Solar panel used to power fan directly probably not the typical brushed motor is pretty voltage tolerant.
Direct connection to solar panel.
How to wire solar panel to 12v battery and 12v dc load 12v dc fan light etc dc load only.
These can be an inverter 12 volts dc box or both.
Connecting solar panels in series the series connection is done by wiring the positive terminal of each panel to the negative terminal of the next panel a connection similar to the ones of the christmas lights until the final panel is connected to the charge controller or inverter.
Direct current motors are the easiest and best motors to power with solar panels.
The lcb takes solar panel power at low current and fixed vmp vmp i sun and converts to high current low voltage used to start the pump motor.
Install solar panels on your roof with the help of a professional or a do it yourself solar kit.
Add a blocking diode on the positive rail between the battery and the panel or as previously suggested and the best solution imho use a small solar charge controller.
A complete note on solar panel installation.
Connect battery to charge controller in the first step you are going to wire the battery to a charge controller.
How to connect a solar panel to a 12v battery.
It is very possible though that you will need a larger solar panel to start the fan and run it under less than full sun.
Wiring the loads the following step is to wire the loads.
Solar panels are more or less current sources 50 sun 50 torque.
Series connection of batteries with solar panel or how to wire 24 v solar panel to two 12v batteries with automatic ups system.
Alternating current motors can also be powered by solar panels but they require a power inverter to change the direct current of the solar panels to alternating current to feed the motor.
Solar panels when there is at least weak direct sun run a constant vmp and low isun current.
If you keep the panel connected as shown in your diagram it will absorb some power when it is not getting sunlight.
You should try to supply about 5000 watts.