Reduce Electricity Usage and Carbon Emissions with Higher Efficiency DC Power Systems

A GREEN REVOLUTION IN DC POWER
HOW A REVOLUTION IN DC POWER SYSTEMS CAN
REDUCE ELECTRICITY USAGE AND CARBON EMISSIONS
21.12.07

WWW.ELTEKVALERE.COM
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TABLE OF CONTENT:

TABLE OF CONTENT: ........................................................................................................ 2
HELPING CARRIERS GO GREEN ....................................................................................... 3
How a Revolution in DC Power Systems Can Reduce Electricity Usage and
Carbon Emissions ...................................................................................................... 3
INTRODUCTION: THE GLOBAL GREEN MOVEMENT.................................................... 3
A TELECOMMUNICATIONS INDUSTRY RESPONSE ..................................................... 4
Efficiency of DC Power Systems ............................................................................ 5
The Cost of Electricity.............................................................................................. 5
THE IMPACT OF RECTIFIER EFFICIENCY ........................................................................ 6
THE PAYOFF ....................................................................................................................... 8
TAKING EFFICIENCY TO A NEW LEVEL .......................................................................... 9
THE ECONOMICS OF THE HE RECTIFIER...................................................................... 10
HIGHER RECTIFIER EFFICIENCY: A DRIVER FOR UPGRADES.................................... 11
Case 1: Access Systems in the Outside Plant .................................................. 12
Case 2: Central Office Power Systems .............................................................. 14
Case 3: Existing Eltek Valere Systems............................................................... 17
CONCLUSIONS.................................................................................................................. 18
REFERENCES..................................................................................................................... 20

A GREEN REVOLUTION IN DC POWER -2- AN ELTEK VALERE WHITE PAPER

HELPING CARRIERS GO GREEN
How a Revolution in DC Power Systems Can
Reduce Electricity Usage and Carbon Emissions

Thinking green is becoming a global phenomenon. Countries, municipalities, businesses,
and even consumers worldwide are focusing more attention on energy conservation and
environmental responsibility. Service providers are also stepping up to this challenge, as
they are significant energy users – consuming billions of kilowatt-hours of electricity per
year. Many have adopted across-the-board reduction programs to ease the impact and
these have yielded good progress. But more can be done to address the most significant
area of power consumption in a telephony network - the DC power systems that power
network equipment.

This paper will outline a revolution in DC power systems that dramatically improves
power conversion efficiency allowing service providers to dramatically cut electricity use
and reduce carbon emissions that contribute to global climate change. Adopting this new
technology is an investment, and this paper will also explore how reduced operating
expenses from these new power systems can provide a return on the investments – both
for the planet and for the bottom line.

INTRODUCTION: THE GLOBAL GREEN MOVEMENT

The green movement is driven by a number of factors. Energy demands are continuing to
rise, despite energy prices that have reached historically high levels. There is growing
concern over the security of the world’s energy supply and the increasing dependence
upon it. The impact of air pollution and global climate change are becoming increasingly
important topics throughout the world. And there is a growing recognition that the
world’s non-renewable energy resources are being depleted.

In combination, these factors have created a heightened awareness of the global issue of
energy conservation, which has generated a call to action around the world.
Governments have put in place incentive programs to encourage the deployment of
alternative energy sources, and are creating mechanisms to regulate carbon dioxide (CO2)
emissions, the principal greenhouse gas associated with pollution and global warming.
CO2 is a byproduct of burning fossil fuels (such as oil, gas, or coal) to create energy.
About 65%1 of the electricity produced worldwide comes from the use of these non-
renewable resources.

Formal energy reduction programs and goals are being established throughout the world.
In 2007, delegates from nearly 190 countries joined together in Bali, Indonesia, to
develop the United Nations Framework Convention on Climate Change, a set of
greenhouse gas emission goals for industrialized countries. The convention was acting


on a UN recommendation that emission be reduced by up to 40% of 1990 levels by the
year 2020.

Some ways governments are reacting to this is by setting internal guidelines for reducing
energy consumption. This is the case with the U.S. Energy Policy Act of 2005 (EPACT),
which requires U.S. government agencies to reduce their energy intensity (measured in
BTUs per gross square foot) by 2% per year resulting in a cumulative 20% reduction by
2015. The overwhelming contributor to achieving this goal has been the reduction in
energy use.

