Can a 3,4V (open circuit voltage) solar panel charge a 3,6V NiMH battery pack?
You would need a higher voltage as 3.6v cells usually charge up to 4.1v or there abouts. You also have to consider thermal effects on the panels(I think telefox eluded to this). 6.5v in direct sunlight on a good day...my panels would drop close to a 1 volt and sometimes more due to the panels heating....I think it's called thermal breakdown or something along those lines...I originally had the panel pushing around 5.25 but the v dropped too much for the vreg and charger to work effectivly.
To be more specific, I was thinking about using this and this (lol sorry for the quality of my English):
but I guess I'll use this with a 1N5817 diode (to prevent the batteries from discharging through the solar panel when there is no sunlight). That will give 18mA at short-circuit and the 300mAh battery will be able to dissipate the extra heat for an any period of time.
Would the 4.5V solar panel work? Or is that too much?
The actual solar panel voltage will drop (sometimes by quite a lot) when feeding the batteries, so you won't be able to charge the battery pack directly to full.
You can either add another panel in series to increase the voltage, or you can use a boost converter (AKA step-up converter) to increase the voltage output. You can probably find a product that integrates both a booster and NiMH charger.