeding a tourism motel plus

electrical power for supplying the main equipments re-

quired for a motel with the electrical power demand. This

study is performed for the region in Hurghada in Egypt.

Four power system configurations using different energy

sources, namely, stand-alone photovoltaic system, stand-

alone wind system, PV-wind-fuel cell hybrid system and

PV-wind hybrid systems are studied in this paper. Also, a

comparative study between these different power sys-

tems configurations is introduced. These different sys-

tem configurations are simulated in HOMER environ-

ment for sizing optimization which minimizes the system

cost. Also, the simulation results are reported in this pa-

per.

2. Proposed Reverse Osmosis Desalination

Unit

Reverse Osmosis process is used chiefly for separating

the solvent (water) from aqueous salt solutions. As

shown in Figure 1, the brackish water, pumped from a

well to a storage tank, passes through the desalination

unit and exits in two branches, one as potable water that

is stored in special tank and another as brine water (ele-

vated salinity) that is directed to an evaporative pond.

The feed water enters the unit at a salinity value of

around 3400 ppm and exits as fresh water permeate at a

salinity of around 30 ppm. An external mixing process is

arranged at the exit to produce water for consumption at

a salinity level of around 300 ppm.

3. Load Data

The main goal of system sizing is to achieve the right

balance between daily needs of electrical energy con-

sumed by the loads and daily produced electrical energy

by the generator. The daily consumed electrical energy

by the loads has to be identified at the beginning of sys-

tem sizing, so as to calculate the daily needed electrical

energy and the total peak power of the generator. Also, it

is very important to determine the amount of water con-

sumed by 20 motel inhabitants and the amount of water

required for the daily operation of the motel which is

calculated to be around 5 m3/day. Therefore, the required

electrical load consists of the power needed for supplying

the small scale RO desalination unit and the electricity

required to operate the domestic electrical load of the

motel. According to Reverse Osmosis manufacturer [12,

13] power required to produce 5 m3 per day is 1.8 kW.

This means that, the daily energy required for desalina-

tion unit is approximately 45 kWh. The BWRO (brackish

water reverse osmosis) load is assumed to operate for 24

hours from 0:00 to 24:00. Also, the motel is populated by

approximately 20 inhabitants (15 guests and 5 workers)

and includes a kitchen, a small garden and a small swim-

ming pool. Table 1 shows the daily electrical load re-

quirement of RO unit and the motel total load of appli-

Figure 1. Block diagram of RO system.

Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and

a Tourism Motel in Egypt

Table1. The daily electrical load requirement.

Appliance No. of unitsRated

power (W)

Operation

periods (h)

Reverse osmosis unit 1 1800 24

TV 1 80 11

Refrigerator 1 100 24

Energy saving lamp 2 40 15

Indoor lamp 18 20 15

Fan 18 100 14

Washing machine 1 1000 4

Blower 1 100 10

ances. Figures 2 and 3 shows the estimated daily load

power variation in summer and winter respectively for

a small scale RO desalination unit and a tourism motel

located in Hurghada in Egypt, with a full load of 8.5 kW

as shown in these figures.

4. Site Characteristics

Site selection is based on the following criteria [14]:

· Availability of brackish groundwater.

· Potential of solar radiation and wind speed.

· Electric grid and fresh water network are not avail-

able in the vicinity of the site.

· The social, economic and ecological situation of the

beneficiaries.

· The demand for fresh water.

Hurghada city is the chosen zone as the site under

consideration. It is located at 27˚17′N latitude, 33˚46′E

longitude, elevation 1m and Red sea climate district. The

city is characterized by an intensive solar radiation. Wind

is also an abundant resource. Two water wells are se-

lected to be the water supply for the reverse osmosis de-

Figure 2. Daily load data in winter.

Figure 3. Daily load data in summer.

salination unit. These wells are Abu Shegala and Umm

Huweitat wells. Each has a depth of 160 m and is located

near Hurghada city [15]. Since the performance of re-

newable energy power system is highly dependant on the

environmental conditions, a site-specific analysis is re-

quired to investigate the associated cost, component size

and overall economics.

