Grid Down, On Batteries

For the first time since my Tesla solar panels and Powerwalls whole house battery backup began operating last December I’m having a significant grid outage. Everything is getting power from the Powerwalls. And I’m learning stuff.

My Powerwalls were at 100% charge fortunately, but now at 92%. There are two, total capacity 27 kWh.

When it started I threw all the 220V breakers… everything except the well pump. Which I eventually realized was silly, as only one of the ones I turned off draw power without me doing something. I’m not going to run the clothes dryer, or charge the car, and the stove won’t turn itself on by itself. So now only the hot water is off.

As I type this the Tesla app on my phone shows the house is using 0.5 kW total. Some of that is the computer I’m on, some the network, but a lot of it is all those things that are always a wee bit on. I think of this as the parasitic load. Garage door openers that are listening for commands. Everything with a clock that flashes after a power interruption. The TV and related boxes (cable, ROKU, Blue-ray). Everything related to the TV is plugged into a power strip, so I thought I could just turn that off or unplug it. But that strip also feeds the mesh box that gets WiFi at that end of the house, and I want that running. So I unplugged it from the strip and into the wall. Nope. There is one more box there, an ethernet switch that feeds all those devices I want off PLUS the mesh box. So I turned the strip back on, and all those things are drawing their token amounts.

The same sort of thing applies to my office, where there is a UPS and three power strips, two of which are plugged into the UPS and one that isn’t. I just didn’t think the arrangement through well enough. When this is over I have some reconfiguring to do!

Meanwhile the utility reports that things in my neighborhood have only gotten worse, and it may be multiple days before everything is restored. And with this weather my solar is contributing only 0.3 kw, compared to (at the moment) 0.6 being used by everything.

Powering down the computer is probably next.


But is it really a “backup” system if you are going to turn everything off anyway? If you stayed at 0.5kW, you have 2 days of backup. Do you think the outage will last longer than 2 days? Also, hopefully the clouds dissipate sometime within the 2 days any you start producing more than 0.3kW!

After Hurricane Wilma in 2005, we didn’t have power for 5 days.


Maybe it’s time to rent a Ford Lightning and plug it into your home?


Or a decent backup generator to recharge the PowerWalls from time to time…I’ve a little 2200 W Honda we use for camping, but they aren’t meant to run full time… An older 35ooW genset could be rebuilt, if I needed it, but if it’s out that long, we’re heading to stay with family somewhere…

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Is that with your fridge actually cycling on or off? That matters because it might consume <5 watts in standby but 200-400 watts when running. So I’d check your consumption when you hear the compressor shut off.

Before I got solar ~9 years ago (no battery backup) I opened all breakers in the house and one at a time turned them on then checked out what was plugged in and how much it consumed and wrote it all down. I was able to decrease my parasitic loads to ~150 watts. Lots of things I already knew the consumption for via a kill-a-watt meter, but many loads are wired in and/or difficult to unplug to measure.
For example my doorbell transformer is always on and consumes 3 watts. My built-in oven/microwave is 11 watts. Sprinkler timers 5 and 6 watts.



I picked up a 13.5k dual fuel on Amazon Prime day earlier in the year. It’ll run everything except the HVAC. (Well, not voluntary things like the dryer, etc.) Runs on propane, which we already have for the stove and fireplace - both of which will replace the HVAC heat if we need to, so that pretty much covers us. Cost $900. Was looking at a “whole house”, but at $25,000 the cost difference was just too much.

The only downside is that I have to walk outside and start it *(electric start) and throw the transfer switch manually, but for $24,100 I’ll get over it.


Thanks for everyone’s input. Power is back, and internet (and cable) restored. In some ways loosing the internet was a bigger PITA, leaving me with just my phone to connect.

I’ve only had the solar/battery system for a year, so this was very much a learning and experimentation event. Last year in December I could not sell power back to the grid. I could for my bill for January, but it was a very small amount. Since then I have never had to pay and have a large surplus built up. For December I am on track to use up some of that surplus, as the solar side is not covering consumption overall. Too many clouds, and the days are short. The capability of the system is TOTALLY seasonal, and December/January are the worst case. If this was any time May to September I would not have worried much at all.

