PV Installation and Troubleshooting Guide
Lunar System PV Installation and Troubleshooting Guide
Purpose
This application note outlines the PV stringing requirements and provides troubleshooting recommendations for the Lunar System, including the Lunar Maximizers (module-level DC converters) and the Lunar Maximizer Hub (PV junction box).
Quick PV Install Checklist
- Confirm continuity from each Maximizer mounting flange to the Hub’s ground terminal
- Measure 20-30Vdc at each of these locations:
- String 1 home run isolated
- String 2 (if applicable) home run isolated
- String 3 (if applicable) home run isolated
- Hub DIN rail terminals with all parallel strings terminated
- Inverter PV terminals
- If < 20Vdc is seen, verify stringing between Maximizers outputs, as well as verify a single solar panel is plugged in to each Maximizer input
- If > 30Vdc is seen, verify grounding of Maximizers, starting at both ends of the string
See below for the expected DC Voltage ranges for each measurement location.
Table 1. Voltage Reference Values
| Multimeter+to-Measurement Location | Expected DC Voltage** |
|---|---|
| 5-20 Maximizers(each individual string)* | 20-30Vdc(actual voltage may fluctuate) |
| Maximizer Hub DIN rail terminals* | 20-30Vdc |
| Inverter PV terminals* | 20-30Vdc |
| 1 Maximizer(output measured with PV connected to input) | 4.5-5.5Vdc |
| 2 Maximizers(2 units in series,each with PV connected to input) | 9-11Vdc |
| 3 Maximizers | 13.5-16.5Vdc |
| 4 Maximizers | 18-22Vdc |
| Line to Ground(at inverter or Maximizer Hub) | Positive to Ground:9-18Vdc Negative to Ground:9-18Vdc |
- To verify at time of install per PV install checklist.
** Measure only when Rotary switch is OFF (Rapid Shutdown) or inverter is disconnected
Design Requirements
| PV Module Requirements | 650W Maximizer | 420W Maximizer |
|---|---|---|
| Maximum Rated Power Output | 650W | 420W |
| Maximum Short Circuit Current(Isc) | 20A | |
| Maximum Open Circuit Voltage(Voc) | 75V | 60V |
| Series String Requirements | 650W Maximizer | 420W Maximizer |
|---|---|---|
| Maximum # of PV Modules per String | 24 PV Modules | 20 PV modules |
| Minimum # of PV Modules per String | 9 PV Modules | |
| Minimum # of PV Modules within +/- 5° pitch and azimuth | 7 PV Modules. Remaining PV modules of the same string can be on different planes and orientations | |
| Maximum Usable Power per String | 6.5kW | |
| Maximum DC Current per String | 16A | |
| Maximum STC Nameplate Power per String | 8.4kW. Based on site specific pitch, azimuth, shade, and weather conditions, Maximizers will curtail power if real world power exceeds 6.5kW per string. |
| Parallel String Requirements | 650W Maximizer | 420W Maximizer |
|---|---|---|
| # of Parallel Strings Allowed | 3 Strings | |
| Uneven String length Allowed | Yes, each string in parallel can have different number of PV Modules/Maximizers | |
| Maximum Total DC Current from PV to Inverter | 37.5A | |
| Maximum Total Usable Power | 15kW. The inverter will curtail power if real world power exceeds 15kW for all strings combined. Note that curtailment is unlikely to occur at 15kW STC with Lunar 9.6kW inverter as the battery charge power plus the inverter output power is capable of handling 15kW. |
PV Troubleshooting Guide
Caution: Whenever working on the DC PV circuits (Maximizer Hub and Maximizers), ensure the inverter rotary switch is turned OFF. This isolates the batteries from the PV circuits. Failure to do so may result in exposure to the full current and voltage of the batteries, posing safety risks.
When System is in Rapid Shutdown
- If the string measured voltage < 20Vdc, it is likely that one or more Maximizers are unplugged on the inputs, unplugged on the outputs, or a subset of Maximizers are installed with reverse polarity.
- If the string measured voltage > 30Vdc, it is likely one or more Maximizers are not properly bonded together and bonded to the Maximizer Hub.
- Grounding and bonding are an important part of Maximizer installation and operation.
- During the roof installation, the Hub and Maximizer grounds should be bonded together but are unlikely to be grounded. This is acceptable for verifying voltages when in Rapid Shutdown. However, once the system is energized and operating, proper grounding from the roof to the inverter is critical for proper product functionality.
