Znanstveniki so uporabili stearinsko kislino in kombinacijo stearinske kisline ter ogljikovega črnega, da so povečali toplotno prevodnost v sistemu fotovoltaike in toplote, povezanem z heliostatskim poljem koncentratorja. Pri temperaturi 30 °C na vhodu so uspeli ogreti vodo do 59 °C.
Raziskovalci z Univerze za inženirstvo in tehnologijo Rajshahi v Bangladešu so zgradili in preizkusili sistem fotovoltaike in toplote (PVT) z integriranim heliostatom, ki uporablja dve različni organski fazno spremenljive materiale (PCM) za izboljšanje toplotne prevodnosti.
Fazno spremenljivi materiali (PCM) so sposobni absorbirati, shranjevati in sproščati velike količine latentne toplote v določenem temperaturnem razponu in so pogosto uporabljeni na raziskovalni ravni za hlajenje PV modulov.
„Organski PCM so dobro primerjeni za shranjevanje sončne energije zaradi svojega majhnega temperaturnega razpona zamrzovanja in taljenja ter njihovega enotnega taljenja. Večina organskih PCM je prav tako lahko dostopna, relativno poceni in netoksična,“ je pojasnila skupina. „V kontekstu sistema za ogrevanje sanitarne vode z sončno energijo je skrbna izbira PCM ključna za zagotavljanje želene temperature vode in reševanje varnostnih skrbi, kot je morebitno puščanje PCM v vodovodni sistem stavbe.“
Eksperimentalna naprava je bila zgrajena na strehi v okrožju Rajshahi v Bangladešu, kjer je povprečna dnevna osvetlitev 6,39 kWh/m² in hitrost vetra 2 m/s. Zgrajen je bil PVT kolektor brez puščanja, na katerega so bili pritrjeni štirje PV paneli. Vsak panel je imel moč 5 W, odprto napetost 21,5 V in kratkostično tok 0,32 A. Za prehod vode skozi kolektor je bil uporabljen bakreni cev, povezan z zbiralnikom opremljenim s centrifugalno črpalko
“To increase the concentration ratio, the PVT system is integrated with a heliostat field concentrator,” explained the academics. “In the designed heliostat field, there are 20 heliostats made of plane mirrors, each having an area of 0.12637 square meters. The height of the central tower is 1.8288 meters from the ground. The heliostats are placed in three different rows.”
As for the PCMs, the scientists analyzed two options. One was stearic acid (SA) only, at a mass of 16.5 kg; and the other was a mixture of 16.5 kg of SA, with 165 grams of carbon black (0.01% of the entire composition). Both compositions were analyzed on different days, from 10:00 to 18:00, each with a water flow rate of 0.0025 kg/s and 0.0035 kg/s. 0.0045 kg/s and 0.0055 kg/s.
“Employing PCM with or without carbon black has little influence on electrical efficiency, which ranges from 10.50% to 13%,” the academics explained. “The maximum electrical output power was found to be 17.77 W at the water flow rate of 0.0045 Kg/s for the system PVT-PCM with carbon black. The increased water flow rate reduced the cell temperature by transferring more heat from the system. Which ultimately increased the electrical output temperature of the PV cell as well as the electrical efficiency.”
As for thermal efficiency, the highest level without carbon black was 45.45%, while 46.56% was achieved with the compound. The highest outlet temperatures reached a flow of 0.0035 kg/s and the water reached 59 C with the compound, and 58 C without it. “Compared to the other flow rates studied, the average thermal efficiency shows a significant increase of 6.83 % when integrating carbon black with PCM at a flow rate of 0.0035 kg/s,” highlighted the group.
The system was introduced in the study “Performance test of a heliostat field integrated PVT solar collector using organic phase change material and carbon black additives,” published on Energy Reports.