5. Resources

The types of renewable energy sources available in the

coastal areas are those of the sun and the wind. Wind and

solar energy resources of Hurghada city are considered

for this study.

5.1. Solar Energy Source

The use of photovoltaic technology, especially in regions

without access to electrical energy from a central power

grid but good solar resources, can play a significant role

in meeting the power demand to run a water-desalination

plant. Red-Sea Coast is known as a rich area of solar

energy and high wind speed. The available solar resource

greatly influences both the configuration and the cost of a

hybrid system. Monthly average solar insolation data for

the selected remote area is shown in Figure 4. We notice

from this figure that, the highest values of the solar inso-

lation are during the summer months (May, Jun., Jul, and

Aug.) and the lowest values are during the winter months

(Nov, Dec. and Jan.). Solar radiation data for this region

was obtained from Egyptian Solar Radiation Atlas [15].

The annual average solar radiation for this area is 6.38

kWh/m2/d.

5.2. Wind Energy Source

Among the coastal areas, the zone of Hurghada is the

highest in wind energy applications. A monthly average

wind speed for Hurghada city was obtained from Egyp-

tian Solar Radiation Atlas. As it is cleared from Figure 5,

the most year months have wind speed values ranging

from 5.7 m/s to 7.8 m/s. The annual average wind speed

in Hurghada is found to be 6.93 m/s [15].

6. Systems Components

In addition to renewable energy sources (wind and solar),

various combinations of PV array, wind turbine, fuel cell,

electrolyzer, battery, and power inverter modules were

taken into account towards identifying an economic solu-

tion that would meet the required load [16].

6.1. Photovoltaic Panels

n this study, photovoltaic panels were specified with

Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and

a Tourism Motel in Egypt

Figure 4. Averages solar radiation profile for hurghada city.

Figure 5. Averages wind speed Profile for Hurghada city.

capital and replacement costs of 8000 $ and 7000 $ re-

spectively, this cost includes shipping, tariffs, installation,

and dealer markups [16]. Some maintenance is typically

required for the batteries of a PV system. A derating fac-

tor of 80% was applied to the electric production from

each panel. This factor reduces the PV production by

20% to approximate the varying effects of temperature

and dust on the panels. The panels were modeled as fixed

and tilted south at an angle equal to the latitude of the

site.

6.2. Wind Turbine

In this analysis, Generic 3 kW model is considered [17,

18]. It has a rated capacity of 3 kW and provides 24 V dc

Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and

a Tourism Motel in Egypt

as output. Cost of one unit is considered to be $1200

while replacement and maintenance costs are taken as

$800 and $75/year respectively [17]. The life time of the

turbine is estimated to be 20 years.

6.3. Fuel Cell

The fuel cell considered in this study has a capacity of 1

kW. Its initial cost is $3000 and its replacement is $2500.

Annual operation and maintenance cost is $175. The life

time of fuel cell is estimated to be 5 years [18,19].

6.4. Electrolyzer

Water electrolyzer consists of several cells connected in

series. Two electrodes of the elcrolyzer are separated by

an aqueous electrolyte or solid polymer electrolyte. Elec-

trical current through the electrolyzer enables the de-

composition of water into hydrogen and oxygen.

The capital cost of one kilowatt of the electrolyzer in-

cludes electrolyzer electronics is 2000 $. The replace-

ment cost of the electrolyzer is assumed to lower than the

capital cost because some components included in the

capital cost have longer life time than the stack itself.

The replacement cost is 1500 $. A durability of 20 years

was given within the scope of this simulation[19].

6.5. Hydrogen Tank

Hydrogen storage tanks are also included in the electro-

lyzer model. Cost of a tank with 1 kg capacity is assumed

to be $1300. The replacement and operational costs are

taken as $1200 and $15/year respectively [19].

