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ALTERNATIVE ENERGY SOLUTIONSFOR OFF GRID SITES

WHY SOLAR AND HYBRID SOLUTIONS HAS BECOMETHE PREFERRED SECOND SOURCE OF ENERGY

February 2010


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ALTERNATIVE ENERGY SOLUTIONS OFF GRID - 2 - AN ELTEK VALERE WHITE PAPER

LOWER THE OPEX WITH ALTERNATIVE ENERGY

Why Solar Power has become the ideal Second Source of Energy,either as Autonomous or Hybrid Solutions

The consumer demand for telecommunications services continues to increase worldwide,

with some of the highest growth areas being seen in the emerging markets. However,

these areas often are not able to provide the clean, reliable electrical energy required by

todays telecommunications equipment.

Traditionally, operators would use AC Generator Set (Gen-set) to provide either the

primary or supplemental site power needs given they are relatively cheap and easy toinstall. However, given Gen-sets typically run on fossil fuels, it also makes them

expensive to run, noisy and harmful to the environment.

With the growing focus on reducing OPEX and being more environmentally responsible,operators are now looking for more cost-effective and cleaner alternative energy

solutions. This is highlighted by the increasing number of installations that are using solar

energy to provide power to their telecommunication sites.

This white paper has therefore been prepared to describe in detail the technologiesinvolved with Solar Power solutions and how they can be utilized to achieve significant

OPEX savings.


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TABLE OF CONTENTLOWERTHEOPEXWITHALTERNATIVEENERGY....................................................................................... 2

WHYSOLARPOWERHASBECOMETHEIDEALSECONDSOURCEOFENERGY,EITHERASAUTONOMOUSORHYBRIDSOLUTIONS

...................................................................................................................................................................2

TABLEOFCONTENT.................................................................................................................................. 3TERMINOLOGY......................................................................................................................................... 4I. ABBREVIATIONS.............................................................................................................................. 41.SOLARPOWER..................................................................................................................................... 5

1.1OFFGRIDSITEPOWERCONFIGURATION........................................................................................................5

1.2HARVESTINGSOLARENERGY.......................................................................................................................6

1.2.1 Energyconversion...................................................................................................................6

1.2.2 Sunpositiontrackingsystems.................................................................................................7

1.3BATTERYTECHNOLOGY..............................................................................................................................8

2.HOWITWORKS.................................................................................................................................... 92.1DIESELGENERATOR,GENSET....................................................................................................................9

2.1.1OPEXintensive.............................................................................................................................9

2.1.2CAPEXfavourable.......................................................................................................................10

2.2CYCLEDDIESELGENERATOR......................................................................................................................10

2.2.1CAPEXintensive..........................................................................................................................11

2.2.2OPEXeffects...............................................................................................................................11

2.3.ADDINGSOLARENERGY..........................................................................................................................11

2.3.1Solardata...................................................................................................................................11

2.4SUNPATHFIXEDTILTANDTRACKINGSYSTEMS..........................................................................................13

2.4.1Fixedtilt......................................................................................................................................13

2.4.2Fixedtiltseasonaladjustment.................................................................................................13

2.4.3EWtracking...............................................................................................................................13

2.4.4Dualaxistracking,addingNStracking.....................................................................................14

2.5PVPANELCHARACTERISTICS ......................................................................................................................15

2.6.CHARGECONTROLLERS............................................................................................................................16

2.6.11stgeneration,directchargecontrol..........................................................................................16

2.6.22nd

generation,MPPTcharger....................................................................................................16

2.6.3.3rd

generation,MPPTchargerw/galvanicbarrier....................................................................16

2.6.4EltekValereSolarchargerFlatpack2HESolar........................................................................17

2.7

BATTERIES.............................................................................................................................................17

2.7.1StandbyAGM..........................................................................................................................17

2.7.2OPzV...........................................................................................................................................17

2.7.3OpzS...........................................................................................................................................18

2.7.4NiCd............................................................................................................................................18

3.INTEGRATINGPVPANELSINTOTHEPOWERSYSTEM........................................................................ 193.1ADDINGSOLARTOASTANDARDSYSTEM.....................................................................................................19

3.2ADDINGSOLARTOCYCLICAPPLICATION.......................................................................................................19

3.3OPTIMIZINGTHEHYBRIDCYCLICAPPLICATION...............................................................................................19

4.CASESTUDY....................................................................................................................................... 21REFERENCES........................................................................................................................................... 23


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TERMINOLOGY

Chapter 1 will introduce various site solution configurations for an off grid site andcompare the relative cost and performance of each of the major technologies available.

