white paper

PRESS RELEASEThe True Cost of Batteries
Why Energy Harvesting is the Best Power Solution for WirelessSensors
Batteries are part of our daily lives and we have become accustomed to changing them as
they die. The growth of mobile and wireless applications yields an increasing number ofdevices powered by batteries. The battery replacement effort becomes more costly andcomplex as scale increases. Batteries are cheap, replacing them is not.
This is particularly true in systems consisting of several tens, hundreds or thousands ofwireless nodes as you find in the field of smart home and building automation. Just think of ahotel, which has equipped each of its 400 rooms with four battery-powered sensors. Every
two to three years, each one of these 1,600 batteries needs to be replaced – it is irrelevant if
the devices are hard to access or hotel guests might be disturbed. Worse still is whenbatteries in a light switch or a remote control fail during guest usage. In commercial orindustrial operation, a battery cost calculation must therefore be included to generate
accurate lifetime costs covering maintenance efforts and proper hazardous materials
disposal. Only Total Cost of Ownership (TCO) calculations reveal the true cost of batteryoperated systems.
Energy harvesting solutions free building owners, facility managers or contractors
from the burden of batteries. They combine the benefits of highly flexible wireless solutions
with the same maintenance-free attributes as wired-in devices with a fast, consistent, andrepeatable return on investment (ROI).

The Wireless Way
Service calculations on a time and materials basis play a significant
role before starting a building automation project. The project sitemust be evaluated, which includes a determination of how andwhere to pull wires for sensors and switches. In retrofit buildings,
this is a particular challenge. Once the work on the project begins,each day requires setup, tear down, clean-up, and travel, as well as the electrician’s time.
These hurdles can be overcome by the use of wireless solutions. Wireless devices can be
flexibly placed and eliminate the need to install wiring and conduits. This significantly eases
and reduces the planning and implementation effort. However, these wireless devices
often still have batteries, but the challenges they present can be overcome.

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Sensor Systems for Sustainable Buildings

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white paper – The True Cost of Batteries_________________________________________

Batteries means Maintenance
There are typically three methods of battery maintenance:
1. Build in a low battery monitor and alarm – such as the beeping smoke detector in the
middle of the night. Security systems have a supervisor signal every hour to informthe base station they are alive. In case of a dead battery, no supervisory signal isreceived, and the alarm triggers. This may also trigger a false call to the alarm
monitoring center.
2. Change all batteries on a preset timetable, usually at the shorter end of their expected
lifespan.
3. Wait for the battery to fail, and then debug the failure as a dead battery. This presents
some problems if the user is unaware that the device is battery-powered, e.g.
thermostat or light switches, which are typically not battery-powered. The consumer
only knows that the light does not switch on or the room does not get warm. This
reactive method results in user dissatisfaction.
Deploying batteries means additional planning and maintenance overhead that result inmeasurable effort for facility managers in order to maintain occupant satisfaction.

“An estimated 20% of U.S. homes have smoke alarms present but none thatare working. Nearly all of this 20% involves dead or missing batteries.”(National Fire Protection Association, NFPA)

Difficulties in Changing
Battery-powered devices are mobile, and their location needs to be documented andupdated as the location changes. In a large building system, hundreds of sensors are
distributed over several floors and offices. Often, the devices are mounted unobtrusively inplaces that are difficult to reach, e.g. on or above drop ceilings. In addition, each device has
a different battery access method and requires different types of batteries. This results inextra work, making the battery replacement a challenging and time consuming effort. Some
batteries even require specially trained technicians for replacement as they can explodewhen handled improperly.
Various devices lifespanThe energy demands of finished devices vary from one type to another, causing
different battery replacement intervals.

Lifespan varies from those devices in high usage areas versus lower. For
example, occupancy sensors in one area see more traffic and more RF signals
than in a back room.

Environmental conditions impact on battery performance and lifespan, e.g. coldor warm temperatures.

