The application here is for an elderly woman who lives alone in a very modest 1200 sq-ft house.

The Powerwall can provide more-or-less whole house electrical back-up from it's solar recharged batteries.   The intent here, though, is to forego the cost of solar (the house is heavily shaded anyway) and recharge the batteries instead from normal utility power.  From the specs on the Powerwall and looking at the last 12 month's of the woman's electrical bills, the 14 kWh unit should provide 20-24 hrs of whole house back-up power w/o air conditioning.   Since she's home 90% of the time, if she loses power in one of the 3 summer months, she can simply shut off the A/C until utility power is restored.  If the power failure is expected to last longer that 24 hrs, which has not happened in the 20 years she's lived there, she has time to make preparations to leave.

Overall, this looks great with it's estimated installed cost of $7k and 10 yr warranty ... and no hassles with the routine servicing of a conventional natural gas powered whole house generator that I experience.  

Comments?

If the powerwall actually likes charge/discharge cycles and the power companies increase rates at peak demand times, you could in theory setup this thing to chatge offpeak and provide some savings.

Our local utility installed "smart" meters county wide a few years ago and offered a version of this service, but they discontinued the program after one year.  I think they lost their shirts and made more money with the old system, selling electricity at a premium during periods of high demand.

Our Generator was cheaper.  

We typically have several power outages a year and the longest outages have lasted us three days.   When our first generator exceeded 600 hours  we installed a 20kw Generac for less than you are quoting for the powerwall.    We are rural and use propane for heat. hot water etc.....   We had our propane supplier upgrade the size of our tank which they did so at no charge.   Now we have a 1000 gallon tank that is almost never below 70% full and it is connected to our on demand generator.   Should we have an extended outage we should be able to go for a couple of weeks without issue.  

We can also run our A/C.   That COULD be significant issue for an elderly person in the summer months.  

We do still have outages and we have them often.   We barely notice them anymore.   The power goes out, the generator starts, and the lights come back on.   When the power comes back on the generator turns itself.   This also could be helpful for an elderly person living alone.

We don't know the cost of running the generator either because it is spread out over the year in our propane bill.  We haven't noticed an increase in usage in propane so it shouldn't be too much.   This could be an issue for someone on a fixed income.  

As always, YMMV.

2Hut8

Thanks for the feedback.

Having propane already available makes a propane powered generator a good choice.  The Powerwall's cost is not a problem, though,  for this woman (I'm giving it as a gift) ; I just want a bulletproof and maintenance free source of backup power.

BTW, here's my 48kW Generac Post from 2011 (sorry that the links to the photos are dead).  I've put 250 hr on the Generator since the installation  almost 8 years ago.  With the Windsor motor powering my Generac, I consider 250 hours equivalent to about 10,000 miles on a car, and I'm hoping to drive it a 100,000 miles

I remember that post.   The information that it contained was factored into our decision to purchase our Generac and the options that we included with it.  

2Hut8

14kWh of energy storage will give you 700W of power for 20 hours.  With that you can run a refrigerator, a TV, and one or two lights.  The electrical bills you're looking at average in the hours she's asleep or not home and drawing less power.  If she's asleep or not home when the power is out, it wont matter what backup she has; if she's awake and home, she's going to be drawing a lot more power than the average from her bills, and a battery backup will run out much sooner than 20 hours.  The other fatal mistake of taking a year-long average of power usage is that lower power months (usually winter) will mask the true demand of high power months (usually summer).  If the power goes out in the summer, she can't just wave a stack of electrical bills at the Powerwall to make it provide the juice she needs.  You'll have sized her a solution based on lower demand than she really has.

Her choices will realistically be:
1.  Get the battery.  When the power goes out, turn most things off, unplug others, and get power usage down to the bare minimum to see if she can wait out up to 20 hours.
2.  Get the battery.  When the power goes out, run things like normal and run out of power in, realistically, 10-15 hours, hoping the power comes back on before the battery is dead.
3.  Get the whole house generator.  Stop worrying and barely notice that your neighbors lost power.

The Powerwall is not a solution for whole house power supply.

