I am trying to use rechargeable batteries. If I recharge two of the below batteries via the solar panel below, how many hours will it need to recharge to 100%? Likewise, what if I recharge four batteries?
Batteries:
- Rechargable NiMH AA HR6 1.2V 700 mAh
Solar panel:
- Related Maximum Power: 3W
- Voltage at Pmax: 9V
- Current at Pmax: 0.33 A
- Open-circuit Voltage: 10.5 V
- Short-Circuit Current: 0.43 A
- Normal Operating cell Temp: 47 +/- 2 C
- Maximum Series Fuse Rating: 10 A
- Operating Temperature: -40 C to 85 C
- Application Class: Class A
- Cell Technology: Ploy-Si
- Dimensions: 306 x 148 x 15 mm
Best Answer
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
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.