Effects of Solar Cell Heating due to Nonuniform Surface Irradiance on the Photovoltaic Conversion Efficiency of a HCPV Module

晶片表面不均照度所致發熱對高聚光型太陽能光電模組發電效率之影響

楊天祥(Tian-Shiang Yang) ； 鄒淵翔(Yuan-Hsiang Zou)

《中國機械工程學刊》 36卷4期 (2015/08) Pp. 341-351

摘要

太陽能晶片表面照度通常分布不均，且因只有部分入射光能可實際轉換為電能，晶片必然發熱，從而導致高聚光型太陽能光電（HCPV）模組整體之發電效率降低。在本文中我們於是利用一個經簡化之模型問題，來檢討晶片發熱及其表面照度不均程度對模組發電效率的影響。在該模型中，我們將模組背板視作一無窮大薄板，而太陽能晶片則為其中心位置上之一圓形區域，且晶片表面照度以軸對稱形式分布。我們再假設晶片上局部之光電轉換效率隨該點溫度上升而線性遞減（或曰晶片局部光電轉換效率之“溫度係數”為常數），便可以解析方法推得此晶片與背板共構模組在穩態時之溫度分布，進而計算晶片之整體（亦即空間平均）光電轉換效率。接著將晶片表面照度設為內外兩區分布，並且採用可在實際系統上實現之參數設定，我們有系統地檢視個別參數對於模組發電效率的影響。結果顯示：晶片表面照度不均會導致模組效率降低，但若能提升模組之散熱能力，同時選用溫度係數較低之太陽能晶片，則仍可將模組整體之發電效率提升至更接近其理想（最大）值。本文所示範之解析研究方法與結果預期將可以協助高聚光型太陽能光電系統工程師優化其模組設計，以是應對其頗有助益。

並列摘要

Here we investigate how inevitable heating of a solar cell, resulting from its nonuniformly distributed surface irradiance, affects the overall photovoltaic conversion efficiency of a high-concentration photovoltaic (HCPV) module utilizing the solar cell. To that end, a thin infinite plate is considered to model the PV backsheet. At the center of the backsheet, a circular spot modeling the solar cell is subjected to an axisymmetrically distributed surface irradiance. Assuming also a linear temperature dependence of the local photovoltaic conversion efficiency of the solar cell, i.e., a constant ＂temperature coefficient＂ of the conversion efficiency, we calculate the steady-state temperature distribution on the cell-and-backsheet module analytically. The overall (or, spatially averaged) photovoltaic conversion efficiency of the cell then is evaluated. Through a systematic and realistic parameter study for a two-zone cell-surface irradiance dustribution, it is demonstrated that cell-surface irradiance nonuniformity tends to decrease the overall module conversion efficiency. But with sufficient cooling and a small temperature coefficient of the cell conversion efficiency, the module conversion efficiency can be brought closer to the ideal value. The analytic methodology and results presented here are expected to be useful for HCPV system engineers to optimize their module design.

並列關鍵字

high-concentration photovoltaic (HCPV) module ； photovoltaic conversion efficiency ； solar cell heating ； cell-surface irradiance nonuniformity