Repowering a Solar System with a Tigo Inverter: The Definitive Guide

Shortcuts:
1. Assessment of Existing System
2. Voltage and Current Checks
3. Inverter Compatibility
4. Regulatory and Code Compliance
5. System Efficiency and Performance Gains
6. Installation Best Practices
7. Warranty and Support
8. Final Testing and Commissioning
9. Installation Resources

Introduction:

Upgrading an aging solar inverter to a modern Tigo EI Inverter can significantly improve system performance and reliability. This process is called repowering and has significant improvements - system efficiency, higher output power, etc. However, even seasoned solar installers need to approach such replacements carefully. Older PV systems may have been designed under different standards and may have components that have degraded over time. This information-heavy guide for residential systems outlines the key considerations to ensure a smooth inverter replacement that maximizes the benefits of a new Tigo unit.

1. Assessment of Existing System

Before swapping in the new Tigo inverter, thoroughly evaluate the current solar PV system. Inspect the physical condition of all modules, wiring, and racks. Look for damage like cracks, delamination, discoloration, or loose connections. Even if everything looks intact, remember that solar modules degrade in output over time – typically by about 0.5% to 0.8% each year after the first year. Over a decade, the array might produce around 5–10% less power than when it was new. This reduced output isn’t usually a deal-breaker, but it’s essential to set expectations that the system’s peak power may be slightly lower than the original installation. Also, consider any changes around the site. New shading obstacles (like grown trees or new structures) could affect performance and warrant mitigation (e.g., trimming or using optimizers, as discussed later).

Evaluate the compatibility of the existing array with current standards. Note the make and model of the solar modules and their ratings (especially Voc and Isc – more on that below).

Check how the strings are configured (how many modules per string, how strings are combined).

You cannot tell module stringing configurations just by looking at the array!

If the old inverter was transformer-isolated with a grounded DC conductor, be aware that the new Tigo inverters are transformerless, requiring ungrounded DC inputs with equipment grounding – you’ll need to remove or reconfigure any old DC grounding electrode conductors or bonding jumpers accordingly. In general, gather all info on the array’s electrical characteristics and design, as this will inform the next steps in ensuring the new inverter is a good match.

 

Another consideration is the array's grounding type. Potential Induced Degradation (PID) is a phenomenon associated with leakage currents in some PV modules with crystalline Si cells. It leads to gradual performance deterioration, reaching up to 30 percent and more after a few years. Module manufacturers recognized and put safeguards in place to prevent PID, but those countermeasures relied on grounding the negative or positive conductor inside the PV inverter. Since the array is floating with respect to ground for a transformless inverter, PID could build up in the array. A PID box is required but not supplied by Tigo. 

2. Voltage and Current String Checks

One of the most critical steps is to verify the open-circuit voltage (Voc) and short-circuit current (Isc) of each PV string in real-world conditions and compare these to the Tigo EI Inverter input specifications.

Use a multimeter (with appropriate DC voltage rating) to measure each string’s Voc, ideally during the coldest part of the day (early morning) when Voc will be highest. In series-string systems, the string Voc is the sum of each module’s Voc; this total must remain below the inverter’s maximum 550V DC input voltage rating at all times. Keep in mind that module Voc increases as temperature drops – a rule of thumb is to multiply the STC Voc by 1.25 to account for cold extremes. For example, a string that is 500 V at 25°C might climb toward ~625 V on a very cold morning. Ensure that even in such conditions, the string won’t exceed the Tigo inverter’s limit. If the measured or calculated cold Voc is uncomfortably close to the limit, you may need to reconfigure strings (e.g., remove a module from each string) to stay within safe bounds.

 

Likewise, measure the Isc of the strings (or at least verify from the module datasheet and string count). The Isc at noon on a bright day (or STC Isc from the module nameplate times number of parallel strings) should not exceed the inverter’s input current or the rating of any DC combiners or fuses in the path. Also, consider the temperature coefficient of the current – in very high irradiance and cooler temperatures, the current can slightly exceed STC Isc. Most modern inverters can handle some overhead (and Code allows 1.25× Isc sizing for safety), but verifying actual values is good practice.

