I think the minimum current rating of the solar panel is the minimum current required for normal operation.
If this is the case you can use a LM7809 to get 9V but you need to give a minimum load of 0.3A for the solar panel to operate.
The maximum rating of the panel is 7A and of 7809 is 1.5V, If you load either devices beyond this you might probably see smoke!
It all depends on you load. If your load consumes less than 1.5A, then you can use the panel along with 7809. If your load current is more the this, you need some other method.
BTW, with the 17V-20V input to 7809 from the solar panel to the 9V output means a drop out of atleast 8V. With the minimum current of 0.3A, this means a power loss of 2.4V just to keep the panel in normal operation. Like goodboy_pl says, it would be very inefficient.
I'd suggest that you go for Switched Mode converters (A Buck converter) to get the voltage. They need more components but are easy to make and would be highly efficient.