solar powerer computing

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White PaperIntel AtomProcessor Z510

Solar-PoweredApplications

How to Design a Solar-PoweredComputing DeviceImproved technology and lower solar panelcosts will spark an explosion of embeddedsolar-powered products

Going beyond useful gadgets powered by the sun, solar-powered computing devices

are just over the horizon. Imagine network routers and surveillance devices soaking

up the sun and running networking, video and security software. Free of power and

Ethernet cables, these embedded systems can be deployed in the field quickly

and cheaply.

These opportunities are upon us because the economics and technologies surrounding

solar are making great strides. The cost of solar panels is coming down rapidly as

production grows, and the power consumption of new processors is decreasing as

technology advances. Clearly not just any CPU can be used in a solar application, butsome of the latest power-optimized processors are up to the task. This is the case

with the Intel Atom processor, which consumes 2.0 watts activei ,1,2 and as little

as 0.1 watts in a Deep Sleep state.

This white paper describes different types of embedded solar-powered computing

devices and provides design suggestions for Intel Atom processor-based platforms.

It covers hardware and software practices for developing ultra-low power devices,

as well as open source software available to designers.


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White Paper How to Design a Solar-Powered Computing Device

2

Table of contentsWhen Solar Makes Sense .............. .............. .............. .............. ............... .............. .............. .............. .............. .............. .............. .............. .............. .............. . 3

Device Opportunities .............. ............... .............. .............. ............... .............. .............. .............. .............. .............. .............. .............. .............. .............. ........ 3

Design Requirements .............. ............... .............. .............. .............. .............. .............. .............. .............. ................ .............. .............. .............. .............. ....... 4

Satisfying the Design Requirements ............ .............. ............... .............. .............. .............. .............. .............. .............. .............. .............. .............. ...... 4

System Example: Surveillance Sensor .............. .............. .............. .............. .............. .............. ............... .............. .............. ............... .............. .............. 5

Designing a Solar-Powered Computing Device ............. .............. .............. .............. .............. .............. .............. .............. .............. ................ ........... 6

Challenge 1: Voltage regulation ............. .............. .............. .............. .............. .............. ............... .............. .............. ............... .............. .............. ....... 6

Challenge 2: Source voltage .............. .............. .............. .............. .............. .............. .............. .............. .............. ............... .............. .............. .............. . 6

Challenge 3: Power management .............. .............. .............. .............. .............. .............. .............. .............. .............. .............. ............... .............. ... 6

Truly Untethered Embedded Devices.............. .............. .............. .............. .............. .............. .............. .............. .............. ................ .............. .............. .. 7


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How to Design a Solar-Powered Computing Device White Paper

3

When Solar Makes Sense

Most embedded computing devices, such as PLCs, ATMs, and

networking appliances, are tethered and have a continuous

source of power. However, there are times when it may be moreconvenient, or even essential, to use devices that arent 100

percent reliant on wired network connections and a steady stream

of power. These cases include setting up and using infrastructure

after natural disasters, during remote military operations or when

power outages are frequent, as listed in Table 1. In these scenarios,

computing devices must operate in settings that are less stable

than standard industrial and enterprise infrastructure.

Device Opportunities

Solar power is not likely to enable new categories of embedded

computing devices. Instead, existing device types will leverage

solar power and wireless connectivity to advance energy sustain-

ability and ease of deployment. These attributes open the door

to slightly different usage models in the following common

equipment segments:

Network routers: Network access is a way of life, and solar-

powered routers can make it even more so. These devices

will enable coverage in areas that were previously too incon-

venient to reach, such as trains, decimated regions or desolate

military campgrounds.

Surveillance system sensors: Today, its hard to go anywhere

without seeing surveillance cameras monitoring public and

business premises. These devices are often situated in difficult-

to-reach places, like the tops of buildings, surrounding walls and

tall trees. In these cases, solar devices are easier to deploy thantethered sensors and can be simply repositioned at a later time

as needed.

Data acquisition: Remote data collection is routinely used

to study a host of disciplines, including meteorology, geology

and astronomy. For example, seismograms taken at different

locations pinpoint earthquakes, and remote sensors help identify

areas rich in oil and gas reserves. This data can be acquired using a

solar-powered sensor board which offers users, such as academics,

businesses and government agencies, more placement options and

data processing capability.