Emissions trading also have emerged as a technique for controlling pollution. The
European Union Emission Trading Scheme is the largest multi-national, greenhouse gas
reduction initiative in the world. In this plan, the European Union establishes limits on
the amount of CO2 emissions that will be permitted in a in a country in a given year, and
provides “allowances” (the total number of allowances equals the acceptable emissions
level). The allowances are allocated among the companies or other groups that are large
CO2 emitters. If a company is going to exceed its allowances for CO2 emissions, it needs
to buy additional allowances from companies that are polluting at a lower than allowed
rate. In effect, reduced emissions are rewarded and excessive emissions are penalized.

Whether through regulations, incentive programs, or appeals to environmental
responsibility businesses, institutions, and consumers are being asked to respond to the
overall energy challenge.

A TELECOMMUNICATIONS INDUSTRY RESPONSE

The telecommunications industry is a major energy user. There is a growing commitment
within the industry, to reduce energy consumption and the associated emission of
greenhouse gases. Companies like AT&T, Deutsche Telecom, NTT, Telefonica,
Verizon, and other large service providers have explicitly stated their social and
environmental responsibility for managing natural resources in their corporate policy.
Energy conservation has become a priority.

In 2006, Verizon consumed 8.9 billion Kilowatt hours (kWh) of electricity and generated
more than 7.1 million metric tons of CO22. This represents not only a massive utilization
of energy, but also an annual cost of almost $900 million (at $0.10 per kWh). The
majority of this energy is associated with the DC power systems that support Verizon’s
network. Verizon estimated in 2003 that 60% to 70% of the energy it uses is for DC
power to run its core telecommunications switching network3. Telefonica estimates that
62% of its total electricity consumption is used to operate its networks4. It is reasonable
to assume that DC power-based systems are the major energy user for most service
providers.

Obviously, reducing the load on these DC power systems is a priority. Great emphasis
has been placed on lower power consumption for the new generation of radio, transport,


access, switching and other equipment being placed into the network. But as wireless
networks continue to expand and broadband capabilities grow, it is a challenge to achieve
significant reductions in the overall need for DC power. In 2004, NTT projected that it
would require 1.5 times its current energy usage level to support the widespread
deployment of always-on broadband connections in 20105.

One clear opportunity for energy reduction is within the DC power system itself.

Efficiency of DC Power Systems

The use of DC power systems has long been the standard in telecommunications
networks. It was chosen for its reliability, safety, and ability to be paired with battery
systems to provide continuous backup power. As with any power conversion technique,
there are associated inefficiencies as electricity is converted to waste heat in the
conversion process. The rectifiers used in DC power systems have improved dramatically
with respect to efficiency.

Rectifiers in a DC power system take AC input from the public utility network and
deliver a regulated DC voltage to operate telecommunications equipment and to charge
the back up batteries. The typical DC power system voltage is 48V, although 12V, 24V,
130V and others are used in some applications.

Switch mode rectifier technology was introduced in the late 1970s, and was a revolution
with respect to the power density and efficiency that it enabled. Typical efficiency for
these first-generation switch-mode power supplies was in the 85% range, operating at 20
kHz switching frequency.

The switch mode technology has continued to advance since its introduction. During the
1990s, MOSFET technology, together with improved soft switching topologies and
control solutions, enabled significantly higher switching frequency and partly lossless
switching. This resulted in further improvements in power density and efficiency.
Today’s 48V rectifiers typically achieve efficiencies of 90% to 91%, with the best-in-
class rectifiers approaching 93% or 94%.

The Cost of Electricity

Service providers have made vast investments in infrastructure over the last 10 to 15
years, particularly in the areas of wireless and broadband networks. These investments
have been very capital intensive and rapid in their deployment. The operational and life-
cycle cost for the installed systems has had less of a focus. This appears to be changing.
Recognizing both the environmental need to conserve energy and the increasing cost of
electricity, service providers have started to give more attention to these operational
considerations.


Figure 1 summarizes 2006 electricity prices in various countries around the world6.

International electricity prices
2006

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Figure 1
International Electricity Prices

The chart demonstrates that there is a wide variation in price from country to country, and
from region to region. Electricity prices have risen during the past decade, and
continuing increases are projected. Since 1998, the typical inflation rate for electricity
prices has ranged from 2% to 9% per year (depending on country).

This paper will demonstrate that electricity cost and rectifier efficiency are significant
factors which should be considered in the selection of a DC power system. For the
examples presented, the price of electricity is assumed to be $0.10 per kWh during the
entire study period. Please note that this is a conservative approach that depresses the
savings that can be expected from increasing DC power system efficiency. Electricity
prices are already higher than that level in many parts of the world, and for simplicity in
the calculations there is no price inflation built into these models.

THE IMPACT OF RECTIFIER EFFICIENCY

It is easy to underestimate the impact of a rectifier which offers a 1 or 2 percent
advantage over an alternative unit. Rather than just focusing on the efficiency number,
its more effective to think in terms of power losses. Let’s look at an example.

