Estimate current produced by an IR photodiode on a typical sunny day
The photodiode data sheet gives you clues. For instance it says that the current produced from a light power of 1 mW per sq cm is typically 50 uA and no lower than 40 uA. Then comes the small print i.e. this is specifically at a colour of 870 nm and with a reverse bias on the diode of 5V.

Then there are more things to consider: -



The peak spectral response is about 870 nm but it also works quite well over the range 750 nm to 1060 nm (30% output levels). You then have to look into what specrum normal sunlight produces and calculate the "useful" power on a sunny day across this range colours. You can probably make a half decent estimate by using the 30% limits. Anyway sunlight looks like this: -



And across the range 750 nm to 1060 nm you could say it averages out at about 0.75 W per sq meter per nano metre but you'll need to check what time of day it is and how far from the equator you are to get the true picture.

Anyway, once you do all of that and assuming the figure is still 0.75 W per sq meter per nano metre, mulitply by (1060-750) to get watts per sq metre (232 W per sq metre). This is 23 mW per sq cm so you might expect to get about 1.2 mA.