New approach to solar energy

Solar systems often produce: either electricity or heat (in the form of steam or hot water). But a new analysis by researchers at MIT shows that: more benefits will be gained by using solar energy extraction systems to produce both electricity and heat.

New research at MIT shows: "a great opportunity for integrating thermoelectric devices in solar thermal systems" , says Evelyn Wang, assistant professor of mechanical engineering at MIT, co-author of the study.

The results of this study were published in the journal "The journal Solar Energy".

The new study is a combination of: thermoelectric devices (which can create an electric current, from a thermal gradient , inside a centralized heat system obtained from a solar source, also known as a Parabolic troughs These solar heat-concentrating systems use long, curved mirrors to focus sunlight into a glass tube that runs along the central line of the trough. A liquid is pumped through a glass tube, which will be heated by the sun, and can then be used, to create steam, to spin a turbine, or be used directly for heating. Warm space or industrial processes require thermal energy.

According to a new proposal by Wang and graduate student Nenad Miljkovic: the researchers embedded a thermoelectric system into a glass tube running along the central line of a parabolic trough system to produce: both hot water and power at the same time. The main device to make this work is called a thermosiphon, which attracts heat from the "cold" part of the thermoelectric system, to maintain its thermal gradient.

Wang and Miljkovic's system will change the shape of a glass tube in a series of concentric glass tubes that run along the central line of a parabolic trough system: the narrower (first) glass tube will contain the internal thermoelectric material, which will affect the narrower tube, in the center of the main " thermosiphon " thermosiphon , absorbs the heat from the "cold" part of the thermoelectric device and makes reduce the need for cooling solution (as in a conventional parabolic system). The thermal energy obtained from the main device " thermosiphon " (thermosiphon) can be used to heat space, operate industrial processes or create hot water.

Such a system will be more beneficial than traditional solar cells (devices that generate electricity from sunlight), Wang added, "Thermoelectric devices can be much cheaper than the use of traditional solar cells " . "In addition, conventional solar batteries do not work well at high temperatures . " However, she explained: "Thermoelectric devices work better in high temperature conditions, allowing them to create a greater gradient temperature".

"Currently there is no system of solar energy systems that can produce both electricity and heat in high temperature conditions," said Miljkovic. However, Miljkovic added, 'there are many companies pursuing this goal.'

"This is an opportunity to gather different technologies," Wang said. The main device "thermosiphon " , which attracts heat from this place and transfers heat to another place (like a liquid nozzle), is "passively used to transfer heat . at a low cost" , Wang added.

"The main equipment" thermosiphon (usually thermosiphon) is usually filled with materials that have undergone a transition period (usually changing from liquid to vapor) when they are heated, and Get the ability to conduct heat - a ability to transfer heat from one place to another is much higher than any solid material , " Wang said. "This is an effective way to transfer heat, to any place you want."

Wang and Miljkovic invented a computer model to find the optimal combination of current materials for thermoelectric devices and main equipment " thermosiphon " . This model allows testing of combinations of different devices (both simultaneous power and thermal production) in different operating conditions to make the whole system of these devices, The most effective operation.

A single system can provide heat and electricity, for a house, Wang said. "In a house, you consume a lot of heat, but you only need to be supplied with enough electricity , " Wang added. "While the performance of such a thermoelectric system is relatively low, in a household, you really don't need too much heat."

Abraham Kribus, a professor of mechanical engineering, working at Tel Aviv University, Israel, who is not involved in the study, said that the study describes a new approach to solar conversion, with Optimistic results show the high efficiency of conversion theory.

"Currently this combined system (generating electricity and thermal energy at the same time) is still at the analysis stage, it is still unclear about the effectiveness of cost-based authentication and system reliability. However, "this is a very good theory, and the team is really capable , " Kribus added.

Evelyn Wang agrees that it may take several years to apply this concept of system design to reality. Currently, Wang and Miljkovic are ahead of the "effort to build a model system to prove".

This study is funded as part of the S3TEC MIT Center (a Potential Energy Research Center) funded by the US Department of Energy.