Preventing Diesel Generator Wet-Stacking and Reverse Power in Sunsynk Microgrids in South Africa

Key Takeaways

• Diesel generators require a minimum load to operate efficiently and prevent issues like wet-stacking and carbon glazing.
• Sunsynk advises installing a generator with twice the rated inverter power to help ensure sufficient loading.
• Reverse power flow from the inverter to the generator can cause damage and must be prevented.
• Sunsynk documentation provides an overview of generator settings but does not detail specific configurations for dynamic solar throttling or reverse power protection.

Why Diesel Generators Need Minimum Loading in Microgrids

In South Africa, diesel generators are a common backup power source, especially during load-shedding. When integrated into a microgrid with solar and battery storage, it is crucial to manage their operation to ensure longevity and efficiency. Diesel generators are designed to run under load. Operating them consistently below a certain percentage of their rated capacity, often cited as 30% or more, can lead to several problems.

One common issue is "wet-stacking" or "carbon glazing." This occurs when the engine does not reach its optimal operating temperature, causing unburnt fuel, soot, and carbon deposits to accumulate in the exhaust system and combustion chambers. This reduces efficiency, increases fuel consumption, and can lead to premature engine wear and failure.

Another critical concern is "reverse power." This happens when the inverter, instead of drawing power from the generator, feeds power back into it. This can severely damage the generator's alternator and control systems, as generators are not designed to receive power.

Sunsynk's Guidance for Generator Integration

Sunsynk provides specific recommendations for integrating diesel generators with their Classic, Acure, and Elite hybrid inverters. These recommendations focus on appropriate sizing and safety features.

For optimal performance and to help prevent issues like wet-stacking, Sunsynk advises installing a generator with twice the rated inverter power. For example, if you have a 5kW Sunsynk inverter, a 10kW generator is recommended. This sizing ensures that even with varying loads, the generator has a higher likelihood of operating above its minimum required load, especially when the inverter is charging batteries or supplying significant household loads.

Sunsynk Classic, Acure, and Elite inverters are also compatible with generators that have built-in leakage protection (RCD). Using a generator with an RCD adds an important layer of safety, protecting against electrical shocks and faults. If your generator does not have an RCD, a registered electrical person must install appropriate earth leakage protection as part of the installation.

Generator Connection and Safety Advice

Managing Generator Load and Preventing Reverse Power

While Sunsynk provides general guidance on generator integration, their documentation does not detail specific inverter settings or procedures for dynamic solar throttling to maintain a minimum generator load (such as a 30% minimum) or for implementing reverse power protection.

The inverter's "Generator Settings" menu for Classic, Acure, and Elite models offers an overview of available configurations. These typically include parameters for generator start/stop conditions, such as battery State of Charge (SOC) thresholds or specific times. However, the available documentation does not specify how to configure the inverter to actively reduce solar production to ensure the generator carries a base load, nor does it describe built-in reverse power protection mechanisms.

Preventing reverse power is critical. If the inverter's output exceeds the load and battery charging capacity while the generator is running, excess power could flow back to the generator. This can be mitigated through careful system design, load management, and potentially external control systems or relays that monitor power flow and disconnect the generator if reverse power is detected.

What you can change yourself, and what you cannot

As a system owner, you can typically adjust basic generator auto-start parameters, such as the battery SOC percentage at which the generator should start and stop, or specific time-based schedules for generator operation. These settings are usually found within the inverter's menu under "Generator Settings" or similar.

However, any work involving the physical connection of a generator to your Sunsynk inverter, including wiring, earthing, and the installation of RCDs or other protective devices, must be performed by a registered electrical person. This work falls under the scope of a Certificate of Compliance (CoC) in South Africa, ensuring the installation meets national safety standards (South African embedded generation standards). Attempting to modify these connections yourself is dangerous and will invalidate your CoC. Similarly, advanced configurations for dynamic solar throttling or reverse power protection, if available, would typically require specialist knowledge and may fall under the purview of an authorised installer.

What the published sources do not tell you

Sunsynk's official documentation for Classic, Acure, and Elite inverters provides essential guidance for generator connections and basic settings. However, it does not explicitly address several key aspects related to advanced microgrid management for diesel generators:

• Minimum Load Maintenance: The documents do not specify how to configure the inverter to ensure a "minimum 30% loading" on the generator, nor do they detail "dynamic solar throttling" procedures to achieve this.
• Reverse Power Protection: There is no direct mention of "reverse power protection" mechanisms within the inverter or how to implement them.
• Wet-Stacking Prevention Settings: The guides do not offer specific inverter settings to prevent wet-stacking or carbon glazing, beyond the general advice on generator sizing.
• Detailed Generator Settings: While an "overview of generator settings" is mentioned, specific values for start/stop thresholds, power limits, or other parameters for generator integration are not provided in the publicly available articles.
• Fault Codes: No specific fault codes or warnings related to generator overloading, underloading, or reverse power conditions are documented.

This means that while the inverter supports generator integration, advanced strategies for optimising diesel generator performance and protection in a solar microgrid may require additional external controls, careful system design by a qualified professional, or information not publicly available in Sunsynk's support articles.