Wouldn’t wearing energy harvesting shoes be like walking on sand or mud? Energy can't appear from nowhere, so those shoes must cause users to tire quickly because they are forced to generate extra energy while walking.

This is probably one of the most common misconceptions related to footwear-embedded energy harvesting. In fact the user does not expend any extra energy while using a footwear-embedded harvester device. The mechanical energy that is converted to electrical energy during the harvesting process is the energy which is lost as heat anyway, independent on whether the footwear has embedded harvester or not. Experimental studies show that up to 20 W of power per foot is simply lost as heat during normal walking. This might sound like a lot, but in fact this is still a small fraction of about 300 W of total metabolic power that the person typically generates during walking. It is important to note that the energy losses are unavoidable and occur even if the person walks barefoot, in which case the energy is dissipated within the person's feet and legs. All what footwear energy harvester strives to accomplish is to take some of that energy loss and convert it into electrical energy.

Because the process of walking (human locomotion) was honed by Nature for hundreds of thousands of years, it must be extremely efficient. Doesn't this mean that only a minuscule amount of power can be harvested from walking without causing interference with the person's gait?

Indeed, human locomotion is the result of a long process of natural selection and thus has to be highly efficient. However, it is important to distinguish between the energy efficiency and the overall efficiency of the locomotion process. Natural selection by itself does not necessarily guarantee high energy efficiency. Natural selection has to balance energy efficiency with other important requirements such as agility, an ability to traverse a broad range of terrains, etc. Detailed experimental investigations revealed that a substantial amount of energy, up to 20 W per foot, is actually lost as heat during the walking process. It is this lost energy that is being captured by the footwear-embedded harvester and eventually converted into useful electrical energy.

What is the efficiency of your harvester? Isn't it true that your harvester has to have fairly high efficiency in order to produce any appreciable power?

The design target is 75% electrical efficiency. However, it is important to understand that efficiency is not necessarily paramount in this application. The mechanical energy that is converted to electrical energy is the energy which is lost as heat anyway, independent on whether the footwear has an embedded harvester or not. Thus, unless the amount of power taken by the harvester (including efficiency losses) starts to approach the power naturally lost during walking, the harvester efficiency really does not matter much.

Your harvester has integrated fluidic chambers. Wouldn't this cause “slushy” feeling while walking?

The presence of fluidic chambers does not alter the footwear comfort. The fluidic chambers are basically polymer bladders which are very flexible and embedded in the resilient midsoles of the footwear. The foot never contacts the bladder directly and instead feels the combined reaction of the midsole/bladder structure which is optimized for the best comfort.

What kind of liquids are used in your harvester? Are those liquids toxic?

Actually, a broad range of fluids works, including such simple choices as water and oil. However, the highest performance is achieved for several special fluid formulations, which are proprietary to InStep NanoPower. These formulations are non-toxic, non-corrosive and inexpensive.

What happens when the person is not moving? Doesn’t your harvester only work while walking?

The harvester has an integrated rechargeable battery, which serves as energy storage. The battery is automatically recharged during walking to provide electrical power when the user is at rest.

Your harvester has an integrated battery. Is this a health hazard? Batteries can explode!

The battery is hermetically enclosure, which reliably isolates it from the environment, thus preventing harm to the user. A number of footwear products on the market have embedded batteries. A good example is the popular Nike Plus brand running shoe.

What happens when the shoes with your harvester get wet? Wouldn't they develop electrical shorts and harm the user?

In addition to being hermetically sealed the harvester battery has integrated safety circuitry which prevents the occurrence of electrical short under any circumstances.

What good is it to generate power in the footwear? How can the generated power be transmitted from the shoes to hand-held mobile devices?

The power generated by the footwear-embedded harvester can be used in one of two ways. It can be used directly to power a broad range of devices, from smartphones and laptops to radios, GPS units, night-vision goggles and flashlights. In this case the power can be delivered to the device using a number of methods, ranging from simple wiring to conductive textiles to wireless inductive coupling.

Alternatively, a Wi-Fi hot spot can be integrated into the harvester to act as a “middleman” between mobile devices and a wireless network. Such an arrangement dramatically reduces power consumption of wireless mobile devices and allows them to operate for much longer time without battery recharge. No direct physical connection between the mobile devices and the harvester unit is required in this case.

I still don't understand how having a smartphone wirelessly connected to the harvester can possibly improve smartphone's battery life?

Here is a more detailed technical description. The main idea is based on the fact that long-range radio (RF) communication requires much more power to operate as compared to their other functions or to short-range RF communications such as those conforming to Bluetooth standards. The high power required for long-range RF communications leads to accelerated battery discharge in many mobile electronic devices, such as smartphones, laptops with Wide Area Network (WAN) cards, cell phones, etc. Thus substantial decrease in power consumption by these devices can be achieved if their long-range RF transmission is minimized or even completely excluded. One of the ways to achieve this is to perform RF communications through an intermediate transceiver (Wi-Fi hot spot) that receives communications from the mobile devices in a low-power standard such as Bluetooth and then retransmits them through a long-range high-power RF link, such as G4, G3, or CDMA wide area cellular telephone network link. Since both short-range and long-range communications are performed wirelessly, the transceiver location can be anywhere in the vicinity of the mobile devices. In other words, the idea is to combine a human-motion-powered energy harvesting device with the wireless transceiver capable of receiving communications from personal mobile electronic devices in a low-power standard such as Bluetooth and then to retransmit them through a long-range high-power RF communication to a wide-area network. Thus a very substantial decrease in power consumption by mobile devices can be achieved since most of the energy consumed by long-range RF transmission will be provided by the energy-harvesting device rather than by the mobile electronic devices themselves.

What is the reliability of your harvester? What about fluid leaks?

Integrated fluid-filled elements (bladders) are not uncommon in footwear products. Our harvester device design utilizes the best practices developed by footwear industry and is manufactured from the highest quality materials which are proven in the industry to reliably contain fluids when subjected to a very broad range of temperatures, humidity, mechanical loads, etc.

What is the cost of your harvester? Is it affordable?

The cost depends on the device model. We are developing several models of the energy harvester device which differ by the performance level, the presence of additional electronics, etc. However, we expect the cost of the most basic harvester device not to exceed the cost of the footwear itself.

If the footwear-embedded harvester is such a good idea, why is it still not available commercially? What prevented people from developing such a product?

Footwear-embedded harvesting of mechanical energy is a long-recognized concept, with its root arguably going back to the beginning of the 20th century. The main reason this concept has not been commercialized in the past is due to the lack of a viable energy harvesting technology. Existing methods of mechanical-to-electrical energy conversion such as electromagnetic, piezoelectric, or electrostatic do not allow effective direct coupling to the human motion during the walking process. Bulky and expensive mechanical or hydraulic transducers are required to convert a broad range of forces and displacements typically encountered during walking into useful electrical power.

To address this problem InStep NanoPower has developed a radically new mechanical-to-electrical energy conversion method, which is uniquely suited for high-power energy harvesting from human locomotion. The mechanical energy is converted to electrical energy by a novel microfluidic device through the interaction of thousands of moving liquid microdroplets with a groundbreaking nanostructured substrate. Advantages of this process include very high power densities, up to 1 KW per sq. m, the ability to directly utilize a very broad range of mechanical forces and displacements, and the ability to directly output a broad range of currents and voltages, from several volts to tens of volts.