DOE/EE-0286 

energy storage systems that can be used as a substitute or supplement to batteries in 

uninterruptible power supply (UPS) systems. Although generally more expensive 

than batteries in terms of first cost, the longer life, simpler maintenance, and smaller 

footprint of the flywheel systems makes them attractive battery alternatives. 

Application Domain 

Batteries for UPS application are typically sized for about 15 minutes of full load 

power. However, the vast majority of power disturbances last for 5 seconds or less. 

Today, many UPS systems are integrated with fuel-fired generators that can come 

up to full power within 10 seconds. Thus, the typical DC flywheel system, designed 

to provide 15 seconds of full load power, could be substituted for batteries in UPS 

systems with fuel-fired generators. Otherwise, DC flywheel systems could be used 

in combination with batteries. Frequent discharging and recharging is much more 

harmful to battery life than flywheel life. Most power disturbances could easily be 

handled by a DC flywheel system, saving the batteries for longer outages and signifiFlywheel Energy Storage 

An alternative to batteries for uninterruptible power supply systems 

Executive Summary 

Flywheels have been around for thousands of years. The earliest application is likely the potter’s wheel. 

Perhaps the most common application in more recent times has been in internal combustion engines. 

A flywheel is a simple form of mechanical (kinetic) energy storage. Energy is stored by causing a disk 

or rotor to spin on its axis. Stored energy is proportional to the flywheel’s mass and the square of its 

rotational speed. 

Advances in power electronics, magnetic bearings, and flywheel materials coupled with 

innovative integration of components have resulted in direct current (DC) flywheel 

cantly increasing battery life. A flywheel could also be used alone for applications where 

longer-term backup capability is not required or economically justified. 

Variations 

In general, flywheels can be classified as low speed or high speed. The former operate at revolutions 

per minute (rpm) measured in thousands, while the latter operate at rpm measured in the tens of 

thousands. As noted above, doubling the rpm quadruples the stored energy, all else equal, so increasing rpm significantly increases the energy density of a flywheel. Operating at higher rpm necessitates 

fundamental differences in design approach. While low-speed flywheels are usually made from steel, 

high-speed flywheels are typically made from carbon or carbon and fiberglass composite materials that 

will withstand the higher stresses associated with higher rpm. Higher rpm also creates greater concern 

with friction losses from bearings and air drag. High-speed flywheels universally employ magnetic bearings and vacuum enclosures to reduce or eliminate the two sources of friction. Magnetic bearings allow 

the flywheel to levitate, essentially eliminating frictional losses associated with conventional bearings. 

While some low-speed flywheels use only conventional mechanical bearings, most flywheels use a 

combination of the two bearing types. Vacuums are also employed in some low-speed flywheels. 

Bringing you a prosperous future where energy 

is clean, abundant, reliable, and affordable 

Leading by example, 

saving energy and 

taxpayers dollars 

in federal facilities 

Illustration courtesy 

of Active Power, Inc. 

Flywheel energy storage 

technologies provide reliable 

backup power with many 

attractive features compared 

with conventional battery 

technologies. 

Internet: www.eere.energy.gov/femp/ 

No portion of this publication may be altered in any form without 

prior written consent from the U.S. Department of Energy, Energy 

Efficiency and Renewable Energy, and the authoring national laboratory. 
Where to Apply 

DC flywheel energy storage systems are 

generally more reliable than batteries, 

so applicability is mostly an issue of 

cost-effectiveness. Batteries will usually 

have a lower first cost than flywheels, 

but suffer from a significantly shorter 

equipment life and higher annual operation and maintenance expenses. Thus, 

flywheels will look especially attractive 

in operating environments that are detrimental to battery life, such as: 

• Frequent cycling stemming from 

main power supply problems. 

• High operating temperatures associated with unconditioned space. 

Flywheels have a much higher power 

densitya

 than batteries, typically by a 

factor of 5 to 10. Therefore, the following conditions are also particularly 

attractive for flywheels. 

• Floor space is expensive 

and has alternative uses. 

• Battery floor space must be 

reclaimed for other purposes 

to the extent possible. 

What to Avoid 

UPS batteries are sized to provide 

backup power for periods measured 

in minutes. The period ranges from 

about 5 minutes up to around 1 hour, 

but is commonly about 15 minutes. A 

period of 15 minutes, more or less, is 

generally presumed adequate to allow 

an orderly shutdown of equipment. 

Flywheels, on the other hand, provide 

backup power for periods measured 

in seconds. The backup period for flywheels is commonly about 15 seconds. 

This is enough time to allow the flywheel to handle the majority of power 

disruptions that last for 5 seconds or 

less and still have time to cover slightly 

longer outages until a backup generator 

can come up to full power (generally in 

10 seconds). However, a flywheel alone 

will not provide backup power for a 

period long enough to allow an orderly 

process shutdown in most cases. Therefore, the following limitations should 

be considered. 

• Flywheels should not be used alone 

for backup power, without batteries 

and/or a fuel-fired generator. 

• Flywheels should not be used without batteries if a fuel-fired generator 

cannot reliably come up to full power 

in 10 seconds or less. 

Conclusion 

Flywheels appear poised to replace or 

supplement batteries as a backup power 

supply in UPS systems. Six companies 

currently offer DC flywheel energy 

storage products. Another half dozen 

or so are developing products they 

expect to bring to market within the 

next few years. Still others offer products where the flywheel is an integral 

part of the UPS system rather than 

being a direct substitute for batteries. 

The current array of available DC flywheel energy storage products includes 

low-speed, unenclosed steel rotors with 

conventional bearings at one end of the 

spectrum and high-speed, composite 

material rotors operating in a vacuum 

with magnetic bearings at the other end 

of the spectrum. Intermediate products 

with elements of these two endpoints 

also exist. It’s not clear yet whether the 

UPS application will move toward one 

end of the technology spectrum or the 

other. Different design approaches may 

each find their niche within the UPS 

application market. 

Although currently developed DC flywheel energy storage systems offer significant advantages over batteries, the 

number of companies currently offering products, and an equal or greater 

number developing products, suggests 

that further product development and 

enhancement is likely to occur. Coupled 

with seemingly ever increasing needs for 

more reliable, higher quality power, the 

long-run prospects for flywheel energy 

storage in UPS applications looks good. 

Flywheels will be a strong alternative 

to batteries in UPS systems with generators that can reliably come on line 

in 10 seconds or less. Otherwise, flywheels could be used to supplement 

batteries, thereby significantly extending battery life and increasing UPS 

system reliability. Although the initial 

cost of a flywheel is typically greater 

than batteries it would be replacing or 

supplementing, its longer life and simpler maintenance will often result in 

lower life-cycle costs. 

a

 Power density is the power output per square foot of building floor space. 

Disclaimer 

This report was sponsored by the United States Department of Energy, Office of Federal Energy Management 

Programs. Neither the United States Government nor any agency or contractor thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, 

or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe 

privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, mark, 

manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by 

the United States Government or any agency or contractor thereof. The views and opinions of authors expressed 

herein do not necessarily state or reflect those of the United States Government or any agency or contractor thereof. 
Contents 

Abstract ............................................................................................................................................. 2 

About the Technology ....................................................................................................................... 2 

Application Domain 

Energy-Saving Mechanism 

Other Benefits 

Variations 

Installation 

Federal Sector Potential ..................................................................................................................... 4 

Estimated Savings 

and Market Potential 

Laboratory Perspective 

Application ....................................................................................................................................... 5 

Application Screening 

Where to Apply 

What to Avoid 

Equipment Integration 

Maintenance Impact 

Equipment Warranties 

Costs 

Utility Incentives and Support 

Additional Considerations 

Technology Performance ................................................................................................................... 6 

Peterson Air Force Base 

Fort Monmouth 

Dallas VA Medical Center 

Case Study ........................................................................................................................................ 7 

Life-Cycle Cost Comparison 

Battery Costs 

Flywheel Costs 

The Technology in Perspective .......................................................................................................... 9 

The Technology’s Development 

Relation to Other Technologies 

Technology Outlook 

Manufacturers ................................................................................................................................... 9 

Who is Using the Technology .......................................................................................................... 10 

For Further Information .................................................................................................................. 10 

Appendix A	 Federal Life-Cycle Costing Procedures 

and the BLCC Software.............................................................................................. 11 

Appendix B NIST BLCC 5.1-02: Comparative Analysis ................................................................ 12 

FEDERAL ENERGY MANAGEMENT PROGRAM — 1 
Abstract 

DC system flywheel energy storage technology can be used as a substitute for 

batteries to provide backup power to 

an uninterruptible power supply (UPS) 

system. Although the initial cost will 

usually be higher, flywheels offer a much 

longer life, reduced maintenance, a 

smaller footprint, and better reliability 

compared to a battery. The combination of these characteristics will generally result in a lower life-cycle cost for 

a flywheel compared to batteries. 

