In this work, we show how the thermal trap effect, triggerable by exposing common semi-transparent materials (e.g., quartz and water) to solar radiation, can increase the viability of solar receivers by suppressing radiative losses at high temperature.
However, they are currently quite inefficient at converting solar energy to temperatures higher than 1000°C, says Casati. To improve the efficiency of such devices, Casati and his colleagues have designed a heat-trapping solar receiver made of silicon carbide with a 300 millimetre layer of quartz around it.
A 3D heat transfer model, validated against the experimental data, is applied to determine the performance map of solar receivers exploiting thermal trapping. These are shown to achieve the target temperature with higher efficiency and/or needing a lower concentration than the reference unshielded absorber.
The capability of the heat transfer device to convert incident solar radiation Q in to heat Q out is characterized by its thermal efficiency, η thermal, which, assuming the absorber is an ideal black absorber emitter, is defined as (Equation 1) η thermal = Q out Q in = 1 − Q HL Q in = 1 − σ T surf 4 η field I DN C.
For the semi-transparent heat exchanger, T surf < T abs > T out ( Figure 1, right). Thus, for a targeted T out, thermal trapping occurring in the semi-transparent heat exchanger results in a lower surface temperature, T surf, which reduces heat losses to the surroundings and, in turn, increases η thermal.
Light trapping is an important performance of ultra-thin solar cells because it cannot only increase the optical absorption in the photoactive region but it also allows for the efficient absorption with very little materials. Semiconductor-nanoantenna has the ability to enhance light trapping and raise the transfer efficiency of solar energy.