Solar Fraction (SF) > 100% in stand-alone PV + battery systems – clarification on E_User vs E_Load definition

[Rafael Vargas]

Hello PVsyst team and community,

I would like to clarify a conceptual point regarding the Solar Fraction (SF) in stand-alone (off-grid) or PV + battery simulations.

From the documentation and forum discussions, I understand that:

• E_Load represents the energy demand of the user (defined load).

• E_User represents the energy supplied to that user.

• Unused energy accounts for PV energy that cannot be used when the battery is full and the load is already covered.

• SF = E_User / E_Load.

However, in several simulations of PV + battery systems with no loss of load (LOL ≈ 0), I observe Solar Fraction values slightly above 100% (e.g. 101–103%), even though E_Load is fully covered and all excess PV production is already accounted for as “Unused energy”.

Conceptually, this raises a question:

If E_User represents the energy supplied to the defined user load, should it not be limited to E_Load, such that SF ≤ 100%, with all additional PV energy going strictly to “Unused energy”?

I understand that this may be related to the internal calculation sequence (i.e. E_User being evaluated before curtailment due to battery full), but I would appreciate clarification from the PVsyst team on:

1. Why E_User can exceed E_Load in the annual balance, leading to SF > 100%.

2. Whether SF > 100% is intended as a design diagnostic indicator of PV overcapacity, rather than a physically bounded performance metric.

3. If there is any recommended way to interpret or report SF in such cases, especially for non-technical audiences.

Thank you in advance for any clarification.

Best regards,

Rafael V