Flywheels intended for UPS application 

(see Figure 1) are typically designed to 

provide power at their maximum rate 

for a period of about 15 seconds. In 

contrast, most batteries for UPS applications are designed to provide their 

maximum-rated power for about 

15 minutes. Therefore, using a flywheel instead of batteries will generally 

require a generator that can come up 

to full power within about 10 seconds, 

which is well within the capabilities of 

standby generators. 

With or without a standby generator, 

flywheels could be used to significantly 

extend battery life and reliability. The 

vast majority of power quality events 

last 5 seconds or less. A flywheel could 

be added to an existing battery-backed 

UPS system and controlled so that the 

flywheel provides backup power for 

short-duration events while the battery 

is saved for longer outages. Such an 

approach plays to the inherent strengths 

of each technology, that is, flywheels 

are highly tolerant to frequent cycling 

(while batteries are not) and batteries 

can provide power for a longer period. 

The first section of this report describes 

the technology, its variations, and installation requirements. The next three 

sections describe the market for the 

technology, application advice, and 

descriptions of the experiences of several federal users. One federal application is highlighted as a “case study,” 

followed by an illustrative life-cycle cost 

comparison of batteries and flywheels. 

Latter sections list manufacturers, 

selected federal users, and reference 

pairs have been used for years as a means 

to isolate electric loads from electricity 

supply disturbances. Flywheels have 

been incorporated into these devices, 

as shown in Figure 2, to increase rotary 

inertia, hence the tolerable disturbance 

period. The usefulness of flywheels 

directly connected in this manner is limited because the frequency of the electricity generated drops in proportion to 

flywheel rpm as energy is extracted from 

the flywheel. Intolerance to significant 

frequency variation will typically limit 

such devices to less than 1 second of 

backup power and only use a few perFigure 1. A flywheel (lower right), integrated cent of the flywheel’s stored energy. with UPS system. 

More effective use of flywheel techmaterials. Life-cycle costing procedures nology in power quality applications 

and results are presented in appendixes. requires some means of disconnecting 

the kinetic energy stored in its rotating 

mass from the electric energy demands About the Technology of the load being served. The addition 

Flywheels have been around for thou- of rectifier and inverter components to 

sands of years. The earliest application the above system, as shown in Figure 3, 

is likely the potter’s wheel. Perhaps the allows voltage and frequency control 

most common application in more while using up to 75% of the energy 

recent times has been in internal com- stored in the flywheel. Adding variable 

bustion engines. A flywheel is a simple speed drive increases system efficiency 

form of mechanical (kinetic) energy and allows the use of a smaller motor. 

storage. Energy is stored by causing a However, the multi-component system 

disk or rotor to spin on its axis. Stored shown in Figure 3 had historically been 

energy is proportional to the flywheel’s too cumbersome and/or too expensive. 

mass (more accurately, its mass moment Advances in electronic power conversion of inertia) and the square of its rota- and control technology, coupled with tional speed. innovative integration of the compoFlywheels are not new to the power nents depicted in Figure 3, have resulted 

quality market either. Motor-generator in DC flywheel energy storage systems 

Motor Flywheel Generator

Illustration courtesy of Active Power, Inc. 

Figure 2. Motor-generator with flywheel. 

Illustration courtesy of Active Power, Inc. 

Figure 3. Motor-generator with flywheel and power electronics. Illustration courtesy of Active Power, Inc. 

2 — FEDERAL ENERGY MANAGEMENT PROGRAM 
that can be used as a substitute or longer outages and significantly increassupplement to batteries in UPS sys- ing battery life. A flywheel could also 

tems. Although generally more expen- be used alone for applications where 

sive than batteries in terms of first cost, longer-term backup capability is not 

the longer life, simpler maintenance, required or economically justified. 

and smaller footprint of the flywheel At least six companies currently offer systems makes them attractive battery DC flywheel energy storage systems, alternatives. The substitution or aug- with another seven companies devel­ mentation of batteries within a UPS oping the technology.

1

 Collectively, system is illustrated in Figure 4. 

several hundred units were 

reported by manufacturers to have been 

Figure 4. UPS system 

with battery and/or flywheel. 

Illustration courtesy of Active Power, Inc. �������

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approximately a 

dozen were at federal facilities. Most 

of these were at military installations, but 

the State Department 

and Veterans Affairs 

were also customers. 

Energy-Saving Mechanism 

Application Domain Flywheels, like batteries, are energy


DC flywheel energy storage systems storage devices. Neither is designed to


could potentially be used anywhere reduce energy consumption; instead,


batteries are currently used in UPS both are designed to provide backup


systems. Batteries for UPS application power when the normal supply is lost.


are typically sized for about 15 minutes Both types of storage devices experi­


of full load power. Historically, this ence standby losses associated with


period was determined by the time maintaining the storage unit in a fully


required for the systems being protected charged condition. Losses also occur as


to come to an orderly shutdown, should energy is charged and discharged, but


power be lost for an extended period of this loss mechanism is relatively unim­


time. Today, many UPS systems are portant in a UPS application, where


integrated with fuel-fired generators the storage devices are not frequently


that can come up to full power within charging and discharging. Standby losses


10 seconds. Thus, the typical DC for flywheels range from about 0.1 to


flywheel system, designed to provide 1.0 % of rated power. This includes


15 seconds of full load power, could recharging power to overcome frictional


be substituted for batteries in UPS losses plus auxiliary equipment. Battery


systems with fuel-fired generators. standby losses, also known as float


Otherwise, DC flywheel systems could power, also vary, but are roughly one-


be used in combination with batteries. tenth of that for flywheels.


Frequent discharging and recharging Other Benefits
 is much more harmful to battery life


than flywheel life. However, the vast While batteries can supply backup


majority of power disturbances last for power for a significantly longer period


5 seconds or less. These disturbances than a flywheel and consumes less


could easily be handled by a DC fly- standby power, most other character-


wheel system, saving the batteries for istics favor a flywheel.


• The design life for a flywheel is typically about 20 years, while most batteries in UPS applications will only 

last 3 to 5 years. 

• Batteries must be kept within a narrow operating temperature range 

typical of space-conditioning requirements for people, while flywheels are 

tolerant of normal outdoor ambient 

temperature conditions. 

• Frequent cycling has little impact 

on flywheel life. In contrast, frequent cycling significantly reduces 

battery life. 

• Flywheel reliability is 5 to 10 times 

greater than a single battery string 

or about equal to two battery 

strings operating in parallel. 

• Flywheels are more compact, using 

only about 10 to 20% of the space 

required to provide the same power 

output from batteries. 

• Flywheels avoid battery safety issues 

associated with chemical release. 

• Flywheel maintenance is generally 

less frequent and less complicated 

than for batteries. 

Variations 

Many design variations exist in the 

flywheels currently available and those 

being developed for UPS application. 

