DC Engineering question.

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Adamjamma said:
However, there is a lot of waste in doing that and this means you must over size your battery systems, and your solar or wind or water generation systems, to account for the waste in the inverters.
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Most/all of the grid tied solar inverters I work with have CEC weighted efficiencies of over 97%.
 
most people who grid tie are not going to worry about 12 volt lighting etc... they just want to reduce their overall electric bill.
Meanwhile, you have people like myself who have first hand experience of storms, storm damage, weeks sometimes waiting to get the electricity fixed... because we live in rural areas and cities and hospitals take priority, so we actually try to set up for long term off grid usage rather than grid tied...

That said, have never actually seen any inverter truly give more than 70 percent power conversion, and used to seeing other losses as well... but, have nort been watching grid tied for last ten years either, so perhaps advances have occurred there. One thing I have been watching is the micro inverter but, it does not really lend itself to too much off grid work.. it can be adapted for off grid but so far only see using it for things like Water Pumps/Pressure Pumps and Cooking and Washing appliances.. specific circuits that can be switched locally if my bypass does not work..lol... or that I can do without for a few days after a storm...

Advantages of micro converter systems is the conversion to 120 or 240 voltage, at panels, usually two panel tied and a series of 7 to make circuit, ties in pretty well with usage circuits in day time. Easier to use the power without extra steps in day time and to set up portable sets for field use... draw back is the complexity sometimes of setting up a local power circuit to trip the inverter shutdown circuits, as usually off grid...
 
Adamjamma said:
That said, have never actually seen any inverter truly give more than 70 percent power conversion...
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Measured how? If you are comparing inverter output to the STC DC power rating of the PV array, the "losses" you are seeing are not happening in the inverter. STC conditions virtually never exist in the real world.
 
Adamjamma said:
Fionna the thread has, like many, gotten away from the original post. Original post started about RGB LED lighting. I myself took it way in one part about why we size wires different sometimes for dc work, and how when doing dc work we go up in size quicker for voltage drop than many electricians are used to, because of how 12v dc and 24 v dc react to voltage drop.
Very sorry for confusing you.

In the normal consumer world, it is perhaps easiest to simply throw a bunch of inverters into the building, running off a big bank of batteries, and just run everything using 120VAC rules as per NEC, or 240 VAC rules as per UK or EU country rules... depending upon where the building will be, and what you are allowed to do.

However, there is a lot of waste in doing that and this means you must over size your battery systems, and your solar or wind or water generation systems, to account for the waste in the inverters. Some of that waste is able to be in part forgotten about by not using inverters for what you do not need to invert, because enough replacement items are available. One area is lighting.
Case in point... You install lighting in bathrooms and ceilings and kitchens using low voltage lighting that requires transformers to go from local AC to 12 volts. You are using solar on the building and have a 12 volt battery bank powering a 120 volt inverter. So, knowing there is loss in the transformer from 120 volt AC to 12 volt DC in the wiring, and also knowing there is loss in obtaining the 120 volt AC from the battery bank via the inverter, do you then wire 12 volts directly from the battery bank to the lighting, thus reducing loss? Or do you just accept the losses?
Currently the answer is Accept the losses, not just because it is easiest but because of two additional factors... Cost of wiring for the 12 volt voltage drop, and the fact it is very hard to find switches rated for the constant use in 12 volt dc systems that look nice for residential and even commercial use. You say then just use nice looking AC switches but they will not hold up due to ARCing... I am not an expert but am simply learning this vast thing called Electrical work, but, from my own forays into off grid living, I can tell yyou that arcing is a problem when using AC switches on DC circuits.

However, some people wire like I do, as far as trying to get around such things, and do use 12 and 24 volt circuits where lighting does not need turned on and off all the time, or where there are other control methods. Methods such as relays.
Sorry again for taking this circuit off what it was asking.
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Why would you switch high DC amps anyway? I would perhaps use mA rated switches and opt for an Omron SSR to switch on/off the amps at point-of-use. This way you dont need any heavy wire at switch location.

Leviton and the like make std looking DC toggles. It's a tad more complicated but at least the heavy load switching is done via solid state and not mechanical contacts.

After reading all the posts I think you are not doing it right, at least not right for the application you are describing.

Anyways, good luck.

And just no make note on some of the inverter comments, Samlex 48vdc/120vac true-sine run at 90% efficiency.
I'll need to dig some, but it appears a play on words that Solar PV's have inverters that run 98% efficient.
 
