Reverse Osmosis From Renewable Energy Sources in Libya

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DES LIN TION

LS XI R

Desalination 153 (2002) 17-23

www.elsevier.com/bcate/desal

Seawater reverse osmosis powered Tom renewable energy

sources

- hybrid wind/photovoltaic/grid power supply for

small-scale desalination in Libya

Sultan A. Kershrnana, Jtigen Rheinl&nde?*, Hansjijrg Gablerb

“General Electricity Company of Libya (GECOL), Tripoli, Libya

Tel. +218 (21) 4808927; Fax +218 (21) 4808927: email: salkershman@hotmail. corn

‘Center for Soiar Energy and Hyakogen Resecuch, Baden- Wiirttemberg @SW), D-70565 Stuttgart, Germany

Tel. + 49 (711) 7870235; Fax +49 (711) 7870200; email: [email protected]

Received 1 April 2002; accepted 15 April 2002

Abstract

GECOL and a consulting consortium of experts from ZSW, German Wind Energy Institute (DEWI) and Lahmeyer

International (Ll) are preparing the installation of an experimental plant for seawater reverse osmosis desalination

powered from renewable energy sources (SWRO+RES) at Libya’s coast of the Mediterranean sea. The nominal

production of the plant will be 300 ml/d for the supply of a village with potable water. Both wind energy conversion

(WEC) and photovoltaic power generation (PV) will be integrated into a grid connected power supply for a reverse

osmosis (RO) desalination plant with power recovery. While the expected nominal power load for the operation of

the RO desalination system is 70 kW (net power after recovery), the solar PV system is designed for 50 kWp,, and

the WEC for 200 kW nominal output. The design aims at a reduction of the annual non-renewable energy consumption

to about 40 . The economic analysis of the integrated renewable energy systems predicts levelized water cost for

the integration of Grid+WEC with RO ofel .8/m3 and for Grid+PV with RO of cl .9/m3 compared to el .3/m3 for the

fossil only operation of the plant from the grid.

Keyword:

Reverse osmosis; Photovoltaics; Wind power; System integration; Hybrid power supply; Performance

analysis

*Corresponding author.

Presented at the EuroMed 2002 conference on Desalination Strategies in South Mediterranean Countries:

Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean.

Sponsored by the European Desalination Society and Alexandria University Desalination Studies and Technology

Center, Sharm El Sheikh, Egypt, May 4-6, 2002.

00 1 -9 164/02/ - See front matter 0 2002 Elsevier Science B.V. All rights reserved

PII:SOOll-9164(02)01089-5



18

S.A. Kershman et al. / Desalination 153 (2002) 17-23

1. Introduction

From an already completed study on layout and

performance all technical and economic information

needed for the specification of equipment and

implementation of the SWRO+RES plant was

obtained. The task comprised:

layout of feasible -configurations for the

SWRO+RES plant,

definition of components and their technical

characteristics and cost,

prediction of performance for the selected design

configurations,

analysis of economics for the selected con-

figurations.

In the beginning several configurations with

integration of a diesel engine and of a battery

system with power conditioning electronics for

stand-alone power supply as analyzed in [I] were

studied by the joint project team. Finally the team

decided for the implementation ofthe version with

permanent connection to the national power grid.

Solutions with either access to the national grid

or to a diesel based village grid will be the most

probable configurations for later exploitation of

the project results at other sites in the country.

Thus a short-term power storage and a stand alone

power conditioning (setting and control of voltage

and frequency) will not be required with the

integrated SWRO+RES system.

The actual concept of the combined integration

of both, PV and WEC into one desalination plant

is explained by GECOL’s interest in the included

technology transfer and training opportunities.

The following basic sizing was obtained:

RO-desalination system with two streams of

up to 150 n-?/d each for stationary full load

operation during 24 h/d, requiring 70 kW

nominal AC power.