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white paper – The True Cost of Batteries_________________________________________
Finally, the question remains “who is in charge of changing batteries?” – The facility
owner, the tenant, or a paid service provider? The person responsible often requires accessto the entire facility and its sensitive security system. For contractors, the maintenance effortof changing batteries causes additional lifecycle costs over the contract period and makes it
more difficult for them to fulfill service level agreements. For larger systems, contractors needto calculate long lead times when ordering new batteries and need to store a certain amountof batteries for replacement as Lithium Ion batteries can only be shipped in small quantities
and in some countries, for example in North America, not by air.

Costs to Calculate
Devices are typically powered by Alkaline AAA with alifetime of two to three years or by Lithium Ion at alifetime between five and seven years. The following
table shows an example cost calculation for both:Commercial
Lithium
Life (years)
5
Cost (US$)
5
20 year replacement cycles required3
Quantity of batteries per node
1
Cumulative battery cost (US$)
15
Change labor cost per node (US$)
2.50
Cumulative labor cost (US$)
7.50
20 year lifetime cost (US$)
22.50
20 year quantity of batteries disposed
4
Batteries purchased and disposed for 50 200
nodes

Residential
Alkaline
2.5
0.65
7
4
18.20
inconvenience

32
1,600

A large system, for example in an office comprising 10,000 wireless units eachpowered by two batteries with a lifetime of two years, could require the facility
manager to change approximately 30 batteries each day.

Battery-less Performance
These costs for battery replacement are a significant disadvantage tothe growth of wireless sensor networks and open the door to EnOcean
energy harvesting wireless technology. Due to the energy harvesting
principle, these wireless modules harness their power from thesurrounding environment and therefore work without batteries. There are a variety ofenergy sources, an electrodynamic energy converter uses mechanical motion, or aminiaturized solar module generates energy from indoor light. Additionally, combining athermoelectric converter with a DC/DC converter taps heat as an energy source.

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white paper – The True Cost of Batteries_________________________________________
EnOcean modules can be powered by the same energy sources as all other traditional
wireless switches and sensors, line voltage, and batteries; however, it is the only
technology that consumes low enough power to operate with the ultra-low power
provided from energy harvesting.

Powerful Energy Converters
In general, traditional battery-powered technology consumes ten times the amount of energy
as self-powered devices. However, due to optimized energy management, energy
converters are unexpectedly powerful. Inside buildings, with eight hours of average lightintensity (400 lux), an economical mini-solar cell with an efficiency of less than 5% and anarea of 10 cm2 supplies approximately one ampere-hour (Ah) of energy over the course of
15 years – the same amount as five CR 2032 Li button cells. Outdoors (8000 lux), thisintensity is as much as 20 Ah over the same period of time, which equals the power of morethan 100 Li button cells. While in this typical example users must change the batteries ofbattery-operated devices every three years and every two months, respectively, energy
harvesting makes equipment truly maintenance-free.

Reliable Operation
Tapping renewable energy sources enables a power output of 10 mW
for radio frequency (RF) transmission of device data. However, thewireless transmission used has an energy requirement of only 50
microwatt seconds for a single telegram. This enables energy
harvesting wireless technology to be scaled to different applications.
At the same time, the energy-optimized radio protocol at sub 1 GHz frequencies
provides a strong signal-to-noise ratio and less interference from other devices at areliable long range wireless communication of up to 100 feet (30 meters) indoors. This
is often twice the range in comparison to battery-powered devices, which typically have
1 mW power output to extend battery life.
The reliable operation of battery-less devices contributes to another key factor: user
satisfaction. It’s not acceptable that an air conditioning system can’t be switched on in thesummer or that a user can’t turn on lights at night because a battery-powered sensor or
switch stopped working. The use of energy harvesting wireless devices avoids frequent

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white paper – The True Cost of Batteries_________________________________________
support calls, which has a positive impact on the users’ satisfaction with the system. This
perception of reliability can result in valuable word of mouth recommendations or repeat buys
when building owners decide on a system extension.

