At Fox ESS, we’re often asked about PV oversizing—connecting a larger solar array than the rated power of the inverter. The good news? PV oversizing is not only permitted with our inverters, but it’s also a widely accepted design strategy that can optimise overall system performance.
However, there are a few important things to understand about how this works across different Fox ESS models, and some key design considerations to keep in mind.
Model-Dependent Oversizing Ratios
Fox ESS inverters support PV oversizing, but the maximum allowable oversize ratio varies depending on the specific inverter model. For example:
- Some models, particularly in our hybrid range, allow PV-to-inverter ratios of up to 200%.
- Others, especially smaller or single-phase units, may support lower oversize thresholds—typically around 120–150%.
Always refer to the technical datasheet for your specific model, or use design tools, to confirm the permissible oversize ratio.
String Design: Keep It Balanced
When oversizing your PV array, string design becomes even more critical. Here are the top rules:
- Keep the strings balanced: Ensure equal string sizing into each MPPT (Maximum Power Point Tracker) channel. Uneven string lengths or mismatched panel configurations can cause energy losses and underperformance.
- Stay within MPPT voltage/current limits: Make sure your design keeps the string voltages within the operating window of each MPPT. Exceeding these limits can lead to shutdowns or inverter damage.
- Always use solar design software: Tools like OpenSolar, PV Sol or Easy PV can help validate system parameters and maximise yield safely.
Understanding Clipping and Its Role
Oversizing your PV array may result in clipping, where the inverter limits power output during periods of high solar irradiance (e.g., sunny midday hours). This is expected and acceptable.
Why do it then? Because oversizing allows you to:
- Capture more energy in low light conditions (morning, evening, cloudy days)
- Boost your overall generation across the year, even if some peak output is curtailed
In short, you’re trading some peak-time energy for greater production when conditions are less than ideal – a worthwhile trade-off in many climates.
G98/G99 Compliance: It’s About Inverter Output
A common misconception is that oversizing PV affects your G98 or G99 application. It doesn’t.
G98 and G99 relate to the inverter’s output capacity, not the size of the PV array. As long as your inverter output remains within the declared limits, you remain compliant—even if your PV array is significantly oversized.
Hybrid Inverters: More Flexibility with Batteries
For systems using Fox ESS hybrid inverters with batteries, PV oversizing becomes even more advantageous:
- The inverter can charge the battery via DC-DC coupling, meaning excess PV power can be stored without first being converted to AC.
- This allows greater effective utilisation of the oversized array, even if the inverter is output-limited on the AC side.
- In some cases, the inverter can simultaneously export to the grid and charge the battery—effectively using more power than its rated AC output.
This makes hybrid systems particularly well-suited to oversizing strategies, especially when paired with time-of-use tariffs or self-consumption goals.
Final Tips for PV Oversizing
- Check local regulations and DNO requirements—some areas have export limits that may influence your design choices.
- Avoid oversizing for the sake of it—there’s a point of diminishing returns. Oversize thoughtfully and in line with your system’s goals.
- Always consult Fox ESS documentation or our technical support team if you’re unsure.
In Summary:
- Oversizing is supported across our inverter range—ratios vary by model
- Keep string sizes balanced and voltage within MPPT limits
- Use design software to validate your setup
- Clipping is normal and balanced by greater low-light generation
- G98/99 relates to inverter output, not PV array size
- Hybrid inverters can take advantage of DC-coupled battery charging
Need help with your design? Get in touch with the Fox ESS technical team or use our official resources on this website for tools, datasheets, and guidance.