For easy understanding, the comparison is displayed in a table matrix format, with the

following symbols being used to represent the different expenditure or performancelevels.

Briefly stated; the more shaded the circle, the better the assessment.

Symbol Capex / Opex Performance

Minimal / No cost Excellent

Cost effective Very Good

Acceptable Satisfactory

Expensive Below Average

Very Expensive Unacceptable

I. ABBREVIATIONSThe following lists the abbreviations used in this paper.

ATM : Standard Atmosphere symbol (unit of pressure).

BTS : Base Transceiver StationDOD : Depth of Discharge

EMC : Electro-Magnetic Compatibility

HE : High EfficiencyMPPT : Maximum Power Point TrackingPV : Photo Voltaic

SOC : State Of Charge

STC : Standard Test Conditions


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1. SOLAR POWER

The first step in finding out how Solar Power can reduce OPEX is to understand what

technologies are used, how they can be combined and what benefits and limitations each

option has.

1.1 Off Grid Site power configuration

When evaluating the use of Solar Power as an alternative power solution to an off-grid orpoor-grid site, there are 4 basic site power configurations to be considered.

a) Gen-set only: A stand-alone (or redundant) Gen-set configuration runs as aprimary power source in an off-grid site, or as a supplemental power source in a

poor grid region.

If the DC power system has batteries, they would typically be used only in

emergency back-up situations.

b) Cycled Gen-set: A stand-alone Gen-set configuration with a large battery bankconnected to the DC power system.

This solution typically runs the site from the batteries and mainly uses the Gen-set

for battery charging only. This method greatly improves both the efficiency andlifetime of the gen-set, whilst at the same time reducing the daily fuel

consumption.

c) Solar Hybrid Site: A combination of Solar Power and Gen-set onsite, with alarge battery bank connected to the DC power system.

This solution utilizes the solar power when available to run the site and charge

batteries. When solar power is not available, the site would typically be

configured to function like the Cycled Gen-set solution.

This solution further reduces Opex by powering the load when solar power isavailable and charging the batteries with any excess power harvested. In doing so,there is less need to use the gen-set for battery charging.

d) Autonomous Solar: Solar Power is configured as the primary power source witha large battery bank connected to the DC power system.

This topology generally requires over sizing of the solar panels and battery bank

due to seasonal variation of the available solar power


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The following table indicates the typical assessment of each of the basic site

configuration.

Configuration CAPEX OPEX CO2 EmissionSite down

Risk

Gen set only

Cycled Gen set

Hybrid Solar only *

* This risk assessment can be improved with CAPEX investment.

1.2 Harvesting Solar Energy

1.2.1 Energy conversion

The radiated energy from the sun is transformed into electrical energy by using PhotoVoltaic (PV) diodes.

Each diode can only produce a very small amount of power by itself, therefore PV diodes

are connected in various series and parallel combinations that help form different types ofPV panels. The specific combination will determine both the panel rated voltage and

rated current capacity.

As the solar energy is instantaneous in nature, any excess energy not used to power a load

must be stored in an energy reservoir; a battery bank for example. There are severaldifferent charge control technologies currently available in the market for this purpose.

a) 1st generation charge control PV panels connected/disconnected to batteries by acontactor.

b) 2nd generation charge control PV panels connected to batteries through a nonisolated dcdc converter with MPPT functionality.

c) 3rd generation charge control - PV panels connected to batteries through anisolated dc-dc converter with MPPT functionality.


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d) Eltek Valere Uses an high-efficient isolated DC-DC converter with MPPTfunctionality.

The following table indicates the performance of each technology as a charge controller

for solar power on a telecom site.

TechnologyConversionefficiency

Panel energyutilization

Surgeprotection

Telecomspecification

1st gen

?

2nd gen

?

3rd gen

?

Eltek Valere

1.2.2 Sun position tracking systems

The amount of energy collected by a PV panels depends on the intensity of sun beams

hitting the front of the panel. As the suns path varies east-west during a day and north-

south with the seasons, tracking systems can be used to adjust the panels orientationtowards the sun, thus helping to maximize the energy harvested by the PV panel.

If sun tracking is not used, then the PV panels are fixed into the most optimal positionbased on the sites latitude from the equator.