Additionally, module degradation over 10 years may have reduced the current a bit and possibly the voltage at maximum power (Vmp) due to output loss. This means your old strings might run at a lower power point than the original, but ironically, the Voc doesn’t drop as much with age (it may drop slightly, but not as proportionally as power). Therefore, never assume an old array’s Voc is safely lower simply because of age – always measure or calculate for worst-case cold conditions.

Also, check that the string Vmp falls within the Tigo inverter’s MPPT operating window under typical conditions. Tigo EI inverters have a wide MPPT range of 80 to 550V. This is great for older arrays because the inverter can still find and lock onto the optimal power point even if module performance has sagged. If your string Voc and Vmp were designed for an older 600 V inverter, they will likely be well within the range of the new Tigo, but verify that the upper end will not exceed the inverter's 550V limit.
 

The Tigo EI Inverter will shut down if the voltage exceeds 550V.
 

Also, ensure the minimum string voltage at the coldest operating cell temperature is above the inverter’s 80V DC startup voltage so it can begin generating.

Lastly, verify that all strings produce roughly similar Voc and Isc (big deviations might indicate a string wiring issue or a bad module that should be addressed while you’re at it).

3. Inverter Compatibility

When replacing the inverter, verify that the existing PV module configuration is compatible with the MPPT channels and features of the Tigo unit. Tigo’s inverters come with multiple MPPT inputs:

• 3.8 kW - 2
• 7.6 kW - 3
• 11.4 kW - 4

If the old inverter had only one MPPT and all strings in parallel, now is a chance to divide strings between separate MPPT inputs for better performance (for example, separating strings on different roof orientations or with different lengths). Check the datasheet for how many strings per MPPT are allowed and how to wire them (some MPPT inputs can take two strings in parallel, etc.).

Proper MPPT allocation will ensure the Tigo inverter can independently optimize each substring of the array, preventing one sub-array’s behavior from dragging down the whole system.

 

ATTENTION
Do not assume that since the old inverter had three strings, you can connect those three strings to their terminals in the Tigo EI inverter! You must perform the checks in Step 2 before connection. Our service line reports that SEVERAL installers have made this costly mistake.

Next, evaluate the need for Module-Level Power Electronics (MLPE) on the array. Tigo is well known for our TS4 platform of MLPE, which can provide optimization, monitoring, and rapid shutdown. In a simple inverter swap, MLPE may be required for the new system. Here are TS4 benefits to consider:

• Module-level monitoring & optimization: By adding Tigo TS4-O (Optimization) units to each module (or selectively, to only those that need it), you enable module-level MPPT and monitoring. This can mitigate issues like shading or mismatch that might have developed over the years (e.g. if a couple of modules are under new shade in the afternoon, the TS4 optimizers will limit the impact on the rest of the string). It can also give you and the system owner granular performance data per module via the Tigo Energy Intelligence platform. Keep in mind that adding optimizers will slightly increase project cost and complexity, so weigh the benefit: on a well-performing unshaded array, a straight swap without optimizers is fine; on a partially shaded or unevenly aged array, optimization could recoup energy that would otherwise be lost.

• Rapid shutdown compliance: If the jurisdiction now requires module-level rapid shutdown (NEC 2017 and beyond), the most straightforward path to compliance on a legacy array is often using TS4 units that have the built-in rapid shutdown function (All TS4's). Tigo’s TS4 devices can act as your rapid shutdown solution, and they are designed to work in tandem with Tigo’s inverters for seamless shutdown signaling.

• Retrofitting considerations: The nice thing about Tigo’s Flex MLPE is that they can be added to existing modules without much hassle (the TS4s clamp onto the frame and connect to the module MC4 connectors). This flexibility means you can upgrade the system’s intelligence and safety at the same time as the inverter swap if needed.
   