Size of PV field for generation of 50 kWpeak

such that one of the RO streams may be

operated on clear days during summer for 6 h/d

from PV output alone.

Selection of a commercially available WEC

for the generation of nominally 200 kW, which

is suitable for the above described operation

conditions.

The reference system for the evaluation of

incremental project cost and avoidance of CO, is

the Grid-only configuration.

2. The SWRO-RES configurations

The components and the basic scheme of their

integration into the SWRO+RES system are

shown in Fig. 1.

For process simulation and optimization the

process simulation environment IPSEpro from

SimTech (Austria) [2] was adapted and completed

with mathematical component models for RO, PV,

WEC, inverters, accumulators and load manage-

ment of a busbar.

The scheme shows the general configuration

as employed for the numerical performance

prediction: The connectors provided by the busbar

model for diesel engine and accumulator are not

used. The grid power connection can represent

either the national grid or a village grid. The power

results in Fig.

1

correspond to an arbitrarily chosen

sample case of moderate irradiance (500 W/m*)

and wind speed (4.7 m/s).

The four configurations submitted to technical

and economic analysis and the acronyms used to

name them in tables and text are:

“Grid only”

“Grid+PV”

“Grid+WEC”

Baseline system powered from the

national grid only

Integration of solar PV power

generation into grid power supply

Integrationofwind energy conversion

into grid power supply

“Grid+PV+WEC”

Integration of PV and WEC into grid

power supply

The RO system is designed identically for all

configurations. The main design data for all SWRO+

RES configurations are summarized in Table 1.

2. Annual technical performance

Themain objective of the analysis of the annual

technical performance of the SWRO+RES plant



S.A. Kershman et al . / Desali nat i on 153 2002) 17-23

19

1 SWRO+RES 1

I..

j 4.QQ 1 Wh m’

[

Fig.

1.

Components and integration of the SWRO+RES system.

Table

1

Design data for SWRO+RES configurations

Sea

Desalination system

Daily water production demanded, m’/d

RO, rated capacity, m’/d

Annual water production, m3/a

Nominal power demand of RO, feed pump system and

auxiliary loads, kW

RO, spec. power consumption, kWh/m’

Annual power requirement, MWh/a

Seawater storage tank, m3

Product water storage tank. m3

300

300

109500

70

5.6

613

100

300

Power system

Grid only Grid+PV Grid+WEC Grid+PV+WEC

Total rated output (including

capacity of grid connection),

kW 70 120

270 320

PV, rated output, kW

0 50

0 50

WEC. rated outnut, kW

0 0

200 200



20

S.A. Kershman et al. / Desalination 153 (2002) I7-23

was the detennination of the fraction of water that

can be produced from the use of renewable energy.

The performance of the integrated system depends

on the daily and seasonal variations of ambient

temperature, solar h-radiance, wind velocity, and

demand for potable water.

The analysis is done for the 24 h of one average

day of every month of a year. The Excel based

performance prediction yields graphs on daily

performance of the system and summary informa-

tion like annual water production, energy conver-

sion, renewable fraction, and fuel consumption.

The method and the software tools involved were

developed and employed earlier for the detailed

feasibility analysis of integrated solar combined

cycle systems for thermal power plants [3,4].

For the layout and performance calculations a

1 year hourly data set for temperature, wind

velocity and irradiation was compiled according

to METEONORM standard. The nearest recorded

station to the project site Ras Ejder is Djerba

(latitude 33 5” and longitude 10.5”, in Tunisia near

the border with Libya and on an island near the

Mediterranean coast). The main results from the

solar and wind data processing are:

1755 kWh/tn*a annual total of global horizontal irradi-

ation (GHI)

738 kWhlm2a

annual total of diffuse horizontal irradi-

ation (DHI)

1829 kWh/m2a

annual total of it-radiance on flat sur-

faces tilted at 25” from horizontal

9 10 W/m2

maximum hourly mean of total irradi-

ante (July 13th h of day)

1660 kWh/mza

annual total of direct normal irradiation

(DNJ)

4.40 m/s annual average of wind speed at 10 m

above ground

The annual profile of the normalized power

output of the selected WEC shows a pronounced

daily peak during early afternoon hours (see Fig. 2).

