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  1. #1
    us
    Apr 2009
    Cornfield, IN
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    Rooftop Solar

    Hi Everyone,

    Our rooftop solar system went fully operational this past Wednesday. YAY!!!

    We got twenty-eight 370W panels and a Tesla Powerwall 2 battery. Our home is fully electric and we have well water. Here's a photo of 18 of the 28 panels:
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    The system is quite smart. The panels prioritize the home's electric demand and feed it first. If the panels are producing more than the home's demand, then they power the home and charge the battery:
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    If the home's demand is greater than the panels are producing, then it starts to draw from the battery to make up the difference:
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    If the panels are producing more than the home's demand and the battery is at 100%, then they divert the excess to feed the grid:
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    The battery only discharges at 5kW, so if the home's demand is greater than the battery and panels, then we draw from the grid:
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    At night, when the panels aren't producing, the home will run from the battery, unless demand is greater than 5kW or if the battery reaches reserve capacity (ours is set to 10%), then the grid kicks in. It has been cold at night here lately, and the electric furnace uses a lot of electricity, so every time it kicks on, we've been drawing from the grid. One the battery reaches reserve capacity, we run of the grid alone, until the panels begin producing again.
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    More to follow...
    Last edited by Kantuckkeean; Apr 04, 2021 at 09:01 PM.
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  2. #2
    us
    Apr 2009
    Cornfield, IN
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    The app also produces graphs and allows for downloading data, which will be handy for long-term monitoring. Here's one of the home's use throughout the day. The big spikes at night (on the left side of the graph) are when the furnace kicks on.
    Attachment 1915758

    Here's one of the grid use throughout the day. The reason that the furnace spikes are highest at around 6am to before sunrise, is because our battery reached 10%, so at that point, we were running entirely from the grid. Prior to 6am, the home was being fed or supplemented by the battery. You can see how grid use drops off to zero, just after the sun has been up for a bit and the panels began providing all of the home's needs.
    Attachment 1915759

    The solar panels (in yellow in the graph below) begin producing all of our home's demand and more, shortly after sunrise. Here's one showing grid use and panel production:
    Attachment 1915760

    Since the panels are producing more than enough for the home during much of the day, they power the entire home and then prioritize the battery and charge it. The battery (green in the graph) is charging when the green is below the baseline and powering the home some when the green is above the baseline. It kicks on and off as needed. When the battery is full, then the excess power is sent to the grid. That can be seen when the white (grid) is below the baseline in the afternoon and evening:
    Attachment 1915763

    Here's home demand (blue), grid (white), solar (yellow), and battery (green) all together:
    Attachment 1915766

    Because last night wasn't too terribly cold, the battery was able to supplement the furnace until around 6am, so there were only about two hours when we were running entirely from the grid.

    I'm sure that I'm going to learn a lot from this and change habits. One thing that we're already doing differently is doing laundry, drying clothes, and running the dishwasher while the panels are producing. That way, we can have a full or nearly full battery at sundown. I'm sure that we'll see what combinations of appliances cause our demand to exceed panels and battery and learn to avoid doing that, so that we draw as little as possible from the grid.

    If anyone else has solar experience, hints, or questions, feel free to chime in.

    Kindest regards,
    Kantuck
    Last edited by Kantuckkeean; Apr 04, 2021 at 09:20 PM.
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  3. #3
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    Bill B

    Sep 2010
    Upstate NY
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    Well said and thank you for sharing,,I’ve seen many homes with panels even panels across the road from homes but never had any knowledge how the system functions
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  4. #4
    us
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    Quote Originally Posted by billb View Post
    Well said and thank you for sharing,,I’ve seen many homes with panels even panels across the road from homes but never had any knowledge how the system functions
    Thank you and you're welcome.

    We'd have gotten a bigger system (more panels) if the economics were more favorable for us (and may do so in the future). I've been looking and I think that we could fit another 32 panels up there, more than doubling our generating capacity. However, our provider doesn't pay enough to make it worth our while (economically) to feed a bunch back to the grid. We pay $0.109/kWh that we use from the grid and they only pay us $0.027/kWh that we send to the grid.