4. Regulatory and Code Compliance

Solar codes and standards have evolved considerably in the last 10 years, so replacing an old inverter must be done under current regulations. Two major areas to focus on are rapid shutdown requirements and general electrical code updates:

• Rapid Shutdown (NEC 690.12): If the PV system is on a building (rooftop), modern codes (NEC 2017 and later, adopted in most states (Rapid shutdown compliance for US rooftop PV systems)) require module-level rapid shutdown capability. When the AC is disconnected, conductors outside the array must drop to ≤30 V within 30 seconds, and conductors inside the array to ≤80 V. A 10-year-old system likely did not have module-level shutdown, so this is a crucial upgrade for safety and code compliance. When paired with TS4s on every module, the Tigo EI Inverter will satisfy the rapid shutdown requirements.
   
• Updated electrical codes: Review any changes in the National Electrical Code (NEC) and local codes since the original installation. The Tigo EI Inverter complies with all rapid shutdown Code cycles and includes arc fault detection.

•  Electrical enclosures and disconnects should meet current standards too – for example, if the old inverter relied on an external DC disconnect switch, the Tigo inverter has one integrated. Ensure that the AC overcurrent protection is sized correctly per current code (usually 125% of inverter max continuous output), and that the AC disconnect (if required by the utility) is present and properly labeled. Use the following breaker sizes for your new Inverter:
  •  
    •  
      • EI 3.8 kW = 20A
      • EI 7.6 kW = 40A
      • EI 11.4 kW = 60A
         
• Breaker Sizing and Inverter Derating: an existing inverter branch-circuit breaker may remain in place when the replacement inverter is configured to limit its AC output current to the same or lower value as the original unit. NEC interconnection and overcurrent protection requirements are based on the inverter’s maximum continuous output current, not its maximum capable nameplate rating. 
  
  Per NEC 705.12, point-of-connection and bus/OCPD loading calculations use the inverter output current value; when inverter output is limited by settings, that limited current is the governing value. Breaker sizing follows the 125% rule for continuous sources (e.g., 24 A continuous × 125% = 30 A OCPD). NEC 705.13 further permits power control systems (PCS), including inverter-embedded current-limiting functions, to control DER output such that conductor, busbar, and overcurrent device ratings are not exceeded. Therefore, when the replacement inverter is documented and commissioned with an AC output limit consistent with the existing 30 A branch circuit (≈ 24 A continuous), the original breaker remains NEC-compliant and does not require upsizing. Installers should retain commissioning records or settings screenshots demonstrating the configured current limit for AHJ verification.
• Permitting and interconnection: Even though this is a “replacement,” treat it professionally with permits and paperwork. Many authorities having jurisdiction (AHJs) treat inverter replacements as like-for-like maintenance items if the new inverter is the same size and specifications. However, since you are upgrading to a different brand and modern specs, you should notify the local utility and update the interconnection agreement as needed. The utility will want to know the make/model of the new inverter (for grid standards compliance like IEEE 1547, UL 1741 SA, etc.). 
  
  Tigo EI inverters are UL 1741 listed and grid-compliant, so it’s usually a formality. Also, provide updated single-line diagrams and labeling if required. All PV system labels should be refreshed if worn out – including the inverter AC disconnect, DC disconnect, rapid shutdown label (NEC 690.56(C) placard), and so on- to meet current NEC Article 690 labeling requirements.
  
  Contact Tigo Support for the IPOC letterhead for the utility. Refer to this article for more information: Application note: EI Inverter (US) power output control (IPOC)
   
• Inspection expectations: Be prepared to demonstrate the rapid shutdown functionality to the inspector. Ensure all wiring is neat and accessible for inspection. Given that you’re working with an older system, the inspector might look at things like module mounting and roof penetrations. While not within the primary scope, it’s good to ensure everything remains up to code (e.g., no bare conductors, proper wire management, intact ground bonds, etc.). In short, don’t just swap the inverter and call it a day – address any legacy code issues so the system is fully compliant and safe as per current year standards.

5. System Efficiency and Performance Gains

One big upside to replacing a decade-old inverter is capturing improvements in efficiency and technology. Inverter efficiency has improved over the years: older string inverters often had peak efficiencies in the mid-90% range, whereas modern Tigo inverters are 97-98% efficient (CEC). This means less energy loss during DC-to-AC conversion. That translates to a bit more of their solar generation making it to the grid or loads, especially during high-production periods. While the percentage difference might seem small, over the lifetime of the new inverter, it adds up, and it can help offset some of the natural module degradation by squeezing more out of what the modules produce.

