Why no AC Panels

icarus
icarus Solar Expert Posts: 5,436 ✭✭✭✭
in General Solar Power Topics #1
Here is a question that belies my own ignorance. Why is it not possible for a panel to be designed to produce AC directly? The subject came in a conversation I recently had and wondered why one could do such a thing, and wouldn't that be an advantge in grid tie applications. For example if you could produce AC at a reliable frequency, then the only. (ha!) issue would be voltage regulation.

Educate me please.

Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Why no AC Panels

    Because photons slamming into P-N junctions of impure silicon can only send the electrons hustling in one direction.
    Much like the electron differential between two plates in a battery, and not at all like waving alternating North and South poles past a coil of wire.

    Now someone is going to pipe up with "but there are AC panels!" and it will have to be explained that a panel with micro-inverter attached isn't really an "AC panel".
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  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    #3
    Re: Why no AC Panels
    Cariboocoot wrote: »
    Now someone is going to pipe up with "but there are AC panels!" and it will have to be explained that a panel with micro-inverter attached isn't really an "AC panel".

    It seems some people are beginning to argue that an AC panel can have exposed DC conductors as long as the panel and micro-inverter go through a listing process together.

    I'm sure they're saying that just to further confuse us all...
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: Why no AC Panels

    Marc,

    You got it. I am not interested in an idea of a DC panel wIth a built in inverter. Like I said, I belie my own ignorance,, so it is fundamentally an issue of physics?

    Got it,

    t
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #5
    Re: Why no AC Panels
    icarus wrote: »
    Here is a question that belies my own ignorance. Why is it not possible for a panel to be designed to produce AC directly? The subject came in a conversation I recently had and wondered why one could do such a thing, and wouldn't that be an advantge in grid tie applications. For example if you could produce AC at a reliable frequency, then the only. (ha!) issue would be voltage regulation.

    Very simply put, it's for the same reason that there are no AC batteries.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Why no AC Panels

    Well, panels are semi-conductors. Big bunch of diodes really. Can't get AC past a diode, you know. :D

    Remember a while back there was a news story about some company putting "shutters" on PV's so they they pulsed on and off and produced a pseudo AC output. That was touted as a "breakthrough" even though it is utter rubbish. Sure, you get pulsed DC which can be used as an AC signal (like the old vibrators in car radios) but since the light has to be blocked half the time to create this the over-all power from the panel drops 50%! As if they aren't inefficient enough already.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #7
    Re: Why no AC Panels
    Cariboocoot wrote: »
    putting "shutters" on PV's so they they pulsed on and off and produced a pseudo AC output.

    WOW! Awesome idea! My next big project! This should be easy! My only question - the shutters I'm working on - - should I have them flap open and shut 60 times a second, or 120 times a second, and will the clatter be worse than the "wosh, wosh, wosh" of a wind turbine. And should I attach flex cables to the shutters so they won't fly off and go through the neighbors windows when the bearings fail?
    You guys are the best and I await you're learned response.
    Wayne :D:D:D
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #8
    Re: Why no AC Panels
    waynefromnscanada wrote: »
    WOW! Awesome idea! My next big project! This should be easy! My only question - the shutters I'm working on - - should I have them flap open and shut 60 times a second, or 120 times a second, and will the clatter be worse than the "wosh, wosh, wosh" of a wind turbine. And should I attach flex cables to the shutters so they won't fly off and go through the neighbors windows when the bearings fail?
    You guys are the best and I await you're learned response.
    Wayne :D:D:D
    I remember hearing about this idea. It was supposedly done with liquid crystal that they could switch between transparency and opacity with an applied AC voltage, sort of like how they make 3D TV. It's a neat idea from a theoretical standpoint but certainly not practical.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #9
    Re: Why no AC Panels

    Oh Crap! There goes my idea of mechanical flappers. Hahahaha
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Why no AC Panels

    Bad news, Wayne; they're LCD "shutters" controlled by a timing circuit.
    Yeah, how much more power production is lost by the photons having to work their way through the LCD?

    It'd be simpler to wire half positive, half negative output referenced to a common conductor and use the timing circuit to switch between the two for the "hot" output on the other wire. Then all you need is a transformer to step up the Voltage, right?

    (Please don't anyone take this seriously!)
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #11
    Re: Why no AC Panels
    Cariboocoot wrote: »

    (Please don't anyone take this seriously!)

    Hahaha The lighter side of solar power :)
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #12
    Re: Why no AC Panels
    waynefromnscanada wrote: »
    Hahaha The lighter side of solar power :)
    There is no dark side of solar power. If it's dark, there's no power.

    :D
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #13
    Re: Why no AC Panels
    ggunn wrote: »
    There is no dark side of solar power. If it's dark, there's no power.

    :D

    Hahaha Well man, ya got me there!!!!!! :D
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #14
    Re: Why no AC Panels

    Bada-bing!