Technology CAPEX OPEX ReliabilityEnergy

utilization

Fixed

Seasonal adjusted

1-axis

2-axis


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1.3 Battery Technology

Choosing the correct battery technology and size is an important step when dimensioninga Solar Hybrid site. The battery must provide the desired backup time, handle the desired

number of discharge cycles to the designed DOD, and give a reasonable lifetime in the

operating conditions.

The following table evaluates the cost and performance of three battery technologies

often used in off-grid applications, against a more-traditional standby battery technology.

Technology CAPEX OPEX Cycling Temperature Environment

Standby

OPzV

OPzS

NiCd


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2. HOW IT WORKS

The previous chapter outlined the pros and cons of the main building blocks whenpowering off grid telecom sites. This chapter will focus in detail on the discussedbuilding blocks.

2. 1 Diesel generator, Gen- Set

The traditional solution for supplying energy to off grid sites is to run diesel poweredgenerators 24h a day 7days a week. The batteries banks are used as standby energy,

which means they will only be active is the generator fails. Autonomy is sized for the

time needed to reach the site for service personnel, typically in the range of 6-12h

2.1.1 OPEX intensive

Operating at a low efficiency

The power rating of the installed diesel generator tends to be oversized compared to the

average telecom load it is supplying:

Factors that influence the size of the generator are :

- Generator is sized for full load plus recharging of standby batteries.- Generator is sized for an air condition start-up current- Historically, Generator reliability was in line with the capacity and physical size.

This means that typically a generator

will be operating for most of itsoperation time to supply a load much

less than its rated capacity. Typicallyas low 10-20%.

As seen from Figure 1, when a

generator is operating against a small

load, the operating efficiency is farfrom optimum.

High maintenance cost

Diesel generators are maintenance

intensive, resulting in frequent site visits. The yearly maintenance cost can easily exceed

the initial investment.

Summarized the OPEX disadvantages are:

Working life is typically at low efficiency, less kWh pr litre fuel.

Large CO2 emissions Maintenance and service intensive

Generator efficiency curveGenset efficiency, kWh/l

0

0,5

1

1,5

2

2,5

3

3,5

0 10 20 30 40 50 60 70 80 90 100

Load [%]

Outputenergy[kWh/l]

Figure 1 Generator efficiency


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2.1.2 CAPEX favourable

When operating a off-grid site mainly on a gen-set however, the site installation and

complexity is quite low, as is the CAPEX investment.

CAPEX advantages are :

Generators are relatively cheap compared to many other off-grid power sources.

Small battery bank with standard batteries

A standard power controller can be used

2.2 Cycled Diesel Generator

To cycle the diesel generator means running the generator for a short period of time,then turning it off and operating from the battery bank. The main benefit of this technique

is that when running, the gen set is operating close to full load to re-charge the batteries.

24h

chargedischarge

?h

1 2 ...n n+1

chargedischarge chargedischarge

Figure 2: Battery voltage, Cycled diesel generator

It this configuration, the battery bank changes from being a backup energy source in a

site with a continuously running diesel generator, to play a more active role in poweringthe site.

As the role of the batteries has changed, the battery technology used must also be

updated. Standard lead-acid batteries are designed to serve as a stand-by backup, and mayonly survive 200-300 cycles, depending of DOD in each cycle. In this case, a daily

cycling period using standard batteries would result in need of replacement of the

batteries in less than a year.


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2.2.1 CAPEX intensive

Comparing only the investment cost for a cycled generator vs. a traditional site works in

disfavour of a cycled site:

The need for intelligent start and stop of the generator increases complexity of thecontroller.

The batteries designed for cyclic application are generally more expensive thanstandby batteries.

The Ah size of the battery bank needs to be increased to provide discharge timeand serve as backup when a normal discharge cycle has ended.

2.2.2 OPEX effectsHowever, when also taking into account the OPEX savings realised during the expectedsite lifetime, the overall business case tends to strongly favour a cycled Gen-set solution

in nearly all situations.

Gen set operates at higher efficiency, more energy pr. litre diesel.

Reduced operating hours means less daily fuel usage and less frequent servicerelated site visits.

An example of a successful implementation of a cycled gen set is described in Chapter 4.

2.3. Adding Solar Energy

Although solar irradiation can not be predicted on a daily basis, a reliable estimate of the

monthly average values can be calculated based on the site location, regional weather

data and historical irradiation information.