Another gain is in the MPPT capabilities and design features of the Tigo EI inverter. If the old inverter had a single MPPT for, say, two or three strings, it had to treat the whole array as one unit. The Tigo unit with multiple MPPT channels can independently optimize different strings. For example, if part of the array is east-facing and part is west-facing, a single-MPPT inverter would have to compromise on the operating voltage. In contrast, a dual-MPPT Tigo can lock each orientation into its ideal voltage. This improves the overall energy harvest, especially in systems with sub-array differences.

Additionally, Tigo inverters allow DC oversizing up to 200% (2:1 DC-to-AC ratio). If the customer is interested and the roof space allows, you could even add a few extra modules (within the inverter’s voltage and current limits) to increase energy production – something that might not have been possible or allowed with the old inverter. Oversizing lets the system produce more power in the mornings and afternoons (though the inverter will cap output at its AC rating at midday), broadening the production curve. It’s a strategy to counteract module degradation or just deliver more kWh per day. When adding storage, it allows more energy to the batteries earlier in the day.

Monitoring and diagnostics also see a big upgrade. Many inverters 10 years ago had rudimentary monitoring (maybe a basic web portal, or even just lights and an LCD readout). Tigo’s solution is part of our Energy Intelligence (EI) platform, meaning that once installed, you get access to detailed system data. If TS4 MLPE are used on modules, you can monitor performance at the module level and get alerts for any issues. Even without optimizers, the inverter itself logs production, voltage, and current and can report that to a cloud platform via built-in Wi-Fi or cellular connectivity. This means easier troubleshooting down the line and better service to the customer. For instance, the Tigo EI app can be used for commissioning and ongoing monitoring, and it’s installer-friendly, allowing remote settings updates and firmware upgrades.

The integrated safety features and grid support functions in new inverters are also worth noting. Tigo’s inverters come with built-in ground-fault protection, arc-fault detection, and meet the latest grid codes (voltage/frequency ride-throughs, etc.). The homeowner might notice more stable behavior (for example, fewer nuisance trips during grid disturbances, thanks to standards like UL 1741-SA that the new Tigo inverter will comply with). And if the system is ever expanded with batteries (since the Tigo EI is a hybrid inverter ready for storage), you’ve laid the groundwork for that future addition. Even if a battery is not added now, the storage-ready aspect can be a selling point – the new inverter could support a battery later without another significant overhaul.

In summary, by replacing the inverter, you’re not just fixing a problem; you’re upgrading the PV system’s brain and heart. The result will likely be a noticeable bump in kilowatt-hour production, a wider operating envelope (capturing energy in low-light conditions due to lower start voltage, etc.), and a much richer dataset to manage the system’s performance. Make sure to communicate these benefits to the customer – it helps justify the investment in a new inverter beyond just “the old one died.”

6. Installation Best Practices

Performing the physical replacement of the inverter requires careful adherence to safety and best practices – both to protect yourself and to ensure the longevity of the new installation. Here’s a step-by-step rundown of best practices:

• Safety Shutdown: Begin by completely de-energizing the PV system. Open (turn off) the AC disconnect to isolate the inverter from the grid. Then, open the DC disconnect or combiner fuses to stop current flow from the modules. Verify the absence of voltage on both the AC and DC terminals with a meter before touching any wiring. It’s wise to do the inverter swap very early in the morning or evening (or cover the modules with opaque material) so that the PV array does not produce significant power. Even with DC disconnects open, wires between the array and disconnect will be live in sunlight – so exercise caution and never short or touch those conductors. Lock-out tag-out the breakers/disconnects to prevent anyone from inadvertently turning things on during your work.
   
• Removal of Old Inverter: Disconnect the wiring from the old inverter in an orderly fashion. Typically, you’ll disconnect AC wires (usually 3 conductors: hot, hot, neutral or ground, depending on split-phase vs. transformerless config), DC wires (PV+ and PV- from each MPPT input or string combiner), and any communication or monitoring cables that might be present. 
  
