- Introduction
- What Is Open-Loop Communication?
- What Is Closed-Loop Communication?
- A Practical Comparison
- Which One Is “Better”?
- Conclusion
Introduction
Recently, a customer wanted to add lithium batteries to their Schneider system. During our discussion, we discovered that this particular model of inverter couldn’t communicate with these newer rack-mount batteries via CAN bus or a closed-loop system. However, the good news is that the system can still be connected using an open-loop setup, and it can perform exceptionally well.
This situation highlights an important topic for anyone considering an upgrade to their solar system: the way batteries and inverters communicate can have a big impact on performance, reliability, and system longevity. In this article, we’ll break down the two main communication methods, open-loop and closed-loop, and explore the advantages, challenges, and real-world considerations for each.
What Is Open-Loop Communication?
Open-loop communication is the more traditional and widely used method of operating batteries in solar power systems. In an open-loop setup, the inverter does not communicate directly with the battery’s internal Battery Management System (BMS). Instead, the inverter makes decisions based on programmed settings and real-time battery voltage.
Key parameters such as:
- Charging voltage
- Float voltage
- Maximum charge and discharge current
- High and low voltage cutoffs
are manually set in the inverter according to the battery manufacturer’s specifications.
The battery still protects itself internally through its own BMS, but the inverter is not dependent on digital communication to operate. This simplicity often makes open-loop systems more stable, more flexible across different brands, and less prone to communication-related faults. Many off-grid and hybrid systems have been running reliably for years using this approach.
What Is Closed-Loop Communication?
Closed-loop communication allows the battery and inverter to exchange data continuously through a communication cable, typically using CAN bus or a similar protocol. In this setup, the battery’s internal Battery Management System (BMS) actively communicates with the inverter, directing how the system charges and discharges.
It’s important to note that this type of communication applies only to advanced lithium batteries designed with built-in communication ports, such as rack-mount or modular battery systems. This discussion does not apply to lithium “drop-in” style batteries, which generally do not include communication ports and operate exclusively in open-loop configurations.
Information shared can include:
- State of Charge (SoC)
- Charge and discharge limits
- Battery temperature
- Fault conditions
- Battery protection status
With this data, the inverter can automatically adjust charging and discharging parameters without manual programming. When properly implemented, closed-loop systems can provide accurate inverter-based SoC readings and fine control over battery behavior.
That said, closed-loop systems depend heavily on firmware compatibility, correct configuration, and ongoing manufacturer support. If communication is lost or mismatched, the inverter may generate errors, limit output, or shut down, even if the battery itself is healthy.
A Practical Comparison
When comparing open-loop and closed-loop battery communication, it’s important to separate theory from real-world performance. Both methods can work well when applied in the right situation, but they solve different problems and introduce different trade-offs.
Reliability and Stability
Open-loop systems are often praised for their simplicity. Because the inverter is not dependent on digital communication with the battery, there are fewer points of failure. As long as voltage settings and current limits are programmed correctly, the system tends to operate predictably and consistently over long periods of time.
Closed-loop systems add another layer of complexity. Communication cables, firmware versions, and protocol compatibility all need to align. When everything works as intended, performance can be excellent, but when communication issues arise, systems may throw errors, reduce output, or shut down even though the battery itself is functioning normally.
Monitoring and State of Charge
Closed-loop systems shine when it comes to inverter-based State of Charge (SoC) reporting. Because the inverter receives data directly from the battery’s BMS, SoC readings are typically accurate and easy for homeowners to understand.
Open-loop systems do not provide inverter-calculated SoC. Instead, system behavior is inferred from voltage trends and runtime. While this requires a bit more understanding from the system owner, many experienced off-grid users are comfortable operating this way and rely on voltage as a reliable indicator.
Flexibility and Compatibility
Open-loop communication is largely brand-agnostic. Batteries and inverters from different manufacturers can often work together as long as electrical specifications match. This flexibility makes future upgrades or battery replacements simpler.
Closed-loop systems tend to lock users into specific battery / inverter pairings. If a manufacturer changes firmware support or discontinues a product line, compatibility can become a concern years down the road.
Long-Term Ownership Considerations
From a long-term perspective, open-loop systems often age quietly. There are no communication protocols to become obsolete, and fewer updates are required over time.
Closed-loop systems rely more heavily on ongoing manufacturer support. Firmware updates, communication standards, and product compatibility all matter. For some users, this is an acceptable trade-off for enhanced monitoring; for others, it introduces uncertainty they’d rather avoid.
Which One Is “Better”?
Neither open-loop nor closed-loop communication is universally better. The right choice depends on the system goals, the customer’s expectations, and the importance placed on simplicity versus data visibility.
In many real-world installations, especially off-grid systems, open-loop communication continues to prove that simple, well-designed systems are often the most reliable. Closed-loop systems can offer valuable insights, but they are not a requirement for a safe, effective, or long-lasting solar installation.
Conclusion
From an education and system-design standpoint, this is where planning really matters. When installing an entirely new solar system, it often makes sense to consider an inverter that can communicate directly with the batteries. That option gives customers the flexibility to choose whether they want to use closed-loop communication now or in the future.
However, when upgrading batteries only, it’s important to pause and ask a different question: is it worth replacing a perfectly good inverter solely for battery communication? In many cases, the answer depends entirely on the customer’s priorities. An open-loop system can function just as reliably and perform extremely well without direct BMS communication, provided it is properly configured.
Ultimately, the choice between closed-loop and open-loop communication comes down to individual needs and expectations. Closed-loop systems offer detailed monitoring and data visibility, while open-loop systems prioritize simplicity, flexibility, and long-term reliability. By understanding the strengths and limitations of both approaches, homeowners and system designers can make informed decisions that align with their goals, not just today, but years down the road.
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For individuals seeking consultation, education, or assistance in system designs related to grid-tie or off-grid solar applications, IOTG Solar stands ready to help. Our team is available to address questions, provide valuable insights, and offer support at every stage of the solar energy journey. Feel free to reach out to IOTG Solar anytime for expert assistance and comprehensive solutions tailored to your specific needs.
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