Femtocells and picocells: Boosting cell phone reception withinbuildings and homes, femtocells and picocells create an intermedi-

ary network that improves coverage and connects customers to

the service provider network. Solar power enables small business

and consumers to deploy these devices in sunlit areas.

In all these examples, the solar-powered computing devices rely

on wireless technology to communicate with the rest of the world.

Therefore, the devices must have enough computing capacity to run

real-world applications, service IP stacks and USB ports and process

security functions such as WEP and encryption. Additional usage

models are listed in Table 2.

Setting Possible scenario Requirement

Emergencies Phone systems losepower during tsunami

or hurricane

Deploy radio-basedphone network forrelief workers

RemoteOperations

No communicationsinfrastructure exists formilitary or industrial (oilexploration) teams

Quickly install a new

network in the field

UnreliablePower Grid

Electrical service isspotty or non-existent

in rural locations oremerging countries

Operate networksand PCs regardless

of energy situation

Table 1. Usage Models for Solar-poweredComputing Devices

Device EmergenciesRemote operations/unreliable power grid

NetworkRouters

Relief organizations

Law enforcement

Transportation: Train/buspassengers

Ad-hoc militaryinstallations

Households andbusinesses withoutpower access or backup

SurveillanceSensors

Search and recoveryoperations

Crowd control

Imaging for military

Security for homesand businesses

DataAcquisition

Environmentalconditions monitoring

Audio and textualreporting

Oil drilling

Agricultural sampling

Environmental protection

Femtocellsand Picocells

Small businesses

Households

Table 2. Solar-powered Computing Device Opportunities


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4

Design Requirements

Besides more stringent control of power consumption, the design

requirements for a solar-powered computing device are nearly

the same as other small form factor networked devices. All these

devices generally operate without fans, use standard peripherals

and interfaces, and run networking and security applications, as

shown in Table 3. Although most space-constrained devices are

low power, solar devices are different because power consumption

directly impacts the size of solar panels and backup batteries, and

consequently overall product cost.

Designers can minimize power consumption by aggressively

pursuing power management. This is normally accomplished with

a combination of hardware and software techniques, which will be

discussed in more detail in the Challenge 3: Power Management

section. The basic idea is to keep the device in a sleep state for as

much time as possible, and only wake up the device when it is needed.

Satisfying the Design Requirements

The classes of solar-powered computing devices discussed thus far

can be based on a generic Intel Atom processor-based platform,

as shown in Figure 1. This platform satisfies the following five

design requirements:

1. Employs a low-power computing system: This two-chip

computing platform has a combined thermal design power

(TDP) under 3 watts1 (0.65W processor and 2.3W chipset),

and features embedded lifecycle support up to seven years.

Using the Deeper Sleep processor state, also called C6, theTDP of the processor drops to 0.1 watts1.

2. Enables a small form factor design: This platform can be

implemented with a board that measures (14 cm x 12 cm),

or slightly smaller than a mini-ITX board (17 cm x 17 cm).

3. Supports standard interfaces and peripherals support:

Designer can use standards based components such as USB

2.0, PCI Express*, DDR2 SDR AM memory, IDE FLASH and other

interfaces supported by commonly used super I/O chips.

4. Executes standard networking and security software:

Since many networking, wireless and security applications are

built for Intel architecture-based PCs, they work seamlessly onthe Intel Atom processor, thereby lowering equipment manufac-

turers development risk. Networking and security software is

available from the open source community, free of charge.

5. Implements power management features: Power

management is accessible using standards-based Advanced

Configuration and Power Interface ii (ACPI) and Linux* utilities

and kernels. ACPI defines common interfaces for hardware

recognition, computing board and device configuration and

power management.

Equipment makers typically find maintaining software code

for general-purpose processors, like the Intel Atom processor, is

easier than for application-specific hardware. This is because Intel

processors are supported by a broad ecosystem offering a wide

range of mature development tools. Developers also benefit from

an extensive Intel tool chain comprising compilers, performance

analyzer and software libraries. And since the Intel Atom proces-

sor maintains Intel Core2 Duo processor-based instruction setcompatibility, it can run the breadth of x86 code written over the

past few decades.

