Overpowering of inverters(con't)

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Overpowering of inverters(con't)

Postby Katie » Mon Jul 18, 2011 4:28 pm

I have previously requested advice on adding 2 more 195W. Solar Enertech panels to my 16 existing panels with my Xantrex 2.8 and was given very helpful advice which turned me off the idea.

I have just read where karlajensen said"
overpowering of a 2kW inverter is fine and recommended by the CEC".
In that thread the overpowering was from 2000 to 2622 which is a 31.1% increase.
My proposal is to increase my setup from 3120W to 3510W which is a 25.4% increase over the 2800W inverter capacity and a 12.6% increase over the spec. of 3100W max. input.

My panels face 42 degrees east of magnetic north (53 degrees east of true north due to magnetic variation) at a pitch of 22.5 degrees.

Max. output which I have seen since May is 2200W. Any furthur advice would be greatly appreciated.

Thank you,
Katie
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Re: Overpowering of inverters(con't)

Postby Gordon-Loomberah » Mon Jul 18, 2011 5:45 pm

Whilst some inverters can handle input significantly over their rated output, and Karl has shown his are working well so far, you might want to enquire as to what maximum PV input you can connect without blowing your warranty. The CEC guidelines are just that, and they do not cover every situation and inverter. As I mentioned in a previous thread, you are already over the manufacturer's recommended input power, but the position of the panels will only lead to a slight reduction in peak possible input power, so it might be best to check the warranty situation before adding any panels. If it wont blow your warranty, then I'd think it is ok to add the extra 2 panels.

There's nothing worse than a blown inverter leading to the discovery of a blown warranty! :o
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Re: Overpowering of inverters(con't)

Postby Gordon-Loomberah » Mon Jul 18, 2011 5:51 pm

Katie wrote:My panels face 42 degrees east of magnetic north (53 degrees east of true north due to magnetic variation) at a pitch of 22.5 degrees.
Max. output which I have seen since May is 2200W. Any furthur advice would be greatly appreciated.


With that orientation and tilt, the sun is never close to face on over winter unless you are in the far North of Australia, so the panels wont be receiving enough solar radiation to produce their rated power- once the sun is more face on, you will see a higher maximum output.
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Re: Overpowering of inverters(con't)

Postby karlajensen » Mon Jul 18, 2011 8:31 pm

If you read the Xantrex book carefully it says not to exceed the inverters max input current with panels that will deliver more than that. (short circuit rating)
It also says you need to remain within the voltage operating window.

Hence 10 panels per string = AOK
and / or upto 4 parallel strings of panels (with short circuit current =<6A)

Ultimately comes down to what your CEC guy will sign off on

24 panels is therefore not out of the question (3 strings of 8 panels) 4560W :D
nor is 20 panels in one string....

Obviously at certain times of the day there will be yield losses :cry:

DC input voltage range 195 - 600 volts DC
Peak power tracking range 195 - 550 volts DC
Recommended PV array size 3070 watts
Maximum array short circuit current 24Adc

Myself:- I'm working in a beaurocratic regime where 5000W is the max inverter and
hence I have to cop some losses with a big array, ask anyone who has a big array
on a smaller inverter and they all tell you the same thing- go for it.

20% overpowering and you wont loose anything more than you can count on one hand yearly
25%overpowering and you'll clip farly regularly but wont be more than 30kWhrs a year or so
30% over and there is going to be some decent clip.

As I said before, I'm perfectly happy running 24 panels on a similarly sized 3000HF SMA
the array over 4300W.

20 panels on the Xantrex is fine by my maths 45V x 10panels =450V gives you a solid 150V up your sleeve
its only 3800W which is 26% overpowered.

I'd be doing that in a heartbeat. :D
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Re: Overpowering of inverters(con't)

Postby karlajensen » Mon Jul 18, 2011 9:43 pm

Oh to put this in perspective
lets take the case of 24 panels on a 5000TL facing Nth at 30degrees
yield would be 7298kWhrs anually

on the 3000HF it would be 6924kWhrs .

Facing East or west on the 5000TL it would be 6370kWhrs

SO for East or West -CEC accredited sparks do this every day but overpowering inverters typically less informed persons call it an unacceptable yield loss, or cheating people.
IN this case just 370kWhrs lost from having insufficient inverter capacity
vs EAST or WEST where some 930kWhrs would be lost for poor orientation

Overpowering Starting to make sense now?
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NW facing SMA 3000HF with 4380W
12x ZNShine panels on 1 string + 12x 180W Solarfuns on the other.
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Re: Overpowering of inverters(con't)

Postby pjp » Fri Nov 18, 2011 12:18 pm

Hi Karl

I have just upgraded my panels from 1.6kw to 2.5kw on a CMS-2000 and it has improved output dramatically, good days 13-14kwh/day and 6kwhr feed in vs previous 1kwhr/day
Since I added rs232 inverter monitoring, through Pro Control, then pvbeancounter and pvoutput.org, I have noticed that once the inverter start producing >2000W, the "clipping" is quite extreme, giving 10minute cycle swings from 2200 down to 600W etc . and hence wasting quite a bit of output (but still outputting 13-14kwhr/day)
I am using a 10w cooling fan (powered by 10W solar panel), which works great, and again monitoring showed a 12deg inverter temp drop. Since then I haven't seen inverter temp over 40deg. so thermal throttling shouldn't be an issue.
Do you monitor your CMS-2000s and if so how does your throttling behave?
I noticed on another thread you were talking about 27-28kwhr yields form 2 CMS-2000 systems, which would agree with what I am getting with my nasty CMS-2000 throttling, although I am in Melb, so you should do even better.
See pvoutput.org, my system is called "CMS2000-2.5kw"
I am talking to Carbon Management Systems and will try a new firmware this wkend hopefully.