    A fella with a different provider is under different rules, and he banks every excess kWh, so that he can use it from the grid later. He hasn't had an electric bill since his system became operational. My parents' system was the same way. Under that model, they're basically using their electric providers as "free" batteries, so they can put up a few extra panels, generate a bunch of excess during the days and summers, and get it back nights and winters. Since we're under unfavorable rules, it doesn't really help us tremendously to over-produce. It looks like we will over-produce a bit though.

    I'm not sure why the photos didn't show in the second post. If you click on the attachments, you can see the graphs that I was talking about. I'll try the final one again:

    Click image for larger version. 

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    Well it seemed to work here. So the above graph shows home use (blue), solar production (yellow), battery (green), and grid use (white). As you can see in the above graph, the solar meets the home demand shortly after sunup, so it charges the battery. Green below baseline means the battery is charging. When the green is above the baseline, the battery is supplementing either solar, grid, or both. When the battery reaches 100% charged, then the excess solar feeds the grid (white below baseline).

    Kindest regards,
    Kantuck
    Last edited by Kantuckkeean; Apr 04, 2021 at 09:52 PM.
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  5. #5
    Dug
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    Just curious as to how many years of electric bill saved/being paid for putting into the grid it will take to pay off the whole investment as well as what is the warranty life of the system?

    For the cost in my area I figured it would take 20 years assuming rates remained the same although they probably won't.
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  6. #6
    Fat
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    How much did it cost up front? Total cost to install? Please
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  7. #7
    us
    Apr 2009
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    Quote Originally Posted by Dug View Post
    Just curious as to how many years of electric bill saved/being paid for putting into the grid it will take to pay off the whole investment as well as what is the warranty life of the system?

    For the cost in my area I figured it would take 20 years assuming rates remained the same although they probably won't.

    Good questions. The panels have a warranty of 92% of their original production capacity after 25 years. There were less expensive panels that we could have purchased that had an 80% production warranty after 25 years, but they were less efficient as well. It would have taken 32 of those panels and I wanted to leave as much open space as possible on the roof, in case we expand later to increase capacity. A lot of R&D is going into panels and as they increase in efficiency and (hopefully) costs continue to decrease, it may become more economically beneficial to increase production later, even with our unfavorable situation. The inverters have a 10 year warranty, as does the Tesla Powerwall 2.

    I will not be able to accurately answer how long it will take to recoup the investment and see a positive ROI for at least one full year of operation. When I calculated our savings, I was simply basing my numbers on the estimated panel production and how much of our annual electricity consumption we'd offset. When designing the systems, companies tend to give conservative estimates of production. Customers are happier if they hear that it will produce 9,000 kWh/year and then it actually produces 10,000 kWh/year, rather than 8,000 kWh/year (it's just an example, but it's better for companies to under-promise and over-produce rather than over-promising and under-producing).

    When I was attempting to figure out when the panels and battery would pay themselves off, like you, I was using a "worst case scenario" where energy rates would not increase over time and I assumed sending nothing back to the grid. I came up with 17 years. Since we went with the more expensive panels, the worst case scenario is 19 years. However, the battery is the wildcard here. Since it is acting essentially as night-time solar, we're able to power much of the home's demand throughout the night with stored solar, and the battery is also able to supplement our home during the day when we need additional electricity and then recharge itself later when our demand decreases, so it's going to be shorter than the what I estimated, simply due to the battery. Also, it's only early April and we are already sending electricity back to the grid, which will be essentially a 25% discount on an equal number of kWh later. My 17-19 year estimation assumed sending nothing back to the grid and as you can see from the graph below, we were sending some electricity to the grid from around 3pm to 7pm (white below the baseline). When summer hits, I'm sure that we'll be sending quite a bit to the grid.

    Here's a graph showing grid use (white), solar (yellow), and battery (green).
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    This was taken at 11:34EST and we've barely used the grid since 8am. It's midnight now and our battery is at 60%, so it may last until sunup... still to new to know...