In general, flywheels can be classified as 

low speed or high speed. The former 

operate at revolutions per minute (rpm) 

measured in thousands, while the latter 

operate at rpm measured in the tens of 

thousands. As noted above, doubling the 

rpm quadruples the stored energy, all else 

equal, so increasing rpm significantly 

increases the energy density of a flywheel. Operating at higher rpm necessitates fundamental differences in design 

approach. While low-speed flywheels 

are usually made from steel, high-speed 

flywheels are typically made from carbon 

or carbon and fiberglass composite 

materials that will withstand the higher 

stresses associated with higher rpm. 

Higher rpm also creates greater concern with friction losses from bearings 

1

 Contact information for companies currently offering or developing DC flywheel energy storage systems, and companies with other UPS products 

incorporating flywheels are listed later in this report. 

FEDERAL ENERGY MANAGEMENT PROGRAM — 3 
and air drag. High-speed flywheels 

universally employ magnetic bearings 

and vacuum enclosures to reduce or 

eliminate the two sources of friction. 

Magnetic bearings allow the flywheel 

to levitate, essentially eliminating 

frictional losses associated with conventional bearings. While some lowspeed flywheels use only conventional 

mechanical bearings, most flywheels use 

a combination of the two bearing types. 

Vacuums are also employed in some 

low-speed flywheels. Currently available DC flywheel energy storage systems 

are shown in Figures 5 through 8. 

Installation 

Flywheel installation is relatively simple. 

Most require hardware to attach the 

flywheel to a concrete slab. All require 

Figure 5. Active Power flywheel.2 

Figure 6. Designed Power Solutions flywheel. 

cabling to connect to the DC bus of 

the UPS system and a DC disconnect 

switch to allow servicing. 120 V AC 

service is required for most flywheel 

systems to operate auxiliary equipment 

such as vacuum pumps. Some require 

a higher voltage AC service for recharging the flywheel. Care must be taken 

to select a DC flywheel system with 

an output voltage that matches the 

UPS system DC bus voltage. The UPS 

manufacturer should be consulted to 

ensure electrical compatibility. 

Figure 7. Piller flywheel. 

Illustration courtesy of Urenco Power Technologies, Inc. 

Figure 8. Urenco Power Technologies 

flywheel.3 

Federal Sector Potential 

The UPS system market grew at doubledigit rates during most of the 1990s, 

before slowing in the more recent years 

in response to the general economic 

slowdown. Increasing demands for 

more reliable and/or higher quality 

power are likely to maintain strong 

growth in this market, especially as 

the economy recovers. The federal 

government, responsible for a broad 

spectrum of critical services, represents 

about 5% of the total UPS market in 

the United States. 

Estimated Savings 

and Market Potential4 

The primary attractions of flywheels 

in UPS applications are not energy 

savings. Instead, flywheels offer the 

possibility of improved UPS system 

reliability and reduced life-cycle costs. 

The UPS market in the United States 

is worth about $2 billion per year. Of 

this, about 20% is spent on systems 

50 kVA and larger, where flywheels 

are potentially applicable. As noted 

above, the federal government represents about 5% of the U.S. market. 

Therefore, the federal market for larger 

UPS systems is about $20 million. This 

is roughly equivalent to 40 MVA of new 

or replacement systems each year. The 

current installed stock is estimated to 

be about 10 times this or 400 MVA. 

As discussed further below, flywheels 

are usually envisioned as an alternative to batteries in a UPS system with 

a reliable generator, but could also be 

used as a supplement to batteries to 

increase system reliability and significantly extend battery life. Therefore, 

flywheels are generally applicable to 

all of the markets identified above for 

UPS systems 50 kVA and above. 

Laboratory Perspective 

Flywheels appear poised to replace or 

supplement batteries as a backup power 

supply in UPS systems. Commercial 

Photo courtesy of Piller, Inc. 

Photo courtesy of Design Power Solutions, Inc. Illustration courtesy of Active Power, Inc. 

2 The Active Power flywheel is also used in products sold by Caterpillar and Powerware, so separate illustrations are not provided for these companies.
 3 The Urenco Power flywheel is also marketed by Beacon Power, so a separate illustration is not provided for the latter company.
 4

 Based on data provided by Acitve Power, Inc.


4 — FEDERAL ENERGY MANAGEMENT PROGRAM 
products are currently offered by several 

vendors, and several additional vendors 

are planning to enter the market in the 

near future. Such competition should 

facilitate further technology improvements and/or cost reductions over time. 

Flywheels will be a strong alternative to 

batteries in UPS systems with generators 

that can reliably come on line in 10 seconds or less. Otherwise, flywheels could 

be used to supplement batteries, thereby 

significantly extending battery life 

and increasing UPS system reliability. 

Although the initial cost of a flywheel 

is typically greater than the batteries it 

would be replacing or supplementing, 

its longer life and simpler maintenance 

will often result in lower life-cycle costs. 

Application 

This section addresses the technical 

aspects of applying DC flywheel energy 

storage. The conditions in which the 

technology can be best applied are 

addressed. The advantages, limitations, benefits, and concerns with 

applying DC flywheel energy storage 

are described. Design and integration 

considerations for the technology are 

discussed, including equipment and 

installation costs, installation requirements, and maintenance impacts. 

Application Screening 

DC flywheel energy storage could be 

applied anyplace batteries are currently 

used to provide backup power for a UPS 

system. The flywheel could be used as 

either a substitute or supplement for 

batteries. Like batteries, DC flywheel 

energy storage is designed to connect to 

the DC bus of a UPS system. The 

technology is not applicable to power 

management technologies lacking 

a DC bus, such as a simple motorgenerator device. 

Where to Apply 

DC flywheel energy storage systems are 

generally more reliable than batteries, 

so applicability is mostly an issue of 

cost-effectiveness. Batteries will usually 

have a lower first cost than flywheels, 

but suffer from a significantly shorter 

equipment life and higher annual operation and maintenance expenses. Thus, 

flywheels will look especially attractive 

in operating environments that are 

detrimental to battery life, such as: 

• Frequent cycling stemming from 

main power supply problems. 

• High operating temperatures associated with unconditioned space. 

Flywheels have a much higher power 

density than batteries, typically by a 

factor of 5 to 10. Therefore, the following conditions are also particularly 

attractive for flywheels. 

• Floor space is expensive 

and has alternative uses. 

• Battery floor space must be 

reclaimed for other purposes 

to the extent possible. 

What to Avoid 

UPS batteries are sized to provide 

backup power for periods measured in 

minutes. The period ranges from about 

5 minutes up to around 1 hour, but is 

commonly about 15 minutes. A period 

of 15 minutes, more or less, is generally 

presumed adequate to allow an orderly 

shutdown of equipment. Flywheels, on 

the other hand, provide backup power 

for periods measured in seconds. The 

backup period for flywheels is commonly about 15 seconds. This is enough 

time to allow the flywheel to handle 

the majority of power disruptions that 

last for 5 seconds or less and still have 

time to cover slightly longer outages 

until a backup generator can come up 

to full power (generally in 10 seconds). 

However, a flywheel alone will not provide backup power for a period long 

enough to allow an orderly process shutdown in most cases. Therefore, the following limitations should be considered: 

• Flywheels should not be used alone 

for backup power, without batteries 

and/or a fuel-fired generator. 

• Flywheels should not be used without batteries if a fuel-fired generator 

cannot reliably come up to full 

power in 10 seconds or less. 

Equipment Integration 

Where a reliable fuel-fired backup 

generator exists, DC flywheel energy 

storage can be directly substituted for 

batteries at the DC bus of the UPS 

system. As previously described, installation is relatively simple, consisting 

mostly of physical attachment to the 

floor, connection via cabling to the 

DC bus, and provision of AC service 

for auxiliary loads (e.g., vacuum pump) 

and (for some models) recharging 

power. Care must be taken to match 

the voltage range of the DC bus with 

that for the flywheel. A mismatch 

would require selection of a different 

model or a custom-built model. Careful consideration should also be given 

to the backup power period required. 

This period will vary depending on 

the specific characteristics of the existing generator and UPS system. Both 

UPS and generator manufacturers 

should be consulted to ensure electrical compatibility. 

