An Eltek Valere Whitepaper: Why Solar and Hybrid solutions have become the preferred second source of energy for the Telecom Industry. For more information, visit www.eltekvalere.com

1. ALTERNATIVE ENERGY SOLUTIONS
FOR OFF GRID SITES
WHY SOLAR AND HYBRID SOLUTIONS HAS BECOME
THE PREFERRED SECOND SOURCE OF ENERGY
February 2010
www.eltekvalere.com
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2. 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
today’s 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 to
install. 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 technologies
involved with Solar Power solutions and how they can be utilized to achieve significant
OPEX savings.
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3.
TABLE OF CONTENT
LOWER THE OPEX WITH ALTERNATIVE ENERGY ....................................................................................... 2
WHY SOLAR POWER HAS BECOME THE IDEAL SECOND SOURCE OF ENERGY, EITHER AS AUTONOMOUS OR HYBRID SOLUTIONS
................................................................................................................................................................... 2
TABLE OF CONTENT.................................................................................................................................. 3
TERMINOLOGY ......................................................................................................................................... 4
I. ABBREVIATIONS.............................................................................................................................. 4
1. SOLAR POWER ..................................................................................................................................... 5
1.1 OFF GRID SITE POWER CONFIGURATION ........................................................................................................ 5
1.2 HARVESTING SOLAR ENERGY ....................................................................................................................... 6
1.2.1 Energy conversion ................................................................................................................... 6
1.2.2 Sun position tracking systems ................................................................................................ 7
.
1.3 BATTERY TECHNOLOGY .............................................................................................................................. 8
2. HOW IT WORKS .................................................................................................................................... 9
2. 1 DIESEL GENERATOR, GEN‐ SET .................................................................................................................... 9
2.1.1 OPEX intensive ............................................................................................................................. 9
2.1.2 CAPEX favourable ....................................................................................................................... 10
2.2 CYCLED DIESEL GENERATOR ...................................................................................................................... 10
2.2.1 CAPEX intensive .......................................................................................................................... 11
2.2.2 OPEX effects ............................................................................................................................... 11
2.3. ADDING SOLAR ENERGY .......................................................................................................................... 11
2.3.1 Solar data ................................................................................................................................... 11
2.4 SUN PATH – FIXED TILT AND TRACKING SYSTEMS .......................................................................................... 13
2.4.1Fixed tilt ...................................................................................................................................... 13
2.4.2 Fixed tilt – seasonal adjustment................................................................................................. 13
2.4.3 E‐W tracking .............................................................................................................................. 13
.
2.4.4 Dual axis tracking, adding N‐S tracking ..................................................................................... 14
2.5 PV PANEL CHARACTERISTICS ...................................................................................................................... 15
2.6. CHARGE CONTROLLERS ............................................................................................................................ 16
2.6.1 1st generation, direct charge control .......................................................................................... 16
2.6.2 2nd generation, MPPT charger ................................................................................................... 16
.
2.6.3. 3rd generation, MPPT charger w/galvanic barrier .................................................................... 16
2.6.4 Eltek Valere Solar charger – Flatpack2 HE Solar ........................................................................ 17
2.7 BATTERIES ............................................................................................................................................. 17
2.7.1 Standby – AGM .......................................................................................................................... 17
2.7.2 OPzV ........................................................................................................................................... 17
2.7.3 OpzS ........................................................................................................................................... 18
2.7.4 NiCd ............................................................................................................................................ 18
3. INTEGRATING PV PANELS IN TO THE POWER SYSTEM ........................................................................ 19
3.1 ADDING SOLAR TO A STANDARD SYSTEM ..................................................................................................... 19
3.2 ADDING SOLAR TO CYCLIC APPLICATION ....................................................................................................... 19
3.3 OPTIMIZING THE HYBRID CYCLIC APPLICATION ............................................................................................... 19
4. CASE STUDY ....................................................................................................................................... 21
REFERENCES ........................................................................................................................................... 23
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4. TERMINOLOGY
Chapter 1 will introduce various site solution configurations for an off grid site and
compare 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 performance
levels.
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. ABBREVIATIONS
The following lists the abbreviations used in this paper.
ATM : Standard Atmosphere symbol (unit of pressure).
BTS : Base Transceiver Station
DOD : Depth of Discharge
EMC : Electro-Magnetic Compatibility
HE : High Efficiency
MPPT : Maximum Power Point Tracking
PV : Photo Voltaic
SOC : State Of Charge
STC : Standard Test Conditions
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5. 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 or
poor-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 a
primary 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 bank
connected 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 and
lifetime 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 a
large 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 is
available 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 with
a 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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6. The following table indicates the typical assessment of each of the basic site
configuration.
“Site down”
Configuration CAPEX OPEX CO2 Emission
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 Photo
Voltaic (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 of
PV 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 several
different charge control technologies currently available in the market for this purpose.
a) 1st generation charge control – PV panels connected/disconnected to batteries by a
contactor.
b) 2nd generation charge control – PV panels connected to batteries through a non
isolated dcdc converter with MPPT functionality.
c) 3rd generation charge control - PV panels connected to batteries through an
isolated dc-dc converter with MPPT functionality.
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7. d) Eltek Valere – Uses an high-efficient isolated DC-DC converter with MPPT
functionality.
The following table indicates the performance of each technology as a charge controller
for solar power on a telecom site.
Conversion Panel energy Surge Telecom
Technology
efficiency utilization protection specification
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 sun’s path varies east-west during a day and north-
south with the seasons, tracking systems can be used to adjust the panel’s orientation
towards 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 position
based on the site’s latitude from the equator.
