we are trying to reduce a solar panel from 9 volts to 3 volts. What do we need to make this work…
Solar panels generate DC power. Changing DC voltage is hard, which is why the power grid is AC voltage. AC voltage can easily be changed with a transformer.
To keep the DC power (watts) the same at a lower voltage you need a DC to DC converter. That basically changes the power to AC with an inverter, changes the AC voltage to the new value, then rectifies it back to DC. It is probably hard to find a commercial unit that handles those voltages and then it will be expensive.
But I have a simple solution in the special case of a solar panel. Solar panels are made up of smaller solar cells. The basic solar cell has a very low voltage, like half a volt. The panel has many of them connected in series to make a higher voltage. Just cover (shade) some of them and the voltage generated by the panel will be less. Of course that reduces the power. And you may need to experiment with shading different parts of the panel and measuring the result with volt meter.