Device Peripheralrequirements

Computing functionsrequirements

GenericRequirements

USB wireless adapter Networking stack

Security

WEP

VPN

Encryption

SurveillanceSensors

USB camera Motion detection

Image processing

Data compression

DataAcquisition

Serial link (RS232)for sensor interface

Data processing

Femtocellsand Picocells PCI Express* links forconnecting to radiosand transmitters (e.g.,CDMA, WiMAX)

Protocol conversion(e.g., CDMA to IP)

Table 3. Peripheral and Computing Requirements

IntelAtom

ProcessorZ510

Intel SCHUS15W

PCI Express* x1

LPC

400/533 MHzFSB

IDE Channel(PATA only)

USB 2.0

(x2)(x1)

(x8)

WiFi 802.11 a/b/gWiMax

USB ports

DDR2 400/533(memory down)

PCI Express* x1

PCI Express* x1

SMBus

FLASH

FWH SIO

Figure 1. Generic Intel Atom Processor-based Platform


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Developers benefit from using one platform for both development

and deployment based on the same Intel architecture that today

supports the majority of the one billion PC users who access the

Internet. Furthermore, developers of software can write their appli-

cations on a standard Intel architecture PC and then drop their codeonto the target platform with high confidence that it will perform

well with minimal tweaking required.

System Example: Surveillance Sensor

Intel constructed a solar-powered surveillance sensor using

an Intel Atom processor-based board, as shown in Figure 2.

The chipset interfaces to a USB wireless adapter, USB camera,

FLASH memory and a console that supports development and

device configuration. The design uses FLASH memory instead

of a hard disk drive to save power and increase reliability.

The board has a voltage regulator module (VRM) that is poweredby an off-board voltage regulator connected to the solar panel.

The solar panel in this design is 10 inches x 10 inches and delivers

5 watts. The voltage regulator also charges the back up battery,

which powers the board when theres insufficient sunlight to

keep the board running.

Upon initialization, the processor sets up the USB camera and

USB wireless adapter. It runs the IP networking stack and starts

communicating with the access node (e.g., wireless router). The

board then acquires images from the camera and executes

applications such as motion detection and image recognitionand compression. The device sends messages and preprocessed

images to the access node using virtual private network (VPN)

technology and Wired Equivalent Privacy (WEP) encryption.

During normal operation, the board consumes approximately

2.5 amps of current at 5 volts. More current is needed at start up,

and the current draw reaches 1.2A. When the processor is in sleep

mode, only about 0.2A is required. Using this data and knowing the

percentage of time the board is in normal operation, designers can

determine capacity requirements for the battery, as shown in Table

4. There are two ratings on every battery: volts and amp-hours (AH).

Based on calculations, a 6 amp-hour, 12V battery can sustain the

board for 19 hours, assuming its in normal operation just 5 percent

of the time. However, battery backup time drops down to 2.4 hours

if the board never enters sleep mode. Developers should conduct

a full characterization of the battery backup system across various

use conditions and manufacturing lots to measure the robustness

of the design.

LPC: Low pin count bus

Device Board

Intel SCH US15W Chipset

Intel Atom Processor

USB PATA LPC

VRM

Super I/O

4 GB IDE Flash

USB Camera

USB Wireless Adapter

Serial LCD Console

Voltage Regulatorand Charger

Solar Panel

BatteryBackup

Figure 2. Surveillance System Sensor Implementation

Normal operation(@ 2.5A)

Sleep mode(@ 0.2A)

Hoursa based on6 amp-hours at 5V

100% 0% 2.4 hours

50% 50% 4.4 hours

25% 75% 7.7 hours

5% 95% 19.0 hours

aExclusive of board start up

Table 4. Battery Hours


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6

Designing a Solar-Powered Computing Device

Compared to other small form factor embedded designs, its

no surprise that solar-powered devices pose additional voltageregulation and power management challenges. Designers need

to integrate a step-down voltage output circuit and a battery

backup scheme and use processor sleep states to conserve

energy. This section discusses these design aspects.

Challenge 1: Voltage regulation

As with most board designs, the voltage regulator module (VRM) on

the solar-powered device does most of the heavy lifting for supplying

the necessary board voltages. For the Intel Atom processor, these

voltages are VCC

(processor core), VCCA

(phase lock loop supply) and VCCP

(front side bus AGTL+ termination voltage). The VRM requires at least

5V at 1 amp from the battery, which is charged by a 24V solar panel.

The battery backup stabilizes the platform because it powers the

VRM and provides a large amount of capacitance which is needed

at start up. The battery can drive the VRM using a step-down

voltage output circuit similar to the one illustrated in Figure 3.

