Cooling design and evaluation for photovoltaic cells within constrained space in a CPV/CSP hybrid solar system

Abstract

A hybrid solar energy system has been designed by combining the advantages of concentrated solar power (CSP) technology and high performance concentrated photovoltaic (CPV) cells which outperforms either single technology. Thermal management is crucial to CPV cells in this hybrid solar system, as concentrated solar radiation onto the PV cells leads to higher heat flux. If the heat is not dissipated effectively, it can cause obvious temperature rise and efficiency reduction in the cell. In addition, the constrained space available for PV cell cooling in such hybrid solar systems presents more challenges. In this study both passive cooling and active cooling techniques were systematically investigated in both numerical and experimental ways. For the passive cooling method, two different designs from off-the-shelf heat pipes with radial fins or annular fins were proposed and studied under various heat rejection requirements. Results shows that heat pipes with radial fins exhibited narrow capability of dumping the heat, while heat pipes with annular fins presented better performances under the same conditions. Numerical optimal designs of annular fin numbers and fin gaps were then carried out and experimentally validated, indicating a capability of dumping moderate waste heat (~45W). For active cooling technique, a comprehensive study of designing plate fin heatsinks were conducted corresponding to high Ingress Protection (IP) rated off-the-shelf fans. Results show that with a less than 2 W fan power consumption, this active cooling method can control the average PV cell temperature below our target temperature of 75 °C even under 45 °C ambient. To evaluate the overall performance in a year round life cycle, the enhancement in the annual electricity output of the PV cells was estimated according to the cooling effects subjected to the climate of Tucson, Arizona. Finally, taking into consideration of both the temperature control results and net gain/loss analysis, an active cooling design was chosen for our system to dissipate a maximum waste heat of 84 W (21.8 W/cm 2) due to its lower cost, lower CPV temperature, and higher net energy efficiency gain. It is also demonstrated that passive cooling will become more attractive when the heat dissipation requirement is less than 50 W (13.0 W/cm 2).

A Review on Solar Concentrators with Multi-surface and Multi-element Combinations

“…While the disadvantage of this system is that electricity conversion efficiency of GaAs solar cells is too low as the working temperature of the solar cells is too high. Sheng Wang [66] presented a hybrid solar energy system, which combines the advantages of concentrated solar power technology and high performance concentrated photovoltaic cells, shown in Fig. 14.…”

“…CSP belongs to the hightemperature thermal application. For CT system, the most important thing is to collect the focused light efficiently, which requires complex composite surface structures [22][23][24][25]27,[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46], or multi-element combination forms [48][49][50][51][52][53][60][61][62][63][64][65][66][67][68][69]79,87]. In general, not a lot attention has been paid to the uniformity of focused light.…”

“…Generally, multi-element combination structures are usually designed to achieve high power concentration so that GCR is ranged from hundreds to thousands. Consequently, acceptance angle of this type of concentrator is relatively small, so that tracking mechanism is required, as introduced in references [50][51][52][53]57,66,[71][72][73][74][75][76][77][78]81,82]. The allowed tracking error angles of these concentrators are generally less than 1°, some even as small as 0.1°, which requires high-precision photoelectrical tracking devices.…”

“…Whereas the f-number of Fresnel lens could usually be designed close to 1.0 or smaller, which allows the concentrator to have a lower height with a larger aperture area. The FK system mentioned in the references [65][66][67][68][69] has an f-number close to 1.0 and references [50][51][52][53]58,59] adopt secondary concentrators with f-numbers less than 1.0. This facilitates the application of the concentrator.…”

A Review on Recent Development of Cooling Technologies for Concentrated Photovoltaics (CPV) Systems

“…The passive cooling would become more attractive with the heat dissipation requirement of less than 50 W (13.0 W/cm 2 ). Wang et al (2017) experimental and numerical studied the passive and active cooling techniques for a novel CPV/CSP hybrid solar system [89]. The schematic of two cooling design options are illustrated in Figure 17.…”