Designing Energy HarvestingSolar Powered Sensors

Dan Wright, Engineering ManagerLeviton Manufacturing Co., Inc.19 November 2014

AgendaWhy Energy Harvest?

Product Landscape

Low Power Wireless Controllers

Solar Cell Landscape

Energy Storage Options

Power Management

Sensor Technologies

Lens for Occupancy Sensors

Design and Product Challenges

Agenda: Energy Harvesting Design

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Our BUILDING Blocks

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Availability of free energy: Light

Reduce energy consumption

Solar cell (Photovoltaic) technology improvements

Low power technology maturity (often wireless)

Easy to install

Images: Microsoft clipart, Plow & Hearth

Why Energy Harvest?

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Many Energy Harvesting products leverage EnOcean wireless module

Product Characteristics:• Very low power, typically passive sensor: PIR, Humidity, CO2, ALS, Temp, Switch

• Solar Powered

• Ability to store charge for extended bridge time

Images: Leviton, KMC Controls, EchoFlex, AdHoc, EnOcean

Product Landscape

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EnOcean: TCM300 (8051 Based): 315, 868, and 902MHz

ZigBee (2.4GHz): TI, Silicon Labs (Ember), Atmel, NXP, etc.• CEL offers MeshConnect based module

Sigma Designs Z-Wave: 868, 908, 921MHz frequencies

Bluetooth technology: Various

Others (no standard, Sub GHz): Micrel, Silicon Labs, Microchip, etc.Images: EnOcean, CEL, Sigma Designs

Hardware: Low Power Wireless Controllers

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Least power consumption possible (< 1uA)

Work under a wide range of voltages (1.8 – 5V)

Average current draw (including radio transmit) < 10uA at 3.0V

May want to have black-out “no transmit” periods (1-2 minutes)

Select low leakage capacitors (Ceramic, Tantalum)

Hardware: General Circuitry Requirements

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Amorphous Silicon Solar Cells (Glass Substrate)• Sanyo (Panasonic Eco Solutions) Amorton

• Sinonar Solar

• Trony (Solars-China.com is reseller)

• Wasonlong / Blue Solar

Alternatives• IXYS – Thicker, more efficient, requires boost

• G24i Power – Flexible, requires boost

• AltaDevices – High efficient (24.1%), flexible, new company

• SolarPrint – High power density, glass base, requires boost

Flexible solar panel efficiencies have reached 18.7% which is on par with silicon (ECN Magazine, 5/2014).Images: Blue Solar, IXYS, and G24i Power

Hardware: Solar Cell (Photovoltaic) Landscape

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Sanyo 55x20mm (AM-1805) I-V Data• At 200 Lux will supply 12uA @ 3.0V (minimum), 15.5uA typical.

• At 50 Lux will supply 8-9uA @ 4.5V using two solar cells in parallel.

Source: Sanyo AM-1805 Datasheet addendum

Hardware: Solar Cell (Photovoltaic) Example

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Sanyo 55x20mm (AM-1805) I, V vs. Lux• Working range up to 1k (~5.5V)

• In sunlight will > 6.0V

Source: Sanyo AM-1805 Datasheet graph

Images: Cooper Industries (Direct, Indirect lighting: Corelite, Class A), Synergy Lighting, 7-11 Goes LED

Hardware: Solar Cell (Photovoltaic) Example

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Bridge Time: Length of time the device will continue to work without light

Selecting correct storage device is critical!• The more storage the device has, the long it will take to CHARGE the device.

• Increase Cap = Increase Bridge Time and Charge time

Example: 0.33F SuperCap charge time:

At around 10uA an hour would drain 0.33F cap: 1V per 24hrs

Last somewhere around 36-48hrs at full charge (4.5-5V).

Hardware: Energy Storage Options – Bridge Time

Charge Time (hr) Light Level (Lux)

28 50

14 100

6 200

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Supercapacitors (aka PowerStor, Gold Cap, Dynacap, EDLC)• Cooper Bussmann, Panasonic, Elna, Cap-xx, Kemet

• 0.33F cost: $0.70/1k

• Time (0.33F) = (0.33 * 2V) / 5uA = 132000s = 36.7 hours

Solid State/Flat Battery Alternatives:• Cymbet Enerchip (CBC050): 50uA (> 5000 discharge cycles)

• ST EnFilm (EEL700A39): 3.9V at 0.7mAh

• Rocket Electric Korea (LIP292240): 3.6V, 5mAh, Lithium Ion Polymer Battery

Traditional Rechargeable Battery:

• Coin cell, AA, AAA, etc.

Images: Cap-XX, Panasonic, and Cymbet

Hardware: Energy Storage Options

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Boost: Necessary for low voltage solar cells

Buck: Good for higher voltage solar cells

Specialized Energy Harversting• BQ25504/05/70: Boost, Iq=1.4uA, use with solar cells, battery/supercap storage

• LTC3107: Has internal shunt, works with battery and optional capacitor storage

• LTC3106: Buck-Boost. Works with solar-cell and battery/supercap. Iq=1.5uA

• LTC3129: Buck-Boost DC/DC converter with Iq=1.3

• LTC3330: Nanopower Buck-Boost

• MAX17710: Can be used with solar cells and rechargeable batteries

• MB39C811, MB39C831 (Spansion): Buck (811) and Boost (831) for energy harvesting

• SPV1050 (ST): Buck-Boost converter with built in LDO. Has battery charger

• ADP5090 (AD): Ultra low power boost regulator with charge management

• TPS82740A/40B (TI): Step down micro SiP module, Iq=260nA

Hardware: Power Management Circuits

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Passive Infrared (Motion)• PYD1096, PYQ1098 (Excelitas): Smart DigiPyro, 2/4 element, 15uA

• LHI1128, LHI944 (Excelitas): Analog sensors

• PaPIR (Panasonic): 1, 2, 6uA Digital PIRs with lens

• DigiPyro (Nicera): Similar to Excelitas, 15uA

Humidity / Temperature / CO2

Door/Window• SM351LT/SM353LT (Honeywell): Magnetoresistive Sensor IC, Average current 360nA

Ambient Light Sensor• MAX44009 (Maxim): I2C controlled with 1uA operating current (lowest in industry)

• ISL29020 (Intersil): I2C controlled with 65uA operating current, 0.5uA sleep

• BH1730FVC (Rohm): I2C controlled with 200uA operational and 1.5uA sleep

Images: Panasonic PaPIR, Excelitas

Hardware: Sensor Technologies

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Optics:• Panasonic – Included with sensors

• Fresnel Technologies – www.fresneltech.com

• Carclo Optics – www.carclo-optics.com/pir-sensor-lenses

Images: Carclo optics

Mechanical: Lens Optics for PIR Sensors

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Making product cost effective

Minimizing current usage (< 10uA), Black-out periods

Startup time at a given light level

Bridge time (48 hours with 0.33/0.47F super cap)

Analog versus Digital PIR

Quite Supply

Battery vs. Supercap vs. Rechargeable battery

Operational Voltage / Shunt Voltage

Wireless communication range / Antenna Position

FCC Certification

Leaky capacitors (Electrolytic, Super Cap) @ Temp

Lessons Learned: Design Challenges

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Customer Expectations vs. Energy Harvesting trade-offs

Value Add cost of Energy Harvesting

Lessons Learned: Product Challenges

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Thanks for Attending

Any Questions?

Contact Information:

danwright@leviton.com, d.m.wright@ieee.org

Questions: 5 Minutes