Consider the case of a power system that needs to deliver 8,000W of 48V power at a site,
not an uncommon situation. To generate that 8,000W of output power using 90%
efficient rectifiers, a DC power system will utilize 8,889W of AC input power. In that
conversion, 889W is lost power in the form of heat.


The use of 92% efficient rectifiers will require 8,696W of input power and will result in
696W of power losses. The use of the higher efficiency rectifiers reduces power losses by
193W, a reduction of 21.7%. This is illustrated in figure 2.

8,000W
DC Output to load
8,889 W 90% efficient
AC input 889 W
DC power system Lost power (heat)

8,000W
DC Output to load
8,696 W 92% efficient
AC input 696 W

Reduction in lost power is 889W – 696W = 193W

Percent reduction in lost power is 193W / 889W = 21.7%

Figure 2
Rectifier Efficiency Comparison

The energy cost for the 8,000W of load power will occur in either case, but the use of
the more efficient rectifier will save 193W of lost power, which equates to 1,693 kWh of
energy annually. At $0.10 per kWh, that results in about $169 of savings per year.

There is an additional benefit associated with higher efficiency rectifiers. The power lost
in the rectifier conversion from AC to DC takes the form of heat. This heat must be
considered in the cooling requirements at a site. As an example, let us assume that the
power system delivering the 8,000W of 48V power is in an outdoor cabinet for a cell site.
Power cabinets such as these are often air conditioned to provide a controlled
environment and to extend the useful life of the batteries. Although it is more difficult to
estimate the effect of the rectifier efficiency on the cooling system, there are some
simplifications that can help provide a reasonable judgment.

In the example described above, the use of 92% rather than 90% efficient rectifiers
resulted in a savings of 193W of lost power. That lost power equates to 659 BTU per
hour of heat that no longer must be handled by the air conditioner. If in this application
an air conditioner with an EER (Energy Efficiency Ratio) of 10 is used, then it follows
that 65.9W of power is required to run the air conditioning associated with that 659
BTU/h of heat. Another factor needed to convert the power to energy usage, is an


assumption about how often the air conditioner is running. That number is certainly
dependent on the location of the site. A conservative view is that the air conditioner runs
30% of the time during the year.

These calculations are summarized in Figure 3. The conclusion is that an additional
173.2 kWh of electricity is saved annually from the reduction in air conditioning needed
when the higher efficiency rectifiers are used.

Note: A rule of thumb for assessing the impact on cooling energy of high efficiency
rectifiers, in a cabinet, is to simply add 10% additional annual energy savings to that of
the rectifier power savings.

Power lost in 90% efficient plant is 889W
Power lost in 92% efficient plant is 696W

Savings in lost power is 889W – 696W = 193W
Savings in heat is 193W x 3.413 = 659 BTU/hr

Assume EER of air conditioner is 10
10 = BTU capacity of air conditioner / Watts to run air conditioner
Power associated with the heat savings is 659 BTU/hr / 10 = 65.9 W

Assuming air conditioner runs 30% of the time
Annual energy savings is 65.9W x 7.2 hrs/day x 365 days/yr = 173.2 kWh

Figure 3
Impact on Cooling System

The overall annual energy savings associated with the use of the 92% efficient rectifiers
is equal to 2116 kWh for the power to run the rectifiers, plus 173 kWh or the power to
run the air conditioner. This is a total of 1866 kWh of annual savings. At $0.10 per
kWh, the cost savings is about $187 per year.

THE PAYOFF

The problem addressed in this paper is one of reducing energy usage, particularly
electrical energy generated from fossil fuels. In the above example, the use of the higher
efficiency rectifiers has reduced losses in the DC power system by 21.7%, which equates
to a 2% overall reduction in energy usage. With this in mind, consider the Verizon usage
statistics cited earlier. If Verizon could achieve a 2% reduction in overall energy usage,
it would translate to a savings of 178 million kWh per year in electricity (worth $17.8M
per year) and a reduction of more than 142,000 tons of CO2 emissions.


Given these cost savings, how much could a carrier spend to get the higher efficiency
rectifiers? The answer depends on the payback period that is targeted for this investment.
With a five-year payback, the calculations look like this: The present value of saving
$187 per year in energy costs for five years (assuming a 5% cost of money) is $810. That
means up to $810 can be spent on high efficiency rectifiers because that up-front
incremental investment will be recovered over the five-year period. For this simple
example, assume the 8,000W plant is comprised of five 2000W rectifiers (providing N+1
redundancy). This translates into an incremental cost of $162 per rectifier to attain the
2% additional efficiency.