Maintenance Impact 

DC flywheel energy storage maintenance requirements vary depending 

on the specific flywheel design features, but are generally less frequent 

and less expensive than for batteries. 

Although modern valve regulated lead 

acid (VRLA) batteries do not require 

monitoring and maintenance of electrolyte fluid levels, manufacturers generally recommend quarterly inspections 

to check the tightness of connections, 

remove corrosion, measure voltages, 

and check for cracks and swells in the 

battery cases. Periodic replacement 

of individual batteries will likely be 

required, while replacement of the 

entire battery system can be expected 

about every 4 years5

. Common routine 

maintenance items for flywheels are 

changing cabinet air filters and checking 

5

 Battery life varies greatly depending on the duty cycle and operating temperature experienced. Powerware reports an average of 3.7 years for battery 

storage systems it provides as part of UPS systems. 

FEDERAL ENERGY MANAGEMENT PROGRAM — 5 
vacuum pump oil level every few 

months. The vacuum pump oil should 

be changed once a year. Magnetic bearings require no maintenance, while 

replacement of mechanical bearings is 

expected every 3 to 10 years, depending on the flywheel design. The vacuum 

pump will also likely need replacing 

every 5 to 10 years. Otherwise, most 

flywheels have a design life of about 

20 years, but will probably last longer 

with regular maintenance. 

Equipment Warranties 

A 1-year warranty covering parts and 

labor is most common, but two flywheel manufacturers provide 2-year and 

5-year warranties as part of their standard package. Extended warranties are 

generally available for a premium charge 

above the standard purchase price. 

Costs 

Flywheel purchase costs will vary from 

$100/kW to $300/kW. The lower end 

of the range represents larger and/or 

lower rpm models, while smaller and/or 

higher rpm models will have higher per 

kW costs. Installation is relatively simple 

and inexpensive, typically running 

about $20/kW to $40/kW, including 

an allowance for electrical connections. 

Operating and maintenance costs will 

generally be modest, but vary significantly depending on the type of flywheel and maintenance approach. 

Routine maintenance (see description 

above) is minimal and simple, and could 

be handled by existing maintenance 

staff for a few $/kW/year. Service contracts are offered by some vendors for 

about $5/kW/year, which may be more 

expensive than using internal staff, but 

may also include 24/7 response and 

extended warranties. Bearing replacement for lower rpm flywheels with 

mechanical bearings will cost from 

$5/kW to $15/kW, depending on flywheel design. Replacing the vacuum 

pump, where required, will likely cost 

about $5/kW. The expected replacement periods for bearings and vacuum 

pumps were noted above. Standby 

power consumption will run about 

$5/kW/year for lower rpm flywheels 

using mechanical bearings or combinations of mechanical and magnetic 

bearings, but generally about 1/10th 

of this for higher rpm flywheels using 

only magnetic bearings. 

VRLA battery purchase costs, measured 

in $/kWm (dollars per kilowatt-minute), 

decrease with increasing minutes at the 

same kW rating, but increase for the 

same battery discharged at higher kW. 

The combined effect is that $/kWm is 

roughly constant for the same number 

of minutes at different kW. Purchase 

costs are roughly $17/kWm for 5 minutes of backup power, dropping to 

about $13/kWm, $10/kWm, and $8/ 

kWm for 10, 20, and 30 minutes of 

backup power, respectively. Battery 

cabinet costs are included in these estimates. VRLA battery installation, like 

flywheels, is also relatively simple and 

should be in the same cost range per kW. 

Routine maintenance requirements for 

batteries are more time-consuming than 

for flywheels; hence, maintenance costs 

can be expected to be higher. Contracted 

maintenance costs are largely driven by 

the number of battery cabinets or strings 

required to serve a particular combination of power and minute ratings. As 

might be expected, service costs per 

cabinet decline where there are more 

cabinets at a single site. Similar to 

purchase costs, maintenance costs 

measured in $/kWm/year are roughly 

constant for the same number of minutes at different kW. Annual battery 

maintenance costs are roughly $3.50/ 

kWm for 5 minutes of backup power, 

dropping to about $2.25/kWm, $1.50/ 

kWm, and $1.25/kWm for 10, 20, and 

30 minutes of backup power, respectively. Standby power consumption, 

or float loss, is negligible for batteries 

compared to flywheels, but the differences in footprint and floor-space 

requirements should be considered. 

Flywheel footprint, including an allowance for service space, ranges from 

0.04 ft2

/kW to 0.12 ft2/kW depending 

on the size and type; 0.08 ft2

/kW is 

typical. Battery footprint per kW varies 

significantly depending on the rated 

backup time. For 5 minutes of backup 

power, VRLA battery footprint, again 

including an allowance for service space, 

will be about 0.15 ft2

/kW. This rises to 

approximately 0.22 ft2

/kW, 0.30 ft2/ 

kW, and 0.36 ft2

/kW for 10, 20, and 

30 minutes of backup power, respectively. The value of the floor-space 

differential will vary, of course, depending on site-specific conditions. 

Utility Incentives and Support 

Neither batteries nor flywheels reduce 

energy consumption or peak power 

demand from a utility in a UPS application. Therefore, it is not surprising 

that no utility incentives or support exist 

for this application of these technologies. 

Additional Considerations 

In general, the use of electromechanical flywheels instead of electrochemical 

batteries will avoid the environmental 

and safety issues associated with the 

latter. This includes battery requirements for material safety data sheets, 

eye wash stations, spill containment, 

hydrogen detection, and relatively high 

room ventilation rates. Batteries must 

also be kept at normal indoor air temperatures or suffer from significant 

degradation in expected life. This adds 

to cooling system operating cost in 

existing buildings and cooling system 

size and initial cost in new buildings or 

when cooling systems are being replaced. 

Technology Performance 

Several hundred flywheels are currently 

being used as backup power sources for 

UPS. Of these, about a dozen are 

installed at federal facilities. Although 

flywheels have been used for many years 

as part of motor-generator devices, flywheels designed as a substitute or 

supplement to batteries in UPS systems have been available since 1998. 

The experiences of a few federal users 

are documented below. 

Peterson Air Force Base 

Peterson Air Force Base (AFB) installed 

three flywheels in 1998 in response to 

looming Year 2000 (Y2K) concerns at 

the time. The flywheels were installed 

as a supplement to batteries to shield 

6 — FEDERAL ENERGY MANAGEMENT PROGRAM 
the batteries from relatively frequent, 

but short-term power glitches. Master 

Sergeant Brian Bills described the 

flywheels as being easy to integrate. 

The control system is set up to draw 

power from the flywheels first, then 

the batteries, and then backup generators for longer outages. The Air Force 

requirements for this computer system’s support application included full 

backup generators, 15 minutes of 

battery power, flywheels to extend 

the life expectancy of the batteries, and 

a battery monitoring system. The overall system reliability requirement is “5 

nines” (99.999% reliable). 

Of 47 power outages experienced 

through 2002, load was placed on the 

batteries only twice; the load was met 

entirely by the flywheels during the 

other 45 outages. Ninety percent of 

the outages lasted for 1 second or less. 

With the vast majority of the outages 

served by the flywheel, the batteries were 

reported to look and perform like brand 

new. Sgt. Bills said they would like to 

get to where they just use flywheels 

because of the environmental concerns 

and costs of batteries, but they are not 

there yet. 

Fort Monmouth 

Fort Monmouth installed a flywheel/ 

UPS/generator system in 2002 to provide backup power and protect their 

exchange, Internet, and Intranet servers and server backup equipment. The 

addition of a generator allowed them 

to remove the batteries, which had previously been used to provide backup 

power. Without the generator, batteries would still be necessary. When an 

outage occurs, the flywheel kicks in 

immediately, then the generator fires 

up if the outage lasts for more than a 

few seconds. The UPS system meets 

the computer power needs, plus lighting and air conditioning. When a storm 

came through that knocked out electric power to the whole fort for several 

days, their computer system never 

went down. 

