A 3V 150mA solar panel is a panel that has a 3V open circuit and a current output of 150 mA. 
The number of amps a solar panel produces depends on: 
The power of the solar panel
The amount of sunshine falling on the panel
The characteristics of the circuit to which the panel is connected
Solar panels can be used to: 
Charge 3.7 volt batteries for telemetry, fence chargers, automatic feeders, and electric gates
Provide battery trickle chargers and small power supplies
Solar panels are made up of solar cells that are arranged in a frame that is either rectangular or square. The size and weight of solar power panels increase as the number of cells increase.