Starter circuit for solar module driven pump motor
The problem is your solar panel can't source that much power with that much load, look at this curve:


Source: https://arstechnica.com/civis/viewtopic.php?f=26&amp;t=1402629

If you draw more current from the cell you get less power. People have fixed this problem long ago, you need a MPPT tracker to regulate the voltage to 24V.

The second problem is power, the motor won't start unless you have enough starting current. Make sure you size your solar system (and MPPT tracker) to have enough power for the starting current. If you need 6A of starting current, you'll need 144W of power. If it's 12A you'll need more.