Tesla Powerwall versus generator

After two storms that knocked out power for hundreds of thousands of people in Massachusetts, where we agree to disagree with the Germans on the merits of underground power cables, folks are talking about their backup solutions. Here’s one message thread:

  • Exurbanite: We have no power. They are talking Tuesday or wed.
  • Me: How long can your gen run? [he is not on a gas line]
  • Exurbanite: About three weeks if I don’t get more fuel. But I can get fuel any day I want. My friend got a stupid Tesla power wall. I told him not to. I calculated that the Tesla battery is equal to one gallon of propane.
  • Exurbanite: I have 500 gallons.
  • Exurbanite: After the first night he woke up. Battery was at 18 percent. And that was with him conserving.
  • Our mutual friend: I am sure the UI is nice!

Readers: From the perspective of a single home, are power outages actually more common and/or longer than in the good old days? Or are we just more addicted to our electrically powered conveniences?

Personally I still like the idea of rooftop solar plus battery (though maybe not too useful after a big snow!). It is silent and does something useful when there is no outage. But my friend’s 500:1 comparison makes it seem ridiculous!



  1. Joe

    March 12, 2018 @ 12:59 pm


    I think they’re probably about the same, at least from my experience. But now that things like septic pumps are (generally) mandatory, as well as electrical control systems for furnaces, we need the power a little more desperately.

    I have a 5kW gasoline generator, cost around $1500. Paid an electrician $400 to wire an inlet. Powers the whole house easily (at least w/o the range or dryer), and a couple of jerry cans of fuel lasted 40+ hours during the last storm. Easy peasy. Propane is an excellent option if you don’t mind the huge tank.

    No maintenance needed, just check the oil once a year or whatever.

  2. Mike Bentley

    March 12, 2018 @ 1:18 pm


    A Tesla Powerwall and a backup generator do not solve the same problem. The Powerwall is used every evening to extend the useful range of solar-provided power into the evening and night hours (and for charging electric cars). A backup generator replaces the solar panels and can be used to charge the Powerwall.

    There’s a huge difference between the solar panels and Powerwall and a power generator, in that the power generator is as loud as can possibly be, with the exception of higher-end Honda generators. Generators also have quite a few moving parts compared to solar panels and Powerwall.

  3. Farshad

    March 12, 2018 @ 1:29 pm


    The answer depends on where you live, what appliances you have, how much power, what is most important to you, …

    I live a in a small town outside of Boston/Cambridge. We have a well, which needs a 230v pump for it to be of any use. Most furnaces won’t run without electricity either. Propane is the best choice for us because the generator doesn’t need cleaning. Otherwise it will have to run the noisy cycle once in a while—annoying—also we have a big propane tank that feeds the grill, the gas top, and a fireplace. In a fit of panic a couple of years ago we got a portable 7.5kw generator that takes both gasoline and propane. I cranked it in the last storm and it certainly allowed us to keep some basic stuff up (read: laptops, phones, iPads, for communication and media, though not the pump, as it needs separate wiring… so perhaps usage patterns have changed.)

    It may be ideal to have both a battery and a generator. Get a house UPS, put the entire house on it, and have the UPS baked by a generator. This ensures filtered power even when there is no official outage.

  4. fd

    March 12, 2018 @ 1:36 pm


    I once was advised not to underestimate the bandwidth of a station wagon full of mag tapes barreling down a highway.

    In a similar vein, I suspect it’s unwise to underestimate the energy density of a full tank of gas.

    According to wikipedia, energy density in MJ/L:

    gasoline: 34
    propane: 26
    lithium-ion batteries: <3

    If I'm reading the wikipedia table correctly, the comparison is even worse for batteries — more like 50:1 — if you compare by kg rather than L. Even if the powerwall had the same battery volume or weight as the propane tank, it'd run out of "juice" far sooner than the fossil fuel.


  5. George A.

    March 12, 2018 @ 1:59 pm


    “Or are we just more addicted to our electrically powered conveniences?”

    We are spoiled beyond belief. We want everything and we want it this very second. In many other countries, power outages are expected and in some countries it is rotational from neighborhood to neighborhood.

