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Thread: Solar power - Tesla power wall question...

  1. #1
    Grandmaster longbow's Avatar

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    Solar power - Tesla power wall question...

    Costs are much better than a few years ago for my two homes at my place.

    28kw system

    70 -400 watt modules on a ground mounts

    24 kw inverters. 6kw x 4

    2 - 13.5 kw Tesla power wall batteries

    $77,900 before tax credits

    Generator hookup, but no generator included

    Anyone work with powerwalls?
    "I know of you"

  2. #2
    Grandmaster longbow's Avatar

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    It's $30,000 cheaper than the last time I had a quote.
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  3. #3
    Grandmaster Cameramonkey's Avatar

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    But still. Whats the ROI on that system? Are you able to buy off peak power to offset the cost of the wall? If so how long would it take to recoup? Or for that matter, disconnect from the grid and just not pay because you are now solar/wind/generator*.


    *Ive heard (not sure if its true) that at least here in IN the cost of electricity per KWH is still cheaper than most generators can create per gallon of gas. Though if prices stay below $2 it could help.
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  4. #4
    Expert jkaetz's Avatar

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    I'm guessing the primary cost of the tesla powerwall is the batteries. Broken down I believe they are still simply a bunch of 18650 cells configured in series/parallel to get the voltage they want.

  5. #5
    Grandmaster BugI02's Avatar

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    Most of the numbers I've seen are that at our latitude a typical home can expect a reasonable area of solar to deliver 30 to 35% of power required for 5 hours per day. No point in storage if you use more than you create, no charging taking place at night when demand is low, it's not going to get you off the grid

    It's a very expensive system if all you want to do is peak leveling, and if the idea is to obviate a generator and be able to run your house during outages how long will a fully charged set of batteries allow that to happen? In the event of a severe outage, how many cloudy days even for a large system to experience inability to both recharge use and run the house?

    IMO you could buy a whole house generator that runs on propane, a modest tank and the LP to fill it as well as a decent rooftop solar array to shave your electric bill for around half what the Tesla system costs, perhaps a bit more
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  6. #6
    Grandmaster longbow's Avatar

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    Quote Originally Posted by Cameramonkey View Post
    But still. Whats the ROI on that system? Are you able to buy off peak power to offset the cost of the wall? If so how long would it take to recoup? Or for that matter, disconnect from the grid and just not pay because you are now solar/wind/generator*.


    *Ive heard (not sure if its true) that at least here in IN the cost of electricity per KWH is still cheaper than most generators can create per gallon of gas. Though if prices stay below $2 it could help.

    We are still playing with the numbers for the ROI. They are not bad, and the interest rates are good. The tax credits also help but the wife is a solid no to the current cost.

    We might build a small system and scale it up with similar items in the quotes. I've wired two houses so I think I'll be ok with a small system. I think Ill focus on our well pump and lighting circuits.
    "I know of you"

  7. #7
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    Would that allow you to completely disconnect from the electrical grid?

    I could probably do it as well if I wait a few years times 2. Lol if the cost dropped 30k each time

    I think my average electricity is about $130. Would take me about 50 years to break even. I probably won't live that long or be in my current home. Am I looking at it the right way or am I missing something. I would definitely love the independence from the grid.
    Last edited by nra4ever; 07-29-2020 at 12:09.

  8. #8
    Marksman Karl-just-Karl's Avatar

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    Quote Originally Posted by longbow View Post
    Costs are much better than a few years ago for my two homes at my place.

    28kw system

    70 -400 watt modules on a ground mounts

    24 kw inverters. 6kw x 4

    2 - 13.5 kw Tesla power wall batteries

    $77,900 before tax credits

    Generator hookup, but no generator included

    Anyone work with powerwalls?

    I'm sorry, but I have to say that is a BIG system. Wow!

    I assume you are going completely off-grid? Or are you selling back at wholesale prices to decrease your ROI time?

  9. #9
    Grandmaster shibumiseeker's Avatar

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    Quote Originally Posted by nra4ever View Post
    Would that allow you to completely disconnect from the electrical grid?

    I could probably do it as well if I wait a few years times 2. Lol if the cost dropped 30k each time

    I think my average electricity is about $130. Would take me about 50 years to break even. I probably won't live that long or be in my current home. Am I looking at it the right way or am I missing something. I would definitely love the independence from the grid.
    That is a huge system that would allow for complete grid independence without any kind of sacrifice (except maybe money).

    A few things:

    1.The cost of money. If you finance then you are paying interest. If you pay cash then you are losing interest.

    2. Even with lithium battery systems there still is maintenance costs. Lower than for a lead-acid system, but still there.

    3. System life is typically 25-30 years. That does not mean after 25 years the entire system needs to be replaced, but that does mean the system cost must be amortized over the life of the system.

    4. The spec'ed system above could be expected to produce over a gigawatt (a thousand megawatts) of power over its lifetime (28kW X 4 hours peak solar per day average for Indiana). At 12 cents a kWh that is over a hundred thousand dollars worth of electricity. Whether the OP actually USES all the potential power is a different story. At $130/month you are only using about 1100-1200 kWh a month or about 350 megawatt/hrs over that same 25 year system life.

    5. Once a system is bought, power costs are locked in. When you buy from the utility you are at the whim of their pricing and what they can convince the politicos to make the utility regulatory commission to allow them to charge you. One thing is sure, that cost will not go down, and when they decide they want to jack your rates to pay for their failed Mr. Fusion plant you get to pay for it.

    I have been off-grid for 30 years now and the latest system I am building for the new house on my property (the old house is on another part of the property and has its own system) currently has 1.6 kW of solar, 4 kW of lead acid battery, and a 1.5kW inverter and if I were to have bought it all at once would cost about $3000. It's been expanded over the last couple of years and runs all of the lighting, 19cu ft fridge, computers, and misc small appliances. Water pump is 12v from a tank that collects rainwater from the roof. Since I started building this system a year and a half ago it has produced about 1.5 megawatt/hrs of power. It would have been more but I started with 800 watts of solar and have been adding panels as I can afford them, and I do not use all of the available power. Occasionally I have to run the backup generator when we have extended clouds or I want to run power tools all day. I've probably burned about 40 gallons of gas over that year and a half. My eventual goal is to basically double the system size I have and build a 10-12kW lithium battery bank.

    It really all depends on your needs and expectations. I've been so power frugal for so long I can't even imagine needing as much power as Longbow, even over two houses.
    IWTFM Eternal vigilance is the price of chickens. JFC advocate.

  10. #10
    Master

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    What is the reason for going a battery power wall when on grid, when a Power Factor capacitor / filter bank has virtually no maintenance and curves out hi peak?

    "Too much agreement kills a chat." ~Eldridge Cleaver

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