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Cumulative electrostatic discharges (ESDs) on spacecraft solar cells result in the degradation of their performances. In this paper, silicon solar cells are tested in inverted voltage gradient situation obtained in plasma. ESDs occurring on the cells are detected by both electrical and optical signatures. To be representative of flight ESDs, the test setup must avoid unwanted coupling with ground arcs. The degradation is then evaluated by measuring the current-voltage characteristic of the cell in darkness. The equivalent shunt resistance allows quantifying this degradation, which can be attributed to material deposition on the cell edge or to local cell carbonization due to arcing. Visual inspection of the cells allows us to correlate ESD location and local degradation of the cell. The important parameter for solar cell degradation is the amount of energy dissipated during the discharge. A model of the plasma expansion from the cathode spot is compared to measurement. This model explains the current rise during the first phase of the discharge, which is the same for normal ESDs and coupling with ground ESDs.