Human Energy Harvesting

Considering the ever increasing demands for electrical energy to power the electrical & electronic appliances/gadgets and scarcity of the same due the over dependency on non-renewable resources to produce power, today there is a dire need to explore alternate energy sources. Some of the popular alternate sources for generating energy are Sun (solar) and Wind. But today with the advent of electronics & sensor technologies power consumption of the electronic products has particularly reduced considerably. And hence many alternate sources of producing electric energy are tried out today to power these low power consuming electronics. On such alternate method is human energy harvesting (HEH). HEH is a broad term describing any system that utilizes the human body as the primary source of energy to generate and store energy in the form of electricity. Capturing the energy from metabolic and other activities such as walking, hand waving, blood pressure, breathing etc. enables harvesting enough energy that is sufficient to power mobile or implantable devices throughout their lifetime. The human energy that would have been otherwise wasted can be a promising candidate for future mobile power.

Human body contains enormous quantities of energy. In fact, an average adult has as much energy stored in fat as a one-ton battery. This energy fuels our everyday activities and the concept of Human Energy Harvesting is to explore measures to use this energy to run electronic devices. According to center for Space Power and Advanced Electronics, a NASA Commercial center in Alabama, the human body on average is 15% fat, capable of producing 11KWh of energy. An average human eats about 3.3KWh per day. The first law of thermodynamics prevents total energy capture but we can have approximately 81W from sleeping person, 128W from standing person, 163W from walking person,407W from brisk walking, 1048W from long distance runner, 1630W from a sprinter.

Using human energy that would normally go waste is an ultimate achievement in recycling. Also, human energy is nonpolluting and hence referred to as green energy. Human body is tremendous storehouse of energy. Just 1g of fat stores about 9000 calories.

• 1gram of fat stores 9 dietary calories, then joules per gram of fat:
  (9000 calories /1g fat) (4.19J / calorie) = 37,700J
• An average person of 68 Kg with 15% body fat stores energy equivalent to:
  0.15(68 Kg) (1000g / 1 Kg) (37,700 J / 1gfat) = 384 MJ

There are various principles that can be used for harvesting devices. Thermoelectrically driven devices are based on seebeck effect and mechanically driven devices are based on piezoelectric effect, dielectric effect, electromagnetic induction, electrostatic property and magneto-restrictive property. Various human activities can aid into energy generation for devices using the above mentioned principles. These principles can be used for motion and oscillation harvesting during activities like walking, running and arm movements. For a 58.7 Kg man maximum power consumed by arm lift can be calculated as follows: (3.2Kg) (9.8/sec2) (0.725m) (1.3 lifts/sec) (2 arms) = 60 W

Even blood pressure has been harnessed for self-powered medical sensors and urine based fuel cells have been made that can generate a power of 0.5 to 1 watt. Thermoelectric watches have been made by Sieko instrument Inc. Human energy harvesting is very useful for implantable device, handheld devices, military operations, space missions, expeditions etc.

By Ms. Anshu Sharma, Assistant Professor, Chitkara University H.P.