Gindy Berkeley said that Fort Monmouth 

went with the flywheel/UPS system 

because the battery system was at the 

end of its useful life and the upfront 

cost of a new battery system was greater 

than the flywheel system. In addition, 

significant maintenance cost savings 

are expected. Ms. Berkeley said the flywheel is expected to require $3,000 in 

maintenance every 3 years to replace the 

bearings. By comparison, it was costing them $35,000 per battery bank to 

replace the batteries every 3 years and 

they had 3 to 4 banks for each computer room. They expect the flywheel 

to last 20 years or more with regular 

maintenance.6 

Fort Monmouth uses the flywheel for 

voltage regulation as well as for outages 

and other electrical disturbances. The 

flywheel produces a smooth 480 V with 

1.0 power factor. John Alexoudis noted 

that the flywheel is installed remotely 

from the computer space. It is located 

in an electrical vault because it can 

tolerate temperatures up to 100 degrees, 

in contrast to batteries, which must be 

kept in air-conditioned space. 

Dallas VA Medical Center 

The VA Medical Center in Dallas has 

also installed a flywheel/UPS/generator 

system. This 2-year-old, 300 kVA system 

was installed to ensure continuous 

power for a cardiac catheterization 

patient care facility. This facility experienced small power disturbances that 

were causing the catheterization unit 

to shut down. This would leave surgeons “blind” to cardiac conditions 

for 8 minutes, while the catheterization unit was restarted. 

The flywheel/UPS/generator system 

is oversized compared with the load it 

protects, but facility personnel wanted 

to ensure they could ride out any outages until the generators came on-line. 

Rick Hart notes they also have a battery-backed 225-kVA UPS system protecting another critical load that fills a 

whole room. On the other hand, the 

flywheel/UPS system is about the size 

of two refrigerators and is installed in 

an unconditioned electrical room. The 

Medical Center went with the flywheel 

rather than another battery-based system because of the lower maintenance 

costs of the flywheel system. 

Case Study 

Fort McPherson is a U.S. Army Forces 

Command (FORSCOM) installation 

located in Atlanta, Georgia. Building 200 

at the Fort houses FORSCOM Headquarters and contains equipment that 

must be kept up and running on a 

24/7 basis. 

Grid power was previously backed up 

by a UPS system incorporating wet-cell 

batteries and diesel-fired generators. 

While the diesel generators could 

reliably come on line within 10 seconds, the existing battery system 

was becoming increasingly unreliable 

and expensive to maintain. Annual 

battery maintenance was approximately $30,000. 

The existing UPS system consisted 

of four 500-kVA units operating in 

parallel, each with its own wet-cell 

battery string. The UPS and battery 

system was about 15 years old, which 

is well beyond expected battery life, 

even for wet-cell batteries. (Wet-cell 

batteries last longer, but are more 

expensive initially, than VRLA-type 

batteries.) In fact, one of the battery 

strings had already failed, which 

created a hazardous condition for 

maintenance personnel, as well as 

significantly impairing system capability and reliability. 

The battery strings occupied a 2400-

square-foot room adjacent to the UPS 

room. Although the batteries would 

have fit into a space about one-half 

this size, the existence of the batteries 

essentially precluded other useful functions in the room. 

It was clear to Fort McPherson personnel that the existing batteries needed 

6 Note that routine maintenance costs for flywheels and batteries, discussed elsewhere in this Federal Technology Alert, are not included in the figures 

provided by Ms. Berkeley. The flywheel will also need to have its vacuum pump replaced at a cost of about $1,500 once every 10 years. 

FEDERAL ENERGY MANAGEMENT PROGRAM — 7 
to be replaced. Their options were to 

purchase either new VRLA or wet-cell 

batteries, or flywheels. Reductions in 

power demand since Building 200 was 

constructed reduced the requirement 

to two 500-kVA units operating in 

parallel, with either unit able to meet 

the building’s critical power demand. 

The two parallel units were judged to 

be necessary to meet overall system 

reliability requirements. 

Fort McPherson personnel decided 

to install a flywheel (actually two flywheels, one for each 500-kVA UPS 

unit) instead of replacement batteries 

for the following reasons. 

• A wet-cell battery would cost approximately the same as a flywheel, but 

would probably have a shorter life 

and was expected to incur higher 

annual maintenance costs. 

•A VRLA battery would cost about 

half as much as a flywheel initially, 

but would have to be replaced several times over the life of the flywheel and was also expected to incur 

higher annual maintenance costs. 

• Using a flywheel would allow the 

Fort to reclaim the 2400-squarefoot room currently dedicated to 

the battery strings. Depending on 

the specific future use, room ventilation and cooling costs could also 

be reduced. 

• The diesel generators could reliably 

come on line within 10 seconds, 

which minimized the value of the 

longer backup period provided by 

batteries. Overall, the flywheels 

were judged to provide equal or better reliability than the batteries. 

• Environmental and safety issues associated with batteries were eliminated. 

One of the flywheels installed at Fort 

McPherson is shown in Figure 9. 

Although the Fort has experienced 

problems (unrelated to the flywheel) 

with the 15-year-old UPS electronics, 

the flywheels have performed flawlessly since being installed in early 

2002, according to Luke Wyland, the 

energy manager at Fort McPherson. 

Figure 9. Luke Wyland with flywheel 

at Fort McPherson. 

Life-Cycle Cost Comparison 

In general, flywheels will cost more than 

batteries initially, but require less maintenance and will last much longer. Thus, 

a flywheel will generally be much less 

expensive on a life-cycle cost basis. Consider a situation where a 250-kW UPS 

system is backed up by a reliable generator that can come up to full power 

in 10 seconds. Backup power for the 

interim period could be provided by 

either batteries or a flywheel. 

Battery Costs 

Photo courtesy of Pacific Northwest National Laboratory 

The comparison developed in the text 

box is based on a low-rpm flywheel 

with a life of 20 years and a VRLA 

battery with a life of 4 years. As previously noted, battery life will vary significantly depending on the operating 

conditions, principally the load duty 

and ambient temperature seen by the 

batteries. A typical lifetime of 4 years 

is assumed in this comparison. In addition, the batteries are assumed to have 

the capability to provide power for 

10 minutes. The cost estimates shown 

in the text box were developed using 

these assumptions and the rules-ofthumb provided earlier. 

These cost estimates were entered into 

the NIST BLCC 5.1-02 life-cycle cost 

model (see Appendix A). The resulting present value of life-cycle costs was 

$248,129 for the battery option, but 

only $105,572 for the flywheel option, 

or a savings of $142,557 or about 60%. 

Although the batteries are initially less 

expensive to install, the extremely short 

battery life compared with flywheel life 

results in much greater life-cycle cost 

for the battery option. The details of 

the life-cycle cost results are presented 

in Appendix B. 

Purchase cost = $13/kWm * 250 kW * 10 minutes = $32,500 

Installation cost = $30/kW * 250 kW = $7,500 

Total initial capital cost = $40,000 

Capital replacement cost every 4 years = $40,000 

Annual maintenance cost = $2.25/kWm * 250 kW * 10 minutes = $5,625 

Annual floor-space cost = 0.22 ft2/kW * 250 kW * $10/ft2 = $550 

Annual standby power consumption cost = 250 kW * 8760 hours * 

0.01% * $0.063/kWh = $14 

Flywheel Costs 

Purchase cost = $200/kW * 250 kW = $50,000 

Installation cost = $30/kW * 250 kW = $7500 

Total initial capital cost = $57,500 

Bearing replacement cost every 5 years = $10/kW * 250 kW = $2,500 

Vacuum pump replacement every 7 years = $5/kW * 250 kW = $1,250 

Annual maintenance cost = $5/kW * 250 kW = $1,250 

Annual floor-space cost = 0.08 ft2/kW * 250 kW * $10/ft2 = $200 

Annual standby power consumption cost = 250 kW * 8760 hours * 

1% * $0.063/kWha

 = $1,380 

a

Average cost per kWh for Federal buildings in FY01. 