2.3.1 Solar data

Solar energy is available all over

the globe, at varying intensity. Theradiated energy from the sun is

shown in irradiation maps, like the

one shown in Figure 3.

The maps give a clear indication of

where the most suited areas forsolar energy are typically found. Figure 3: Global irradiation map


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The available energy for a specific location can then be analyzed.

Figure 4 shows an example of an average monthly energy profile, whilst Figure 5 showsan estimated daily energy graph.

Figure 4: Monthly irradiation

Figure 5: Daily irradiation

Solar data are historical data, typically 10 years average. Predicting the exactly amount

of future solar energy on daily basis is not possible, but the historical data gives a good

indication of what can be available as an average.


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2.4 Sun Path Fixed Tilt and Tracking Systems

The PV panels are mounted into PV stands. There are two major categories of stands, thefixed tilt, and the tracking systems. The best solution will depend on the location of the

site, but generally installations close to equator will perform well with fixed tilt, whileinstallations located further north or south will gain from a tracking system.

2.4.1Fixed tilt

The fixed tilted stands are simple in design, and demand no maintenance. The optimum

tilt angle is normally equal to the latitude, but may vary depending on the application. An

installation with fixed tilt will not collect the maximum available solar energy throughout a year.

AM PM AM PM AM PM

2.4.2 Fixed tilt seasonal adjustment

A variant of the fixed tilt adds the possibility of letting the tilt is manually adjusted.Depending on the regularity of site visits, the tilt can be adjusted to increase the monthly

or seasonally collected solar energy.

2.4.3 E-W tracking

An east west tracker is a 1-axis automated tracker that follows the suns position fromeast to west during the day. The tracking will only increase the amount of direct radiated

energy and the mix of solar radiated energy (direct diffuse reflected) determines how

large the total gain is.

Generally a 1-axis tracker will be more expensive than a fixed, it will have moving parts

that are a single point of failure, and it may also require maintenance. In addition, thetracking systems will use power to operate, thus reducing the overall gain it may provide.

AM PM AM PM AM PM


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2.4.4 Dual axis tracking, adding N-S tracking

In a dual axis tracking system, the daily and seasonal north-south variation of the sunsposition is also tracked. The gain is stated to be as high as 40% compared with a fixed

installation during summer by manufacturers, but the real gain will depend on the mix of

the solar energy (direct diffuse reflected) available. The higher the share is of diffuseirradiation, the less is the gain from a tracking system.

The cost of a dual axis tracker is higher than the 1-axis tracker, and will have moremoving parts than the 1-axis tracker.

Winter

Summer

Spring/Autumn

Winter

Summer

Spring/Autumn

Winter

Summer

Spring/Autumn


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2.5 PV panel characteristics

PV panels are used to transform the solar irradiation into electrical energy. Differenttechnologies are used to do the transformation, in this paper mono-crystalline and poly-

crystalline are considered most suitable.

The rating of a panel is given at ideal test conditions, so called STC (25C panel temperature,irradiation 1000W/m

2, and ATM=1.5). As seen in

Figure 6 and

Figure 7, the available power varies significantly with irradiation and panel temperature.

Power vs panel voltage at varying irradiance, Tpanel=25C

1000W/m

800W/m

600W/m

400W/m

200W/m

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30 35 40 45

Panel voltage [V]

Outputpower[W]

Direct

charge

Figure 6: Available power as function of irradiation, 25C panel temperature

Power vs panel voltage at varying irradiance , Tpanel=45C

1000W/m

800W/m

600W/m

400W/m

200W/m

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30 35 40 45

Panel voltage [V]

Outputpower[W]

Direct

char

e

Figure 7: Available power as function of irradiation, 45 C panel temperature


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2.6. Charge controllers

As outlined in chapter 1, different technologies are used to charge batteries from PVpanels.

2.6.1 1st generation, direct charge control

With a direct charge control, the PV panels are combined in series to match the requiredbattery voltage and paralleled in junction boxes to get the desired power. The charger has

no active components, other than over/under voltage relay control the contactor.

The battery voltage will in all charging modes determine the point of operation for the PV panel. As

seen in

Figure 7, a battery voltage of typically 24-25V will reduce the output power to ~70% of

the maximum available power. So even though the direct charge controller has low losses(only conduction losses and junction box diode losses), the utilization of the PV panel is

poor.

