According to the current PV system price calculation, users usually get a return on investment after 7-8 years. Government incentives and PV systems must last for 20 years or more. The return on investment of a solar PV system depends on the annual power generation of the system, so the PV system that users need must be efficient, reliable and easy to maintain, so that the maximum power generation can be obtained.
Today, many users of solar PV systems have realized that partial or intermittent shielding can affect the amount of power generated by the system.
The effect of partial shadow shading on solar photovoltaic systems:
When shadows projected by trees, chimneys, or other objects obscure the photovoltaic system, it can cause "mismatch" problems in the system. Even if the photovoltaic system is only occluded by a little shadow, it will lead to a sharp drop in power generation. The actual impact of the system mismatched power generation caused by partial shading is difficult to obtain by a simple calculation formula. There are many factors that affect the amount of power generated by the system, including interconnection between internal battery modules, module orientation, series-parallel problems between photovoltaic cells, and inverter configuration. The photovoltaic module is formed by interconnecting a plurality of battery strings, and each battery string is referred to as a "group column." Each group of columns is protected by a bypass diode to prevent damage to the entire battery string due to overheating when one or more of the batteries are shielded or damaged. These series or parallel battery arrays enable the panel to generate a relatively high voltage or current.
The photovoltaic array consists of photovoltaic modules connected in series by parallel connection. The maximum voltage of each string of photovoltaic modules must be lower than the maximum input voltage rating of the inverter.
When the photovoltaic system is partially shielded, current in the unshielded battery flows through the bypass diode of the shielded portion.
When the PV array is shielded and the above occurs, a VP electrical curve with multiple peaks is generated. Figure 1 shows a standard grid-connected configuration with a centralized Maximum Power Point Tracking System (MPPT) feature in which two panels in one group are obscured. The centralized MPPT cannot set the DC voltage, so the output power of both groups cannot be maximized. At high DC voltage points (M1), MPPT maximizes the output power of the unshielded group. At the low DC voltage point (M2), the MPPT will maximize the output power of the occlusion group: the bypass diode bypasses the shielded panel and the unshielded panel of this set will provide the full current. Multiple MPPs of the array may result in additional loss of concentrated maximum power point tracking (MPPT) configuration, as the maximum power point tracker may get error information stopped at the local maximum point and stabilized with the secondary advantage of having a VP feature.
Figure 1: Standard grid-connected configuration with centralized MPPT functionality in which two panels in one group are shaded.
Different case studies and field tests have shown that partial shading has a serious impact on the power generation of photovoltaic systems. By using distributed MPPT control, the adverse effects of shadowing on the system can be mitigated.
Minimize system mismatch issues with distributed MPPT:
In order to maximize the power output of every solar PV panel in the array, National Semiconductor has developed SolarMagicTM technology. With this technology, each panel can still output the maximum power even if other panels in the array have mismatch problems. SolarMagic technology uses advanced algorithms and advanced mixed-signal technology to monitor and optimize the capacity of each solar PV panel, thereby compensating for up to 50% of power generation losses due to mismatch problems. The SolarMagic Power Optimizer can be quickly and easily installed in traditional solar PV systems.
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