6.6. Batteries

One of the major requirements for renewable energy

power systems is to ensure continuous power flow by

storing excess energy from the renewable sources. Tor-

gan L16P lead acid battery type was chosen because it is

a popular and inexpensive option. HOMER considered

the battery sizes from 0 - 20. The voltage regulated lead

acid battery is rate at 24V and has a capacity 360 Ah.

Initially cost for one battery is $275. The replacement

batteries will cost another $275. The operation and main-

tenance cost add further 3 $ with a minimum life time of

5 year [16].

6.7. Inverter

A reliable and efficient power electronic inverter is

needed to maintain flow of energy between the ac and dc

components. The inverter size of 1 kW is taken in this

model. Lifetime of the inverter is considered to be 15

years with an efficiency of 90%. It is one of the major

costs of the system. For a 1 kW inverter, the initial and

replacement costs for the inverter each is $700, with no

cost for operation and maintenance [16].

7. Basic Economical Modeling

The total Net Present Cost (NPC) of the power system is

the objective function to be minimized in the optimiza-

tion process. To calculate the NPC of the system we si-

mulate it throughout its lifetime, obtaining the energy

produced and consumed by the components, their own

lifetimes, the number of times in which the components

must be replaced, the operating and maintenance costs,

the fuel costs, etc.

The renewable energy system cost represented by the

net present cost (NPC) is expressed as:

Ti ii

CCICMOCRc



 

i

S (1)

where CT is the total system cost, This cost takes into

account the initial (capital) and all other costs required

for the system to operate properly over its life. m is the

number of used energy sources, five main parts are con-

sidered: PV array, wind turbine, battery bank, fuel cell

and the inverter. CI is the initial capital cost, CR is the

replacement cost, CM & O is the operation and mainte-

nance cost and CS is the salvage value at the end of the

project [20,21].

The constraints of the optimization problem are ex-

pressed as follows:







Subject to loadpower output

maxunserved load%Load







8. Simulation

We perform the simulation to obtain the optimum power

system configuration that meets the previously men-

tioned load profile. National Renewable Energy Labora-

tory (NREL)’s, Hybrid Optimization Model for Electric

Renewables (HOMER Version. 268Beta) has been used

as the sizing and optimization software tool. It contains a

number of energy component models and evaluates suit-

able technology options based on cost and availability of

resources [18,22,23]. Analysis with HOMER requires

information on resources, economic constraints, and con-

trol methods.

The four previously mentioned power system con-

figurations which are submitted to the technical and eco-

nomical analysis can be addressed as follow:

Power system 1: “PV-wind hybrid system”.

Power system 2: “stand-alone wind system”.

Power system 3: “stand-alone PV system”.

Power system 4: “PV-wind-fuel cell hybrid system”.

Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and

a Tourism Motel in Egypt

9. Optimization Results

The simulation results of the four power system configu-

rations are displayed in Table 2. Power system 1, which

is the PV-wind-battery hybrid system offers the much

lower NPC and Levelized cost of energy (LCOE) with

PV and wind combined together. On the other hand,

power system 3 has higher Initial Capital Costs, NPC and

LCOE. While system 2 has the cheapest initial capital

cost while the NPC and LCOE are higher than power

system 1. This is due to considerable increase of re-

placement, O&M costs. It is cleared that the use of initial

capital cost as the primary decision criteria in remote

area power generation systems is misleading and inap-

propriate. Relying on LCOE, NPC as the key decision

parameters instead of using initial capital cost will result

in the better selection of remote energy technologies.

Also, the high PV-wind-fuel cell power system cost

over PV-buttery system is due to the high capital cost of

fuel cell system and electrolyser compared to the battery.

Economic competitiveness for hydrogen energy systems

is obtainable only with a significant reduction of capital

costs together with a strong decrease in energy prices.

According to the results of the optimization process the

optimal power system comprises a 5 kW PV array, a 6

kW wind turbine, a 10 kW inverter and 10 batteries.