  6. dwight looi

    March 12, 2018 @ 2:13 pm


    The problems with battery storage as a backup or alternative to the power grid are the same ones as the problem with battery storage in transportation. Namely, batteries are expensive and batteries have horrible energy densities compared to hydrocarbon fuels. Let’s look at the freaking numbers shall we?

    The energy content for liquid hydrocarbon fuels like diesel or gasoline is around 46 MJ per kg mass and 36 MJ per liter in volume. Today it costs about 50 cents to buy a liter of these hydrocarbon combustibles.

    A Lithium-Ion battery like that you find in Tesla vehicles and home power solutions gets you about 0.8 MJ/kg and 2.5 MJ / Liter. That 2.5 MJ in battery capacity (0.7kWh) costs about $105 (at ~$150/KWh for LiCoO2 batteries).

    Even when we take into account the reality that internal combustion engines and jet turbines are only 30~40% efficient at energy conversion whereas electric motors can frequently be 85% efficient or better, you still get 24 times as much power per unit fuel mass with combustible hydrocarbons. Also, even assuming that electricity is free (it isn’t) the cost of the battery itself is 240 times the cost of the fossil fuel with the same energy content!

    Electric Cars do not make economic sense at today’s hydrocarbon fuel scarcity and prices. The cost of the battery is the total fuel cost of an economy car for over 10 years and you can’t top it off in 5 minutes at a gas station. BTW, a typical economy car may carry about 90 lbs of gasoline in a full tank good for 300~400 miles, that Tesla battery in the Model 3 is in excess of 1000 lbs while being good for about half to 2/3rds the range. Electric cars are a “feel good” products for Global Warming Coolaid drinkers — nothing more. This is also why you don’t see Electric 777s making Pacific crossings. It’ll make it 1/20th of the way — from San Francisco to LA (maybe).

  7. Fake Elon

    March 12, 2018 @ 2:50 pm


    Most people with Tesla solutions live where it rains & snows, because that’s the only place a house doesn’t cost 8 figures. Cleaning the snow from the solar panels sounds problematic. In the stacks with everyone else who has a job, power outages are much more common than they were 30 years ago. Blown transformers & repairs are the mane reasons. In the old days, we just had power outages from storms.

  8. bobbybobbob

    March 12, 2018 @ 3:54 pm


    Is it really worth thousands of dollars and maintenance hassle to avoid simply putting up with no electricity for a few days every few years? I mean, you could just go stay in a hotel if it lasts longer than two days.

    I can understand buying a little generator to power a freezer/refrigerator, so food doesn’t rot. Have a kerosene heater and a charcoal grill for cooking.

  9. dwight looi

    March 12, 2018 @ 6:01 pm


    bobbybobbob — a $250 Walmart generator makes 4 kW. A full sized refrigerator is 800W while your LCD TV is 100~200W max. A Hair Dryer may be 500 to 1500W. LED Lights bulbs are usually less than 12W a piece, even the incandescent ones are 60W or so. 4000W is enough for most of your daily household conveniences.

  10. Ivan

    March 12, 2018 @ 6:05 pm


    1. I live in one of the W-towns west of I-95 in MA. From my perspective, power outages today take much longer to repair than they used to. Between 1993 and perhaps 2005, we have not experienced an outage lasting longer than a couple of hours. I saw crews working almost immediately on the problem, removing fallen trees and fixing the cables.

    Not now. I’ve been through at least 3 multi-day outages since 2009. The usual picture I see in the neighborhood is a tree sitting for a couple of days on the wires with no repair crew in sight. Finally, a crew arrives, very often out of state, and fixes the problem. Not sure why outages became so much worse. Perhaps, it is specific to my location.

    2. After the 2011 three (?) day power outage, my wife forced my hand and made me buy a whole house generator which I have considered sort of sacrifice to pacify electricity gods, not a practical thing. Since 2011, there were a couple of outages lasting about 2-6 hours each. However, the last power outage lasted about 60 hours (Thr-Sat), so I was pretty happy to have the luxury.