For a two year payback period, the present value of the energy savings is $348. In this
case, an additional $70 can be justified for each of the five rectifiers to get the efficiency
advantages. Our experience in the marketplace suggests that a payback of two years or
less is certainly achievable for rectifiers used in this example. The energy cost savings in
years three and beyond simply provide additional recurring benefits. This trade-off
makes good economic sense and is a very effective way to address the energy reduction
challenge.

TAKING EFFICIENCY TO A NEW LEVEL

Having demonstrated the very tangible value of deploying higher efficiency rectifiers in
DC power systems, let us now take that approach to the next plateau.

Eltek Valere has been the technology leader of the DC power systems industry, driving
the development of rectifiers with the highest efficiency and power density. The company
has, through intensive research, developed new technology for its next generation of
rectifiers, labeled the HE series for High Efficiency. These rectifiers will offer
efficiencies of greater than 96%, an unheard of level in the industry. The HE rectifiers
will be offered as plug-in compatible alternatives to Eltek Valere’s existing, lower cost
rectifiers, which will continue to be available.

As discussed above, the significant energy savings associated with high efficiency
quickly offset the higher price. It should be noted that the incremental price paid for
these HE rectifiers will have a payback time typically between one and three years,
depending on the local electricity price level. Over a ten-year life cycle, the energy
savings make the HE rectifier “nearly free” as will be demonstrated later in this paper.

The graph below (figure 4) shows efficiency as a function of load for the HE rectifier,
compared to its sibling, the standard Flatpack 2, which is representative of the higher-end
rectifiers on the market today. It should be noted that not only is the overall efficiency
significantly improved with the HE rectifier, but it has been optimized to have a
maximum efficiency in the most typical load range for real life applications, which is
between 30%-70% of full load.


Figure 4
Efficiency Curves for HE and Standard Rectifiers

THE ECONOMICS OF THE HE RECTIFIER

To examine the economics of the HE rectifier, let us consider a realistic example of a DC
power system being placed in an air-conditioned, outdoor cabinet at a cell site. Such
systems are typically in the range of 10-25kW, equivalent to 200-500Adc at 48V. The
systems are designed to support the anticipated load (telecom equipment), have spare
capacity for battery charging after an AC power outage, and have redundant capacity in
case of a rectifier failure.

For this example a system equipped with14kW capacity is the configuration for
comparing performance using the standard and the HE versions of Eltek Valere’s 2kW
rectifier.

The 14kW system utilizes seven 2kW rectifiers. As in the previous example, the
assumption is that the average load on the system is 8kW. Therefore, the rectifiers are
operating at 57% of their capacity (approximately 1143W per rectifier). Note from the
efficiency curves in figure 4 that the standard rectifiers will operate at 92% efficiency
under these conditions, while the HE rectifiers are at 96%. The use of the HE rectifier
reduces the power losses by 50% (from 8% down to 4%).

Using the calculation methodology described earlier in the paper, the annual energy
savings associated with the HE rectifiers versus the standard models is 3490 kWh. This
includes a 317 kWh reduction associated with the operation of the air conditioner. At
$0.10 per kWh, this represents an annual savings of $349 in overall energy charges for
the site.

This example illustrates another economic benefit of the HE rectifiers. The use of HE
rectifiers reduces the amount of heat generated in the cabinet by 1236 BTU/h. This heat

A GREEN REVOLUTION IN DC POWER - 10 - AN ELTEK VALERE WHITE PAPER

reduction will likely allow the use of a one-size smaller air conditioner. This would
reduce the CAPEX (capital expense) cost of the cabinet by about $200.

Let us examine the economics of the HE rectifiers over a ten-year operational life for that
site:

For the purposes of this analysis, let us hypothetically assume a $100 incremental price
for the HE rectifier versus the standard unit. With seven rectifiers in the system, the
additional purchase price for the power system is $700, which is partially offset by the
$200 savings on the cost of the cabinet (due to the smaller air conditioner). The net
CAPEX impact on the overall cost is $500.

The reduced OPEX (operating expense) due to energy cost savings is $349 per year,
making the payback of the incremental $500 CAPEX outlay about 18 months. The Net
Present Value of the overall economics over the 10-year period (assuming a 5% cost of
money) is $2,195. That means that the use of the HE rectifiers will generate $2195 of
savings (in today’s dollars) compared with the standard rectifiers. That $2,195 will pay
for a major portion of the DC power system.

The results are more dramatic in the example, when the results of the HE rectifier are
compared to a 90% efficient unit (rather than the standard Eltek Valere unit of 92%
efficiency). The annual energy cost savings would grow to $535. The payback period
would be within 1 year and the net present value would grow to $3,631.