Install and Forget
Battery-less sensors and switches free building owners, facility managers, occupants,
and contractors from maintenance effort and costs for typically 20 years or more. This“no maintenance” characteristic significantly reduces the TOC over the system’s whole
lifecycle. It enables wireless components to be installed and forgotten just like wired-incontrols, even in places that are difficult to reach.
The elimination of battery access doors also simplifies embedding the wireless sensors andswitches in door locks, window panes or cable locks while the energy harvesting modules
allow smaller device form factors and environmentally sealed enclosures at the same time.
Benefits of energy harvesting

Reduced planning and installation costs, no wires needed

Maintenance-free for > 20 years, no battery replacement
needed

Equivalent functionality as wired devicesFlexible positioning and updating

Reliable, long range communicationNo hazardous waste disposalWorldwide use of battery-less technology

The Environmental Factor
When considering battery costs, the environmental impact needs to be included as well.
Batteries contain heavy metals such as mercury, lead, cadmium, and nickel, which are
detrimental to the environment. At the end of their lifetime, batteries are hazardous waste
due to the toxicity (chromium D007), ignitability (D001) and reactivity (D003) and need
to be carefully and expensively disposed of by the manufacturer or the user. Dependingon the battery technology in use, a user will dispose between
200 and 1,600 batteries over 20 years in a residential homewith only 50 nodes.

“Battery recycling is energy-intensive. Reports revealthat it takes 6 to 10 times more energy to reclaim
metals from some recycled batteries than it does to
produce it through other means, including mining.”(Battery University)

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white paper – The True Cost of Batteries_________________________________________The safe storage of batteries requires high standards and can be a real challenge. Batteries
stacked carelessly on top of one another can burst or generate heat. All of the negativeenvironmental impacts and challenges related to battery disposal and storage are eliminatedby utilizing EnOcean energy harvesting technology.

Technology with a Future
Energy harvesting offers significant advantages over batteries when it comes to ecobalance
and maintenance-free operation. Based on the battery-less wireless technology, a wide
range of self-powered applications are available today, including switches, intelligent window
handles, temperature sensors, humidity and particle sensors, light sensors, occupancy
sensors, relay receivers, heating valves, control centers, and smart home systems. For all ofthese wireless devices, the self-powered technology eliminates the dependency on batteries.
For more power-hungry devices such as programmable thermostats with LCD panel andbacklight, the energy-efficient EnOcean radio can extend battery lifetime significantly overtraditional radios.
Batteries will not disappear and for some applications they will remain a necessity. But froma design, environmental and reliability standpoint, energy harvesting is the technologyof the future. In the years to come, energy harvesting will increase its lead over batteries
further – especially since energy converters and storage elements continue to improve theirperformance and costs.

Someday, it might be that up to 10 trillion wireless sensors deliver the needed
data for the Internet of Things. 10 trillion battery-powered sensors would
require 1 million tons of Lithium – the combined worldwide Lithium productionof 10 years. Based on a 10 year average battery life time, 10 million
maintenance workers would be requested to change batteries, each of them
100,000 per year.

About EnOcean Alliance
Leading companies worldwide from the building sector collected to form the EnOcean Alliance and establish
innovative automation solutions for sustainable building projects – and so to make buildings more energy-efficient,more flexible and lower in cost. The core technology of the Alliance is energy harvesting wireless technology for
flexibly positioned and service-free sensor solutions. The EnOcean Alliance aims to internationalize the energy
harvesting wireless technology, and is dedicated to creating interoperability between the products of OEM partners.
Basis for this is the international standard ISO/IEC 14543-3-1X, which is optimized for wireless solutions with ultra-low
power consumption and energy harvesting. The headquarters of the non-profit organization is located in San Ramon,
California. www.enocean-alliance.org

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