this is the cheapest solution.. every other solution is 20k + in a quality product or just buy a proper hybrid inverter.
the ore batteries you have, your 24V or 48V system will be able to draw more power easily and charge more batteries, more backup, less load on CC and many many other advantages.. it is not necessary to buy the biggest batteries with solar power, it is important to buy the max num of batteries you can get, even much smaller..
40 amp power is rater for 48V operations. divide by 2 for 24V, divide by 4 for 12V .. one battery will only be able to handle what exact power it requires. max charging for a 12V battery should not be higher than 15amps.. MAX.. usually 8-12A is enough. rest of your power is going waste unless utilized by appliances if you dont have more batteries.
also, manually turn off wapda switch yourself.. use mobile alarm for reminder daily
Real men do it manually.!!