At 96% efficiency, the argument for deploying the HE rectifiers is quite compelling. The
incremental price is projected to be well within the $100 hypothetical level used in the
analysis, and the significant energy savings provide rapid payback.

HIGHER RECTIFIER EFFICIENCY: A DRIVER FOR UPGRADES
The cases examined so far are those in which a new DC power system is required, and a
comparison is made between alternative solutions of different efficiencies. However, it
may still make sense for carriers to upgrade existing DC power systems with new high
efficiency rectifiers.

Many older power systems can be characterized as approaching obsolescence. That
generally means increasing rectifier failures, more difficulty in obtaining replacement
units, and escalating prices for those replacements. Added to that is the fact that these
older systems are significantly lower in efficiency than those purchased in the last
decade. The result is a strong business case for upgrading the DC power systems at those
sites.


Case 1: Access Systems in the Outside Plant
An access system is the general term given to the electronics that connect subscribers to
the telecommunications network. In the 1970s, the concept of placing electronics in the
outside plant network emerged as a technique for serving subscribers who were located at
long distances from central office switching centers. Previously, those subscribers were
connected via very long, expensive runs of copper cables. In the ensuing decades, that
technique has evolved through the use of digital loop carrier systems, DSL access
multiplexers and fiber to the node or fiber to the home systems. With the placement of
electronics closer to the subscriber, the deployment of outdoor cabinets grew
tremendously. These cabinets housed the access equipment and its supporting power
system.

Unlike the outdoor cabinets that are used at cell sites, the majority of the access system
cabinets do not include air conditioners. The equipment was designed to operate over a
wide temperature range, with fans and/or heat exchangers as the cooling mechanism. The
thermal design of these integrated cabinet systems was an important consideration and a
challenge.

The access systems installed over the last 30 years have performed well and continue to
do so. The exploding subscriber demand for higher speed Internet access has created a
new challenge for service providers to upgrade these cabinets with broadband capability.
Equipment manufacturers have designed a number of solutions for providing the
broadband service. However, there are three obstacles that must be overcome in
implementing these broadband upgrades in the existing cabinets.

The first issue is the availability of space. The broadband solutions generally involve the
installation of a new shelf of equipment (i.e. a DSLAM) into an already crowded cabinet.
The second obstacle relates to power. The broadband equipment will increase the DC
power consumption, sometimes beyond the capacity of the existing power system. And
the final hurdle relates to the thermal design of the cabinet. The additional broadband
equipment (and its associated power demand) will increase the thermal load on the
cabinet, often beyond its design limitations. A solution that addresses all of these
obstacles is the replacement of the existing power system with one of higher efficiency
and power density.

Eltek Valere has created a family of power systems targeted specifically at the upgrade of
existing access systems. Many of the older power systems in these access cabinets are
reaching the point of obsolescence. Failure rates are going up and replacement units are
difficult and /or expensive to obtain. The design of these older systems did not include
such beneficial capabilities as temperature compensation for battery charging, and in
some instances did not allow for N+1 redundant operation. The replacement of the old
power systems can often be justified based solely on the improvement of these two
conditions.


However, the new systems offer additional benefits that are key to broadband upgrades.
The compact design of the power systems, due to a more digital design and higher
efficiency, enables them to provide increased power and more fused distribution.
And, these systems have a footprint that ranges from 50% to as little as 10% of existing
systems. This means more room to install the broadband electronics, and the availability
of power to support it. This addresses the first two obstacles discussed earlier.

What is often overlooked is the impact of higher efficiency rectifiers in addressing the
issue of the thermal design of the cabinet. Let us consider a specific example. Take the
case of an 80 Type Cabinet (double-sided, 2 racks on each side) which is housing a SLC
Series 5 digital loop carrier system, a fiber multiplexer, and the associated power system.
This is a typical application used by service providers in the U.S. Let us assume that the
power system has an average load of 500W (~10A on a 48V plant). The efficiency of the
existing power system in that cabinet is about 80%. This means that 625W is required to
generate that 500W of load power, and 125W is lost as heat (see figure 5 below).

500 W
DC Output to load
625 W 80% efficient
AC input 125 W

500 W
DC Output to load
521 W 96% efficient
AC input 21 W

Reduction in lost power is 125 W Š 21 W = 104 W

Percent reduction in lost power is 104 W / 125 W = 83.2%

Figure 5
Rectifier Efficiency Comparison: Access System

Consider now the replacement of the existing power system with one utilizing Eltek
Valere’s family of HE rectifiers. Operating at an efficiency of 96%, input power of
521W is required to deliver the 500W of load power. Only 21W is lost as heat, a savings
of 104W. This is a reduction of 83.2% in those losses.

