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electrical:solar:shading [2020/01/07 23:16] frater_secessus [even shading] |
electrical:solar:shading [2021/03/31 10:55] frater_secessus [exception: high voltage strings + mppt] |
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- | ====== Shading ====== | + | Words of Wisdom: |
- | Shading can have surprisingly dramatic effects on panel output. | + | ====== Partial shading ====== |
+ | Partial shading can have surprisingly dramatic effects on [[electrical: | ||
- | ===== even shading | + | ===== reminder: |
- | Even shading (as with overcast skies) will reduce output but not as critically as partial shading. | ||
+ | **Before we begin:** solar panels are " | ||
+ | Partial shading in this context means: | ||
+ | * light is falling on the panel | ||
+ | * but not evenly on the panel -- it is different on some cells | ||
- | ===== partial shading ===== | + | To prevent power from rushing into the shaded string and overheating them, panels have bypass diodes between the strings. |
- | Partial shading is problematic for solar panels because: | ||
+ | ===== panel configuration for partial shade ===== | ||
- | - partial shade causes //voltage differences// | + | The way to avoid the problems associated with partial shade is to avoid partial shade. |
- | | + | |
- | - overheating | + | |
- | When a panel is partially shaded the individual cells are running at differing voltages. | ||
+ | * **avoiding shade** is best | ||
+ | * a **dedicated controller for each panel** is the next best thing | ||
+ | * [[electrical: | ||
+ | * With **PWM controllers, | ||
+ | * With **MPPT controllers** and **low-ish voltage** serial panel configurations (where the total Vmp is <=2x battery bank voltage) **parallel will probably still yield more**. | ||
+ | |||
- | The takeaway: | + | ===== exception: high voltage strings + mppt ===== |
- | | + | There is another approach, which is to **bring the shaded cells/ |
- | * With MPPT controllers and **low-ish voltage** serial panel configurations | + | |
- | * With MPPT controllers and **higher voltage** serial configs | + | |
+ | This occurs because the MPPT has a broader range of voltages to sweep and can find [[https:// | ||
+ | ===== examples ===== | ||
+ | |||
+ | * [[https:// | ||
+ | * [[https:// |