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MPP SOLAR Comparison of AC Grid and AC Inverter


MetalFiber
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I was doing a comparison of my rebranded MPP SOLAR AC Inverter output to AC Grid/Utility output.  In my area (Provincial Philippines), it really made a difference in clean power.  The Utility power can fluctuate up to 70 volts on a 230V 60Hz grid system.  I was wondering if anyone else has this experience or is this normal...?

 

 

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Grid power, in places where the grid is well maintained, is usually much cleaner than what even the best sine-wave inverters can supply. A voltage fluctuation in itself doesn't necessarily mean the waveform isn't clean, for that you need to use an oscilloscope.

But a fluctuation of as much as 70V is in itself not a good sign and is definitely not normal. There is a good chance the waveform isn't very clean, though this is mere guesswork at this point.

As a comparison, Power in Cape Town (where the grid is moderately well maintained) fluctuate by less than 10 volts across a normal 24 hour day. What is more interesting here is that the frequency sometimes shifts a bit, I sometimes observe it coming down to 49.8Hz for brief periods. In the last week my Ziehl Anti-Islanding device disconnected once because the grid parameters went out of bounds... but that has been the first time in literally years.

Edit: The reason I can say that grid power is usually cleaner, is that this is what audiophiles tell you. Ask anyone who is into sound or who does sound at big events: They prefer a large Diesel generator over an inverter.

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  • 1 month later...

I absolutely agree with you.  Grid is definitely much more consistent "if it is well maintained".  I can't say that for this area.  It's not just the fluctuation, but pretty sure its not pure sine wave as you can hear buzzing when using appliances that run almost silent on another grid.  Additionally the power outages are ridiculous.  Two days without power is normal.  There are times where five days of no power can occur.  And you might have five days of no power, the power comes back and then power outage for two days.  Really just ridiculous.  Modern does not exist here.  :)

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On 2018/04/02 at 10:19 AM, plonkster said:

What is more interesting here is that the frequency sometimes shifts a bit, I sometimes observe it coming down to 49.8Hz for brief periods.

I worked at Tutuka Power Station for a short stint in the mid 80's. In the control room the station manager had two wall clocks with second hands, one driven from the 50Hz grid and the other by a separate accurate source. Part of the station managers responsibility was to co-ordinate (with other stations on the national grid) speeding and slowing of the grid so that the second hands of the two clocks remained in sync.

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What is quite fascinating to me is that though you'd expect the entire country to be perfectly in sync (at least anything where the AC is interconnected), it appears that it is possible for smaller parts of it to lead/lag for short time periods, essentially the kind of vector shift stuff that you also find with anti-islanding. I once read a paper about how such signals can be used to predict outages, I think the research/poc was done in India.

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  • 3 months later...

We work on 50Hz here, but even though I live in a semi-decent power area, I have had to allow my Invertors over the years to accept at least a 2Hz offset, and I personally don't think that anything other than extremely sensitive devices are outside a 4Hz offset. My internal SineWave UPS for my computer systems (which I cannot control their settings) do at least once per week switch and scream at me for a few seconds until the Hz comes back into range, but my new house invertor also assists with that.

When it comes to the voltage though, its a lot more tricky, since you are usually feeding more sensitive devices. If your base grid is supposed to be 220VAC, then try not to let your invertor supply less/more than about a 15V difference. Since I have other UPS systems on my sensitive feeds, I do allow my Invertor to do about a 30VAC difference, but remember that our official rate is 220-240VAC. Since 99.8% (my guess) of appliances are normally the same in the rest of the world, then non-sensitive items like stove, kettle,water heater will be fine down to 195VAC (even less, but not really supported). Sensitive items like computers, cell chargers, etc, shouldn't really go below 215VAC, but most will happilly still work properly at 205-210VAC. It really depends on the device.

If you get these fluctuations very quickly (like over a few seconds/millseconds), then you will have a problem with devices that are more sensitive and breakages could occur, then you need to look at surge protectors and probably more complicated protection. But if your day starts at 220VAC, and slowly goes down to 190VAC over 3-4 hours, and then back up to 245VAC (watch the highs over 240, they aren't as forgiving) in the next 5-10 hours or so (ie: extremely gradual movements) then you are probably ok. I worked in Nigeria where we only had bad Generator power for only 1/2 the day and with a decent surge protector we had no major issues.

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