As stated earlier, the thermal design of the access cabinet can limit its use as a broadband
system. This example however, has demonstrated that the use of HE rectifiers will
eliminate 104W of lost power. That is power that can now be put to use to feed the
additional broadband equipment that will be placed in the cabinet. This is demonstrated
in figure 6.


500 W
DC Output to load
625 W 80% efficient
AC input 125 W

600 W
DC Output to load
625 W 96% efficient
AC input 25 W

Additional power available for load (without impacting
cabinet thermal performance) is 600W Š 500 W = 100 W

Figure 6
Load Power Availability Comparison

It is assumed that the thermal design of the cabinet was adequate to support the 625W (or
2133 BTU/h) of power input to the existing system. By upgrading the power system to
96% efficiency, a 600W of load output (up from 500W) can be delivered while keeping
the total input power at 625W. That additional 100W can support broadband service for
about 75 subscribers, without affecting the overall thermal performance of the cabinet. In
many instances this efficiency improvement will allow the cabinet to be equipped with
broadband capability, without the need for an upgrade to the cooling system. This is a
major benefit.

In summary, the replacement of the older power plant with the HE system has improved
reliability; added beneficial features such as thermal compensation on battery charging;
and has enabled the deployment of broadband capability without any impact on the
cabinet or its cooling system.

Case 2: Central Office Power Systems

Central office power upgrades are a prime application for higher efficiency rectifiers.
Many of the DC power systems in central offices have been in service for 15 - 20 years,
sometimes even longer. As these plants continue to age, rectifier failures become more
frequent. Obtaining replacement units becomes more difficult, and certainly more
expensive, as suppliers are forced to raise the prices on these low-volume products.
Service providers are faced with the decision of upgrading the systems versus extending
the life of the existing equipment. The economic advantages of higher efficiency
rectifiers can make the decision a relatively easy one.


There are several factors that make the impact of high efficiency so dramatic in central
offices. The first is that the DC loads are generally much higher in a central office than
the levels needed for access system cabinets or cell sites. Many central offices are
equipped with power systems of capacities ranging from 1200A through 10,000A, and
the DC loads on these systems are hundreds or thousands of amps. At these power levels,
energy savings resulting from higher efficiency rectifiers are quite significant.

A second factor relates to the rectifier technology used in the existing systems. Having
been installed decades ago, many of the power systems found in central offices still
incorporate ferroresonant rectifiers. While being an extremely robust technology,
ferroresonant designs are much less efficient than the switched mode rectifiers available
today. Qwest has developed a composite efficiency curve7 for the collection of
ferroresonant rectifiers it uses in central office applications. That curve, which is shown
in figure 7, is assumed to be a reasonable estimate for any service provider. From the
curve it can be seen that the efficiency of ferroresonant rectifiers found in central offices
will be much lower than the 92% or more that can be achieved with today’s switch mode
rectifiers. This is particularly true of rectifiers operating under 80% of capacity (which is
the usual case in central offices).

Ferroresonant Rectifier Efficien
90
87
85
80 82
80
77
70 75

66
60
57
50
48
40
39
30
30
20
0 10 20 30 40 50 60 70 80 90 100
Percent of Full Load
Composite Curve

Figure 7
Composite Ferroresonant Rectifier Efficiency Curve

A third consideration in central offices is the large impact of rectifier efficiency on
cooling systems. The impact is different in the central office compared with the air
conditioned remote cabinet, where the rule of thumb is that for every kWh of energy
saved by the use of higher efficiency rectifiers, an additional 10% of energy savings is
derived from the reduced operation of the air conditioning system. For central offices,
that impact on cooling is even higher because the air conditioning systems essentially run
continuously. Several service providers report that for every kWh of energy saved by the
use of higher efficiency rectifiers in a central office, an additional 35% of energy savings
is derived from the reduced operation of the air conditioning system.


All of these factors contribute to a very favorable business case for upgrading central
office power systems with higher efficiency rectifiers. Let us consider a typical
example. Assume an existing central office power plant equipped with 2000A of
ferroresonant rectifier capacity. The load on the plant is 1200A (approximately 60 kW).
Because of concerns over obsolescence, the service provider has determined to begin a
power system upgrade program, and have chosen a “cap-and-grow” strategy.