8 — FEDERAL ENERGY MANAGEMENT PROGRAM 
The Technology 

in Perspective 

As indicated elsewhere in this report, a 

few hundred DC flywheel energy storage systems have been installed with 

approximately a dozen of these known 

to be installed at federal facilities. The 

earliest of these installations dates back 

to 1998 while most have been in the 

last 2 years. The experiences to date have 

been good. All of the federal installation 

representatives contacted provided positive descriptions of their flywheel systems 

to date. Still, the number of existing 

installations is relatively small compared 

to the number of potential applications. 

The Technology’s Development 

Flywheels have been around for centuries and are not new to the power quality market either. Motor-generator pairs 

have been used for years as a means to 

isolate electric loads from electricity 

supply disturbances. Flywheels were 

incorporated into these devices to 

increase rotary inertia, hence the tolerable disturbance period. However, 

such directly integrated devices used 

only a small fraction of the kinetic 

energy stored in a flywheel and generally provided at most a second of ridethrough capability. 

More effective use of flywheel technology in power quality applications 

required some means of disconnecting 

the kinetic energy stored in its rotating 

mass from the electric energy demands 

of the load being served. The addition 

of variable speed drive, rectifier, and 

inverter components to the above system provided a technological solution, 

but was cumbersome and/or too expensive. Advances in electronic power conversion and control technology, coupled 

with innovative integration of the components noted above, have been keys 

to the technology’s development. 

The superior energy storage density 

of flywheels compared to batteries is 

widely recognized. Much of the flywheel development occurring in 

recent decades has been oriented 

toward potential applications in 

vehicles and satellites, where mass 

and volume constraints are more rigorous than for UPS applications. The 

focus of flywheel development for 

these applications has been toward 

increasing the rotor speed to maximize 

energy density. Such speeds require 

the use of magnetic bearings, which 

are now used in some moderate rpm 

flywheels as well. 

Relation to Other Technologies 

As indicated throughout this Federal 

Technology Alert, DC flywheel energy 

storage systems are an alternative or 

supplement to lead-acid batteries. Batteries have the advantage of providing 

backup power for a period measured 

in minutes rather than seconds, but 

this advantage has limited value if 

reliable backup generators are available. 

Batteries will usually have lower first 

costs, but their significantly shorter life 

and greater maintenance requirements 

compared to flywheels generally makes 

the latter more life-cycle cost effective. 

Technology Outlook 

Six companies currently offer DC flywheel energy storage products. Another 

half dozen or so are developing products they expect to bring to market 

within the next few years. Still others 

offer products where the flywheel is 

an integral part of the UPS system 

rather than being a direct substitute 

for batteries. 

The current array of available DC flywheel energy storage products includes 

low-speed, unenclosed steel rotors with 

conventional bearings at one end of the 

spectrum and high-speed, composite 

material rotors operating in a vacuum 

with magnetic bearings at the other end 

of the spectrum. Intermediate products 

with elements of these two endpoints 

also exist. It is not clear yet whether the 

UPS application will move toward one 

end of the technology spectrum or the 

other. Different design approaches may 

each find their niche within the UPS 

application market. 

Although currently developed DC flywheel energy storage systems offer 

significant advantages over batteries, the 

number of companies currently offering products, and an equal or greater 

number developing products, suggests 

that further product development and 

enhancement is likely to occur. Coupled 

with seemingly ever-increasing needs 

for more reliable, higher quality power, 

the long-run prospects for flywheel 

energy storage in UPS applications 

looks good. 

Manufacturers 

Manufacturers of flywheels for application in UPS systems were primarily 

identified via searching Internet web 

sites. This search was conducted during fall 2002. Although the focus of 

this Federal Technology Alert is on 

stand-alone DC flywheel energy storage systems that could substitute or 

supplement batteries in a UPS system, 

this list also includes manufacturers 

that offer flywheels as an integral part 

of a UPS system. Also included are 

developers who intend to have a DC 

flywheel energy storage system on the 

market within the next few years. 

Despite our efforts, it is practically impossible to ensure that all manufacturers of DC 

flywheel energy storage systems have been 

identified. To those we missed, we extend 

our apologies. This list is provided as a service for those interested in obtaining information on specific flywheel products for 

UPS applications. No endorsement or other 

judgment regarding qualification of any 

manufacturer listed is given or implied. 

Acumentrics Corporation 

14 Southwest Park


Westwood, Massachusetts 02090


Contact: Gary Genet


Phone: 404-713-0364 or 781-461-8251


Fax: 781-461-1261


ggenet@acumentrics.com


www.acumentrics.com


Products: Flywheel-based UPS; DC flywheel


energy storage; under development as of fall 2002


Active Power, Inc. 

2128 West Braker Lane, BK-12


Austin, Texas 78758


Contact: Stephen Burke


Phone: 512-836-6464 Fax: 512-836-4511


sburke@activepower.com


www.activepower.com


Product: Flywheel-based UPS; DC flywheel


energy storage


FEDERAL ENERGY MANAGEMENT PROGRAM — 9 
AFS Trinity Power Corporation 

6724D Preston Avenue


Livermore, California 94551


Contact: Gerald Starr


Phone: 925-455-7231 Fax: 925-455-7993


gstarr@afstrinity.com


www.afstrinitypower.com


Product: DC flywheel energy storage;


under development as of fall 2002


Beacon Power Corporation 

234 Ballardvale Street


Wilmington, Massachusetts 01887


Contact: John Jesi


Phone: 978-661-2081 Fax: 978-694-9127


jesi@beaconpower.com


www.beaconpower.com


Product: DC flywheel energy storage,


Flywheel-based UPS


Caterpillar, Inc. 

100 N.E. Adams St.


Peoria, Illinois 61629


Phone: 800-947-6567 or 309-675-1000


www.CAT-ElectricPower.com


Product: Flywheel-based UPS


Designed Power Solutions 

International 

2348 Meyers Avenue


Escondido, California 92029


Contact: Mike Dean


Phone: 760-480-0760 Fax: 760-480-0780


miked@designedpower.com


www.designedpower.com


Products: Flywheel-based UPS with


generator; Flywheel-based UPS; DC flywheel


energy storage


Flywheel Energy Systems, Inc. 

25C Northside Road


Nepean, Ontario Canada K2H 8S1


Contact: Dean Flanagan


Phone: 613-596-0856 Fax: 613-596-6052


fesi@magma.ca


www.magma.ca/~fesi


Product: DC flywheel energy storage;


under development as of fall 2002


GE Digital Energy 

2018 Powers Ferry Road, Suite 500


Atlanta, Georgia 30339


Contact: Mark Klaiber


Phone: 678-627-0954 Fax: 678-627-0986


mark.klaiber@indsys.ge.com


www.gedigitalenergy.com


Product: Flywheel-based UPS with generator


Indigo Energy, Inc. 

535 Westgate Drive


Napa, California 94558


Contact: Chris Gabrys


Phone: 707-254-9302 Fax: 253-981-0243


info@indigoenergyinc.com


www.indigoenergyinc.com


Products: Flywheel-based UPS; DC flywheel


energy storage; under development as of fall 2002


Optimal Energy Systems 

2560 W. 237th Street


Torrance, California 90505


Contact: Dwight Swett


Phone: 310-257-0301 Fax: 310-257-0303


sales@optimalenergysystems.com


www.optimalenergysystems.com


Products: Flywheel-based UPS; DC flywheel


energy storage; under development as of fall 2002


Pentadyne Power Corporation 

20750 Lassen Street


Chatsworth, California 91311


Contact: Chandler Williamson


Phone: 818-350-0370, ext. 207


Fax: 818-350-0385


info@pentadyne.com


www.pentadyne.com


Product: DC flywheel energy storage;


under development as of fall 2002.


Piller, Inc. 