Cheers

Phil
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Re: Overpowering of inverters(con't)

Postby Inspector » Fri Nov 18, 2011 7:00 pm

Katie, if you're in NSW and on the 60c tariff, adding panels will void your 60c tariff, so not worth proceeding.

pjp, what discussions are you having with CMS? I presently have what Karl used to have (two strings of 7) and I have not had the drop to 600w output you described, but the inverter definitely clips at just under 2000w even when kept below 45 degrees (cooling fans) for about 3-4hrs of the day (I have output graphs showing this from last summer, and from recent graphs I'm already at the time of the year where it happens). This time I plan to run ducting to provide cold air to the fans from under the house to see if the inverter manages continuous output up to 2200w or so. Another option I have (as I'm not restricted to inverter capacity like people in WA) is to replace that inverter with a 2800 model. But if your firmware upgrade allows modification of the inverter's maximum output then that would be the preferred option (certainly cheaper). I know the CMS2000 can reach over 2500w as I've seen it with my own eyes and have evidence of it datalogged.
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Re: Overpowering of inverters(con't)

Postby karlajensen » Sun Nov 20, 2011 12:32 am

yep me too
but richt and I are in the business of trying to keep it there!

I dont think the throttling is a big enough issue to worry about
16panels 18kWhrs/day
14 panels 16kwhrs a day
12 panels 13kwhrs a day
11 panels 12 kwhrs a day
10 panels 11 kwhrs a day

obviously rough but you get the drift, clip at these levels is costing kwhrs / year not kwhrs/day
hence keep it as cool as you can and add as many panels as you can fit.
16x Nth Garage CMS2000-1 with 2960W in 2 strings of 8.
NW facing SMA 3000HF with 4380W
12x ZNShine panels on 1 string + 12x 180W Solarfuns on the other.
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Re: Overpowering of inverters(con't)

Postby pjp » Wed Nov 23, 2011 1:39 pm

Thanks for the feedback on how your CMS-2000s behave in clipping guys.
I keep getting this 10 minute cycle "oscillation" but haven't had a cloud free day for a while.
Was home yesterday to compare dips with clouds and I think it vaguely correlated.
Maybe there is some natural 10 minute cycle to clouds?? I would have expected more randomness.
Smooth climb up to 2kw observed in morning before oscillating might again be clear morning then clouds developing.
Anyway, can't be sure its not clouds until a nice clear day. Will wait until then before posting again.
23/11/11 1:25PM 6.600kWh 2.619kWh/kW 1,035W 1,200W 0.476kW/kW 47.62%
23/11/11 1:20PM 6.500kWh 2.579kWh/kW 2,099W 2,400W 0.952kW/kW 95.24%
23/11/11 1:15PM 6.300kWh 2.500kWh/kW 620W 1,200W 0.476kW/kW 47.62%
23/11/11 1:10PM 6.200kWh 2.460kWh/kW 624W 1,200W 0.476kW/kW 47.62%
23/11/11 1:05PM 6.100kWh 2.421kWh/kW 2,239W 1,200W 0.476kW/kW 47.62%
23/11/11 1:00PM 6.000kWh 2.381kWh/kW 2,342W 2,400W 0.952kW/kW 95.24%
23/11/11 12:55PM 5.800kWh 2.302kWh/kW 210W 1,200W 0.476kW/kW 47.62%
23/11/11 12:50PM 5.700kWh 2.262kWh/kW 958W 1,200W 0.476kW/kW 47.62%
23/11/11 12:45PM 5.600kWh 2.222kWh/kW 2,105W 1,200W 0.476kW/kW 47.62%
23/11/11 12:40PM 5.500kWh 2.183kWh/kW 1,131W 1,200W 0.476kW/kW 47.62%
23/11/11 12:35PM 5.400kWh 2.143kWh/kW 671W 1,200W 0.476kW/kW 47.62%
23/11/11 12:30PM 5.300kWh 2.103kWh/kW 810W 1,200W 0.476kW/kW 47.62%
23/11/11 12:25PM 5.200kWh 2.063kWh/kW 2,243W 1,200W 0.476kW/kW 47.62%
23/11/11 12:20PM 5.100kWh 2.024kWh/kW 1,535W 1,200W 0.476kW/kW 47.62%

On pvoutput.org my system is CMS2000-2.5kw if you want to have a look at graphs
P.S. It's a real pain that CMS-2000 only reports ETotal with 0.1kW resolution and not higher resolution EToday. It makes the pvoutput Avg Power graphs really choppy.
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Re: Overpowering of inverters(con't)

Postby Tracker » Thu Nov 24, 2011 8:33 am

pjp wrote: giving 10minute cycle swings from 2200 down to 600W etc .

Gee, That's not clipping - That's dumping.. .. The notion of clipping, is that you get a flat-top to the output curve..

What you could try is getting a "Personal Fan" and stand it so as to blow under the inverter, and see what the figure of 600 changes to.
I can only suspect that the CMS2000 is going into a protection mode, and the 10 minutes is the cool down time.
It's a fairly simple job to to use "Stand-Offs" behind the inverter, and bolt 5" computer fans over the cut-outs to provide forced cooling.

PS - I bought a 5" (12V) computer fan yesterday and it is VERY quiet.. Two would be great, and silent.
My 240V fans make a deal of noise, but that does not matter that much, because the inverters are out of the way. The noise is actually handy, as it lets me know that the cooling is cycling correctly.
I can't help but suggest that if "Over-Drive" is planned, then "Over-Cooling" REALLY does go along with it.
Like putting a V8 on a moped and think that the original tyres are suitable.. :lol:
..
.
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