Solar panel night light

[mike_mike]

Hello! I have a 12V/3W and a 12V/10W solar panel. I would like to build a solar night light, which will charge a battery in daylight and at night it will power on a few 5mm white leds.
I have the following problems:
1. Which type of battery should I use for this project ? The battery needs to survive when the temperature is high... because it will stay outside. Also, it need to survive at low temperatures, when it is cold outside.
2. I would like to use only one of the 2 mentioned solar panels.
3. I drew a schematic, please have a look and tell me what you think.

I know that there are MPPT solar chargers and circuits that I can buy from the internet... but my circuit needs to be simple.

[fordem]

Basic math ...

(How much power does your load draw) multiplied by (how many hours per day will the load be drawing power) multiplied by (number of days of autonomy (how many days of bad weather you want it to be able to work through)) = required storage capacity.

(How much power does your load draw) multiplied by (how many hours per day will the load be drawing power) divided by (number of sun hours per day your location gets) will give you an idea of how much power your panel needs to be able to deliver.

Type of battery cannot be determined without knowing how cold or hot your location gets, and these basic formulae ignore all losses so you're going to need perhaps double the battery capacity (batteries last longer if they are not fully discharged on every cycle) and perhaps double the panel capacity (conversion efficiency and also recharging after multiple days with bad weather.

I hope at this point my basic equations have brought you to the realization that you simply have not provided us with anywhere near the level of detail we would need to assist with a night light design.

[JimRemington]

Battery lifetime during periods when recharging is not possible can be roughly estimated from the battery capacity, in mAh, and the average current draw of your entire system in mA (lifetime in hours ~ mAh/mA).

Choose a battery with at least twice the minimum capacity you think you need, to account for nonlinearity and battery aging.

[Zero999]

I would use a lead acid battery, because it's easy to use and robust. The charging voltage should be limited by a shunt regulator, which will depend on the size of the solar panels. A single transistor can be used to turn the LEDs off, when the solar panel isn't charging the battery, with a diode in series with the solar panels to prevent the battery discharging, when it's dark. Connect the LEDs in strings of three in series, to save energy. Note that 5mm LEDs don't produce much light. You might want something brighter.