We have a Tesla Energy PV system and two Powerwall 2's which were commissioned about two months ago. We live in the Phoenix AZ area.
A few days ago, during a thunderstorm, my wife and I were working at our computers in our office when, at 4:30pm, we noticed that the lights flickered off once, and our DSL modem retrained. Our computers were unperturbed. Such a flicker is not all that unusual during thunderstorms, so we went about our internet activities. But about 10 minutes later, I started thinking, "what if there was a power outage, and our home batteries were switched in?" I looked outside, and sure enough, the neighborhood was dark, and we were the only ones with power. I might not have known.
The Tesla application revealed that our battery system was indeed powering the house, and the solar panels were providing no power due to the clouds.
When we realized that we were on backup for a yet undetermined period of time, we increased the thermostats from 80 degrees F to 85 degrees F and turned off unnecessary lights and phantom loads. The main loads resulting in the 0.7kW draw were the refrigerator and a medical device required for recovery from a recent hospital stay. We left a few house lights (LED's) and fans on, but turned off the outside lights to avoid being accused of witchcraft. Our home network, router, and modem were left on. The result was a 0.7kW load.
The backup power source consists to two Tesla Powerwalls 2's in our garage configured via the application to retain a 45% reserve for possible outages throughout all of their activities.
Given the reduced house load, that reserve would last us about 12 hours. After that, we would not open the refrigerator and we would need to use (and possibly order additional, which had me a little worried) mechanical backup for the medical device. The utility company's web page indicated that the outage in our area was projected to last until 8:30am the next day, but they're usually pessimistic. Nevertheless, we had to plan for that.
So, we didn't watch television or listen to the stereo, but we did use the kitchen facilities (blender, seed grinder and lights, while opening and closing the refrigerator numerous times) to make smoothies. And we read and surfed.
I periodically checked the application for status to monitor our reserve capacity, and eventually, round 9:30pm (five hours later), the application indicated that the grid was back up, and the battery reserve was no longer in use.
If we had known that the outage would have been this "short," we may have streamed a movie on our big system or cooked a meal with electric appliances. But, we plan for the worst.
The outage depleted our 45% reserve to 32%. I was concerned that the following day, with extreme AC demand and cloudy weather, there would not be enough excess PV production to recharge the battery to the reserve threshold. However, as soon as the sun came up, all PV production was diverted by the energy gateway to the batteries, and when I got out of bed and checked, the capacity had already been replenished to 45%, and normal operation had resumed. I was impressed with the sophistication of this control algorithm, and overall, my expectations have been exceeded.
One problem that I see is that, whether we were at home or away, we may not have been aware that an outage was in progress and would have gone about running the AC and pool pump and charging the car, thus depleting the battery much more rapidly. We have to keep an eye on that. Since the application runs on a mobile device (not windows, unfortunately ... we had to acquire an android device specifically to run this application), we can monitor the system remotely and get home quickly if we need to.