- If string measured voltage is negative, check polarity of Multimeter probes. If the probes are correct, the Maximizer string is likely installed with reverse polarity.
Common PV Layouts Issues
Maximizer Hub Installation and Troubleshooting
The Maximizer Hub should always be installed between the Inverter and all Maximizer output strings. The positive (+) and negative (-) wires of the inverter circuit, and all Maximizer strings (including ground), should terminate in the Maximizer Hub.
When the system is installed correctly, the measured voltage on the Maximizer Hub terminals should match the voltage on the inverter’s PV terminals. This applies both when the system is in Rapid Shutdown and when it is active.
Roof Doctor
Roof Doctor is an optional PV commissioning tool that ensures solar panels and Maximizers are correctly wired early on the day of install, before the ESS is operational.
The Roof Doctor Hub is a palm-sized, USB-powered device that enables phone to Maximizer communication. The Hub and the commissioning phone can remain on the ground while communicating wirelessly with Maximizers located over 100 feet away on the roof. Communication can begin as soon as a Maximizer receives input power from a solar panel.
Installers can use the following Roof Doctor features on the Lunar Installer App:
- Update Maximizer firmware
- Verify Maximizer power, communication, and state
- Send a 1V signal to the Maximizer
- When a Maximizer is updated to the latest firmware and is actively communicating with Roof Doctor, it outputs approximately 1V. This functionality allows the installer to use a multimeter to verify PV strings by comparing the measured string voltage to the expected voltage based on the number of Maximizers in that string.
Getting Started on Roof Doctor
- Disconnect the Maximizer Hub.
- Power the Roof Doctor Hub with a USB-C cable with a phone (iPhone 15 or higher) or other external power source. Two blue LED lights should be on.
- Log in the Installer App, click “Roof Doctor” in the bottom right corner.
- Join the Roof Doctor wifi network. No QR scanning or text entry is needed.
- Scan Maximizer QR codes.
- Confirm all Maximizers communicating using the Health Check feature. It takes ~30 seconds to update.
- Push Firmware update
- Confirm all have healthy state as instructed by the Installer App
NOTE: Issues may occur if multiple Roof Doctor Hubs are powered simultaneously and within range of a phone. Use only 1 Roof Doctor Hub at a time. NOTE: A Maximizer cannot communicate with a Roof Doctor Hub and Maximizer Hub simultaneously.
- For a Maximizer fresh out of the box, it will connect to Roof Doctor as soon as the QR code is scanned.
- For a Maximizer previously commissioned and communicating with a Maximizer Hub:
- Turn the Inverter rotary switch to the OFF position
- Unplug home runs from Maximizer Hub to de-energize the Maximizer Hub
- Wait up to 5 minutes before the Maximizer will connect to Roof Doctor
FAQs
- Do you recommend 1 string of 20 Panels or 2 strings of 10 Panels? 1 string of 20 panels is recommended over 2 strings of 10.
- Is the Lunar Inverter grounded or ungrounded (aka functionally grounded)? The Lunar inverter is an ungrounded (aka functionally grounded) inverter. Therefore the PV ground wire must remain isolated from both the positive and negative DC circuits.
- Does an installer need to verify the voltage of each individual string? Yes, we strongly recommend verifying the voltage of each individual string. It is possible that one series string is wired correctly, but a second series string is wired incorrectly. After the strings are combined in parallel at the Maximizer Hub, voltage at the Maximizer Hub DIN rail terminals may still read 20-30Vdc. This could falsely indicate that wiring is correct.
Lunar Support
Email: installersupport@lunarenergy.com
Hotline: (650) 535-1969 or contact us directly in the Lunar Installer App
Support Hours: 8:00 a.m. to 7:00 p.m., Pacific Standard Time, Mon-Fri.
Revision History
| Revision | Description of Change | Effective Date |
|---|---|---|
| 1 | Initial Release | 12/13/2024 |
| 2 | Allow 2 PV Strings | 01/07/2025 |
| 3 | Allow 9 modules per string | 02/25/2025 |
| 4 | Allow 3 PV Strings | 03/17/2025 |
| 5 | Table 1. Voltage Reference Values Updated | 03/26/2025 |
| 6 | Maximizer Expected DC Voltage Updated | 04/10/2025 |
| 7 | 650W Maximizer | 09/24/2025 |
| 8 | Roof Doctor | 11/25/2025 |