Figure 6 shows the PV-wind-Battery hybrid system ar-

chitecture simulated in HOMER. The proposed system

gives us a total net present cost of $69,524. The cost of

energy is 0.321 $/kWh and the initial capital required is

$40,750.

As shown in Figures 7(a), (b) the load is supplied

with a hybrid system comprising of a PV array, wind

generator and battery storage. As cleared in Figure 7(a),

the PV/Wind hybrid system is able to provide energy

approximately all time of the day. It can be observed that,

the load could be met right through the day .The battery

state of charge varies between 83% and 99% as shown in

Figure 7(b).

Figure 6. HOMER implementation of the PV-wind-battery

hybrid system.

(a)

(b)

Figure 7. Hourly data for pow er system 1.

Table 2. Optimization sizing results.

tem Power system 1

PV-Wind-Battery system

Power system 2

Wind-Battery system

Power system 3

PV-Battery system

Power system 4

PV-Wind-Fuel cell system

Optimization sizing results

5 kw PV array

6 kW PV wind turbine

10 battery each 8.64 kw·h

10 kw inverter

12 kW wind turbine

20 battery each 8.64 kw·h

10 kw inverter

10 kw PV array

10 battery each 8.64 kw·h

10 kw inverter

100 kw PV array

120 kw wind turbine

14 kW fuel cell

80 kw electrelyzer

50 kg hydrogen tank

10 kw inverter

Capital cost ($) 40,750 36,500 51,250 799,800

O & M ($) 5,016 10,033 314 37,790

Replacement cost ($) 26,983 30,677 40,175 127,996

Net Present cost ($) (NPC) 69,524 74,652 87,956 903,281

Levelized cost of energy

(LCOE) ($/kwh) 0.321 0.356 0.414 4.305

Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and

a Tourism Motel in Egypt

Figure 8 shows the hourly data for wind-battery sys-

tem. It can be observed that the load could be met right

through the day with excess energy. The battery state of

charge varies between 93% and 100%. The use of stand-

alone wind electricity generation systems is limited in

rural areas as wind resource is site dependent and de-

pends on the season. It does not produce usable energy

for a considerable portion of time during the year.

Figure 9 presents the same hourly data but for PV

stand alone system. A PV stand alone system may not

easily satisfy loads on 24-h basis as the variation of solar

electricity generation does not always match with the

time distribution of load demand. As shown the battery

state of charge varies from 30% to 44%. Figure 10 pre-

sents the hourly data for PV-wind-fuel cell hybrid system.

As shown in this figure, the system easily satisfies loads

on 24-hours basis.

10. Conclusion

In this paper, the design of an optimum–efficient cost

renewable energy system that meet a known electric load

of small scale brackish reverse osmosis desalination unit

and a tourism motel was developed. The computer pro-

gram (HOMER Pro.) solves the optimization problem to

minimize the objective function considering the different

constraints and provides the optimum wind, solar and

battery ratings. In addition, the comparison between the

four suggested different power system configurations

was illustrated with details. These systems are compared

(a)

(b)

Figure 8. Hourly data for pow er system 2.

(a)

(b)

Figure 9. Hourly data for pow er system 3.

(a)

(b)

Figure 10. Hourly data for power system 4.

with respect to the total net present cost (NPC) and lev-

elized cost of energy. The PV-wind- battery system, of-

fers the much lower NPC and LCOE. On the other hand,

PV-fuel cell wind hybrid system has higher initial capital

costs, NPC and LCOE. PV-wind-battery system confi-

Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and

a Tourism Motel in Egypt

guration comprising of 5 kW PV array, a 6 kW wind

turbine and 10 batteries each has a capacity of 8.64 kWh

is the most economic solution under given resource and

load conditions. Also, the high PV-wind-fuel cell system

cost over PV-buttery system is due to the high capital

cost of fuel cell system and electrolyser compared to bat-

tery. Therefore, the major obstacle in using hydrogen as a

storage medium is the high cost associated with it.

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