In this plan, a new rectifier-only power system will be connected to the existing power
plant (Eltek Valere has a methodology for operating the co-existing systems). Rectifiers
will be added to the new plant over time, as the office load grows or as existing rectifiers
need replacement. The load distribution (breakers/fuses, cabling etc) will be left on the
old plant to minimize the cost and disruption of the upgrade. One objective of this
strategy is to initiate the plant upgrade with a minimum number of new rectifiers, thereby
deferring capital expenses until they are required. This is a sound strategy that balances
CAPEX costs with reduced OPEX costs when based on a standard efficiency rectifier.
However, the economics of high efficiency rectifiers may enable the service provider to
accelerate their replacement strategy.

The rectifiers in the existing power system are operating at 60% of their capacity. Using
the ferroresonant rectifier efficiency curve in figure 7, the overall plant efficiency is 77%.

The service provider has decided to install an Eltek Valere Flatpack2 Power System to
upgrade the plant. The original plan was to equip the new plant with a minimal number
of rectifiers initially. However, for this example, let us assume that enough rectifiers are
purchased to enable the replacement of all of the ferroresonant units on day one. That is
accomplished by providing 1500A of rectifier capacity (1200A for load and 300A for
battery recharge/spare), utilizing the new Flatpack2 HE rectifier. The efficiency of this
system, operating at 80% of capacity, is 95.8%.

Figure 8 compares the energy usage associated with the existing ferroresonant rectifiers
with that of the new HE rectifiers from Eltek Valere. Using the 35% factor for cooling
impact, the total energy savings associated with the plant upgrade is more than 180,000
kWh per year. This equates to $18,084 per year of energy cost savings at $0.10 per kWh.
Assuming that the service provider had already decided to install the new rectifier bay,
the cost of all the rectifiers is recovered in approximately ten months by the energy

60,000W
DC output to load
77,922W 77% efficient
AC input
DC power system 17,922W Lost power (heat)
(61,168 BTU/h)

60,000W
DC output to load
62,630W 95.8% efficient
AC input
DC power system 2,630W Lost power (heat)
(8,978 BTU/h)

Annual energy savings: 133,954 kW/h (for rectifiers)
46,884 kW/h (for cooling*)
180,838 kW/h TOTAL

* Based on typical factor of 35% for additional
A GREEN REVOLUTION IN DC POWER
energy associated with cooling system - 16 - Energy Savings of VALERE WHITE PAPER
AN ELTEK

180,838 kW/h per year

savings.
Figure 8
Central Office Energy Savings

Using energy savings as a catalyst, the service provider can eliminate the concerns over
obsolescence-related failures; implement state of the art controller capabilities; achieve
recurring annual savings in energy expenses; and utilize the removed ferroresonant
rectifiers as spares for other plants that use similar rectifiers. The result is a very
compelling business case for replacing all of the old rectifiers.

Case 3: Existing Eltek Valere Systems

Eltek Valere has shipped hundreds of thousands of their Flatpack2 and V Series rectifiers
to locations throughout the world. These rectifiers are performing extremely well in the
wide-range of applications and environments for which they are designed. While these
are successful installations, the economics – and green benefits – of high efficiency
rectifiers make many of these locations good candidates for upgrade to HE versions of
the product.

The Flatpack2 and V Series of rectifiers have been selected as the initial products to be
offered in the HE (high efficiency) design. As stated earlier, these products will achieve
efficiencies of approximately 96% across their normal load range. And the products are
designed to be plug-in replacements for the standard rectifiers from which they evolved.
That means that a service provider can replace their existing rectifiers with the HE
version to achieve a 4% efficiency improvement, while maintaining all of the exisiting
controller and plant capabilities.

A 4% efficiency improvement makes a significant contribution to corporate initiatives
aimed at energy reduction. The question becomes whether the business case for
replacing a relatively new rectifier is attractive.

Let us go back to the example of the air-conditioned cell site cabinet discussed earlier to
demonstrate the value of the Flatpack2 HE rectifiers. This was a 14KW capacity system,
utilizing seven Flatpack2 (2000W) rectifiers, with an average load of 8KW on the plant.
Assume that the plant was installed using the standard version of those rectifiers. From
the curve in figure 4 it can be determined that the existing rectifiers will be operating at
92% efficiency. If those rectifiers are replaced with the new Flatpack2 HE version, the
efficiency will improve to 96%.

The impact of the 4% efficiency improvement on this system is an annual savings of
3490 kWh. This includes a 10% impact factor for the cooling system. At $0.10 per
kWh, this equates to a savings of $349 per year. The question now becomes how much
one can afford to spend to achieve those savings.


Eltek Valere recognizes that the replacement of relatively new power equipment is not
something that is routinely done in the industry.