Immunity to lightning pulses is low, as there is a direct galvanic connection from the PV

panels into the telecom system. Adding surge protection devices on this equipment will

have limited effect.

2.6.2 2nd generation, MPPT charger

The evolution from 1st

to 2nd

generation charge controller solves the issue of the batteryvoltage determining the operation point of the PV panels. A dcdc converter enables the

possibility to let the output voltage of the charger to be independent from the PV voltage.

The charger needs intelligence in form of a microcontroller etc. to perform Maximum

Power Point Tracking (MPPT) algorithms. With a proper algorithm the charger should be

able to operate at close to 100% PV panel utilization.

The topology of dcdc converter is normally one stage non isolated. This topology will

give conversion efficiency in the range of 92-96%. The charger has the same weakness as1st gen, direct galvanic connection from the PV panels into the telecom system, and

limited effect of surge protection devices.

2.6.3. 3rd generation, MPPT charger w/galvanic barrier

The 3rd inherits the MPPT functionality of the 2nd generation equipment and solves theissue with galvanic barrier by introducing a 2nd stage in the dcdc converter. The added

stage affects the efficiency of the charger; it decreases to typically 86-91%.


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In combination with a correctly sized surge protection, a 3rd generation charge controller

will give good surge protection for the telecom load.

2.6.4 Eltek Valere Solar charger Flatpack2 HE Solar

The Eltek Valere solar charger has all the functionality of the 3rd

gen equipment, but dueto the patented HE technology the efficiency is raised to typically 96%.

The Flatpack2 HE Solar Charger is a product derived from the standard HE technology,and follows the normal telecom standards with respect of safety, EMC, electrical

characteristics and transportation.

The converter is an extension to the standard telecom range offered by Eltek Valere, that

all share the same control interface.

2.7 BatteriesAs mentioned in chapter 1, a large part of configuring a hybrid site is choosing the

optimum battery technology. To find the best fitted technology several parameters must

be evaluated, such as CAPEX, OPEX, ambient temperature, size, expected lifetime,

weight, and fright.

2.7.1 Standby AGM

Standby lead-acid batteries are designed to work as a backup source, and not in cyclicapplications. There they will only survive a limited number of discharge cycles, and if

used in cyclic application it will lead to frequent battery replacement.

2.7.2 OPzV

The abbreviation OPzV is German, and refers to German standard DIN 40742.O: Ortsfest = Stationary

Pz: Panzerplatte = Tubular plate (+)V: Verschlossen = Valve regulated

The batteries are sealed gel based. They are slightly better with respect

of ambient temperature than regular gel batteries but also more

expensive. The lifetime of the battery is a function of DOD, and thenumber of cycles is stated in the datasheet. Typically the number of

cycles can be 1200 cycles at 60% DOD at 20C.


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2.7.3 OpzS

The abbreviation OPzS is German, and refers to German standard DIN 40737.

O: Ortsfest = StationaryPz: Panzerplatte = Tubular plate (+)

S: Spezial = Special, Fluid electrolyte with special seperator

OPzS is a flooded battery designed for cyclic application. They are

better than OpzS with respect of ambient temperature, but as they are

flooded they will require refilling at regular basis. The refill interval andlifetime of the battery is a function of DOD and temperature. The

number of cycles is stated in the datasheet. Typically the number of

cycles can be 1200 cycles at 60% DOD at 20C

Transport restrictions of the product may exist, and must be considered when planning a

project.

2.7.4 NiCd

The characteristics of NiCd batteries are specified in DIN 61427. An advantage of nickel

cadmium is the batterys ability to tolerate extremes in heat and cold without adegradation of its useful life. NiCd batteries can be charged at a higher rate than lead-acid

batteries. NiCd has more cycles at shallow DOD compared with an OPzV/OPzS battery,but less at deeper DOD. The number of cycles is stated in the datasheet

The NiCd requires water topping at an interval given by temperature and DOD. The

Cadmium in the battery is a toxic, and special recycling arrangements must be in place inthe region of deployment.


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3. INTEGRATING PV PANELS IN TO THE POWER SYSTEM

Charge control

G AC/DCLOAD

Figure 8: Symbolic system configuration

3.1 Adding Solar to a Standard SystemIf Solar Power is simply added to a standard 24/7 gen-set site, the PV panel power will bean addition to the available power from the diesel generator. The added power will of

course reduce the power drawn from the diesel generator, but it will actually force the

diesel generator to operate at an even lower efficiency, as the load on it will be less.

