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AC power from solar installation into home wiring?

Discussion in 'Power Electronics' started by hriosm, Feb 22, 2020.

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  1. hriosm

    hriosm

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    Aug 24, 2014
    What's the best way to inject AC power from solar installation into home wiring?
     
    davenn likes this.
  2. davenn

    davenn Moderator

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    Go to a licenced installer
    There are very specific regulations regarding this work
     
    hevans1944 likes this.
  3. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Yes, please DO FOLLOW @davenn's advice!

    Generally, several panels are connected in series and several of those series combinations are connected in parallel to provide sufficient POWER (voltage times amperes) to make it worthwhile to connect the panel outputs to an AC inverter to power home wiring. But there is more to it than just solar panels and an inverter. The resulting panel installation has very specific National Electrical Code regulations (at least here in the States) regarding the wire gauge and insulation necessary for a safe install. The resulting panel voltages are backed by enough current capacity to be LETHAL, so this is nothing for an amateur Do-It-Yourselfer crawling around on a steep roof to be messin' with.

    To provide a stable power input to the inverter generally requires a storage battery charged by the solar panels through a sophisticated battery management electronics package. This will take care or those times when clouds pass between the solar panels and the Sun and panel output varies wildly. It might even help during overcast days when solar panel output dwindles to almost nothing. But of course it doesn't help keep the batteries charged at night. If you want to run the AC inverter to power your home wiring at night, you will need a LOT of LARGE batteries. It behooves you to seek professional advice on this because next in cost to the solar panels are the batteries needed to store electrical energy.

    You cannot just connect an AC inverter to your house wiring if your house normally accepts power "from the grid" as supplied by your electric utility. Their power-pole workers look unkindly toward houses that feed low-voltage (120 or 240 volts) AC back into their pole-mounted transformers (pole pigs, in USA parlance), thus energizing what the worker may think is a "dead" high-voltage (7000 volts and up) line they are tasked with repairing. Unless you have an approved installation that allows you to sell your solar panel power output back to the utility (see below) you MUST have an approved transfer and disconnect switch installed between the input to your house circuit-breaker panel and the electric feed from the utility to your house. The AC inverter is connected to one side of this transfer switch, so power to the circuit-breaker panel comes EITHER from your AC inverter OR from the power company utility. Again, installing the transfer and disconnect switch is a job best performed by a licensed installer, as @davenn stated.

    Converting an existing home to solar power requires a system solution, provided by a knowledgeable and experienced professional, to evaluate the proposed installation. Obviously a study of where the sun shines, and more importantly where it doesn't shine, is necessary to properly site the panels. For example, here in southwestern Florida where I live sunshine is very abundant and there is a move on to use more solar energy. Recent legislation makes it profitable for companies to offer to install solar panels for free! My home happens to have hip roofs that are ideally oriented for solar panels, but I am not accepting those offers.

    First, it is unknown what effect even properly installed solar panels will have on the integrity of my roof, especially during a hurricane. Hurricanes occur with some frequency here. Second, the home owner does not own the solar panels. The panels are leased by the installer to the home owner. How does this affect the re-sell value of a home here in Florida? Is the lease transferable to a new home buyer? Who pays to restore the roof if the panels must be removed after a home sale? Third, no provision is generally made for sun tracking to maximize solar panel power output. That means panels must be oversized in compensation if compared to a panel equipped with sun tracking. Sun tracking is expensive, even if only on one axis, especially for roof-mounted systems.

    There are other considerations, too numerous to mention here, that make DIY whole-house solar power risky. I have considered doing it since moving here, speculating that my large side yard on a corner lot would we ideal for a few dozen ground-mounted, sun-tracking, DIY solar panels. I think it would even save money (after a few back-of-the-envelope calculations) but I probably won't do it because of considerations described above. The amortization of cost over a period of, say, fifteen or twenty years, even at the low interest rates (hovering in the neighborhood of two percent) available today make it impractical for me living on a fixed retirement income. Your mileage (or kilometers) may differ, depending on where you live... which place doesn't appear, under the Information Tab, on your profile page here.

    As a side note, the "free" solar panel installations here in Venice, Florida do not use batteries between the solar panels and the AC inverter, thus saving a fortune in initial cost and future maintenance and replacement. The AC inverter is connected directly to the incoming AC power line (with the permission of the utility company), synchronized with AC grid power, and used to run the watt-hour meter "backwards" so the utility company pays YOU for the power generated by the panels during most of the day. Not ALL the power, and certainly not at the same rate they charge you for power, but it is said to lower the yearly cost of your electric utility bill because legislation requires the utility to accept, and pay for, power generated by the home owner... this is probably how you are supposed to pay for the solar panel lease. I think the power utility may swap out the usual remote-readable and remote controlled power meter for this purpose, but I don't know for sure. What I do know for sure is Florida Power and Light knows exactly how much electrical energy I use every minute of every day. I can even go online to their website and check it myself instead of going outside to read and transcribe the electronic meter manually.
     
    Last edited: Feb 22, 2020
    davenn likes this.
  4. oliverm

    oliverm

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    Mar 3, 2020
    Very useful answer, thanks. I have a van, I need to know the size, capacity, cost, for each cell, to construct, a solar plant, in the ceiling, and to be able to move it, to any side, has two air conditioners, refrigerator, Surveillance, I want to know, how serious, the most economic possible, for this project?
     
  5. davenn

    davenn Moderator

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    That's a huge power load and probably well out of the range of anything that could be mounted on the roof of a van, or any other vehicle for that matter.

    Not be specific ....
    what are the wattage ratings of those things ? without that info, it's impossible to give advice
     
  6. oliverm

    oliverm

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    Mar 3, 2020
    It seems useful.
     
  7. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    As a "rule of thumb" solar insolation is about one kilowatt per square meter. An efficient solar panel can extract at the most about 15% of that, say, about 150W/m2. You would be lucky to be able to carry in a van, and present it to the Sun, as much as two square meters of solar panels providing at the most 300W of power. That's enough to power an amateur radio station, perhaps, but hardly enough for two air conditioners, refrigerator and surveillance. Leave the engine running in the van, and make sure its alternator can handle the electrical load. Most automotive alternators won't even come close, but the solar panels can help on bright, sun-shiny days. Also, add some batteries and a battery management system to your solar array for backup during the inevitable cloudy or rainy days. As @davenn said:
    Impossible to give good advice. GIGO principle applies here: Garbage In, Garbage Out.
     
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