Here, the battery voltage is stepped down to 5V to supply the

VRM on the circuit board. Likewise, the solar panel voltage sources

an intermediate 12V step to charge the backup battery. The solar

panel may supply as much as 1.2A at 25V.

A significant limitation of the simplified schematic shown in

Figure 3 is its full board battery charging. A production system

would normally deploy a trickle charge scheme to prolong thebatterys useful life.

Challenge 2: Source voltage

The VRM does most of the work as long as the battery has

sufficient charge. As mentioned earlier, designers must also

account for the additional current draw and power demands

when the board boots up.

An additional circuit (not shown here) is needed to prevent the

board from attempting to boot up when neither the solar panel

nor the backup battery can supply sufficient power. For example,

suppose the battery runs down when theres no sunlight; the board

will stop running. Later, when the sun begins to charge the solar

panel, the board could try to reboot continuously even though

theres not enough power in the system to maintain it. Likewise,

the battery never has a chance to recharge because power is

incessantly wasted by failed reboot attempts. Therefore, its

necessary to deploy a safeguard that permits the board to

reboot only after theres enough available energy to sustain

normal operation.

Challenge 3: Power management

Optimizing the system for minimum power consumption is usually

done as a combination of software (operating system) and hard-

ware elements. Most modern operating systems (OS) operate on

buffers associated with the ACPI specification that instruct the

processor to transition between various power-saving states. The

sleep state control logic in an ACPI-enabled processor assumes

the core(s) implements different power-saving states (also termed

sleep states) called C0 to Cn. When developing code for a solar-

powered device, software developers should proactively control

the power state of the processor as opposed to leaving it up to

the OS.

The following describes ACPI and open source efforts available

to assist developers.

ACPI:This is an open industry specification co-developed by

Hewlett-Packard, Intel, Microsoft and Toshiba. ACPI establishes

industry-standard interfaces for OS-directed configuration and

power management on laptops, desktops, servers and embedded

devices. It advances the existing collection of power management

BIOS code, Advanced Power Management (APM) application

programming interfaces (APIs), PNPBIOS APIs and Multiprocessor

Specification (MPS) tables into a well-defined power management

and configuration interface specification. The specification enables

new power management technology to evolve independently in

operating systems and hardware while ensuring that they continue

to work together.

Vsolar up to 25V, 1.2A

~12.5V charge

GND

220F

5K Tip29

3055

Battery

5K Tip29

3055

200F

Tantalum

GND

~5V to circuit board

Figure 3. Step-down Voltage Output Schematic


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Figure 4 illustrates the basic mechanisms used by a traditional

ACPI software layer to control the sleep states of the processor.

When the core is active, the processor always runs at C0. When

the core is idle, the application transitions the processor to a

sleep state that balances the overhead of entering and exiting

the state and the corresponding power consumption. Thus, C1

represents the power state with the least power savings; howev-

er, it can be switched on and off almost immediately. In contrast,

the Deep Sleep states (C4 and C6) consume negligible power, but

the time to enter into these states and respond to activity (back

to C0) is quite long. Note: The Deeper Sleep state (C6) is similar

to the Deep Sleep state (C4), except it further reduces core volt-

age levels.

The power management capability of the Intel Atom processor

entails more capability than presented here, and a full description

is available in the datasheetiii . In Deeper Sleep (C6), the Intel Atom

processor Z510 consumes less than one-eighth the power1 of

the Active (C0) state.

ACPI also enables device drivers to power down peripherals

when idle during normal operation. For example, a driver for

the Intel 82541ER Gigabit Ethernet Controller goes into Smart

Power Down mode when no signal is detected on the wire. The

Ethernet controller supports power-down states without software

assistance, which frees application developers from being respon-

sible for every system-level power management mechanism.

MobileLinux*:The Mobile Linux workgroup has as its mission

to accelerate adoption of Linux on next-generation mobilehandsets and other converged voice/data portable devices,

and to provide a mobile profile for the Linux Standard Base

(LSB). One advantage of this approach is that developers can

remotely develop for target hardware, so its not necessary to

have hardware in hand (e.g., headless development environment).

The workgroup holds regular conference calls and posts platform

guidelines on its Web site. For more information, visit www.linux-

foundation.org/en/Mobile_Linux.

