摘要
1.1This test method provides a procedure to determine the ability of a photovoltaic (PV) module to endure the long-term effects of periodic “hot spot” heating associated with common fault conditions such as severely cracked or mismatched cells, single-point open circuit failures (for example, interconnect failures), partial (or non-uniform) shadowing or soiling. Such effects typically include solder melting or deterioration of the encapsulation, but in severe cases could progress to combustion of the PV module and surrounding materials.1.2There are two ways that cells can cause a hot spot problem; either by having a high resistance so that there is a large resistance in the circuit, or by having a low resistance area (shunt) such that there is a high-current flow in a localized region. This test method selects cells of both types to be stressed.1.3This test method does not establish pass or fail levels. The determination of acceptable or unacceptable results is beyond the scope of this test method.1.4The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.6This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ======4.1The design of a photovoltaic module or system intended to provide safe conversion of the sun's radiant energy into useful electricity must take into consideration the possibility of partial shadowing of the module(s) during operation. This test method describes a procedure for verifying that the design and construction of the module provides adequate protection against the potential harmful effects of hot spots during normal installation and use.4.2This test method describes a procedure for determining the ability of the module to provide protection from internal defects which could cause loss of electrical insulation or combustion hazards.4.3Hot-spot heating occurs in a module when its operating current exceeds the reduced short-circuit current (Isc) of a shadowed or faulty cell or group of cells. When such a condition occurs, the affected cell or group of cells is forced into reverse bias and must dissipate power, which can cause overheating.Note 1:The correct use of bypass diodes can prevent hot spot damage from occurring.4.4Fig. 1illustrates the hot-spot effect in a module of a series string of cells, one of which, cellY, is partially shadowed. The amount of electrical power dissipated inYis equal to the product of the module current and the reverse voltage developed acrossY. For any irradiance level, when the reverse voltage acrossYis equal to the voltage generated by the remaining (s-1) cells in the module, power dissipation is at a maximum when the module is short-circuited. This is shown inFig. 1by the shaded rectangle constructed at the intersection of the reverse I-V characteristic ofYwith the image of the forward I-V characteristic of the (s-1) cells.FIG. 1Hot Spot Effect4.5By-pass diodes, if present, as shown inFig. 2, begin conducting when a series-connected string in a module is in reverse bias, thereby limiting the power dissipation in the reduced-output cell.FIG. 2Bypass Diode EffectNote 2:If the module does not contain bypass diodes, check the manufacturer’s instructions to see if a maximum number of series modules is recommended before installing bypass diodes. If the maximum number of modules recommended is greater than one, the hot spot test should be preformed with that number of modules in series. For convenience, a constant current power supply may be substituted for the additional modules to maintain the specified current.4.6The reverse characteristics of solar cells can vary considerably. Cells can have either high shunt resistance where the reverse performance is voltage-limited or have low shunt resistance where the reverse performance is current-limited. Each of these types of cells can suffer hot spot problems, but in different ways.4.6.1Low-Shunt Resistance Cells:4.6.1.1The worst case shadowing conditions occur when the whole cell (or a large fraction) is shadowed.4.6.1.2Often low shunt resistance cells are this way because of localized shunts. In this case hot spot heating occurs because a large amount of current flows in a small area. Because this is a localized phenomenon, there is a great deal of scatter in performance of this type of cell. Cells with the lowest shunt resistance have a high likelihood of operating at excessively high temperatures when reverse biased.4.6.1.3Because the heating is localized, hot spot failures of low shunt resistance cells occur quickly.4.6.2High Shunt Resistance Cells:4.6.2.1The worst case shadowing conditions occur when a small fraction of the cell is shadowed.4.6.2.2High shunt resistance cells limit the reverse current flow of the circuit and therefore heat up. The cell with the highest shunt resistance will have the highest power dissipation.4.6.2.3Because the heating is uniform over the whole area of the cell, it can take a long time for the cell to heat to the point of causing damage.4.6.2.4High shunt resistance cells define the need for bypass diodes in the module’s circuit, and their performance characteristics determine the number of cells that can be protected by each diode.4.7The major technical issue is how to identify the highest and lowest shunt resistance cells and then how to determine the worst case shadowing for those cells. If the bypass diodes are removable, cells with localized shunts can be identified by reverse biasing the cell string and using an IR camera to observe hot spots. If the module circuit is accessible the current flow through the shadowed cell can be monitored directly. However, many PV modules do not have removable diodes or accessible electric circuits. Therefore a non-intrusive method is needed that can be utilized on those modules.4.8The selected approach is based on taking a set of I-V curves for a module with each cell shadowed in turn.Fig. 3shows the resultant set of I-V curves for a sample module. The curve with the highest leakage current at the point where the diode turns on was taken when the cell with the lowest shunt resistance was shadowed. The curve with the lowest leakage current at the point where the diode turns on was taken when the cell with the highest shunt resistance was shadowed.FIG. 3Module I-V Characteristics with Different Cells Totally Shadowed4.9If the module to be tested has parallel strings, each string must be tested separately.4.10This test method may be specified as part of a series of qualification tests including performance measurements and demonstration of functional requirements. It is the responsibility of the user of this test method to specify the minimum acceptance criteria for physical or electrical degradation.