    Kindest regards,
    Kantuck
    Last edited by Kantuckkeean; Apr 04, 2021 at 11:27 PM.
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  8. #8
    us
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    Quote Originally Posted by Fat View Post
    How much did it cost up front? Total cost to install? Please
    PM sent. We had to pay 20% up front and 80% after it went operational... Although they haven't sent the second invoice yet.

    Kindest regards,
    Kantuck
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  9. #9
    Charter Member
    us
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    Based on our previous electric cost, the rate of return on my roof's solar panel investment is about 6 years.
    Don.....
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  10. #10
    us
    Apr 2009
    Cornfield, IN
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    Quote Originally Posted by Mackaydon View Post
    Based on our previous electric cost, the rate of return on my roof's solar panel investment is about 6 years.
    Don.....
    That's awesome. There are so many factors that go into the economics... latitude, roof pitch, roof alignment (N-S-E-W), roof shading, whether you're electric-only or electric and gas, family size, state laws, tax credits, net-metering, etc., etc.

    One thing that I'm having to deal with is with our insurance company. They came out to take photos and said that the rebuild cost of our house had increased by twice the cost of the solar system. It's just so that our insurance premium would go up. The rebuild cost of the house should only have increased by the cost of the system, not twice the cost of the system.

    Kindest regards,
    Kantuck
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  11. #11
    us
    Mar 2018
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    Do the panels produce 110V AC or 12 volt DC? Gary
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  12. #12
    Dug
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    Thank you for the in depth response. Two reasons I did not pursue solar was one, being old as dirt we would be past our average life expectancy before we would recoup any investment; 2nd I just had a metal roof installed since we live in a coastal area and would cringe at what the workers would do to it. At this point in time it would appear that going solar is best for younger couples who plan on retiring in their home.

    I wonder how many others have been blindsided with their insurance companies increasing their premium after their install? I feel your pain in that regard as I inherited a premium increase after having my metal roof put on. I had inquired whether there would be any coverage issue with a metal roof beforehand and was told no, but they must have been rubbing their hands together with the thought of more money from me. I had thought that putting up a stronger more storm resistant roof would have reduced my premium but found out that they looked at the replacement factor instead so I got a premium increase instead of a decrease. Still would have done it anyway as we had leak issues on our two previous roofs due to roof angles/previous owner addons etc that the metal roof has cured and like the solar panel we will be well past our life expectancy before the roof warranty runs out.
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  13. #13
    What happens when you need a new roof on your home ? This is a serious question (I'm not being funny) as I'm not familiar with the panels, or how they are attached to the roof, although I do see them on homes.
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  14. #14
    us
    Apr 2009
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    Quote Originally Posted by ToddsPoint View Post
    Do the panels produce 110V AC or 12 volt DC? Gary
    They produce DC, so we have 2 inverters mounted to the side of the house near the meter that convert to AC. I think that a system of our size would typically need only one inverter, but the battery needed a separate inverter.

    I think that the battery is well worth it though. We won't need a generator for power outages, since the battery backs up the entire house (with the exception of the furnace and range... too many amps), and just based on how it has performed so far, I think that it will significantly decrease the time for the system to pay for itself.

    Kindest regards,
    Kantuck

  15. #15
    us
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    Quote Originally Posted by Trezurehunter View Post
    What happens when you need a new roof on your home ? This is a serious question (I'm not being funny) as I'm not familiar with the panels, or how they are attached to the roof, although I do see them on homes.
    It will increase the cost. When replacing the roof, we'll need to have certified installers remove the panels, mounting hardware, and electric components from the roof so that the roofers can do their work. If non-certified people do it, it would void the warranties. So when we get to that bridge, we'll have them come out, take the system off, have another contractor install a metal roof, and then the solar folks will have to come back and re-install the panels, likely with different mounting rails. I don't think that it will be too bad though. They were really fast about putting up the hardware and panels. It seemed that most of their time working was installing the battery, inverters, and backing everything in the fuse box up.

    Kindest regards,
    Kantuck
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