In cases when the radiated energy exceeds the instant load and the batteries are fully load,

the excess power from the PV panel will be lost.

3.2 Adding Solar to cyclic application

Adding PV power to a cyclic application, where the generators are prevented to run whenthe PV most likely will deliver energy, will most likely increase the PV energy fraction.

Still there is a potential to increase the harvested PV energy.

3.3 Optimizing the hybrid cyclic application

To optimize the hybrid application several factors needs to be considered. As the batterieswill operate most of the time in partly SOC, batteries suitable for this condition must be

used.

The batteries must be sized so that they can supply the energy on at least one daywithout solar energy, and still give the desired backup time if the diesel generatorfails to start.

The diesel generator and rectifiers must be sized so that the maximum chargecurrent of the batteries gives an optimum point of operation of the dieselgenerator.

The control of the diesel generator must be timed so that the potential PV energywill be fully utilized.

If using lead acid batteries, the battery cells must be regularly balanced by a boostcharge, as the batteries will work in a partial SOC. The battery manufacturers

recommendation must be followed.


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A typical charge/discharge cycle involves the phases shown in Figure 9.

From midnight until sunrise the load is supplied by the batteries, and thus thebatteries are discharged.

From after dawn the PV panels delivers energy, and after awhile it is sufficient tocharge the batteries.

At sunset the load is again supplied by the batteries, and they are againdischarged.

At a given time or DOD the generator starts, and supplies the load and charges thebatteries. At a DOD above 0% the generator stops, making sure that the remaining

battery capacity can be charged by the PV panel energy the next day.

24h

c

h

ar

ge

d

isc

ha

rg

e

Partlychage

disc

harge

c

h

ar

ge

d

isc

ha

rg

e

Partlychage

disc

harge

chargePartly

chage

disc

harge

?h

1 2 ...n n+1

Figure 9: Battery voltage, Cycled diesel generator with solar panels


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Energy split, August 2009

79 %

21 %

Gen set Solar

4. CASE STUDY

Site Location: In the equatorial zone with a stable and predictable regional weather

pattern.

Initial site power configuration : Off-grid BTS site powered with 1+1 15KVA diesel

generators, running 24 hours a day, 7 days a week.

A small lead-acid battery bank connected to the DC power system for emergency back-

up only.

Stated site load profile: The average load was stated as ~2.5kW and autonomy

requirement was 3 days.

Upgrade project target: The initial requirement was to upgrade the site to be partly

powered by PV panels to reduce the OPEX with a limited CAPEX.

Upgrade activities

The site was upgraded as follows:

- Original gen-sets removed and replaced with a single 20KVA gen-set.- DC power system upgraded to 18kW- 3kW solar solution installed.- Upgraded the battery bank to 3000Ah (with OPzV)

- All components integrated and monitored by the DC power system controller.

Gen-set cycling was enabled, with an initial DOD value set at 30%.

Studying the results from the first months showed that the average load was 40% less

than specified, so the actual autonomy was approximately 5 days. After discussion with

the battery supplier the restart charging level of the batteries was increased to 50% DOD,resulting in longer intervals between starting of the diesel generator.

Conclusions

With the current configuration the energy supply split

for a collection of sites in August 2009 is shown in

Figure 10.

Approximately 21% of the energy used on the

sites was delivered by PV panels. The remaining

energy was supplied by the diesel generator.

Figure 10 : Energy split August 2009


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Figure 11 shows a comparison of diesel consumption between the original configuration

and the Eltek Valere hybrid configuration. The fuel reduction of 75% has been confirmedby the operator, reducing the monthly carbon footprint by 10 ton, and significantly

increasing the diesel generator service interval.

Fuel usage, August 2009

0

1000

2000

3000

4000

5000

6000

Diesel[l]

Gen set site Eltek Hybrid solution

Figure 11: Fuel usage comparison, August 2009

For this project, the payback time for the extra investment will be approx 3 years,including battery replacement after 7 years.


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REFERENCES

Electric Power Monthly, November 2007 Edition (Energy Information Administration)

Verizon Corporate Responsibility Report 2006

Verizon Communications Green House Gas Emission Reduction Initiatives(on Clean

Air, web site)

Telefonica CR Report 2006

NTT Group Environmental Protection Activity Report 2004Energy Information Administration

Qwest Power Engineering Organization - Central Office Rectifier Replacement Study


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