For the actually implemented configuration

with integration of both renewable energy sources,

Grid+WEC+PV, the largest monthly deficit of

power supply to the RO process (constant 70 kW

required) is found for November (see Fig. 3). Grid

Time of day [hour]

Fig. 2. Normalized power output of WEC (monthly averages

of hourly values).

connection is required during the whole day. The

largest renewable contribution is associated with

May.

Thanks to the good wind potential in May no

grid supply is required for 8 h. Unfortunately the

peaks of PV and WEC occur practically simulta-

neously. Up to 45 kW power are fed back into the

grid.

Fig. 4 shows a breakdown of the fractions of

annual energy offered by the various sources to

the RO process. The accumulation ofthese fractions

may exceed the value 1 when excess power is

generated and fed into the national grid. The Grid-

only reference system and the Grid+PV system

will consume just the energy required for the RO

process from the grid connection.

For the Grid+PV system the energy fraction

required from the grid is reduced to 89 by the

50 kW PV system. In the Grid+WEC system the

annually available WEC power will cover 57

of the energy required for RO. About 2 excess

power is fed into the grid. Up to 43 of the annual

energy demand are still requested from the grid.

In case of the combined configuration Grid+

PV+WEC the effect of excess power potential is

more pronounced: Additionally to the 57 from



S.A. Kershman et al. /Desalination 153 (2002) 17-23

21

SwRO+RES,

Grid + PV + WEC

120,

SWRO+RES, Grid + PV + WEC

.., . , .., _._.

., ., .,

m Grid

I Desel

ACCU

40 I. ._.. . .._ _I. _ ._.-I-..____.“.. __“_._--.___.._ I

40 I ._ ..._.I____~

I-- --......--.--._-..L

Solar time of day in November [h]

Solar time of day in May [h]

Fig. 3. Performance of grid, PV and WEC power supply in November and May.

1.20

5

_

pi

4 1.w

e

P

1 .80

2

c

0

0.w

2

g

0.40

B

s

‘g 0.20

IF

0.90

SWRO+RES

rid

only

Grkl W

Grid+WEC Gfld+PV+WEC

Fig. 4. Fractions of energy contributions to annual power

supply to SWRO.

the WEC another 12 are available from PV. But

the excess energy cannot be stored and an amount

equal to a fraction of 8 of the demanded annual

energy will be fed back into the grid. Fig. 4 already

includes information on the total levelized water

cost LWC.

Levelized production cost is separately evaluated

for the production of the electricity and potable

water. In this context the power generation is seen

as a local de-centralized small-scale power plant

and the levelized electricity cost (LEC) calculation

excludes the cost components of the SWRO. The

levelized water cost (LWC) includes all cost com-

ponents of the project. The evaluation method was

developed earlier for the comparison and assess-

ment of small-scale technologies for the desalination

or distillation of typically 10 m3/d of water [5].

The performance data required for comparison

The pronounced differences between the LEC

of systems and for the economic analysis are

for the configurations reflect the impact of the

summarized in Table 2.

larger incremental investment costs for de-central

3.

Economic analysis Table 3)

The

total project cost is calculated as the present

value of the project at start, and includes all cost

items expected during the assumed life of 20

years. The conventional Grid-only SWRO plant

is evaluated at 1.69 Me total project cost. The

incremental costs allocated with the different con-

figurations for integration of RES compared to

the grid-only reference system amount to 39 for

the Grid+PV system, 3 1 for the Grid+WEC

system, and 7 1 for the Grid +PV+WEC system.