  As you remove wires, label them if not already labeled – especially if multiple strings or circuits were landed in one place. Remove mounting hardware and carefully take the old inverter off the wall or rack. Have a helper ready since some old inverters are heavy (some reaching close to 150 pounds!) The new Tigo units are relatively light ~32 to 45 pounds. 
  
  Inspect the area for any signs of moisture or heat damage – e.g., discoloration on the wall from past overheating. This can guide where to mount the new unit, maybe a slightly different location for better ventilation.
   
• Mounting the New Tigo Inverter: Follow the Tigo mounting instructions for clearances and bracket installation. The inverter should be mounted vertically and in some shade (to avoid direct sun heating, which will cause premature derating). Use appropriate fasteners for the wall (lag bolts for wood, anchors for masonry, etc.). 
  
  Check that there’s adequate clearance around the inverter for cooling: 12 inches on all sides. Also, account for any required clearances per code (e.g., working space if the inverter has an integrated disconnect handle that a person needs to access). If the old inverter’s conduit entries don’t line up with the new one, you may need to reroute or extend the conduits. Plan the wiring so that water cannot enter the inverter (drip loops on exterior conduits, use of rain-tight fittings, etc.).
   
• Wiring the DC Side: Most Tigo inverters will have either MC4 connectors (European models) or terminal blocks for the PV inputs. If it’s connectors and your existing array leads have compatible MC4s, you might be able to plug them directly. 
  
  ATTENTION!
  Check the polarity before connecting! Reversing polarity on the DC input is a common mistake that could damage the inverter. 
  
  The inputs are labeled PV1+, PV1-, PV2+, PV2-, etc., corresponding to different MPPTs. Match your strings accordingly. If your old inverter had a single input and now you have two MPPTs, split the strings as planned and ensure each goes to the correct input pair. Use a DC combiner or splitters as needed. 
  
  If you had to remove any modules from strings to adjust Voc, make sure the remaining string wiring is properly terminated and safe (unused module leads should be capped and isolated, and perhaps inform the owner if you leave a module disconnected). 
  
  Also, check PV Grounding: connect the array equipment grounding conductor to the inverter’s ground lug if it runs to that point (or to the disconnect ground bar per the wiring method). All metal parts should be bonded – this likely already exists, but ensure continuity when you reassemble everything.
  
  
• Wiring the AC Side: Connect the inverter's AC output to the dedicated circuit feeding the main service module or submodule. This usually involves three wires for a split-phase 240V inverter: L1, L2, Neutral, and Ground.
  
  North American Tigo inverters support both 208V and 240V. Use the specified wire gauge (AWG #8 or #6 for a ~7.6kW inverter, depending on run length and breaker size). Ensure the breaker is appropriately sized. If not, change the breaker to the correct size and use conductors that match that rating. 
  
  Outside North America, Tigo inverters support the typical 400/230V wiring connections.
  
  Torquing: torque all terminals to spec using a torque screwdriver/wrench – loose connections cause many problems down the road. Route the wires neatly and clamp any strain reliefs. Connect any communication wires if applicable (e.g., TAP to inverter if using TS4-Os, generator start wiring if using the Tigo 200A ATS when the Tigo EI Battery is used, etc.)
  
  
   
• Integration of Rapid Shutdown Devices: If you are installing Tigo TS4-O units, you must install the Tigo Access Point (TAP) that communicates with them. The TAP is usually a small antenna box that sits under the array and connects to the Tigo inverter to coordinate shutdown signals. 
  
  Ensure the TAP is placed as per Tigo’s guidelines (e.g., centrally located in the array to talk to all TS4 units, not blocked by metal, etc.). Do NOT install the TAP in the attic! The signal is too attenuated and will cause abnormal system operation. Connect the TAP cable to the inverter’s communication port as instructed. 
  
  The Tigo Inverter has an integrated RSS Transmitter for rapid shutdown if installing the TS4-F units. 
  
  Also, mount the rapid shutdown switch (included with the Tigo Inverter). Place the code-compliant rapid shutdown sticker (included) near the switch.
   