Energy
Technology CAPEX OPEX Reliability
utilization
Fixed ● ● ● ◔
Seasonal adjusted ◕ ● ● ◑
1-axis ◔ ◑ ◑ ◕
2-axis ○ ◑ ◑ ●
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8. 1.3 Battery Technology
Choosing the correct battery technology and size is an important step when dimensioning
a 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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9. 2. HOW IT WORKS
The previous chapter outlined the pros and cons of the main building blocks when
powering off grid telecom sites. This chapter will focus in detail on the discussed
building blocks.
2. 1 Diesel generator, Gen- Set
The traditional solution for supplying energy to off grid sites is to run diesel powered
generators 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 it’s Generator efficiency curve
Genset efficiency, kWh/l
operation time to supply a load much 3,5
less than it’s rated capacity. Typically 3
as low 10-20%.
Output energy [kWh/l]
2,5
2
As seen from Figure 1, when a 1,5
generator is operating against a small 1
load, the operating efficiency is far 0,5
from optimum. 0
0 10 20 30 40 50 60 70 80 90 100
Load [%]
High maintenance cost Figure 1 Generator efficiency
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
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10. 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.
1 2 ...n n+1
cha cha
discharge discharge discharge charge
rge rge
24h ?h
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 powering
the 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 may
only 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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11. 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 the
controller.
• The batteries designed for cyclic application are generally more expensive than
standby batteries.
• The Ah size of the battery bank needs to be increased to provide discharge time
and serve as backup when a normal discharge cycle has ended.
2.2.2 OPEX effects
However, when also taking into account the OPEX savings realised during the expected
site 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 service
related 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. The
radiated 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 for
solar energy are typically found. Figure 3: Global irradiation map
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12. 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 shows
an 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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13. 2.4 Sun Path – Fixed Tilt and Tracking Systems
The PV panels are mounted into PV stands. There are two major categories of stands, the
fixed 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, while
installations 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 through
out 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 from
east 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, the
tracking systems will use power to operate, thus reducing the overall gain it may provide.
AM PM AM PM AM PM
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14. 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 suns
position 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 diffuse
irradiation, 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 more
moving parts than the 1-axis tracker.
Summer Summer Summer
Spring/Autumn Spring/Autumn Spring/Autumn
Winter Winter Winter
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15. 2.5 PV panel characteristics
PV panels are used to transform the solar irradiation into electrical energy. Different
technologies 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 (25ºC panel temperature,
irradiation 1000W/m2, 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=25°C
200
180
1000W/m²
160
800W/m²
140
Output power [W]
120
600W/m²
100
80
charge
400W/m²
60
Direct
40
200W/m²
20
0
0 5 10 15 20 25 30 35 40 45
Panel voltage [V]
Figure 6: Available power as function of irradiation, 25ºC panel temperature
Power vs panel voltage at varying irradiance , Tpanel=45°C
200
180
1000W/m²
160
140
800W/m²
Output power [W]
120
600W/m²
100
80
charge
400W/m²
60
Direct
40
200W/m²
20
0
0 5 10 15 20 25 30 35 40 45
Panel voltage [V]
Figure 7: Available power as function of irradiation, 45 ºC panel temperature
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16. 2.6. Charge controllers
As outlined in chapter 1, different technologies are used to charge batteries from PV
panels.
2.6.1 1st generation, direct charge control
With a direct charge control, the PV panels are combined in series to match the required
battery 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 battery
voltage 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 as
1st 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 the
issue 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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17. 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 due
to 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 Batteries
As 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 cyclic
applications. 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 the
number of cycles is stated in the datasheet. Typically the number of
cycles can be 1200 cycles at 60% DOD at 20ºC.
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18. 2.7.3 OpzS
The abbreviation OPzS is German, and refers to German standard DIN 40737.
O: Ortsfest = Stationary
Pz: 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 and
lifetime 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 20ºC
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 battery’s ability to tolerate extremes in heat and cold without a
degradation 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 in
the region of deployment.
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19. 3. INTEGRATING PV PANELS IN TO THE POWER SYSTEM
Charge control
LOAD
G AC/DC
Figure 8: Symbolic system configuration
3.1 Adding Solar to a Standard System
If Solar Power is simply added to a standard 24/7 gen-set site, the PV panel power will be
an 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 when
the 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 batteries
will 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 day
without solar energy, and still give the desired backup time if the diesel generator
fails to start.
• The diesel generator and rectifiers must be sized so that the maximum charge
current of the batteries gives an optimum point of operation of the diesel
generator.
• The control of the diesel generator must be timed so that the potential PV energy
will be fully utilized.
• If using lead acid batteries, the battery cells must be regularly balanced by a boost
charge, as the batteries will work in a partial SOC. The battery manufacturer’s
recommendation must be followed.
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20. 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 the
batteries are discharged.
• From after dawn the PV panels delivers energy, and after awhile it is sufficient to
charge the batteries.
• At sunset the load is again supplied by the batteries, and they are again
discharged.
• At a given time or DOD the generator starts, and supplies the load and charges the
batteries. 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.
1 2 ...n n+1
d d
i i
c c
s s
h h
disc c disc c disc
Partly a Partly a Partly
harg h harg h harg charge
chage r chage r chage
e a e a e
g g
r r
e e
g g
e e
24h ?h
Figure 9: Battery voltage, Cycled diesel generator with solar panels
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21. 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 Energy split, August 2009
21 %
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. 79 %
Gen set Solar
Figure 10 : Energy split August 2009
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22. 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 confirmed
by the operator, reducing the monthly carbon footprint by 10 ton, and significantly
increasing the diesel generator service interval.
Fuel usage, August 2009
6000
5000
4000
Diesel [l]
3000
2000
1000
0
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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23. 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 2004
Energy Information Administration
Qwest Power Engineering Organization - Central Office Rectifier Replacement Study
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24. www.eltekvalere.com