Solar power - Tesla power wall question...

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  • longbow

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    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?
     

    Cameramonkey

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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.
     

    jkaetz

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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.
     

    BugI02

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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
     

    longbow

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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.


    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.
     

    nra4ever

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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:

    Karl-just-Karl

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    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?
     

    shibumiseeker

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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.

    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.
     

    Clay Pigeon

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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?
     

    Cameramonkey

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    That is a huge system that would allow for complete grid independence without any kind of sacrifice (except maybe money).

    A few things:


    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.

    Dont get me started on that point.

    "Hey everybody! We need to save the planet (and your wallet) by reducing energy consumption. Here, have these cancer bulbs and you'll cut your consumption by 25%!"
    (several years later)
    "Dear IURC: We are selling 25% less power than we used to and are now not making enough to cover our costs. We need to raise the rates to recoup our losses." :xmad::xmad::xmad:
     

    longbow

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    The system is big enough to power the homes, and store enough that I'm getting KW credits on the power I grid tie into the system. It can charge, use and grid tie power at the same time. I'm all electric and my power bill is at least $400 a month. Double in the coldest months, but it is two homes. I'm on UDWI REMC...
     

    longbow

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    The system is big enough to power the homes, and store enough that I'm getting KW credits on the power I grid tie into the system. It can charge, use and grid tie power at the same time. I'm all electric and my power bill is at least $400 a month. Double in the coldest months, but it is two homes. I'm on UDWI REMC...
     

    Sigblaster

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    Forgive my ignorance and off-topic question, but I only paid a passing interest in this type of system when it was first announced, and haven't paid much interest since.

    As I understand it now, the power wall is intended to be used with solar to power your house and store excess energy. Is it possible to use the power wall another way?

    Could you, for instance, charge the battery bank off of your electrical service, and keep it topped off with a trickle charge when necessary, then switch to the battery backup for short-term outages? Of course, I mean using a switch that severs the connection to the grid so the guy repairing the grid doesn't get zapped.
     

    shibumiseeker

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    Forgive my ignorance and off-topic question, but I only paid a passing interest in this type of system when it was first announced, and haven't paid much interest since.

    As I understand it now, the power wall is intended to be used with solar to power your house and store excess energy. Is it possible to use the power wall another way?

    Could you, for instance, charge the battery bank off of your electrical service, and keep it topped off with a trickle charge when necessary, then switch to the battery backup for short-term outages? Of course, I mean using a switch that severs the connection to the grid so the guy repairing the grid doesn't get zapped.

    Yes, that's all off the shelf stuff these days.

    It's also one of the pieces of advice I give people who want to dip their toes in but not fully invest. Basically you put a few critical circuits on what amounts to a large UPS. Many real inverters will automatically pass through grid or generator power while charging batteries at the same time then switch if outside power goes off. Then you can get a bigger battery system when it comes time to upgrade. You can add a few solar panels and put the pass-through power on a timer so it passes through at night but powers off the solar panels and battery during the day. You can get load diverters that shunt excess incoming solar or wind or hydro into some other load such as a water heater.

    Back when I started doing this you basically had to homebrew this stuff for yourself. Now it's more or less plug and play.
     

    churchmouse

    I still care....Really
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    Dont get me started on that point.

    "Hey everybody! We need to save the planet (and your wallet) by reducing energy consumption. Here, have these cancer bulbs and you'll cut your consumption by 25%!"
    (several years later)
    "Dear IURC: We are selling 25% less power than we used to and are now not making enough to cover our costs. We need to raise the rates to recoup our losses." :xmad::xmad::xmad:

    The same thing with natural gas prices. When everyone went High Eff. gas fired units consumption went down tremendously. Then the prices were jacked up to make up the diff.
     

    shibumiseeker

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    near Bedford on a whole lot of land.
    The same thing with natural gas prices. When everyone went High Eff. gas fired units consumption went down tremendously. Then the prices were jacked up to make up the diff.

    I am amused by the people who, back in the 80s told me "yeah, I tried that solar thing, it didn't work."

    The first solar panels I bought cost $16 a watt in today's dollars in the late 80s. The last batch I bought a few months ago cost $.81 (eighty one cents) a watt delivered to my house and are better built. I have 15 year old panels going strong (lost my first array in a house fire) that I paid $2.50 a watt for in adjusted dollars. The cost of inverters has steadily gone down. Lead acid batteries are slightly cheaper in adjusted dollars, but the real stars are lithium cells which have come way down in price and now have a better ROI than lead-acid, not to mention drastically lower maintenance. And to top it all off, the technology has matured to allow it to be plug and play as I mentioned above.

    So yeah, glad to have been able to ride this ride over the years and give the finger to the naysayers from back then. Meanwhile, what exactly is a power outage? Haven't had one of those in 30 years.
     

    JeepHammer

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    I've been off grid for more than 20 years, so no hyperbole, conspiracy theories, political slants...

