Recoverable energy in photovoltaic systems with submodule level dispersion losses

•In the past, dispersion due to ageing has been analyzed at the module level.•The paper presents novel submodule-level measurements of PV modules which are 7, 8 and 9 years old.•The dispersion of the maximum power point current exhibits higher values, with respect to previous literature.•A new statistical model to account for the distribution of the maximum power point currents is proposed.•The new model predicts that the recoverable energy due to submodule-level mismatch is in the range of 4–6%. Photovoltaic (PV) ageing is known to cause a linear degradation of the short-circuit and maximum power point currents, which results in the corresponding power loss. Nonetheless, besides of degradation, also a dispersion of these currents has been reported in the past. Such a dispersion induces significant mismatches in the PV system, even in the absence of partial shading, further increasing the power loss. Such a phenomenon has attracted the interest of investigators, as the fraction of power loss due to mismatch is recoverable. Nonetheless, all previous works have considered module-level ageing data, whereas the recoverable power at the submodule level may be larger. This paper investigates the effects of ageing at the submodule level, and compares the results with previously reported data. It is shown that previous works have underestimated the amount of recoverable power, and that the lifetime improvement of the energy yield may add up to 4–6% of the total.