Researchers from China's Xi’an Jiaotong University have sought to combine photovoltaic-thermal (PVT) energy with thermal storage provided by ground heat exchangers (GHE) that utilize volcanic tuff stones as a heat storage material.
“This approach leverages the unique thermal properties of volcanic tuff stones, such as their high porosity and thermal conductivity, to enhance cooling, thermal regulation, and energy storage efficiency,” the research's lead author, Ahmad Alqatamin, told pv magazine. “By addressing the limitations of traditional PVT systems under fluctuating temperature conditions, our system provides sustainable energy storage while also cooling the photovoltaic cells.”
The combined system consists of a PVT array integrated with a GHE, a heat exchanger within the thermal storage tank a capacity of 150 L, a centrifugal magnet pump, a fan, a flow meter, a data logger, a fan coil unit, and several pumps and sensors positioned at various points.
The scientists built a prototype in Tafila, Jordan, a location with high solar radiation levels, moderate humidity and wind conditions, as well as rugged terrain and distinct temperature fluctuations. The PVT modules used for this project have each a nominal power of 50 W, a cell efficiency of 18%, a short-circuit current of 3.01 A and an open-circuit voltage of 21.6 V.
The GHE is based on a single hole filled with volcanic tuff stones made of basaltic pumice which are abundant in Jordan and are commonly used as construction materials due to their lightweight properties and high percentage of silica, which the scientists said significantly enhances their thermal capacity.
The GHE is placed in a 2.5 m x 2 m x 3 m excavation. “At the outlet of the square duct, a fan was installed to draw ambient air through the system,” the research group explained. “As the air circulates through the system, it interacts with geothermal energy, resulting in heat dissipation during the summer and heat absorption in the winter.”
The system's thermal and electrical performance was measured through a pyranometer, a digital multimeter, and a variable mass flow meter, while temperature readings were taken via K-type thermocouples. These data were then compared to those of a reference PVT system operating without the GHE.
The experiment showed that the volcanic tuff stones contributed to reducing PV module temperature by up to 23% and achieved a power conversion efficiency of 17.25% and a 6.25% higher power output compared to the benchmark the PVT system without the GHE, which achieved an efficiency of only 16.65%.
The proposed system also reached a thermal efficiency of 70.61%, which compares to 58.66% in the reference array. “The ground heat exchanger consistently raised outlet air temperatures by an average of 10 C above ambient, even under varying environmental conditions,” the academics further explained. “This highlights the volcanic tuff stones’ capability to stabilize heat exchange through their porous structure, ensuring reliable thermal performance.”
The novel approach was described in the paper “Experimental investigation of the photovoltaic thermal integrated with ground heat exchanger using volcanic tuff stones,” published in Applied Thermal Energy.
Looking forward, the research team said it wants to investigate how the system operates under different environmental conditions and assess its potential scalability for large-scale applications, while also conducting economic feasibility studies to evaluate costs and potential energy savings.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.