Last year, I had a Tesla solar power station and Powerwall battery installed at the house. The system can display a cool little graphic that shows how much power the house is using, and whether it’s coming from the utility grid, the solar array, or the Powerwall. It also shows when the Powerwall is charging and when the system is selling excess energy back to the utility. The charge state of the Powerwall is also displayed.

I find watching the system status fascinating, and watching it has allowed me to fine-tune the system and likely save a few pennies (maybe even dimes) in power costs. I found, though, that I constantly felt the need to unlock my laptop or phone to glance at the power.


I have never found a use for a tablet in my life. They seem cool enough, but I could never really figure out anything to do with one. Nonetheless, when I found a decently-specced Asus tablet on Woot for $40, I decided to buy it. I figured that Josh could play with it, learn some things about Android OS, and maybe come up with a use for it. Or, perhaps, when I actually had one in my hands I would be hit with an inspiration of some cool thing I could make it do.

Neither really happened. Josh played with it for a bit, and I had some ideas. I thought that perhaps it could display the app for my Netatmo weather station or my Tesla solar, but the version of Android it was running was too old to support any interesting apps. I couldn’t even get the Carrot Weather app to run on it.

I was hacking the Powerwall to try to improve its scheduling to better match my utility’s time-of-use billing, however, and I discovered that the Powerwall has a built-in web server will display a similar cute animation to the app; actually better in that the display is much more real-time than the app: you can watch the power flow change as a cloud floats between the sun and the roof. So, methought, I could use that display to have an always-on view of the solar array. I was disappointed, again, when the animation refused to run on the tablet’s default Chrome browser, but Josh loaded Firefox on it, and the animation displayed like a charm.

3d printer

I then needed to mount it on the wall, so I designed some brackets using FreeCAD and printed them. They hold the tablet perfectly. I will put up pictures and files for the brackets once I get my Macbook Pro back from Apple — it’s there having a cracked screen replaced.

adding weather

Having just the solar display looked rather lonely, and one thing I also wanted was an hourly weather prediction. A local TV station had just what I needed, but the Android tablet had no provision for a side-by-side display. Instead, I wrote a simple little web page that I put on one of my servers that put the Powerwall website and the TV station weather report in side-by-side iframes and refreshes the weather every 900 seconds:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
<html lang="en">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<meta http-equiv="refresh" content="900">
<base href="">
<!-- tesla powerwall status -->
<iframe src="https://10.-.-.-" width="41%" height=470px>
<!-- KCRA hourly weather -->
<iframe src="" valign=top width="57%" height=470px>

(Yes, you can access this page at, but the Powerwall status is local to my network so all you’ll get is the weather and probably some ads that are filtered from my network.)

So one $40 tablet, probably $500 in engineering time, and I have a cool solar array and Powerwall monitor with integrated weather display. Tablets aren’t useless after all!