22


Table 2

Results from technical performance prediction

Design and performance Grid Grid PV Grid+WEC Grid+PV+WEC

(reference)

Power system

Grid connection, nominal capacity, kW

PV, rated power output, kW

WEC, rated power output, kW

Grid+RES, total cumulative capacity, kW

Energy balance

Grid+RES, energy supplied to SWRO, MWh/a

Grid, annual energy to SWRO, MWh/a

PV, annual energy generated, MWhla

WEC, annual energy generated, MWh/a

Grid+RES, total energy processed, MWhIa

Energy lost, rejected or fed into grid, MWh/a

PV, fraction of total energy processed,

WEC, fraction of total energy processed,

PV+WEC, fraction of total energy processed,

Fuel and emissions

External fuel LHV consumption, MWh,,,/a

External fuel consumption, t/a

COz emission, external, t/a

Total CO*-emission specific for power, kg/kWh

Relative GHG(-CO*)-avoidance,

70

70

613

613

613

0

1753

148

526

0.857

70

50

120

613

543

70

613

0

11.4

0

11.4

1551

776 694

131

65 59

465

233 208

0.759 0.379 0.340

11.5 55.8 60.4

70

70

50

200

200

270

320

613 613

271 243

70

347 347

619 660

6 47

0 10.6

56.1 52.6

56.1 63.2

Table 3

Project cost and levelized cost

Grid

Grid+PV Grid+WEC

Grid+PV+WEC

Investment, c 1,020,345 1,634,970 1,490,595 2,105,220

Project cost (present value), c 1,691,103 2,345,817 2,221,780 2,89 1,907

Incremental cost of the project, c 654,714 530,678 1,200,804

Levelised cost (LEC), &/kWhnergy 3.7 13.0 11.2 20.7

Levelised water cost (LWC), (Z/m3 1.346 1.868 1.769 2.303

Avoidance of COz-emission, t/a 0 60 293 317

Cost of CO,-avoidance

, W

542 91 189

renewable power generation compared to central

conventional power production from fossil energy.

The environmental benefit from the Grid+PV

configuration would be rather modest with 11

solar fraction only. The attractive benefit of 56

wind energy fraction would be achieved with a

3 1 rise of the LWC

only.

The key results for the configuration proposed

for implementation (Grid+PV+WEC) are:

63 fraction of energy from RES

2.11 M‘Z investment

0.25 Mela annual costs

2.89 Me total project cost (present value)

1.20 Me

incremental cost of the project



20.7 EclkWh

2.30 iYm3


23

LEC compared to 3.7 t?c/kWh for the

reference configuration

LWC compared to 1.35urn3 for the refer-

ence configuration

P

131

Thus the LWC for the Grid+PV+WEC con-

figuration too is not more than 7 1 higher than

the LWC for the reference system.

References

[l]

H.G. Beyer, T. Degner and H. Gabler, Operational

behavior of wind diesel systems incorporating short-

term storage: an analysis via simulation calculations,

Solar Energy, 54 (1995) 429-439.

[41

PI

IPSEpro: Integration Process Simulation Environ-

ment, Ver. 3.1, SimTech Simulation Technology, Graz,

Austria, 2000.

J. Rheinlander, M. Horn and H. FUhring, Integrated

solar combined cycle system for Egypt - technical

and economic feasibility of an ISCCS power plant at

Kuraymat in Egypt, 7th Arab Conf. on Solar Energy

and Regional World Renewable Energy Congress,

Sharjah, UAE, 19-22 February 2001.

J. Rheinl nder, M. Horn and Heiner Ftihring, GuD-

KraRwerk mit integriertem Solarsystem, BWK, 6

(2001) 55-58.

J. Rheinlilnder and F. Grater, Technologies for the

desalination oftypically 10 m3/d ofwater- DESALlO

-a tool for the identification of appropriate de-central

solutions, Desalination 139 (2001) 393-397.

Documents

Reverse Osmosis From Renewable Energy Sources in Libya