334 County Rte. 49


Middletown, New York 10940


Contact: Travis Gerould


Phone: 845-355-5000 Fax: 845-355-9005


info@piller.com


www.piller.com


Product: DC flywheel energy storage, Flywheel-


based UPS, Flywheel-based UPS with generator


Powerware 

8609 Six Forks Rd.


Raleigh, North Carolina 27615


Contact: Barry Needle


Phone: 919-870-3045 Fax: 919-870-3450


barry.needle@psd.invensys.com


www.powerware.com


Product: Flywheel-based UPS; DC flywheel


energy storage


Precise Power Corporation 

P.O. Box 9547


Bradenton, Florida 34206


Phone: 888-522-1600 Fax: 941-729-4337


info@precisepwr.com


www.precisepwr.com


Product: Flywheel-based UPS


Regenerative Power and Motion 

Contact: Dick Fradella


Phone: 949-496-4274


fradella@earthlink.net


www.rpm2.8k.com


Product: DC flywheel energy storage;


under development as of fall 2002


Reliable Power Systems, Inc. 

399 Perry Street, Suite 300


Castle Rock, Colorado 80104


Contact: Michael Warner


Phone: 720-733-8970 Fax: 720-733-8976


warnermd@attglobal.net


www.reliablepowersystems.com


Product: Flywheel-based UPS


SatCon Power Systems 

835 Harrington Court


Burlington, Ontario, Canada L7N 3P3


Contact: Martin Valeri


Phone: 905-631-4402 Fax: 905-639-0961


martin.valeri@satcon.com


www.inverpower.com


Product: Flywheel-based UPS with generator


Urenco Power Technologies 

Suite 610, Watergate Building


2600 Virginia Avenue NW


Washington DC 20037


Contact: Colin Davies


Phone: 202-333-7971 Fax: 202-337-2421


cdavies@urencoinc.com


www.uptenergy.com


Product: DC flywheel energy storage


Who is Using 

the Technology 

Several hundred DC flywheel energy 

storage systems have been installed, 

with about a dozen of these in federal 

applications. Most of the federal applications have been in the Department 

of Defense, but at least one system each 

have been installed at State Department 

and Veterans Affairs facilities. Contacts 

for the four federal applications previously described are listed below. 

Fort McPherson 

Luke Wyland—404-469-3563 

luke.wyland@forscom.army.mil 

Fort Monmouth 

John Alexoudis—732-532-6368 

john.alexoudis@mail1.monmouth.army.mil 

Gindy Berkeley—732-532-6171 

gindy.berkeley@mail1.monmouth.army.mil 

Peterson Air Force Base 

Staff Sgt. (retired) Brian Bills 

719-550-8670 

brian.bills@psd.invensys.com 

VA Medical Center, Dallas 

Rick Hart—214-857-1052 

rick.hart@med.va.gov 

For Further Information 

Perhaps the best sources of additional 

information are the manufacturers’ Web 

sites listed above. In addition to containing information about their specific 

products, many of the Web sites contain 

generic tutorials about flywheels, batteries, and other energy storage devices. 

10 — FEDERAL ENERGY MANAGEMENT PROGRAM 
Appendix A 

Federal Life-Cycle Costing Procedures and the BLCC Software 

Federal agencies are required to evaluate energy-related investments on the basis of minimum life-cycle costs (10 CFR Part 436). 

A life-cycle cost evaluation computes the total long-run costs of a number of potential actions, and selects the action that minimizes the long-run costs. When considering retrofits, sticking with the existing equipment is one potential action, often called 

the baseline condition. The life-cycle cost (LCC) of a potential investment is the present value of all of the costs associated with 

the investment over time. 

The first step in calculating the LCC is the identification of the costs. Installed Cost includes cost of materials purchased and the 

labor required to install them (for example, the price of an energy-efficient lighting fixture, plus cost of labor to install it). Energy 

Cost includes annual expenditures on energy to operate equipment. (For example, a lighting fixture that draws 100 watts and 

operates 2,000 hours annually requires 200,000 watt-hours (200 kWh) annually. At an electricity price of $0.10 per kWh, this 

fixture has an annual energy cost of $20.) Nonfuel Operations and Maintenance includes annual expenditures on parts and activities required to operate equipment (for example, replacing burned out light bulbs). Replacement Costs include expenditures to 

replace equipment upon failure (for example, replacing an oil furnace when it is no longer usable). 

Because LCC includes the cost of money, periodic and aperiodic maintenance (O&M) and equipment replacement costs, energy 

escalation rates, and salvage value, it is usually expressed as a present value, which is evaluated by 

LCC = PV(IC) + PV(EC) + PV(OM) + PV(REP) 

where	 PV(x) denotes “present value of cost stream x,” 

IC is the installed cost, 

EC is the annual energy cost, 

OM is the annual nonenergy O&M cost, and 

REP is the future replacement cost. 

Net present value (NPV) is the difference between the LCCs of two investment alternatives, e.g., the LCC of an energy-saving 

or energy-cost-reducing alternative and the LCC of the existing, or baseline, equipment. If the alternative’s LCC is less than the 

baseline’s LCC, the alternative is said to have a positive NPV, i.e., it is cost-effective. NPV is thus given by 

NPV = PV(EC0

)– PV(EC1)) + PV(OM0) – PV(OM1)) + PV(REP0)– PV(REP1)) – PV(IC) 

or 

NPV = PV(ECS) + PV(OMS) + PV(REPS) – PV(IC) 

where	 subscript 0 denotes the existing or baseline condition, 

subscript 1 denotes the energy cost saving measure, 

IC is the installation cost of the alternative (note that the IC of the baseline is assumed zero), 

ECS is the annual energy cost savings, 

OMS is the annual nonenergy O&M savings, and 

REPS is the future replacement savings. 

Levelized energy cost (LEC) is the break-even energy price (blended) at which a conservation, efficiency, renewable, or fuelswitching measure becomes cost-effective (NPV >= 0). Thus, a project’s LEC is given by 

PV(LEC*EUS) = PV(OMS) + PV(REPS) – PV(IC) 

where EUS is the annual energy use savings (energy units/yr). Savings-to-investment ratio (SIR) is the total (PV) savings of a 

measure divided by its installation cost: 

SIR = (PV(ECS) + PV(OMS) + PV(REPS))/PV(IC). 

Some of the tedious effort of life-cycle cost calculations can be avoided by using the Building Life-Cycle Cost software, BLCC, 

developed by NIST. For copies of BLCC, call the FEMP Help Desk at (800) 363-3732. 

FEDERAL ENERGY MANAGEMENT PROGRAM — 11 
Appendix B 

NIST BLCC 5.1-02: Comparative Analysis 

Consistent with Federal Life-Cycle Cost Methodology and Procedures, 10 CFR, Part 436, Subpart A 

Base Case: Battery 

Alternative: Flywheel 

General Information 

File Name: 

Date of Study: 

Project Name: 

Project Location: 

Analysis Type: 

Analyst: 

Base Date: 

Beneficial Occupancy Date: 

Study Period: 

Discount Rate: 

Discounting Convention: 

Comparison of Present-Value Costs 

PV Life-Cycle Cost 

Initial Investment Costs: 

Capital Requirements as of Base Date 

Future Costs: 

Energy Consumption Costs 

Energy Demand Charges 

Energy Utility Rebates 

Water Costs 

C:\Program Files\BLCC5\projects\Battery-Flywheel Comparison.xml


Fri Jan 31 11:56:20 PST 2003


Battery-Flywheel Comparison


U.S. Average


MILCON Analysis, Energy Project


Daryl R. Brown


January 1, 2003


January 1, 2003


20 years 0 months (January 1, 2003 through December 31, 2022)


3.2%


End-of-Year


Savings from 

Base Case Alternative Alternative 

$40,000 $57,500 -$17,500 

$0 $19,566 -$19,566 

$0 $0 $0 

$0 $0 $0 

$0 $0 $0 

Routine Recurring and Non-Recurring OM&R Costs $90,200 $21,180 $69,019 

Major Repair and Replacements $117,929 $7,326 $110,604 

Residual Value at End of Study Period $0 $0 $0 

Subtotal (for Future Cost Items) $208,129 $48,072 $160,057 

Total PV Life-Cycle Cost $248,129 $105,572 $142,557 

Net Savings from Alternative Compared with Base Case 

PV of Non-Investment Savings $49,454 

- Increased Total Investment -$93,104 

Net Savings $142,557 

12 — FEDERAL ENERGY MANAGEMENT PROGRAM 
About FEMP’s New Technology Demonstrations


The Energy Policy Act of 1992 and subsequent Executive Orders mandate that 

energy consumption in federal buildings 

be reduced by 35% from 1985 levels by 

the year 2010. To achieve this goal, the 

U.S. Department of Energy’s Federal 

Energy Management Program (FEMP) 

sponsors a series of activities to reduce 

energy consumption at federal installations nationwide. FEMP uses new technology demonstrations to accelerate 

the introduction of energy-efficient and 

renewable technologies into the federal 

sector and to improve the rate of technology transfer. 

