Throwing away the batteries in many un-tethered designs and shifting energy harvesting techniques seems to have caught the imagination of designers as the next “big thing” in embedded systems design.
This seems to be even more so, given the emphasis in U.S. President Barak Obama's emphasis on green energy technologies in his recently approved economic stimulus and infrastructure investment plan.
But according to TI's Adrian Valenzuela, while enormous design opportunities are possible, energy harvesting as an alternative to the use of batteries and external power sources in many embedded designs is not without its problems. Using such techniques, he said, will require designers to analyze very carefully the parameters of their system design to see if these techniques can be used effectively, and if so, which ones.
Valenzuela, a product marketing engineer at Texas Instruments is teaching a class in “Batteryless Energy Harvesting in Embedded System Design (ESC-305)” at the Silicon Valley Embedded Systems Conference in San Jose, Ca., March 30 to April 2, 2009.
Modern ultra low power embedded processors have reached a level of integration and processing efficiency that traditional batteries are no longer required for many applications including complex and often power intensive wireless sensor networks that may involve sampling various sensors and communicating wirelessly.
“By harvesting miniscule amounts of wasted energy from the environment, systems are enabled with near infinite up-time without a battery as its primary power source,” said Valenzuela.
While traditional batteries have served us well for many years, he said, they have hard limitations on the amount of power they can provide without growing in size. Additionally, battery replacement can be very costly, and they create unnecessary waste when their energy has been depleted.
Not only does energy harvesting enhance current applications by eliminating their dependency on the battery, they also enable entirely new applications that weren't feasible given the finite lifetime and size of batteries.
“Micro-energy harvesters from various sources such as light, motion, thermal, or RF will open the doors to engineers to decouple themselves from the physical burden of batteries and applications no longer have to be limited to their accessibility for maintenance,” said Valenzuela. ” Low cost, autonomous sensor networks will not only enrich our lives by providing valuable data about the status of our environment but they will do so with no long term, reoccurring cost or impact on the environment. “
Energy harvesting, he believes, will extend the usable life from existing products and they will enable design options that weren't possible before. Some applications may sound like science fiction today, said Valenzuela , but the technology exists to enable a new generation of applications. By harvesting the vibrational energy, intelligent sensors will be able to be implanted in roads, bridges, and buildings at the time of construction providing real time feedback on the structural integrity guaranteeing our safety.
By harvesting energy from the sun, farmers will be able to monitor the health of their crop using low-cost, disposable sensors producing greater crop yield with lower maintenance, he said. “By harvesting the heat from the skin, smart bandaids no larger than a quarter will be able to monitor a patient's vital signs and transmit the information wirelessly to a central medical base station without having to tether a patient to a machine,” he said.
One of the things that are making energy harvesting a practical design reality, said Valenzuela, are the flexible power requirements of a new breed of ultra-low-power microcontrollers which not only reduce power consumption by allowing lower supply voltages than typical embedded processors with a fixed supply voltage, they also allow a wider variety of energy sources.
“For example, ultra-low power MSP430 microcontrollers support a wide input voltage range between 1.8v to 3.6v,” he said. “By allowing a lower operating voltage, not only is the overall power consumption of the system reduced, it also allows the energy harvester to provide usable power at much lower voltage levels.”
But as promising as energy harvesting is for many embedded designs, Valenzuela said there are some caveats to seriously consider when looking at this alternative in your next design.
“While we'd all like to eliminate our dependency on wires and are ready to replace our last set of batteries forever,” he said, “Unfortunately, not all applications are good candidates be to fully autonomous energy harvesting systems. In addition to hard requirements that must be met such as having an energy source available to harvest from, there are practical concerns such as set up cost. “
For example, he points out, if a given application only needs to be functional for 2 years and this is easily achievable with a set of batteries, and an energy harvesting power source is more costly than the batteries and consumes more space, then it probably doesn't make sense to switch the power source.
Valenzuela said that in addition to having an energy source available to harvest from, applications that could benefit from energy harvesting share some of the following characteristics: it is difficult to install or access for maintenance, cords for power or communication are too costly or cumbersome, environmental friendliness is required, or very high uptime is demanded. “If one or more of these characteristics apply to a given application, it would benefit from energy harvesting. “
In an ideal world, it would be possible simply take your existing power supply, replace it with an energy harvesting system, and the system would function. However, in reality, this is rarely the case. “This would only be possible if the energy harvester was guaranteed to meet the applications power requirements at all times as if it were using the original power supply,” said Valenzuela.
“In practice, energy harvesting systems are finely tuned for ultra-low power operation and must accommodate for wide fluctuations in input power including the possibility that the power source becomes unavailable for some period of time.”
Other green engineering classes at the ESC include:
“Control Networking – Energy Management for Homes and Buildings (ESC-223),” taught by Bob Dolin.
“Meeting the ultra Low-power Demands of Tomorrow's Applications (ESC-263),” presented by Dominic Pajak.
“Advanced Control Algorithms for Reducing Power Consumption of Embedded Systems (ESC-326)” taught by Christian Fritz.
“Energy Pacing Strategies in Green Embedded Computing Applications (ESC-403),” presented by Bill Mercer.
“OS Strategies for the Next Generation of Green Devices(ESC-581)” from Stephen Olsen
“A Single Controller-based LED Lighting System (ESC-465)” presented by Hrishikesh Nene.
If you want to learn more about this important topic, attend the