Yes, I was overly cautious without a clearer idea of how it was going to go. As it happens, the skies cleared enough that in the afternoon the sun handled the load and even put a bit back in the batteries, from down around 92% to 97%. I turned several things back on because I saw that.

I have one refrigerator and two chest freezers. One belongs to my grandson, but both are pretty full of his venison. Loosing all that would have been a big disappointment. (Ironically, he is a lineman and working his posterior off repairing storm damage, but not around here.) I’m also on a well, and keeping that powered matters a lot. The oil-fired furnace (hot water baseboard heat) needs power, but not all that much, and today wasn’t especially cold.

Below is what today’s consumption looked like*. Gray is from the grid, green from the batteries, and yellow from solar. You can see that power went out before 6 AM, came back, then died again. The sun started to contribute around 10 AM; the yellow rises toward late afternoon not so much because the sun was stronger as that I turned things back on and drew more power. Solar generated 3.9 kWh today**. When it changes from green to gray again, that was the power coming back on. The huge spike is charging my car one power was restored.

At my last house I had a small, portable, borrowed, gasoline powered generator. It came in handy when a tornado took out trees and power for a few days, but it was warmer then, and everything that had it supported was in the garage. I thought about a real backup generator for this house, but when I went with Tesla solar panels adding the Powerwalls seemed like a simpler solution. Today it has shown what I expected it to show, that even on days with very poor sun I can get by.

*(I can also see the same sort of graph for the battery, solar and the grid. I downloaded the numbers for the day - so far - too. Numbers in kWh, to one decimal point, at five minute intervals. Normally I just save numbers at the one-set-per-day level, but I’ll keep today’s details just for fun.)

**(Yesterday it generated even less, 2.1 kWh. But the day before that, Saturday, 34.1 kWh, of which 24.9 kWh was exported to the grid.)


Hi @RHinCT,

Yeah. know what you mean except I don’t have reasonable cell service, so …

I added small UPS’s on:

  1. Sprinkler System: If it is running zone 3 of 22 spray zones when the electricity goes off, it did not resume. The UPS bridges the 30 second latency before the generator starts.
  2. Dish box: The electricity “always” drops when something is recording. Even a couple seconds drops it.
  3. Fibre interface box and the WiFi: This keeps my connection live so the 2 second blips don’t bother me.

My computer, monitor and direct attachments are all on my larger UPS.

My primary reason for buying the 24Kw whole house unit was to avoid any manual intervention. During a September storm, it ran for 6 hours at night. The A/C stayed on, the drip irrigation zones ran, I was on the internet when it first went down and nothing even blinked except the lamp on my desk for 30 seconds.

Sure, the generator was $11,000 installed including a winter kit w/oil heater, but having it all just happen without any intervention or loss of power in the house was worth it for me.

I did not put the shop on it though.

All holdings and some statistics on my Fool profile page (Click Expand)

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Gene, if I lived as far off the beaten track as you I’d probably have a whole house generator too! :sunglasses:

I actually have two small UPS boxes. Both were in place long before I got the Tesla system. One is for my computer, the other for the network modem and primary router. In fact I found out about the power outage first by the beeping of one of them. Strangely, it was complaining while it was getting power from the Powerwalls. Eventually I found on a Tesla owner’s discussion site that the problem with UPS units from APC complaining while being fed from Powerwalls was known. After a while they both shut up for the remainder of the outage.

Two mid range UPS’s here, for safety of the computers, and a nice line conditioner for the big screen TV, cable box… Any recording is, at least in Xfinity, done at their en, their server, then streamed, similar to On-Demand, really, small boxes, no HD or SSD, well, maybe a buffer, memory for apps…

We once had a lot of power fails as we were an early underfunded area of town, slices weren’t all that waterproof, so after a storm, a lot of banging about, thumping, dimming of lights, but the UPS’s protect stuff, even if we’re not home…

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