I have no experience with this particular unit but want to point out several things, if you don't mind.
I could not find any information on the PowerWall unit's output rating and specs. Is it 240 VAC, dual pole with neutral or is it just a simple 120 VAC (hot and neutral) output? In layman's terms, a standard 240 VAC house system has two "hot" wires and a shared neutral wire. "hot" to "hot" measures at 240 VAC and "hot" to neutral measures at 120 VAC. Neutrals must be grounded at the main SES breaker box. This is important because all houses have 240 VAC system and a 120 VAC backup source may only power a portion if the house and will not run any 240 VAC appliances.
You will need some kind of a transfer switch. A transfer switch may be wired to power the whole house or only some receptacles and appliances that must operate during an outage. A automatic transfer switch will cost a lot. There is a way to install an inexpensive manual interlocking linkage bracket to switch the power from city power to a generator/battery power manually. She will also need to manually switch off the breakers for the major appliances that the battery cannot run.
Also, there is a term called - Zone Heating or Zone Cooling. She does not need to suffer from heat if the power is lost and her battery or a generator can't run the central A/C unit. She can purchase a $99, 5000 BTU, 120VAC window air conditioner and install it in the room she wants to be kept cool (usually a bedroom). A 5000 BTU window unit will only draw about 8 amps when running but will keep one room at a comfortable temperature.  

Just my 2 cents....

Not to hijack but the pictures are dead and I'm curious to see the installation details as well as a review of the generator and lessons learned if you were doing it all again from scratch. Very curious, I've contemplated this type of project before (with less than half the size generator) but never followed through.

IMHO, I would not spend that kind of money just to get 20 hours of back-up power.  I would look into a NG powered modestly sized back-up generator that will just kick on when the power goes out.  Or maybe it could be hooked up to a propane tank if NG isn't an option.  That may cost a little more than a powerwall but it would be more of an actual solution.

Spend 4 to 6 grand on a battery with limited capacity & finite life or buy a diesel generator(or a couple Eu 2000's)?

The cost/use ration doesn't sound all that great, but it's a package so a lot will appreciate that.

I have thought of getting one for my parents that are in there 80s but its not enough juce for there needs. I would need 4 and that's just prohibitive.
I think a forklift battery with an automatic waterer would serve better for my needs.
More maintenance than I want but much cheaper.

While Tesla gets all the press, they are hardly the only company selling home battery backup systems. Many other options exist.

Detailed specs on the Powerwall are extremely difficult to find, and Tesla has not responded to my requests for additional information (not a good sign).

I did find a FAQ that says the Powerwall is simple 120 VAC only. Three Powerwalls can be used to provide power to 3-phase homes, or the addition of a "Fronius hybrid inverter " ... more and unacceptable cost.  The 240 VAC in her home supplies power to only her central A/C and clothes dryer.  During an outage, she can do without the clothes dryer, and your small bedroom window mounted 120 VAC air conditioner is an excellent and simple solution.

And thank you for your comments and suggestions.

I have never heard of a three phase home. Hobby machine shop with big motors? Even then I'd suspect they would use a converter. Perhaps a giant mansion with commercial HVAC?

On demand automatic standby generator hooked up to the propane FTW here.

She will want/need air conditioning should the power be off during a warm spell. I would not expect her to be able to mentally/physically turn off and un-plug everything not necessary every time the power is out to make her batt actually get that 24 hours. And ONLY 24 hours. You can run for a LONG time on a 500 gallon propane tank, even if you abuse the engine and skip changing oil. If she has a full fridge, all her meds, food/water, heat/air conditioning, why leave after only 24 hours? I mean a summer storm can easily knock out power for more than 24, and the world doesn't go all Mad Max during that.

I'm sure your already aware, but the better standby units even self exercise monthly.

ETA: The other thing is heat. How long would that batt run the furnace? Its easy to freeze to death quickly after an ice storm knocks out power, and after an ice storm is NOT the time to bug OUT, but to hunker down.

If your going to spend that kind of money go with an automatic whole house generator.  It will not only raise the value of the home a bit, but will actually provide the necessary power when needed.
Don't get me wrong, I am all for off grid electric options, but reality is they are not there yet.  Not affordable compared to the old standards.

If you have money to blow go for it, but if you are trying to be somewhat frugal well...

Same for an electric car, I really want an electric car but they need to bring the range up to about 150~200 miles to make it realistic for me.  The hybrids IMHO are worthless.  Why spend double the cost on a vehicle just for an increase in mpg.  Do the costs difference weigh out over the life of the vehicle. -NO.  They are getting close but still very hard to justify when you compare the numbers.  Again close but I want significant savings, nut just to say I own a hybrid car.

You still have to get 120 power to each of leg 1 & leg 2 in order to power all circuits, even if they are 120. Which involves some sort of switching equipment that will short Leg 1 to leg 2 in the event of a power failure, but detect and break that short BEFORE damage occurs once power is restored. An automatic transfer switch (like those used on auto generators) could likely perform that task with a little creativity, but it's another "step" and added expense.

Backup gennies aren't really that maintenance intensive. The ones I've seen auto-start once a month to keep the engine in good shape, keep the battery topped off, and reduce condensation in the oil etc. In all reality, an auto backup generator could likely go several years with little to no maintenance and still function in the event of a power failure.