Vpanel >> Vbattery so panel acts as ~~ constant current source.
2 batteries in series or 4 batteries in series will still be << 9V so charge in the same time.
Imp < Icharge < Isc or
0.33A < Icharge < 0.43A
Say ~~= 350 mA.
T charge ~= Battery_mAh / Ichg x 100 / Battery_efficiency %
NimH CURRENT acceptance efficiency probably 80%-90%
= 700 Mah / 350 mA x 100/80 ~~~= 2.5 hours
That's in full mid-day sun with panel square on to sun.
Charge for longer than this and you will quickly "cook" the batteries.
Vbattery_max at that charge rate should probably not be more than about 1.5V/cell when charging.
Google: your_city_name gaisma
eg Bangalore gaisma gives
http://www.gaisma.com/en/location/bangalore.html
to get SSH = sunshine hours per day (= kWh/m^2/day)
Your panel will produce ABOUT 350 mA x SSH mAh per day
Bangalore example -
Half a day on an average day will be more than enough in any month - see below.
Chart from Gaisma entry for Bangalore as above.
- It's common for a voltage source to drop in voltage when current is drawn. This is down to the source resistance inside the voltage source. When you measure the output voltage of the panel without it connected, then you a measuring the voltage of the panel without any current passing through its internal source resistance. When current flows, it passes through that source resitance and there is a voltage drop across it, so the output voltage now drops.
How much the voltage drops when under load depends on how much current you are trying to draw and the internal source resistance of the panel.
a) It could be natural and a function of the solar panel itself.
b) You could be drawing too much current from the panel and the voltage drops greatly.
Battery discharging: it could be that the battery is pushing power back into the panel. You can stop this by putting in series a suitable diode.
You'd have to measure voltages and currents to work out what it is going on, measure the battery voltage with the panel disconnected at this point. An ammeter in series will tell you which way the current is flowing and hence which voltage is greater than the other and this will help you work out what is going on.
Answer: Yes.
I can't answer, I don't actually know what's defined by 'bulk charging'.
Best Answer
I see no reason this wouldn't work. Of course, you can only charge a single cell at a time with the Max1555, but you should be able to connect the solar panel directly to the chip as the Max1555 accepts input voltage from 3.7 - 7 V. As long as the output voltage from your solar panel is going to stay in that range I think you'll be fine. Just be aware, 100 mA could take a long time to charge your battery, depending on its capacity.