Determination and evaluation of the optical properties of dielectric liquids for concentrating photovoltaic immersion cooling applications

The optical properties of the immersion dielectric liquids are highly important for concentrating photovoltaic (CPV) systems with direct liquid-immersion cooling applications. A method for experimentally determining the optical transmittance of immersion dielectric liquids was proposed, based on the spectrophotometer measurement and photometry correction. Through the method, the optical transmittance of five candidate immersion dielectric liquids, both before and after long term stability test, was determined. Further, normalized photocurrent density (Jnp) was introduced to evaluate the effect of transmittance loss on CPV solar cells photocurrent. Results show that all the selected liquids exhibit much higher transmittance than that of EVA and silicone encapsulants in the spectrum range of 300-1100 nm. De-ionized water is shown to be the strongest absorber in the longer wavelength range and thus it is not suitable for immersing multi-junction CPV solar cells. With the other four initial organic liquids presence, the bottom subcell Jnp of the specified three-junction solar cells decreased. In fact, this is a beneficial property, especially for dimethyl silicon oil and ethyl acetate. In addition, results from the long term stability test show that the most stable liquid for CPV immersion cooling applications was observed to be dimethyl silicon oil. This is because no degradation in its optical transmittance was detected after immersion tabbed CPV solar cells for 180 days.