Design of a microscale organic Rankine cycle for high-concentration photovoltaics waste thermal power generation

Abstract

High-concentration photovoltaics (HCPV) is a highly promising technology to directly convert plentiful solar en ergy to electricity. However, even for the most advanced HCPVs, about 60% of the concentrated solar energy is rejected as waste heat; therefore, it is desirable to utilize the massive waste heat from HCPV modules. Considering the nature of low-grade waste thermal energy, a microscale organic Rankine cycle (MaRC) offers a promising solution. In a subcritical MaRC, subcooled refrigerant is usually pumped into a microchannel heat sink of each multi-junction photovoltaic cell. In this paper, a complete microchannel flow boiling model is developed based on distributed mass, energy and momentum conservation laws. Detailed MaRC thermal-fluid analysis is conducted to evaluate the effects of working fluid, inlet subcooling, axial fluid/cell temperature distribution and critical heat flux on cogeneration efficiency. The performance analysis indicates that the HCPV/MORC system can achieve a net 8.8% increase of power generation efficiency in comparison to liquid-cooled HCPV at ambi ent temperature. The proposed HCPV /MaRC configuration shows great promise in large-scale applications of HCPV solar power generation. A cross-sectional area (m2) Dh hydraulic diameter (m) G mass flux (kg/m2-s) h specific enthalpy (J/kg) L channel length (m) m mass flowrate (kg/s) p channel perimeter (m) P absolute pressure (Pa) Q heat load (W) r vapor core radius (m) s specific entropy (J/kg-K) T temperature (0C) V volume (m3) W work (W) z channel location (m)

An operating characteristics study on a small-scale CPV-ORC power generating system in summer typical day

“…But they didn't inspect whether the chosen fluid was the optimal type for this novel combination system. Zhang and Wang [8] designed a highconcentration photovoltaic system combined with a small ORC. They also developed a complete microchannel flow boiling model based on the laws of mass, energy and momentum conservation.…”

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

“…For linear concentrators and densely packed cells under high concentrations over 150 Suns, an active cooling system is necessary, while passive cooling is usually insufficient to handle this situation since less area is available for heatsinking. For high power concentrations, forced air cooling [10][11][12][13][14], jet impingement cooling [15][16][17][18][19], and single-or two-phase forced convection cooling with manifold/microchannel heatsinks [20][21][22][23] have been reported as adequate solutions. Many researchers are also seeking novel cooling options based on the aforementioned cooling methods, for instance, using high efficiency cell backing materials [24] and highly-conductive coatings with carbon nanotubes for passive cooling [25], and water immersed cooling [26,27].…”