Feasibility of Energy Harvesting for Low-Power Applications

Energy harvesting (energy scavenging) has always been attractive since sources are almost always available and the energy available is just wasted if not used.  In addition to the three sources discussed in the reference below (light, vibration, and heat), another attractive source is available from automotive vibrations (particularly for sensors) and the more significant and now more widely used source of regenerative braking.

Quoting from the excellent Design News article of April 22, 2015 by Warren Miller:

“Energy harvesting in particular seems to be moving at an accelerating pace. We now seem to be at a point where it is possible to run low-power systems primarily from energy harvesting sources. This is a big shift from even just a couple of years ago.

Three key trends seem to have accelerated this dramatic shift. The first is the wild growth in the low-power market. New applications like wearable devices, smart sensors, and disposable devices are driving the insatiable need for more processing power on a low-power budget.

This rapidly growing market drives the second trend: the availability of low-power MCUs and FPGAs. These devices now offer considerable, power-efficient processing that can be applied to the wide range of applications in the growing low-power market. The third trend is the growing availability of energy harvesting sources that produce enough power to run low-power MCUs and FPGAs for enough time to do useful work.

Shown in the Figure below, is a summary of the power harvesting capabilities of three common harvesting technologies. We are all familiar with solar power as an energy harvesting technology, and it has probably been the main energy harvesting technology to power electronic devices up to this point.

But new technologies that provide alternative — and often more convenient power sources – have been developed. Piezoelectric effects, for example, can be used to harvest energy from vibration, motion, and pressure. This can be convenient for powering a variety of devices in areas such as wearable electronics for athletics and sensors on trucks or trains and for material flow control.

A piezoelectric energy source, as with many harvested energy sources, can be derived in bursts, which often need to be stored and accumulated for later use. In very simple systems, a simple capacitor storage system may be sufficient to give a very low-power MCU the juice needed to power up and perform simple calculations several times a second.

Smart use of the MCUs’ low-power states is usually critical in low-power applications, and newer MCUs can sleep indefinitely while using only microamperes of current, which makes it possible to use them in these types of very low-power applications.”

Energy_Harvesting_Data_Figure-1-Imec

“Perhaps surprising is the large amount of harvested power available from thermal energy. On par with solar harvested power, thermal energy can perhaps be best used in industrial applications where sensors monitor extremes of pressure and temperature.

The large temperature gradients available in industrial process control applications can easily power low-power FPGAs to implement very complex sensing algorithms using digital signal processing filtering or transform functions. Small rechargeable batteries can be used to store power when the temperature gradient isn’t available, but because sensing is normally only required while temperature extremes exist, batteries can be small without impacting sensor availability.

Perhaps even more interesting is the possibility of harvesting small amounts of thermally produced energy when temperature differences are not as extreme. A wearable device, for example, might have available a 10- or 20-degree temperate difference. This might be sufficient to generate enough power over just a few hours to power an activity monitor, heart rate sensor, or position tracker.

A small wristband could provide enough area to generate the power required to run a monitor or sensor. Combining energy harvesting techniques, thermal and vibration for example, could be an even more efficient method for powering an activity monitor.”

 

 

 

The California Drought and Potential Technology Solutions

The drought in California is in its 4th year. Water conservation and development of new water resources are becoming more important than ever.  Clever ideas and the development and application of new technologies to improve our water supplies are critical.  I also feel that the massive commercial and residential development that is going on in Silicon Valley and other highly-populated areas of California is rapidly increasing demand at the same time that supplies are falling.  Water may become the new currency, especially when you include the voracious water appetite in the agriculture industry!!

Clever ways to apply technology to make a real impact on water saved through conservation should all be addressed immediately.  Conservation measures are the easiest to implement quickly. However, most are at the household level and require participation by many to have an impact.

Large-scale sources of new water supplies also most be pursued aggressively.  Desalination plants offer a great opportunity to develop new supplies near the Pacific Coast.  Cost and energy requirements are major issues that must be addressed to make desalination more feasible.  I believe that the cost factor can be improved by standardized designs that are applied to the development of a large number of plants.

The energy required for desalination can be reduced and at least “green” energy sources can be substituted for traditional power sources.

Transporting of water supplies from geographic areas with huge supplies far in excess of their demand to areas where water supplies are limited also need to be explored.  What are the most efficient options?  What are the sizes required for either pipeline or canal transportation of large quantities of water?  Canals and pipelines are already used in California for water transportation, but the sources are also in California and are also affected by the drought (the reduced Sierra snowpack, etc.).

An excellent article by Michael Goldman gives great detail and context on the current historic drought.  The article has the provocative title  of:  The California Drought — “Whiskey’s fer drinkin’ – Water’s fer fightin'”     and is posted here :

http://calpensionsbrief.blogspot.com/2015/04/the-california-drought.html

A high-percentage of the total water used in California goes to agriculture.  Drip-irrigation can dramatically reduce the water used and is appropriate for many types of crops.  Incentives to promote the rapid conversion to drip-irrigation for agriculture should be put in place immediately.

For the remaining part of the water that goes toward commercial and residential use, a large fraction is used for landscaping. Grey-water and other sources of reclaimed water can certainly be used for landscape applications.