1.1本试验方法提供了一种程序，用于确定光伏（PV）模块承受与常见故障条件（如严重开裂或不匹配的电池）、单点开路故障（例如互连故障）、部分（或不均匀）阴影或脏污相关的周期性“热点”加热的长期影响的能力。这种影响通常包括焊料熔化或封装劣化，但在严重情况下可能会导致光伏组件和周围材料燃烧。1.2有两种方式可以导致细胞热点问题；通过具有高电阻使电路中存在大电阻，或通过具有低电阻区域（分流器）使局部区域中存在高电流。该测试方法选择两种类型的单元进行应力测试。1.3本试验方法不确定合格或不合格水平。可接受或不可接受结果的确定超出了本试验方法的范围。1.4以国际单位制表示的数值应视为标准值。本标准不包括其他计量单位。1.5本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。1.6本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。====意义和用途======4.1旨在将太阳辐射能安全转换为有用电能的光伏模块或系统的设计必须考虑模块在运行期间部分遮挡的可能性。本试验方法描述了一种程序，用于验证模块的设计和构造在正常安装和使用期间提供了足够的保护，以防止热点的潜在有害影响。4.2本测试方法描述了一种程序，用于确定模块提供保护的能力，以防止内部缺陷造成电绝缘损失或燃烧危险。4.3当模块的工作电流超过阴影或故障电池或电池组的降低短路电流（Isc）时，模块中会发生热点加热。当这种情况发生时，受影响的电池或电池组被迫反向偏置，必须耗散功率，这可能导致过热。注1:正确使用旁路二极管可以防止热点损坏的发生。4.4图1说明了由一系列单元组成的模块中的热点效应，其中一个单元为单元Y，部分阴影。中耗散的电功率量Y等于模块电流和在模块上产生的反向电压的乘积Y. 对于任何辐照度水平，当反向电压通过Y等于剩余电压(s-1） 在模块中，当模块短路时，功耗达到最大值。如所示图1通过在反向I-V特性的交点处构造的着色矩形Y具有正向I-V特性的图像(s-1） 单元格。图1热点效应4.5旁路二极管（如果存在），如所示图2，当模块中的串联串处于反向偏置时开始导通，从而限制减少的输出单元中的功耗。图2旁路二极管效应注2:如果模块不包含旁路二极管，请在安装旁路二极管之前检查制造商的说明，以查看是否建议最大数量的串联模块。如果建议的最大模块数量大于一个，则应使用该数量的串联模块进行热点测试。为了方便起见，可以用恒流电源代替附加模块以保持指定电流。4.6太阳能电池的反向特性可能有很大差异。电池可以具有高分流电阻，其中反向性能受电压限制，也可以具有低分流电阻，其中反向性能受电流限制。每种类型的细胞都会出现热点问题，但方式不同。4.6.1低分流电阻电池:4.6.1.1当整个单元（或很大一部分）被遮挡时，会出现最坏的遮挡情况。4.6.1.2由于局部分流，低分流电阻电池通常采用这种方式。在这种情况下，由于大量电流在小面积内流动，因此会发生热点加热。由于这是一种局部现象，因此这种电池的性能有很大的分散性。当反向偏置时，分流电阻最低的电池极有可能在过高的温度下工作。4.6.1.3由于加热是局部的，低分流电阻电池的热点故障很快就会发生。4.6.2高分流电阻电池:4.6.2.1当一小部分单元被遮挡时，最坏情况下会出现遮挡情况。4.6.2.2高分流电阻电池限制了电路的反向电流，因此会发热。分流电阻最高的电池将具有最高的功耗。4.6.2.3由于在电池的整个区域内加热是均匀的，电池可能需要很长时间才能加热到造成损坏的程度。4.6.2.4高分流电阻单元定义了模块电路中对旁路二极管的需求，其性能特征决定了每个二极管可以保护的单元数量。4.7主要的技术问题是如何识别最高和最低并联电阻单元，然后如何确定这些单元的最坏情况阴影。如果旁路二极管是可拆卸的，则可以通过反向偏置电池串并使用红外摄像机观察热点来识别具有局部分流的电池。如果可以接近模块电路，则可以直接监测通过阴影电池的电流。然而，许多光伏组件没有可拆卸的二极管或可接近的电路。因此，需要一种可以在这些模块上使用的非侵入性方法。4.8所选方法基于为模块获取一组I-V曲线，每个单元依次阴影。图3显示了样本模块的I-V曲线的结果集。当分流电阻最低的电池被遮挡时，取二极管导通点处漏电流最高的曲线。当具有最高分流电阻的电池被遮挡时，在二极管导通点处获得泄漏电流最低的曲线。图3完全遮蔽不同电池的模块I-V特性4.9如果要测试的模块具有并联串，则必须单独测试每个串。4.10该试验方法可规定为一系列鉴定试验的一部分，包括性能测量和功能要求演示。本试验方法的用户有责任规定物理或电气劣化的最低验收标准。
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