As part of this effort, FEMP sponsors 

the following series of publications that 

are designed to disseminate information 

on new and emerging technologies: 

Technology Focuses—brief information 

on new, energy-efficient, environmentally friendly technologies of potential 

interest to the Federal sector. 

Federal Technology Alerts—longer 

summary reports that provide details on 

energy-efficient, water-conserving, and 

renewable-energy technologies that have 

been selected for further study for possible implementation in the federal sector. Additional information on Federal 

Technology Alerts (FTAs) is provided 

in the next column. 

Technology Installation Reviews—concise reports describing a new technology 

and providing case study results, typically from another demonstration program or pilot project. 

Other Publications—the program also 

issues other publications on energy-saving 

technologies with potential use in the 

federal sector. 

More on Federal 

Technology Alerts 

Federal Technology Alerts, our signature 

reports, provide summary information 

on candidate energy-saving technologies developed and manufactured in the 

United States. The technologies featured 

in the FTAs have already entered the market and have some experience but are 

not in general use in the federal sector. 

The goal of the FTAs is to improve the 

rate of technology transfer of new energysaving technologies within the federal 

sector and to provide the right people in 

the field with accurate, up-todate information on the new technologies so that 

they can make educated judgments on 

whether the technologies are suitable for 

their federal sites. 

The information in the FTAs typically 

includes a description of the candidate 

technology; the results of its screening 

tests; a description of its performance, 

applications, and field experience to date; 

a list of manufacturers; and important 

contact information. Attached appendixes 

provide supplemental information and 

example worksheets on the technology. 

FEMP sponsors publication of the FTAs 

to facilitate information-sharing between 

manufacturers and government staff. 

While the technology featured promises 

significant federal-sector savings, the FTAs 

do not constitute FEMP’s endorsement 

of a particular product, as FEMP has not 

independently verified performance data 

provided by manufacturers. Nor do the 

FTAs attempt to chart market activity 

vis-a-vis the technology featured. Readers should note the publication date on 

the back cover, and consider the FTAs 

as an accurate picture of the technology 

and its performance at the time of 

publication. Product innovations and 

the entrance of new manufacturers or 

suppliers should be anticipated since the 

date of publication. FEMP encourages 

interested federal energy and facility 

managers to contact the manufacturers 

and other federal sites directly, and to 

use the worksheets in the FTAs to aid 

in their purchasing decisions. 

Federal Energy Management Program 

The federal government is the largest energy consumer in the nation. Annually, the total primary energy consumed by the federal 

government is 1.4 quadrillion British thermal units (quads), costing $9.6 billion. This represents 1.4% of the primary energy consumption in 

the United States. The Federal Energy Management Program was established in 1974 to provide direction, guidance, and assistance to federal 

agencies in planning and implementing energy management programs that will improve the energy efficiency and fuel flexibility of the 

federal infrastructure. 

Over the years, several Federal laws and Executive Orders have shaped FEMP’s mission. These include the Energy Policy and Conservation 

Act of 1975; the National Energy Conservation and Policy Act of 1978; the Federal Energy Management Improvement Act of 1988; the 

National Energy Policy Act of 1992; Executive Order 13123, signed in 1999; and most recently, Executive Order 13221, signed in 2001, and 

the Presidential Directive of May 3, 2001. 

FEMP is currently involved in a wide range of energy-assessment activities, including conducting new technology demonstrations, to hasten 

the penetration of energy-efficient technologies into the Federal marketplace. 
A Strong Energy Portfolio for a Strong America 

Energy efficiency and clean, renewable energy will mean a Federal Energy Management Program


stronger economy, a cleaner environment, and greater energy Leading by example, saving energy and taxpayer dollars

independence for America. By investing in technology break- in federal facilities

throughs today, our nation can look forward to a more resilient

economy and secure future. FreedomCAR & Vehicle Technologies Program


Less dependence on foreign oil, and eventual transition to 

Far-reaching technology changes will be essential to America’s an emissionsfree, petroleum-free vehicle 

energy future. Working with a wide array of state, community,

industry, and university partners, the U.S. Department of Geothermal Technologies Program


Energy’s Office of Energy Efficiency and Renewable Energy Tapping the earth’s energy to meet our heat and power needs

invests in a portfolio of energy technologies that will: Hydrogen, Fuel Cells & Infrastructure Technologies 

• Conserve energy in the residential, commercial, indus- Program 

trial, government, and transportation sectors Paving the way toward a hydrogen economy and net-zero 

carbon energy future • Increase and diversify energy supply, with a focus on 

renewable domestic sources Industrial Technologies Program 

Boosting the productivity and competitiveness of U.S. industry

• Upgrade our national energy infrastructure through improvements in energy and environmental performance 

• Facilitate the emergence of hydrogen technologies as Solar Energy Technology Program 

a vital new “energy carrier.” Utilizing the sun’s natural energy to generate electricity and provide water and space heating 

The Opportunities Weatherization & Intergovernmental Program


Biomass Program Accelerating the use of today’s best energy-efficient and renewUsing domestic, plant-derived resources to meet our fuel, able technologies in homes, communities, and businesses

power, and chemical needs Wind & Hydropower Technologies Program


Building Technologies Program Harnessing America’s abundant natural resources for clean

Homes, schools, and businesses that use less energy, cost power generation

less to operate, and ultimately, generate as much power as To learn more, visit www.eere.energy.gov they use

Distributed Energy & Electric Reliability Program 

A more reliable energy infrastructure and reduced need 

for new power plants 

Log on to FEMP’s Web site for information 

about New Technology Demonstrations 

www.eere.energy.gov/femp/ 

You will find links to 

• A New Technology Demonstration Overview 

• Information on technology demonstrations 

• Downloadable versions of publications in Adobe Portable 

Document Format (pdf ) 

• A list of new technology projects under way 

• Electronic access to a regular mailing list for new products 

when they become available 

• How Federal agencies may submit requests to us to assess 

new and emerging technologies 

For More Information 

FEMP Help Desk 

(800) 363-3732

International callers please use

(703) 287-8391

Web site: www.eere.energy.gov/femp

General Contacts 

Ted Collins 

New Technology Demonstration 

Program Manager 

Federal Energy Management Program 

U.S. Department of Energy 

1000 Independence Ave., SW EE-92 

Washington, D.C. 20585 

Phone: (202) 586-8017 

Fax: (202) 586-3000 

theodore.collins@ee.doe.gov 

Steven A. Parker 

Pacific Northwest National Laboratory

P.O. Box 999, MSIN: K5-08

Richland, WA 99352

Phone: (509) 375-6366

Fax: (509) 375-3614

steven.parker@pnl.gov

Technical Contact 

Daryl Brown 

Pacific Northwest National Laboratory

P.O. Box 999, MSIN: K8-07

Richland, WA 99352

Phone: (509) 372-4366

Fax: (509) 372-4370

daryl.brown@pnl.gov

Produced for the U.S. Department

of Energy, Energy Efficiency and

Renewable Energy, by the Pacific

Northwest National Laboratory

DOE/EE-0286

September 2003