    .................................
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #15
    Re: Why no AC Panels

    I guess that was sort of my point. Is there not technology out the however infect that could be integral to the PV to produce AC however cumbersome at this point? Is this a worth while endeavor and I wind if anyone is working on it, or is it just too much trouble? Going forward,,, who knows?

    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: Why no AC Panels

    Tony;

    When you look at the complexity of the existing systems (GT being the "simplest") you can see that squeezing it down to the panel level, whereas not impossible (for those of us who remember germanium transistors: compare to an IC) at this point is certainly impractical. Miniaturization certainly comes with a cost of power handling ability, so you end up with the "big" box of a microinverter bolted on to a panel. That's only about 200 Watts too.

    In theory the PV could drive a 60 Hertz oscillator circuit directly, but it surely wouldn't be able to handle any significant amount of power. Even a small panel would overwhelm it, so you'd end up with one circuit per cell rather than panel. On the whole it would probably be so complex and expensive to make that it would be completely impractical compared to the existing "inefficient" separate panels/inverter.

    At the panel cell level, however, there's no way of getting AC pulses out of the semiconductor material at this point in time.
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  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    #17
    Re: Why no AC Panels
    icarus wrote: »
    I guess that was sort of my point. Is there not technology out the however infect that could be integral to the PV to produce AC however cumbersome at this point? Is this a worth while endeavor and I wind if anyone is working on it, or is it just too much trouble? Going forward,,, who knows?

    Tony

    Going forward I see a DC future for home power. AC is increasing being turned to DC internally in even traditionally 60hz AC motor products like refrigeration so a native DC power buss, interconnects and smart power management is were technology is headed. We are starting to see hints of it in factory automation power management systems at work.

    http://ecmweb.com/contractor/dc-house

    http://www.cpes.vt.edu/public/showcase/d1.2FutureHome.php
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #18
    Re: Why no AC Panels

    There is a 380 VDC project for computer server farms:

    http://www.vde.com/en/dke/dkework/newsfromthecommittees/2011/documents/2%203%201.pdf (pdf presentation)

    I am not sure we will ever see that in homes... And I am not sure that I would want to see that in a data center unless it is maintained by trained master electricians.

    Don't know all of the issues, but I see high voltage DC as less safe vs 120/240 VAC for many reasons.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #19
    Re: Why no AC Panels
    Cariboocoot wrote: »
    Tony;

    When you look at the complexity of the existing systems (GT being the "simplest") you can see that squeezing it down to the panel
    At the panel cell level, however, there's no way of getting AC pulses out of the semiconductor material at this point in time.

    put the panel on a lazy susan, and spin it around very very fast :roll:
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #20
    Re: Why no AC Panels
    bmet wrote: »
    put the panel on a lazy susan, and spin it around very very fast :roll:

    To avoid the waste of only using one-half of the cells at a time, one would have to have a circuit that swapped the + and - leads of the cell string inside the panel at the desired output frequency. Wait a minute, that is just a very dumb mini-inverter. :-)
    I do like toying with the idea of a rotating commutator that converts the DC to a nice square wave. Solid State! That can be achieved by putting the panel on a the lazy susan and taking the output from a commutator and brushes. And the lazy susan can be turned by a wind turbine.
    SMA SB 3000, old BP panels.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #21
    Re: Why no AC Panels

    How about tubular modules (a la Solyndra) spinning at 60Hz? You could split the tube circumference into two banks of cells and capture their output separately. Unground the array and flip the polarity of half the tube. Each half would generate half the AC wave and the current waveform would taper to and from zero according to how much of its surface is exposed to sunlight. Handle the overlap with offset biasing the same way you handle the output of push and pull tubes in a class AB amplifier.

    You heard it here first, folks! :D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #22
    Re: Why no AC Panels
    BB. wrote: »
    Don't know all of the issues, but I see high voltage DC as less safe vs 120/240 VAC for many reasons.

    -Bill

    DC is less safe than AC. No doubt about it. DC Voltage doesn't change. AC crosses zero Volts repeatedly through its cycling, making it easier to interrupt.

    A long time ago you had batteries running a DC motor which spun an AC generator to get the conversion. That was a real world solution along the same lines as the "lazy susan" or spinning cylinders suggestion. Same problems exist: extra energy use to provide the AC output, greater complexity of the device (compare to existing inverters), and cumbersome size. Not at all like Tony's inquiry into doing it at the solar panel level (solid state device directly outputting AC from photon exposure).
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #23
    Re: Why no AC Panels

    Not to mention that - supposedly - while you get thrown off of AC if you accidentally touch it, you clamp down on DC so ... you never let go. Makes sense. So that's another strike against using DC as the standard. Not to mention the massive wires necessary if you stick with lower-voltage DC.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #24
    Re: Why no AC Panels
    techntrek wrote: »
    Not to mention that - supposedly - while you get thrown off of AC if you accidentally touch it, you clamp down on DC so ... you never let go. Makes sense. So that's another strike against using DC as the standard. Not to mention the massive wires necessary if you stick with lower-voltage DC.

