Malaysia’s Multimedia University researchers have designed and analyzed a novel hybrid system that integrates PV with thermoelectric generators (TEGs). While the PV panel produces power during the day, the TEG utilizes temperature differences around the cell to produce electricity at night.

TEGs can convert heat into electricity through the “Seebeck effect,” which occurs when a temperature difference between two different semiconductors produces a voltage difference between two substances. The devices are commonly used for industrial applications to convert excess heat into electricity. However, their high costs and limited performance have thus far limited their adoption on a broader scale.

“While previous studies have primarily focused on enhancing the daytime efficiency of PV-TEG systems, or study explores the impact of TEG surface area and series configurations specifically for nighttime applications,” the research's corresponding author, Chan Kah Yoong, told pv magazine. “The research aims to bridge the gap in the existing literature by demonstrating how larger TEG areas and optimized configurations can significantly enhance nighttime power output, offering a sustainable solution for continuous energy generation.”

In their testing, the team placed a heater under the heat sink to control and simulate different temperature differences. Three different TEG surface areas were tested: one system measuring 3 cm × 3 cm; another one with a size of 4 cm × 4 cm; and and two TEG connected in series measuring each 4 cm × 4 cm. The PV cell to which they were attached was a polycrystalline device with an operating voltage of 9 V and a working current range of 0–100 mA, capable of producing a peak power of 1 W.

“The 3 cm x 3 cm TEG can produce up to 0.9 mW of power when the temperature difference reaches 55 C, while the 4 cm x 4 cm TEG has a maximum power of 3.8 mW,” the academics said. “The two quantities of 4 cm × 4 cm TEG in series have double the output power compared to 4 cm × 4 cm TEG. The maximum power here reaches 7.7 mW.”

In all three TEG cases, the maximum power produced was just above zero when the temperature difference was minimal at 5 C. In the 3 cm x 3 cm TEG, the peak voltage was 114.9 V, and the peak current was 8.67 A. The peak voltage for the 4 cm × 4 cm TEG was 180.2 V, and the peak current was 21.5 A. In the case of two TEGs connected in series, the maximum voltage was 340.4 V, while the peak current was about 21.5 A.

“This research demonstrates how the system is useful and affordable,” the team concluded. It also noted that if a PV system with a double 4 cm × 4 cm TEG is placed on the average U.S. roof with a free area of 1,500 square feet, the TEGs alone would produce an additional 375 W of power.

“The system could be used for some household appliances such as desktops, laptops, phone chargers, LED TVs, and lighting,” Yoong said. “Its potential scalability suggests that, with adequate rooftop space, a significant amount of energy could be generated at night.”

The system was presented in the study “Solar-based nighttime electric power generator based on radiative cooling,” published in Energy Reports.