In the realm of rooftop solar power systems, one critical issue that often goes overlooked is the impact of proper arrangement on power generation.
Improper layout can lead to significant energy losses, but with careful design and an understanding of key technical principles, these issues can be minimized. This article explores how to ensure your rooftop PV system avoids power reduction due to layout design and PV string connections, focusing on shadow avoidance, PV string connection, and MPPT (Maximum Power Point Tracking) matching.
1.Understand the Core of Efficient Power Generation: MPPT Tracking
The Basics of Rooftop PV Power Generation
Solar panels convert sunlight into direct current (DC), which is then converted by an inverter into alternating current(AC) for home loads.
Among them, the MPPT function of the inverter is crucial. Because it can adjust the operating voltage of the PV string to the point where the power output is maximized. Only when it works at the most suitable voltage(Vmpp) can the maximum output power be achieved.
For the MPPT to effectively track the maximum power point, two conditions must be met:
1.1 Optimal I-V and P-V Curves of PV Strings
A single solar panel has a characteristic I-V (current-voltage) curve and P-V (power-voltage) curve, which describe the relationship between current, voltage, and power under different operating conditions. When panels are connected in series to form a string, the combined I-V and P-V curves of the string should ideally be smooth and consistent. A normal single panel’s I-V/P-V curve shows a distinct maximum power point. When multiple identical strings are connected, their combined curves should also maintain a clear and singular maximum power point, as shown in the illustrations of a single string and two identical strings' curves.
1.2 Proper Matching Between MPPT and PV Strings
Each MPPT in an inverter is designed to work optimally with one PV string or multiple strings that have nearly identical electrical characteristics. When strings with different electrical characteristics are connected to the same MPPT, they interfere with each other. This causes the tracker to perform suboptimally. For example, a single MPPT module can handle one string or multiple identical strings without issues, but mixing strings with different performances, such as those affected by varying shading or different orientations, will disrupt the tracking process.
2.Several factors can influence the maximum power point of PV strings, leading to power losses:
2.1 Shadow and Hot spot effect
Shadowing: Chimney-caused local shadows on a glazed tile roof, or shadows caused by the narrow installation distance of solar panels on the cement flat roof, resulting in uneven lighting.
Solution: Remove the panels in the shadowed area; Reduce the number of panels to increase the spacing between them, allowing more sunlight to reach each panel throughout the day. Alternatively, use double-sided ballast brackets, which can help capture more reflected light and minimize the impact of shadows
Hotspots: Issues like bird droppings or leaves on panels can create hotspots, where a small area of the panel overheats due to reduced sunlight absorption. This not only affects the performance of the affected panel but can also impact the entire string's curve.
Solution: Regularly inspect and clean PV panels surfaces
2.2 Orientation Differences
Such as a glazed tile roof with two different facing directions, if PV strings on two different facing directions connect to one MPPT, due to the angle and intensity of sunlight received may vary, the MPPT might struggle to track the accurate maximum power point effectively.
Solution: Either reduce the number of orientations by adjusting the panel layout to focus on the main sunlight direction or upgrade to an inverter with more MPPTs. This allows each string (or group of similar strings) to have its own MPPT, ensuring better tracking for each PV string with similar characteristics.
2.3 Improper String Parallel Connection
When strings with different electrical characteristics are connected in parallel, the combined I-V and P-V curves become irregular.
For example, 22pcs 630W solar panels connect to a 1-unit Deye 14kW hybrid inverter (model: SUN-14K-SG05LP3-EU-SM2). This inverter has dual MPP trackers, per MPP tracker can connect to 2 strings of PV modules, and it request the number of different strings connected to each MPPT must be consistent.
Suitable plan- PV1-1 (7pcs)+PV1-2 (7pcs)+PV2-1 (8pcs)
Wrong plan- PV1-1 (7pcs)+ PV1-2 (8pcs) + PV2-1 (7pcs), two PV strings connected to the same MPPT have different quantity will confuse the inverter and reduce the overall efficiency.
Conclusion
A well-planned rooftop PV system ensures that the inverter's MPPT module achieves maximum power point tracking while eliminating shading and orientation conflicts, thereby maximizing the power generation of the rooftop solar system. Don't let layout flaws affect your profits - every detail is critical to maximizing solar output.