A "constant voltage" source. Solar panels, for the most part, are "constant current sources". If you have an Imp = 10 amps solar panel (current maximum power)... Under full sun the panel will (for a first approximation) output 10 amps from zero volts to Vmp (voltage maximum power).
With 10:1 current increase only causing 10% or 8% increase in voltage, the solar cell seems Constant Voltage. To clarify, at constant room temperatures, the saturation current will remain constant?
Much like voltage, there are two important values for current. The first is the short circuit current (Isc). Isc is the maximum amount of current a module can supply and it occurs when the module is shorted and there is no voltage produced by the solar. The second important current is the power point current (Ipp).
Solar panels produce Direct Current (DC) voltage. They can be built to provide nearly any DC voltage. The voltage of the panel is impacted by cell size, cell construction, number of cells, panel size, and panel wiring. The result is panels from 0.5 volts to near 50 volts. Each volt range has a use.
There are two voltages that are important for a solar modules. The open circuit voltage (Voc) is the maximum voltage that the cell will produce and it occurs when there is no current supplied by the module. The power point voltage (Vpp) is the voltage at which the maximum power is available from the cell.
For instance, on a sunny day, a solar panel might produce a higher current compared to a cloudy day. Wattage, measured in watts (W), is the product of voltage and amperage (W = V x A). It represents the total power output of a solar panel.