• Grounding and Bonding: We touched on this, but to reiterate, bond the new inverter to the existing grounding system. A grounding bus bar is in the inverter beneath the AC terminal block. Connect it to the array EGC and the AC ground. Ensure the main service ground and PV ground are common. Post-replacement, all metal enclosures (rails, junction boxes, inverter chassis) should be electrically continuous to ground for safety.
   
• Additional Protective Devices: Consider whether you need to add or replace surge protection devices (SPDs) on the AC or DC side. The old system might not have had SPDs, but it could be a good value-add to install them to protect the new electronics while upgrading. Also, check the condition of any fuses or breakers in DC combiner boxes – replace any that show signs of wear or heating. The Tigo EI Inverter has an integrated DC disconnect, but verify the new stringing configuration is within specifications.

Taking these steps will ensure a clean and reliable installation. The mantra is to leave the site safer and more code-compliant than you found it. With the new Tigo inverter properly mounted, wired, and integrated, you’re ready for the next phase: testing and commissioning.

7. Warranty and Manufacturer Support

When you install the new Tigo inverter, it’s important to handle the warranty registration and understand the support structure provided by the manufacturer. Tigo offers strong warranty terms – for example, the Tigo EI inverters come with a standard warranty of 152 months (12 years 9 months), notably longer than the old typical 10-year inverter warranty.

Be sure to register the inverter via the Tigo EI App when you set up the system. This ensures that the installation date is recorded and the customer (or you as the installer) can claim warranty service if needed. Failing to register might default the warranty to the manufacturing date, which could leave the owner with less coverage, so it’s a simple but crucial step.

Familiarize yourself with Tigo’s warranty policies. The warranty documentation will outline what is covered and the claim process. Since you are the installer, you’ll likely be the first line of support if something goes wrong, so knowing how to quickly engage Tigo support is key. Tigo has been actively supporting installers with its Green Glove Service for select installers, which hints at premium support. Check if you qualify or if there are training resources (Tigo Academy, webinars) that can bolster your knowledge. These resources can help you troubleshoot issues without reinventing the wheel.

Preventative maintenance is required to keep the warranty valid, which involves periodic checks. Keep records of the installation and commissioning data (perhaps print the final settings or save screenshots from the app). Proper installation documentation can be helpful in case of a future warranty claim.

If the customer is interested, you can inform them of extended warranty purchases that cover the equipment for up to 25 years! However, with 12+ years standard, many homeowners are satisfied. Still, commercial clients or long-term owners might opt for 25-year coverage if available, aligning the inverter’s guaranteed life closer to the module warranties.

Finally, ensure the owner (and you) know how to get technical support. Tigo's support line is reachable by phone, email, or EI App messaging. The monitoring portal/app often has diagnostic info – if you see any alert or unusual behavior during the life of the system, reaching out to Tigo with that data can expedite service. As the installer, you might be called upon to replace the unit if something fails, so keep your contact info updated in the Tigo EI portal. Tigo’s warranty includes a $250 truck roll reimbursement fee. Check the warranty documentation for details.

In short, treat the warranty and support aspect as part of the install deliverables: register the product, educate the owner on their coverage, and keep yourself in the loop for future support needs. This protects the customer’s investment and solidifies your role as a trusted installer for any follow-up work.

Tigo Support is available to answer questions, and we highly recommend contacting us before removal and replacement to ensure everything goes smoothly.

Also, check out our Green Glove Service if you are new to Tigo products. We offer services for residential and commercial projects.

8. Final Testing and Commissioning

With the new Tigo inverter installed and everything wired up, the last step is to test and commission the system. This is where you verify that the system is operating correctly and safely and configure the inverter’s settings for optimal performance and reporting. Always refer to the EI Inverter quick-start guide during installation. Here’s a checklist for this stage:

• Pre-Power Checks: Do a final once-over of all connections. Ensure all PV strings are landed in the correct terminals with proper polarity and all AC wires are tight. Check that no tools are left inside the inverter and that any covers are properly closed.
• Initial Turn On: Turn on the DC side first, then the AC side. Close the DC disconnect and watch the inverter’s LEDs or display. The inverter might take a minute to boot up on DC power (if sufficient sunlight is present). Then close the AC disconnect/breaker to let the inverter sync with the grid. There will be a 5-minute wait per UL 1741 before exporting power, so be patient.
• Commission via App/Portal: Using a smartphone or laptop, connect to the inverter and then follow the steps in the Tigo EI app. This will involve setting the inverter to the correct country/grid profile (make sure it’s set to the proper utility grid standard), connecting it to the local Wi-Fi network (unless using cellular), and adding the system to the monitoring account. If you installed TS4 optimizers, the app will detect and register those after scanning their barcodes. During commissioning, the inverter firmware may require an update.
• Testing Functionalities: Once the system is live, conduct the following tests:
  • Power Production: Compare the inverter’s reported output with your expected values for the given sunlight conditions. For example, if each module is ~250 W and you have 20 modules (5 kW array) and it’s near noon with full sun, you’d expect somewhere in that ballpark (minus some losses). If the output is significantly low, investigate if an MPPT is not enabled or if a string is miswired.
  • Rapid Shutdown Test: Simulate a grid power loss to ensure the rapid shutdown works (if applicable). This can be done by opening the AC disconnect while the system is running. The inverter should shut off, and the TS4 units should de-energize the array quickly. Measure the string voltage at the inverter DC terminals (with a meter) a short time after shutdown – it should drop to safe levels (<30 in 30 seconds outside the array boundary).
  • Monitoring Check: Log in to the Tigo EI App and confirm the system reports data. Check that all PV modules or strings are represented and giving readings if you have optimizers. A successful commissioning will show each optimizer’s serial and its metrics. If any are missing, try the discovery again or check connections. Also, verify that the inverter’s network connection is solid. A quick way is to see if real-time data is refreshing or check the EI portal from a web browser away from the site.
• Customer Orientation: After you’re satisfied with performance and safety, walk the customer through any new interfaces or changes. Show them the new inverter, pointing out any differences (for instance, “this inverter has no display, so you’ll check production on the app”). Ensure they have access to the monitoring (create a login for them on the Tigo EI App in the Add Users screen). Explain the indicator lights and basic operation – e.g., what to do if they see a red light, how the rapid shutdown switch works (if one was installed), etc.
• Documentation: As a final step, update the system documentation. Fill out any commissioning checklist for your company records. Provide the homeowner with any warranty info or manuals (or let them know it’s all digital if that’s the case). If required, submit the closure documents to the authority having jurisdiction or utility (some need a sign-off that the system was commissioned under an install permit). Basically, tie up the paperwork so the project is officially complete.

After these steps, the new Tigo inverter should be fully integrated, and the solar PV system should be running better than ever. Monitor the system over the next few days (many installers do a quick remote check after the first day or two of operation to ensure all is well). If something is amiss, it’s easier to address it immediately than after months. But if all checks out, you can confidently hand off a rejuvenated solar system to the owner, knowing that you’ve enhanced its safety, compliance, and performance for years to come.

Key Takeaways

Replacing a 10+ year-old inverter with a modern Tigo inverter is a substantial upgrade that can breathe new life into a solar PV system. For experienced installers, it’s an opportunity to apply current best practices and fix any legacy issues.

By approaching the inverter replacement methodically, you not only swap a piece of hardware but also deliver a safer, smarter, and often more productive system to your customer. The solar industry’s technology evolves quickly, and as this case shows, even a system installed a decade ago can be significantly improved with the right upgrade. With the new Tigo inverter in place, the system is now prepared to serve the owner well into the future, potentially for another decade or more, while meeting all current standards. As an installer, taking the time to address each of the considerations above will result in a successful project, happy customers, and a stellar reputation for quality work in solar upgrades.

Removal and Replacement Checklist

Use this summary checklist during the inverter replacement process. It summarizes this article. If you have any questions, please contact Tigo Support.

Checklist: Repowering PV Systems with Tigo EI Inverters

Installation Resources:

• Installing the Tigo Rapid Shutdown Button
• Tigo String Sizing Tool
• EI Inverter Unboxing Overview
• Help Center: TS4 PV Module Compatibility
• Help Center: PV Module Current Correction for High Irradiance Locations
• Help Center: Tigo String Sizing Tool
• Help Center: Can I run my TAP Communication Cable in the PV Array Conduit?