    We just had a lightning strike on a transformer pole a couple days ago. I didn't realize these poles had fuse protection. The 'fuse' was thrown off its connection by the strike. An electric co-op crew showed up a couple hours later and simply pushed the the fuse back onto its connection point, we had power again!.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #25
    Re: Why no AC Panels
    techntrek wrote: »
    Not to mention that - supposedly - while you get thrown off of AC if you accidentally touch it, you clamp down on DC so ... you never let go. Makes sense. So that's another strike against using DC as the standard. Not to mention the massive wires necessary if you stick with lower-voltage DC.

    One of those subjects where you can find an authoritative published source for any opinion you want to put forward.
    Unambiguous (IMHO) common threads:

    1. In terms of lethality of a given current for short exposure, AC in the 50/60 Hz range is more than four times as dangerous as DC in terms of setting the heart into fibrillation. (Defibrillators use a DC pulse to stop fibrillation and allow the heart to beat again.) Higher frequency AC (Tesla coil range) is much less harmful since it flows mainly on the surface layers of the body. But nobody will use that for power transmission.

    2. If you just brush against the live conductor, DC is marginally more likely to throw you away from it. But if you grab the conductor, either AC or DC will cause muscle contractions that will keep you gripping the conductor with enough strength that a bystander (wearing insulated gloves) will have trouble pulling you away. Opinions differ about the relative strength of the contraction between AC and DC for the same current.

    3. If there is a short circuit at very high voltage, DC is much harder to interrupt because the current does not pass through zero allowing the ionized air carrying the arc current to dissipate, preventing the arc from restarting. (Does anyone want to make comparisons between AC and DC arc welding?)

    4. When swimming in electrified water, there is no question of "letting go" and the increased lethality of AC to the heart is the determining factor.

    5a. Nobody will question that just comparing AC to AC or DC to DC, higher voltage is more dangerous as long as the current is not limited. (I see the rebuttals coming in already.....)
    5b. But a high voltage source which is limited to a low current is less dangerous than a lower voltage source that can deliver more current through the body.
    SMA SB 3000, old BP panels.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #26
    Re: Why no AC Panels
    bmet wrote: »
    We just had a lightning strike on a transformer pole a couple days ago. I didn't realize these poles had fuse protection. The 'fuse' was thrown off its connection by the strike. An electric co-op crew showed up a couple hours later and simply pushed the the fuse back onto its connection point, we had power again!.

    We call those circuit breakers, not fuses. Pushing on a blown fuse should have no effect at all. But it is common to call something which is protected by either a fuse or a circuit breaker "fuse protected" or "fused".
    SMA SB 3000, old BP panels.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #27
    Re: Why no AC Panels

    It may be a semantic difference but I believe that utility transformers duo use fuses. The difference is that a fuse is a link that melts and opens when subjected to over current. A breaker opens under over current, but can be reset. The utility fuses can be opened, but when they blow, they need to be replaced if I am correct.

    The fuse is on the inlet side of the transformer. If you look up at the pole, you will see the primary, with the pig tail feeding the transformer, you can see it clearly. If you watch a lineman working on your service drop, he will pull that fuse open with a clamp pole to open the circuit. Since the fuse is on the primary, it is (I'm sure) a smaller amperage fuse.

    Tony
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #28
    Re: Why no AC Panels
    icarus wrote: »
    It may be a semantic difference but I believe that utility transformers do use fuses. The difference is that a fuse is a link that melts and opens when subjected to over current. A breaker opens under over current, but can be reset. The utility fuses can be opened, but when they blow, they need to be replaced if I am correct.
    Tony

    Not doubting that, Tony.

    Just looking at bmet's description of pushing the fuse back into place rather than inserting a new fuse and deducing that what opened in his case was not a fuse.
    (Unless the protector in question could either open mechanically under violent overload or open thermally as a fuse under chronic overload.) Also the protective fuses are, I believe, usually mounted internally in the transformers, not externally on the pole.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #29
    Re: Why no AC Panels

    Attachment not found.

    He's talking about the line disconnect as seen in this photo: upper left of the transformer. Technically it is a type of circuit breaker in that it breaks the circuit when overloaded. So does a fuse. But a fuse has to be replaced. These are meant to literally pop out (swings down from the top) when current is too high and can be pushed back in to restore service. In fact the linemen use long hooked poles to pull them out when there's a wide-spread blackout so that they can control where the power goes when its available again rather than have the whole demand hit the grid at once which would just cause another blackout!
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #30
    Re: Why no AC Panels

    That's the picture I was looking for! Doesn't the disconnect have a fusible link in it however?

    T.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #31
    Re: Why no AC Panels

    I took that outside the house in Langley when we were trying to determine something about power for a guy in the Philippines I believe. Useful reference photo! :D

    As far as I know there's no fusable link; nothing to replace. Honking big bimetalic element pushes the rod out when the current goes critical. Not an area I ever worked in so I could be wrong about that. Someone on this forum must be a lineman; we've got every other kind of tech here!
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