Introduction - Energy Harvesting Autonomous Sensor Systems - page 21

TABLE 1.3
Energy Harvesting Opportunities and Demonstrated Capabilities

Energy Source Performance Notes

cm 2

Ambient light 100 mW / (direct Common polycrystalline solar cells are 16%

to 17% efficient, while standard
monocrystalline cells approach 20%

sunlight)

cm 2
(illuminated office)

100 W /

W/cm 2 Thermal a. 60 at5K Typical efficiency of thermoelectric

generators are gradient ≤ 1% for T < 313 K

W/cm 2 b. 135 at 10 K a. Seiko Thermic wristwatch at5Kbody heat

b. Quoted for a ThermoLife generator at gradient

T=10K

Blood pressure 0.93 W at 100 mmHg When coupled with piezoelectric generators,

the power that can be generated is on the
order of microwatts when loaded
continuously and milliwatts when loaded
intermittently

W/cm 3 (human
motion-Hz) 800

Predictions for 1-cm 3 generators; highly
dependent on excitation (power tends to
be proportional to

Vibration 4

W/cm 3
(machines-kHz)

, the driving
frequency, and y o , the input displacement)

2 mW/cm 3 Hand linear

generator

Shake-driven flashlight of 3 Hz

Push button 50 J/N Quoted at3VDCfortheMITMedia Lab

Device

118 J/cm 3

Heel strike Per walking step on piezoelectric insole

1 mW/cm 2 Ambient wind Typical average wind speed of 3 m/s in the

ambient environment

W/cm 2 Ambient radio

frequency

< 1 Unless near a RF transmitter

14 mW/cm 2 Wireless energy

transfer

Separation distance of 2 m

Source :C.Mathna, T. O'Donnell, R.V. Martinez-Catala, J. Rohan, and B. O'Flynn, “Energy scav-
enging for long-term deployable wireless sensor networks,” Talanta , vol. 75, no. 3, pp.
613-623, 2008 [29].
5. Provide long-term solutions. A reliable self-powered sensor node will
remain functional virtually as long as the ambient energy is available.
Self-powered sensor nodes are perfectly suited for long-term appli-
cations that are looking at decades of monitoring.
6. Reduce environmental impact. EH can eliminate the need for millions
of batteries and energy costs of battery replacements.
Having said that, energy supplied by the EH technique is not perfect but
has its own set of challenges:
1. Low power generation densities causes insufficient power for con-
tinuous operation