Does your roof have different angles/orientations?
Does your system have panels on different tilts?
Does your system have different heights?
This article provides recommendations on design in order to maximize the potential of your PV system, along with example scenarios.
If your PV modules are wired in series, and your design includes a hard angle (some facing east, and some facing west), the early morning and late afternoons may see a short period where there is a complete drop-off of production for the heavily shaded PV-Modules. This is a normal function of Optimization.
Tigo Optimization allows the strongest modules to produce at their best, through impedance matching. If there is light shading, the units will optimize for more current. However, if modules are heavily shaded, their output will be reduced so that the lack of current will now no longer affect the entire string's production.
Note: The expected production result is also dependent upon the quality of the inverter's MPPT algorithm.
Tigo optimization enables PV modules (solar panels) in a string to have different
- Orientation to the sun's angle (or azimuth)
- Tilt angles (elevation)
Tigo optimizers do everything possible to recover reduced production due to shade, but no optimizer can compensate for all electrical design, azimuth, and tilt issues. Stay within the design recommendations (below) for a successful solar harvest.
Recommendations
- Use only one string per Maximum Power Point Tracker (MPPT):
A system with serious orientation issues requires a specific focus (only one string per MPPT). Otherwise, the inverter will have to select an operating power point that is a compromise between parallel strings (and thus not allowing maximum power production on either string). - For maximum shaded power recovery:
Try to keep all PV modules within a string, faced at the same angle and elevation. - If multiple strings per MPPT (parallel), each PV module must have a TS4-A-O optimizer:
For information on this, see our article on Full Deployment. - For parallel strings, do not use a different number of panels per string.
But if you must: Check that number of panels per string comply with Mix and Match module types, String Lengths. - Design for the highest voltage per MPPT.
High string voltage improves inverter efficiency but keeps in the MPPT specified range. It also reduces the number of home-run wires needed and thus MPPT required. However, be aware to always calculate the PV Modules' expected voltage range for the temperature in your area. - IMPORTANT: Each MPPT must receive the minimum voltage necessary for the Inverter to start up.
This is especially true for strings that have orientation issues. Each angled section of a string must meet the minimum MPPT voltage specification on its own. This helps to maintain the minimum voltage if hard-shade conditions cause a portion of the string to drop off in production.
PV modules that are not receiving direct irradiation (light rays from the sun) must not be counted as adding to the string voltage. This is because, in low solar irradiance conditions, they are not contributing significant current (power) to the inverter.
The last part of this article covers a discussion on this specific application and provides focused examples.
How the Azimuth affects power production of a PV module
The image below gives great insight into the quantitative benefits of South, South West, and South East exposure on a PV-Module. The best production is when the sun is overhead (straight up).
West and East are also significant power azimuth (those orientations have strong seasonal variations in the tropics regions. For example, a panel mounted in East orientation at 45° N latitude will have incoming irradiance of about 600W/m2 in winter and about 1000W/m2 in summer at the peak of their production.
Reference: Seasonal variation of the solar irradiance across panels mounted on different latitudes
North is not to be ignored by any means, especially for those near (or below) the equator or in conditions where refraction irradiation can yield additional production.
Orientation Case Studies: Opposing angles
Example 1: Imbalanced Orientation (wired in series)
The system is comprised of:
- One string of 9 PV-Modules (in series)
- 6 PV-Modules facing south, and 3 facing west
- Each PV-Module is 30 Vmp
- The Inverter requires a minimum of 150 VDC for start-up
In this layout, the west-facing PV-Modules will cause impedance issues in the morning (when shaded). The inverter may only start to produce when additional irradiation from the sun reaches both angles during the middle portion of the day (when the sun is overhead).
To lower costs, TS4-A-O units can be deployed on a limited amount of PV-Modules (the 3 west-facing PV-Modules). THIS will prevent impedance of power production to the longer south-facing group of PV-Modules during early morning shade events. For more info, see TS4 Systems - Partial Deployment.
However, deploying TS4s on all the PV-Modules will give you full data visibility and rapid shutdown for the entire system.
For installations like this, please also consider the following:
Both south and west-facing portions of the string must meet the minimum required voltage if there are harsh shade conditions in the mornings or evenings:
- South-facing modules: 6 x 30 V = 180 V (meets or exceeds the minimum 150 V)
- West-facing modules: 3 x 30 v = 90 V (does not meet the minimum 150 V)
Since the west-facing PV-Modules do not supply the minimum voltage necessary for the inverter to stay active, you may still see a shorter day's yield (if the south-facing PV-Modules receive hard shade in the evening).
Example 2: Balanced Orientation (wired in series)
In this installation, there are enough PV-Modules facing each azimuth to meet the MPPT minimum voltage requirement of the inverter.
The system is comprised of:
- 1 string of 12 PV-Modules (in series)
- 6 PV-Modules facing south, and 6 facing west
- Each PV-Module is 30 Vmp
- The Inverter requires a minimum of 150 VDC for start-up
This site has 2 orientations (facing south and west), with enough voltage on both angles to satisfy the inverter's minimum voltage requirement. However, TS4-A-O Units would be required on all of the PV-Modules to prevent the impedance of power production during periods of extreme shade (mornings and evenings). For more info, see TS4 Systems - Full Deployment.
Tigo recommends dividing the string into two separate strings in series going into separate MPPTs:
- Each string would produce enough voltage for the inverter to start up and maintain the MPPT specified voltage range - along with enough current (power) for good production.
- Because all modules on the separate strings face the same azimuth, the irradiance per panel is nearly equal (unless shaded), ensuring the string voltages and currents are always contributing to power production.
Example 3: Split orientation with parallel strings
In this installation, there are 2 opposing strings that are wired (in parallel) to a single MPPT inverter.
The system is comprised of:
- 2 parallel strings of 6 PV-Modules
- 1 string facing south, and 1 facing west
- Each PV-Module is 30 Vmp
- Single-MPPT Inverter requiring a minimum of 150 VDC for start-up
This site has 2 strings wired in parallel, but facing different orientations (facing south and west). Each string has enough voltage to satisfy the inverter's minimum voltage requirement. However, since they are wired in parallel, they will always be contending with each other, when either orientation is in hard-shade conditions.
Designing parallel strings under these conditions is not recommended, because it causes a mismatch of over 25%. However, TS4-A-O Optimizers can help if the system is in Full Deployment, and the shade conditions are not extreme (i.e., the roof orientations are at a wide or obtuse angle).
For example:
Acute Angle - Parallel string (or split single/series string) design over hard angles is not recommended because hard-shade conditions at the ends of the day could cause the shaded string to produce less than 25% (or even stop producing entirely). This would cause the inverter's MPPT to react poorly (during the mornings and evenings), and you may experience a significant loss of production.
Obtuse Angle - If the angle is more relaxed, there will be lighter shade conditions in the mornings and evenings. This allows more impedance matching opportunities for the Tigo TS4 MLPEs (if the system has Optimizers on every PV-Module).
To learn more about Impedance matching vs. the 25% rule, see our article on Uneven Parallel Strings.
Conclusion:
There is no limit on how different the angles or orientations might be, just as long as the minimum string voltage of the inverter is met and any parallel strings are within the 25% rule. If designed correctly, each string orientation would be able to produce enough string voltage for the inverter to start and stay ON (producing) throughout the majority of the day.
To get assistance with your design, Tigo Sales Engineers can help : se@tigoenergy.com.