From computer chips to car engines, from cell phones to laptops; they all release excess heat in order to perform at their optimal level. More than half of the energy consumed worldwide is wasted, most of it in the form of this excess heat. According to researchers from the Massachusetts Institute of Technology this waste heat is a great potential source of energy if harvested correctly. They recently uncovered a new method of obtaining electrical power from otherwise wasted heat.
Waste heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found, and is regarded as a waste by-product. The burning of transport fuels is a major contribution to waste heat. When excess heat is released the efficiency of the equipment will decrease below 100 %. When, for instance, the waste heat from a car engine in the winter is being used for the car radiator, the efficiency will increase. In theory the same principal would apply for cell phones and laptops. If this wasted energy is cleverly harnessed and utilized we might not, for instance, have to recharge our phones or computers that often.
There are many different approaches to transfer thermal energy to electricity, these approaches are mostly still in development. Peter Hagelstein, one of the main researchers from MIT, is of the view that the existing solid-state devices that are already available to convert heat into electricity are not very efficient. It is known as high-throughput power. According to Hagelstein it converts heat from a less efficient system and you get more energy. But it is a larger and a more expensive system in which you get either high efficiency or high throughput. But the MIT team found that by using their new system, it would be possible to get both.
Theoretically a limit is set on the maximum amount of efficiency any device van achieve when converting heat to electricity. This limit is called the Carnot Limit, based on a formula set in the 19th century. Hagelstein found that current devices can only go as far as one tenth of that limit. Hagelstein and collegues claim to have reached an efficiency as high as 40 % of the limit by using their new technology. They say in the future it might be possible to achieve up to 90 %.
The MIT researchers chose to not try upon improving existing devices but to start from scratch designing the ideal thermal-to-electric converter. It’s not entirely clear how the new system works. It involves a single quantum-dot device – a type of semiconductor in which the electrons and holes, which carry the electrical charges in the device, are very tightly confined in all three dimensions. Such devices are still in development and will not appear on the market for a couple of years to come.