Autonomous WLAN Router Experiment: Part 1

I’ve been wanting to build an autonomous WLAN router for quite some time. That WLAN router should be powered by a solar cell and a battery. I have spoken about the TL-WR702N at RaumZeitLabor a while ago, and it is very small, draws 150mA max and is therefore suitable for such a project.

Some time has passed, and yesterday Doozer gave two Lead–acid batteries to me, rated 12V 5Ah each. So now I have to do this project!

I’ll use one battery for the project. I have made the following assumptions:

Ed: Average daily electricity production (kWh)
Em: Average monthly electricity production (kWh)

  • The router will permanently draw 150mA at 5V, or 0.75W (worst-case)
  • The solar charger circuit will have a power requirement of 15mA at 12V (0.075W)
  • The DC-DC converter I’ll be using has an efficiency of 80% (worst-case assumption, will probably be much higher)
  • To be on the safe side, all further calculations assume that our overall power usage is 2W
  • Overall yearly power: ~18kWh, 1.5kWh per month
  • Using the interactive photovoltanic calculator (linked below) I was able to calculate that a 20Wp cell is not sufficient from October till February.
  • As we assumed the worst-case scenario, and this is an experiment only, I decided to go with two 20W panels, where I’ll experiment with one panel, then two if it’s not sufficient.

I now have to buy the solar panels and the charge controller, which I’ll do in may.

Useful resources:

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