    3. Speaking of solar, my neighbor has his roof covered with panels. On day 3 of the last outage, he caved in and bought a portable generator at HD.

  11. It wasn't me

    March 12, 2018 @ 6:29 pm


    I’m near south Florida, and didn’t lose power during Hurricane Matthew during early Oct. 2016. I did lose power for five brutally hot days and nights after Hurricane Irma during mid-September 2017. This was the first time I’ve lost power for more than a few minutes in over ten years. Over the past couple of months I researched portable and whole-house generators. I got three estimates for installation of a 16kW whole-house generator, ranging from $8500 to $10,500; much more than I wanted to spend. A couple of weeks ago, I purchased a brand new Chinese-built tri-fuel 7200 running watt portable generator for $1500. It runs on gasoline, propane, or natural gas. The other day I connected it to my natural gas service with a 6-foot quick-connect NG line, wired it into my electric panel, and ran everything in my house at the same time, including refrigerator, three 10,000 btu portable AC units, three ceiling fans, every light, and my 4-ton central AC – all at the same time!

    Last week, my neighbor had a 22KW Generac whole-house generator installed for $9000.

  12. Jack D

    March 12, 2018 @ 10:46 pm


    I’ve never considered it worth the $ to invest in a generator where I live. We lost power for a couple of days last week and that was, IIRC, the longest outage ever in almost 30 years of living in my house. The last time we had an outage, it was for less than 24 hrs and I bought a propane mantle lantern (this provides a nice amount of light and also some heat – good in winter, not so good in summer) for as long as your propane supply lasts (it runs on the little 1 lb propane tanks and 1 tank lasts for hours). I think that was maybe 3 years ago.

    OTOH (and it’s a long story) this time I was working on a crucial deal (my office is in my home) and a client offered to get me connected to a generator out of his own self interest so I could keep working (I could have taken a laptop to a hotel but my productivity would not be the same). They brought in this huge diesel 60kw generator on a trailer and it ran everything in my house the same as if I was on the grid. I must say it was nice to be warm and well light when the whole neighborhood was in the dark. But I’m still not sure it is cost justifiable for the rare times I lose power.

    I could have run half the neighborhood on that thing. All the lighting in my house is LED and most of the time when I checked the meter on the generator I was pulling maybe 1 or 2 kw. Of course in the summer with the HVAC going it would be more but the blower motors for the gas furnace don’t draw that much. I have an electric double oven and an induction range and if you turned both of them on full blast that’s 15kw but no one ever does and certainly not in a power outage.

    You can get a cheap Chinese propane/gas 8,000 watt (10K surge) generator for under $1K and maybe a few hundred more for an electrician to hook up a power inlet and a couple of hundred for a 50 amp cable so you could have a passable (if noisy) rig for well under $2K. Or for $5 or 6k installed you could have a gas powered permanent setup. But I still don’t think it is worth it for a day or 2 every 3 years – if I hadn’t been in the middle of a big deal I was willing to make do and improvise for a little while – it’s not the end of the world.

  13. Tiago

    March 13, 2018 @ 5:46 am


    @dwight looi: Electric cars can make economic sense. It depends on where you live, and how fuel and electricity costs compare. I can assure you that in most of Western Europe they make a lot of economic sense.

    But aside that, they are far from a “feel good” tool. Even if you assume they are powered by the dirtiest power plants, they are a huge improvement because the dirty pollutants are not deposited right in the cities and where people live and work. This for itself should be reason enough for non-electric cars to be banned from cities (this is already happening in many places in Europe, and I suspect it will accelerate). With the economies of scale, electric cars will get cheaper and battery technology will advance so much that in a decade or so people won’t be writing about range anxiety. In fact, the range of electric cars will most likely exceed the current range of diesel cars in the not too distant future.

    It may not make economic sense for many right now (especially in places like the US and Russia where petrol is cheap and the distances are long), but the change is coming whether you want it or not. You can embrace it or keep living in the past. For myself, I am a happy EV owner, and it costs me about 5x less per mile to drive electric vs. petrol, all charged on 100% renewable energy.

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