FionaZuppa said:
I'll need to dig some, but it appears a play on words that Solar PV's have inverters that run 98% efficient.
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I'd like to see what "play on words" you are speaking of. PV inverters are tested and vetted by the California Energy Commission and their CEC weighted efficiencies are published on their data sheets.
 
ggunn said:
I'd like to see what "play on words" you are speaking of. PV inverters are tested and vetted by the California Energy Commission and their CEC weighted efficiencies are published on their data sheets.
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well, most true-sine power inverters, the good ones that i know of and have used, get only up to ~92% efficiency. i am curious as to how PV micro inverters gain an extra 6%.

i have a few contacts i am asking.
 
FionaZuppa said:
well, most true-sine power inverters, the good ones that i know of and have used, get only up to ~92% efficiency. i am curious as to how PV micro inverters gain an extra 6%.

i have a few contacts i am asking.
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It's not just micros. I don't know of a PV GT inverter with a quoted CEC efficiency less than 96% or so.
 
FionaZuppa said:
well, most true-sine power inverters, the good ones that i know of and have used, get only up to ~92% efficiency. i am curious as to how PV micro inverters gain an extra 6%.

i have a few contacts i am asking.
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There are fundamental design differences between standalone inverters (whether pure sine or Modified Square Wave) and grid interactive inverters which may allow the latter to reach greater overall efficiency.
 
But many of us in the off grid and backup emergency style systems do not purchase grid tied inverters. Micro inverters show the greatest conversion percentage and that makes sense because first your dc line loss is less than two feet usually... your panels are usually the better panels with three areas on each panel, and then you are running most of your system in AC power, which suffers less loss at low and medium voltage than DC power does.

However, you then, if using a DC battery bank, still need to convert from AC to DC, charge the batteries, and when needed, convert from DC to AC... the shorter your dc runs the better, but still you are converting the power three times, with even 6 percent losses each time adding up.

No panel eve4 gets what the manufacturers claim, due to sun angle and other factors... but they still do a decent job of conversion to DC... and keeping your losses down along the way, from voltage drop to consumer use, is key. The big advances in grid tied seem to be in commercial sectors using large transformers rather than 120 volt inverters. Also you are starting to hear of AC battery banks being developed.

No, I do not know everything about solar, but I have been looking at alternative energy and conversions since I was a teenager, building my first transformers using parts from the radio shack and ham radio stores to make my radios work. I don’t keep track of newest inverter designs as have so many items on my plate. But, I do know 5hat any time I hear of an inverter having anything above 90 percent efficiency, I treat it like I do the free energy from air claims, with some skepticism until I can get more facts. If only because even your car alternator has losses when charging a battery, or at least all my mechanics and friends who repair alternators tell me, and that loss is in heat usually.
 
Just one comment on the above: Microinverters are grid tied inverters, just as string inverters are. They can only produce AC when connected to a stable, low impedance source of AC with the capability of absorbing essentially limitless power (i.e. the grid or a very particular microgrid). They are not particularly useful in off grid or battery backup applications.
 
Adamjamma said:
...any time I hear of an inverter having anything above 90 percent efficiency, I treat it like I do the free energy from air claims, with some skepticism until I can get more facts.
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Apples and oranges. The "free energy from air" claims are by fly by night websites and such with no oversight of any kind. The published efficiencies of grid tied inverters are backed by a reputable evaluating agency with rigorous testing facilities. What other facts do you need?
 
GoldDigger said:
Just one comment on the above: Microinverters are grid tied inverters, just as string inverters are. They can only produce AC when connected to a stable, low impedance source of AC with the capability of absorbing essentially limitless power (i.e. the grid or a very particular microgrid). They are not particularly useful in off grid or battery backup applications.
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That's gonna change next year with something called the Enphase IQ8.
 
GoldDigger said:
There are fundamental design differences between standalone inverters (whether pure sine or Modified Square Wave) and grid interactive inverters which may allow the latter to reach greater overall efficiency.
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What diff? Most are IGBT based.

The CEC & Euro efficiency rating are weighted across some points of % rated output. This leads to higher numbers.

I simply like to see input power vs output power across every 1% of rated max power output.
 
after some digging, it appears PV inverters are really no different than standard RV style inverters. PV ones though get gain in efficiency (literal Eff, not CEC weighted) because they operate at higher DC voltages thus reducing amps and reducing input losses.

In general, the silicon used across most modern-day inverters, be it PV ones or other, are about the same.

600vdc to 480vac are very efficient because the amps are low.
12vdc to 120vac not so efficient because the amps are way higher.

so the simple relationship of transmission loss still apply:
<A | >Eff
>A | <Eff
 
ggunn said:
That's some pretty old data, but the ones I looked at all showed efficiencies >96%. Isn't that what I was saying?
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old or new, probably just there because they were rated for CEC at some point.

the higher Eff #'s come from the higher voltages used in PV systems.
 
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