Photovoltaic-thermal solar air heater based on PCM cylinders, air convection

Researchers in Malaysia designed a photovoltaic-thermal system that can be used in solar drying, space heating, rooftop systems, and off-grid thermal applications. It relies on a double-pass cooling technique based on air convection and phase change material that can reportedly increase PV efficiency from 7% to 9% and thermal efficiency by 31.45%.

Researchers from the Universiti Kebangsaan Malaysia have developed a photovoltaic-thermal double-pass solar air heater (PVT-
DPSAH) that utilizes a double-cooling system relying on air convection and cylinders made of phase change material (PCM), which also serves as a heat storage unit.

PCMs can absorb, store, and release large amounts of latent heat over defined temperature ranges. They have often been used at the research level for PV module cooling and the storage of heat.

“This is the first time a  integrates encapsulated cylindrical PCM capsules in a sandwich structure,” the research's lead author, Sahibzada Imad Ud Din, told pv magazine. “The PCM cylinders are connected from the PV panel to the back plate, providing dual heat transfer
through both conduction and convection, without inducing mechanical strain on the PV panel.”

“The compact and self-powered design enables its use in solar drying, space heating, rooftop systems, and off-grid thermal applications, providing sustainable thermal-electrical energy without external power sources,” he went on to say. “The system enhances PV performance through a dual cooling mechanism: forced air convection and passive cooling via PCM. This significantly reduces PV surface temperature, thereby improving PV efficiency.”

In the proposed system configuration, the PCM is heated in one of the PVT panel's two channels through conduction from the PV unit's back side, which in turn conveys thermal energy directly into the PCM. Furthermore, hot air from the other channel heats the outer surface of the cylinders.

The dual heating of cylinders accelerates the phase change process and reduces the time needed for the PCM to reach a fully molten state. Additionally, the staggered PCM cylinders induce turbulence, which improves air mixing in the second channel, thus increasing the heat transfer coefficient.

The first channel has a depth of 0.035 m and is placed on the PV panel, while is located underneath and has a depth of 0.07 m. The 28 cylindrical PCM capsules were deployed in a 4–3-4 configuration.

For the cylinders, the researchers prepared a nano-enhanced PCM using RT-45 paraffin wax doped with silicon carbide (SiC) nanoparticles. The mixture included 100 g of SiC per 2.5 kg of wax, yielding a 1% volume concentration.

Through a series of outdoor experiments, the scientists found that PCM was melted around 11 am, when it started to act as a thermal buffer. It released stored heat despite changes in solar radiation, with the output temperature remaining “suitable” for efficient drying practical uses.

Ultrasonic mixing was conducted for 3 hours at 80 C to ensure homogeneity and thermal stability, with further analysis also showing that the proposed system configuration can increase PV efficiency from 7% to 9% and thermal efficiency by 31.45%.

“This increase is due to the effect of integrating PCM cylinders, which acts as thermal energy storage, heat transfer enhancement, cooling down the PV surface temperature, and maintaining higher output temperatures,” said Ud Din. “This improved thermal performance has significance implications for various applications, such as solar drying and space heating.”

“Combined PVT efficiency peaked at 99.43%,” he concluded. “The design maintained high output temperatures even during cloudy or fluctuating weather conditions, validated through both indoor and outdoor analysis.”

Other research groups at the Universiti Kebangsaan Malaysia recently designed a PVT panel based on twisted absorber tubes and nanoparticle-enhanced PCM, a bifacial (PVT) panel that utilizes circular jets impinging as a cooling medium, a PVT system based on PCM cooling, multi-level fin heat sinks for solar module cooling, and passive technology for solar module cooling based on fin heat sinks.