For the purpose of this analysis, let us assume that the seven new rectifiers will be
purchased for a net total price of $1,750. This assumes purchase volume discounts and
potential rebates for returned rectifiers or other promotions. With an annual savings of
$349 in energy, the simple cash flow for a 10-year life cycle is depicted in figure 9.

SAVINGS

$349 $349 $349 $349 $349 $349 $349 $349 $349 $349

Year Year Year Year Year Year Year Year Year Year Year
0 1 2 3 4 5 6 7 8 9 10

EXPENSES Rate of Return: 15%
$1750

Figure 9
Rate of Return on Flatpack2 Replacement

In this example, the payback on the rectifier investment will occur in approximately 5
years. Over the 10 year period, the energy savings will provide an overall 15% rate of
return on the investment in the new HE rectifiers. This is an attractive business case for
service providers who are committed to reducing energy usage. Obviously, the five-year
payback period must be weighed against other uses of capital.

The case for replacement of existing Eltek Valere rectifiers is the most challenging one
since the installed units operate at the highest efficiency in the industry today (prior to the
HE products). The analysis is presented here to demonstrate that, even in this extreme
case, the HE rectifiers provide significant energy reduction and a favorable rate of return.

CONCLUSIONS

Eltek Valere estimates that the global telecommunications industry uses nearly 1% of all
the electricity consumed in the world. That estimate is based on an extrapolation of
energy usage statistics from some of the largest service providers in the world, such as
Telefonica, Deutsche Telekom, NTT and Verizon. The data suggests that about 2/3 of that
electricity is used by the DC power systems that supply the telecommunications network
That projects to 115 billion kWh of electricity in 2007, associated with DC power
systems for telecommunications.


A major focus of service providers throughout the globe is the reduction of energy usage
and the emission of greenhouse gases. This is both an environmental and social
responsibility, as well as an economic opportunity. A broad-range of energy
conservation initiatives is being evaluated, and some are being implemented. One of the
most logical and attractive opportunities for energy reduction is found in the DC power
system itself.

Eltek Valere has unquestionably been the technology leader in rectifier design, advancing
efficiencies from an industry standard near 88% to the current benchmark of 92% or
higher. Even at 92% efficiency, 8% of the AC power is lost as heat in the power
conversion process. But the technology advancement continues. Eltek Valere is
introducing its new HE series of rectifiers, which cuts the lost power in half by achieving
unprecedented efficiency of 96% or more.

As demonstrated through numerous examples in this paper, the HE rectifiers enable
service providers to achieve both significant reductions in energy usage and a lower
overall cost than the alternative solutions provide. A life cycle analysis of these typical
cases clearly shows that the energy savings from the use of the HE rectifiers will quickly
payback any existing first-cost premium. These cases are further improved by the
positive impact of the HE rectifiers on cooling systems, or on the thermal performance of
cabinets that do not have air conditioning. For the replacement of older systems, there is
the added benefit of improved reliability and operational features.

The specific payback period for the use of the HE rectifier is dependent on a number of
factors including capacity and load on the system, efficiency of the alternative product
being compared, the cost of electricity at the site, etc. For new systems, the payback
period is generally in the range of two years or less. For retrofit applications, particularly
those involving older rectifiers, the payback period is often closer to one year. In nearly
all instances, a 10-year life cycle analysis will result in an extremely favorable rate of
return on the initial rectifier investment.

What impact could the HE rectifier have on energy usage? As stated earlier, the
telecommunications industry used an estimated 115 billion kWh of electricity to run DC
power systems for its services in 2007. If all of those systems could achieve a 4%
efficiency improvement, which is the minimum offered by the HE rectifiers, then the
overall result would be a savings of 4.8 billion kWh of electricity and a reduction of 3.5
million tons of CO2 emissions. Those annual reductions are equivalent to the electricity
used by 480,000 homes, and the emissions from 580,000 automobiles. In addition to
improving the environment, this 4% efficiency increase would result in an annual savings
of $480 million (at $0.10 per kWh for electricity).

The introduction of the HE rectifiers has given service providers an outstanding vehicle
to help accomplish both their environmental and financial objectives. This product has
reinforced Eltek Valere’s technology leadership in the industry, and it has enabled the
start of a Green Revolution in DC Power Systems.


REFERENCES
1
Electric Power Monthly, November 2007 Edition (Energy Information Administration)
2
Verizon Corporate Responsibility Report 2006
3
Verizon Communications – Green House Gas Emission Reduction Initiatives (on Clean
Air, Cool Planet web site)
4
Telefonica CR Report 2006
5
NTT Group Environmental Protection Activity Report 2004
6
Energy Information Administration
7
Qwest Power Engineering Organization - Central Office Rectifier Replacement Study


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