Solar panels do not obey Ohms law, or have a fixed Thevenin equivalent to calculate from.
The problem is that unlike say a battery, the output voltage and current are not linear with increasing load, and the whole thing also varies with how much sunlight there is.
You are never going to see both maximum open circuit voltage, and maximum short circuit current together.
Another problem is there are different types of solar panel technologies, from very efficient to very crappy performance. So its not really possible to even guess what to expect. You will have to actually get one and test it.