Charging NiMH batteries with 1W solar panel, charge controller needed?
If your goal is to make the working circuit as cheap as possible then direct connect is OK for your numbers - it won't charge very well but the battery will likely survive for a year or two. You'd still need a diode to prevent draining the battery through a PV at night.

If you're designing for maximum battery life then you don't want to trickle charge at all. Also, for outdoor environment NiMH discharge curve moves up and down with temperature while maintaining shape - you need to check max and min voltages for whatever temp. extremes your circuit is about to encounter.