MobileLinuxInternetProject: Moblin.org is an open source

community for sharing software technologies, ideas, projects,

code and applications to create an untethered computing

experience across Mobile Internet Devices (MIDs), Netbooks and

embedded devices. The computing hardware is based on Intel

Atom Processor Technology for use in low power, small footprint,

wireless-enabled solutions. The Moblin Core Linux Stack, an

integrated open source software stack, serves as a starting

point for developing applications for these devices. For more

information, visit www.moblin.org.

LessWatts:This open source project aims to improve the powerefficiency of the Linux operating system and applications.

LessWatts is about creating a community around saving power

on Linux, bringing developers, users and system administrators

together to share software, optimizations, tips and tricks. For

example, theres information about WiFi power-saving modes

(Power Save Poll, PS-Poll) that enable the WiFi adapter to notify

the access point when it powers down the radio to save power.

While the radio is powered off, the access point stores any

network packets for the device and sends them after the adapter

powers back up. Other discussions on the Web site include Wake

on LAN (WOL), which allows a master system to send a magic

packet over Ethernet to wake up the solar-powered device.

However, WOL keeps the network card active so it consumes

power even when the processor is in a sleep state. For more

information, visit www.lesswatts.org.

Truly Untethered Embedded Devices

Before the Intel Atom processor, it wasnt really practical to employ

an Intel architecture processor in a solar-powered application.

However, the revolutionary performance per watt and power

management features of the Intel Atom processor have led to

tremendous advances in reducing power consumption. And the

open source community is sharing best known methods and

creating standards to help realize even greater power savings.

These capabilities are available to equipment makers seeking to

bring the convenience of untethered operation (no power and

network cables) to embedded applications.

Idle States

Scheduler idle

Break

C0 Active

C2 C4/C6C1

Figure 4. ACPI-based Power State Management


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Intelprocessornumbersarenotameasureofperformance.Processornumbersdifferentiatefeatureswithineachprocessorfamily,notacrossdifferentprocessorfamilies.Seewww.intel.com/products/processor_numberfordetails.

i Powerconsumptionnumbersarethethermaldesignpower(TDP)fora1.1GHzIntelAtomProcessorZ510.Pleaseseedisclaimersnumbers1and2.ii ACPISpecificationathttp://www.acpi.info/spec.htmiiiPleasedownloadtheIntelAtomProcessorZ510datasheetforthemostcurrentproductspecificationsathttp://download.intel.com/design/chipsets/embedded/datashts/319535.pdf.

1 Intelmaymakechangestospecificationsandproductdescriptionsatanytime,withoutnotice.Designersmustnotrelyontheabsenceorcharacteristicsofanyfeaturesorinstructionsmarkedreservedorundefined.Intelreservestheseforfuturedefinitionandshallhavenoresponsibilitywhatsoeverforconflictsorincompatibilitiesarisingfromfuturechangestothem.Theinformationhereissubjecttochangewithoutnotice.Donotfinalizeadesignwiththisinformation.Theproductsdescribedinthisdocumentmaycontaindesigndefectsorerrorsknownaserratawhichmaycausetheproducttodeviatefrompublishedspecifications.Currentcharacterizederrataareavailableonrequest.ContactyourlocalIntelsalesofficeoryourdistributortoobtainthelatestspecificationsandbeforeplacingyourproductorder.Copiesofdocumentswhichhaveanordernumberandarereferencedinthisdocument,orotherIntelliterature,maybeobtainedbycalling1-800- 548-4725,orbyvisitingwww.intel.com.

2Performancetestsandratingsaremeasuredusingspecificcomputersystemsand/orcomponentsandreflectapproximateperformanceofIntelproductsasmeasuredbythosetests.Anydifferenceinsystemhardwareorsoftwaredesignorconfigurationmayaffectactualperformance.Buyersshouldconsultothersourcesofinformationtoevaluatetheperformanceofsystemsorcomponentstheyareconsideringpurchasing.FormoreinformationonperformancetestsandontheperformanceofIntelproducts,visithttp://www.intel.com/performance/resources/benchmark_limitations.htm

Thisdocumentisforinformationalpurposesonly.INTELMAKESNOWARRANTIES,EXPRESSORIMPLIED,INTHISDOCUMENT.*Othernamesandbrandsmaybeclaimedasthepropertyofothers.

Copyright2008IntelCorporation.Allrightsreserved.

Intel,theIntellogo,Atom,andCorearetrademarksofIntelCorporationintheU.S.andothercountries.

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