I had two ideas how I can increase the lifetime of the whole system. First, I can add a solar panel to charge the powerbank, this will increase the lifespan of the whole system. Second, I am building my own external timer two completly shutdown the ESP board will all its components.

The Solarpanel Idea

This is my current circuit to stabilize the output from the solarpanel to charge the powerbank. The solarpnale outputs somewhat between 0-8V, I feed that into a DC/DC to convert it to 5V and use that to charge the powerbank.

The charging lamp is on so I guess it is working.

All is 5V so I will use Ah instead og Wh or J. If the system needs 10mA at most this will be 240mAh per day, So if I get 50mA over about 5h it will be enough to operate for that day. The only window I have is facing west, so we can say we got 2h at most, lets say it still has gets 100mA somehow, so we have 200mAh. Lets say the ESP only needs 6mA (min I mesured), so we have 144mAh per day.

It can work, I have to see how long the system keeps runningn until it runs out of energy again... It will atleast runs longer than 7 days, so we have an improvment here.

External Timer

Completly shutting of the ESP8266 has tha major problem of data loose. Currently I am using the volatile memory which will be held as long as the ESP gets some juice, but as long as its unpowered for more the an hour the data is lost. A good low power solution seems to FRAM, I could also use an SD card, but they tend to need more power.

Most likely the external timer will be an NE555. If I get the timing to be about 50min off and 10min on, I can execute longer operatipns (like uploading all the data, or actually watering the plant). To still save energy I can use deep sleep. Actual experimenting will most likely proof better timings.