    BIG production is to offset low winter sun with short peak sun hours.
    Less production because of shorter days and indirect sun angle.
    Panels are MUCH cheaper per Watt than they were, but there isn't much you can do about the sun in winter except add more panels to take full advantage of short days, and angle of panels relative to sun (optimum is 90°).

    There will still be a lot of atmosphere between panels & sun in winter/summer (30° off horizontal opposed to 10°).

    The second thing the guys brought up, COST.
    A grid tied system, connected to the power grid, your excess production goes back onto the grid for credits/cash savings...
    A grid tied system has a nearly limitless amount of back up power, so you are saved the cost of generators, batteries, alternate production capacity.
    You excess production has somewhere to go, so you get credit for it. (Indiana being a coal state, the deal usually sucks for the solar producer)

    Off Grid, the system costs what it costs, produces what it produces, and the LONGEVITY of the system determines the final cost (per kWh).
    If it lives for 5 years,costs are high, if it lives for 25 years, costs are MUCH lower.
    Like generators, fuel, maintenance, the costs depend on initial/running costs, and how long it lives/produces.

    Specific Systems,
    There is the standard (larger) Grid Tied, where you make part of your own power, draw off the grid when needed, and off set the bill somewhat when you produce more than you use.
    The system still goes down when the grid does, a requirement so you DO NOT back feed the grid, endanger line workers...

    There are HYBRID systems that have battery backup,
    These will automatically disconnect from the grid when the grid fails, provide power for the home during blackouts.
    The duration of backup power depends entirely on the battery size and your consumption.

    There are MICRO-GRID/OFF GRID systems,
    These are completely independent of the consumer grid, operate on their own.
    These have at least one battery powered inverter and battery bank connected to the panels.
    (What I have, grid power was way too costly to have installed when I built, so about 1/4 the cost of having the grid ran back to my property)

    Depending on what you want, any of these can accommodate alternate forms of production, micro-hydro, wind, etc.

    ----------------------------

    From my personal experience,
    $15,000 in cash, $118,000 added to the bill over 30 years to get poles, transformers, wires ran a mile to my property over 20 years ago.

    I made a lot of costly mistakes,
    Starting small and having to update about everything as my electrical needs increased.
    Starting with lead/acid 'automotive' type batteries for storage,
    Not having sun tracking panels to maximize production of the stupid expensive panels at the time,
    Running a DC (direct current, battery voltage) dual system, everything wired twice, double the expense,
    The list goes on...

    I upgraded to an AC coupled system, the power is immedately converted to AC, what the home/shop consumes, and if DC is needed we use a transformer plugged into the wall like everyone else.
    The system runs on 240 VAC just like every other home/shop in the country, no specialized equipment costs.
    The inverter line connections are like every other home/shop, 3 wires (L1, L2, Neutral), no rats nest of DC wires running everywhere.
    I use a LiFePo4 battery for it's charge density, return of charge & safety.
    I use a hybrid (battery) inverter to simulate the grid input, and I use MUCH LESS EXPENSIVE common grid tied inverters at my panel stations to produce normal power,
    The hybrid inverter allows for alternate power from generator in the event I don't get sun for several days.

    The hybrid inverter acts as 'The Grid', producing an AC sine wave form so grid tied inverters connect and allow production into the lines,
    It also converts battery (DC) into AC the rest of the system uses,
    And it acts as a 'Regulator' to keep Voltage/Amperage consistent throughout the system no matter how much, or how little the panels are producing.
    Obviously 'Off Grid' this piece of equipment is needed because you don't have the 'Grid' as a fill in or dump for low/high power situations.
    You also don't need the power company...

    Before *I* bought a 'Power Wall' or anything else, I would ask around, find someone with full scale solar, that knows the difference between AC coupled, DC coupled, frequancy shifting, etc.
    Knowledge is power, and research is knowledge!

    It's also good to know you have a system that's expandable, will grow with your needs.
    Since I replaced my 20+ year old panels, switched battery chemistry, we actually have excess power now.
    I had racks/mounts for the old low power panels, and about half of the racks are now used, we have excess...
    No more watching the SOC (State Of Charge) meter to know if its a good time to wash cloths or run the well pumps!

    Just some ideas from someone that's actually been through it, use it if you can.
     

    Karl-just-Karl

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    Ah Ha! TWO homes. That makes a little more sense.

    I get it, some people have remotely located, very large, very expensive, very energy intensive homes and do not want to give up anything for convenience. I've seen some systems doing just that combining wind and solar. More POWER to the folks able to swing all that! :):

    28KW is a very impressive system. I've considered going this route (vastly oversize compared to required amount) to be a micro power generator for resale. As previously stated, Indiana isn't that great of a state to be a micro power generator.


    Thanks for sharing your knowledge and experience JeepHammer. So are you using 24 or 48VDC for storage?



    My target is still about 4.5 years out before I can cut all the cords...

    ...if society as we know it lasts that long.:(
     
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