1. The future planning is for V2.1 Charge controller is to  implementing 3 stage charging algorithm. 

2. Hardware modification for better control 

3.  Option to implement multi chemistry  battery charging 

4. Adding a USB port to charge USB charging gadgets like smartphone/tablets.

5. Making a custom PCB for the  circuit.

6. Making a 3D printed enclosure for the project.

7. Adding an ESP8266 for remote monitoring through Smartphone App

PWM Charge Controller -V2.1  Algorithm 

When the controller is connected to the battery, the program will start the operation.

Initially it checks if the panel voltage is sufficient for charging the battery. If yes, then it will enter into the charge cycle. The Charge Cycle consists of 3 stages. 

Stage 1 Bulk charge: 

Arduino will connect the Solar Panel to the battery directly ( 100 % duty cycle). The battery voltage will increase gradually. When the battery voltage reaches 14.4V, stage 2 will begin.

In this stage current is almost constant. 

Stage 2 Absorption charge: 

In this stage Arduino will regulate the charging current by maintaining the voltage level at 14.4 for one hour. The voltage is kept constant by adjusting the duty cycle. 

Stage 3 Float charge: 

The controller generates the trickle charge to maintain the voltage level at 13.5V. This stage keeps the battery to be fully charged. If battery voltage is less than 13.2V for 10mins,

The charge cycle will be repeated. 

Load Control: 

In the evening, when the PV voltage level falls to +8V for 5mins, the controller will turn on the light. In the morning when the PV voltage is larger than battery voltage for 3mins, the light will be turned off.

Low Voltage Disconnect: 

The charge controller will disconnect the load from the battery at LVD point, 11.5V.

Low Voltage Reconnect: 

Once the load is disconnected, it will reconnect again only when the battery voltage is more than LVR point, 12.5V

Set point values

Float set point: 13.5

Bulk set point: 14.4

Charge Restart set point: 13.2

Absorb time limit: 1 hour

Charge restart time limit: 10 minutes 

Offset for AGM (vs flooded): -0.2 

Low voltage disconnect: 11.5

Low voltage reconnect: 12.5 

Temperature compensation: -20 mV / degree C