PV Output Exceeds Inverter Rating

What does the manual say about short-term overload capability and duration? Most inverters are designed to handle large overloads for short periods of time and small overloads for longer periods of time.

I read an article on inverters an it said some people go over significantly and that you only have to watch for over heating.

Generally true but this reduces the life of the inverter electrolytic capacitors and as such the life of the inverter resulting in potential premature (and expensive) inverter failure. I cannot stress this enough (heat is not their friend). Overloads should be kept to a minimum if at all possible.

http://en.wikipedia.org/wiki/Electrolytic_capacitor

The article also said to ask the mfgr, but when I do the salesmen are ether clueless or they say "yea, sure, no problem" (I think they just want to sell me the inverter).

Generally salesmen have know idea about these technical sort of things.

GA, thx

I really don't understand this, "results from the PV panel production keep saying....", are you trying to say that your inverter is being overloaded? What is the rated output capacity of the inverter? What is the load? What is the rated output of PV array, is there a battery bank involved? Further what is this mysterious unit "kwac"?

Cheers

Martin

The SAM simulator says PV panel output exceeds inverter rating 1040kwac for 43 hours, The inverer is a pvp260 kw(by PV Powered), have 1491 panels that produce 169.2 watts each (according to CEC and Sandia labs tests). its a 600 volt system. Grid tied, no batteries. I not an electrician by kwac IMHO is kilowatts AC.

If I knew what was going on I wouldnt be here asking questions.

bet you had to rub more than a few pennies together for that

any other sort of data logging?

I thought the inverter had DC as an input from the pv panels?

if kwac is indeed ac, then perhaps your input is wrongly configured?

just a thought.. I'm not an electrician either.

chris

Something doesn't add up here; 1491 panels @169W each equals 252KW (The math is really simple). Now, assuming that 1040kwac, really means 1040KW on the output side (ac) of the inverter, where did the inverter get the energy when the input side is only capable of supplying 250KW?

I take exception to the term "kilowatts AC", Watts are a unit of power, they are not ac or dc, would you describe the output of your car engine as 150hpac?

Cheers

Martin

Accept it, or first read post 8, that poster took the trouble to find the meanings.

Inverter take in DC and put out AC, but as the explanation said, the AC out put is normally smaller than the DC input, thus the rating is given for the output.

Yes, I agree, the question is not clear. Is this (a) An online situation with PV panels connected to inverter and output of inverter fed to grid? OR (b) Is this happening during testing in the production line? & yes, kwac?

Ashok Toshniwal

GAs to more, for the thoughts. I understand everybodies frustration with the lack of info from the post. I am a medical professional trying to develop a 1MW solar farm, so I will try to answer the questions... Don't Know Why.

The SAM simulator from the National renewable energy lab spits this info out at me when I check the boxes.

I guess the bottom line question is; What happens when the input power to an inverter exceeds the the rated input capacity of the inverter for 43 hours out of the year? Does the extra power produced just go to waste like a cup over flowing with water or does it convert the exceeded rating energy to AC but the inverter gets hot and is not happy about it? reducing the life of the inverter?

Thx all for your opinions

Spacecannon

Post #1 still stands, some of the excess power above the inverter's rating still gets converted but with a higher percentage lost through heat (potentially degrading the inverter life).

43 hours out of a year isn't all that much, but again it depends on just how much it exceeded the inverters rating by. There should be enough information in the inverter manual and/or application sheets off the company's website to give you a better idea if this will be an actual problem or if the inverter can indeed handle these (likely) short term overloads during some summer days.

If you haven't already purchased you will likley need to either reduce the number of panels in your design, increase the size of the inverter or perhaps look at your data to ensure you are using accurate real-world (de-rated) figures for sunshine hours rather than ideal model data. Again the application notes on the inverter company's website and solar simulator (?) program should be of help.

Now who took my GA from post #1?

"Now who took my GA from post #1?"

i gave you a replacement ga. _{^{(while your other one is in the shop)}}

I still do not see how the inverter can output more power than the PV array is capable of supplying. There are no batteries in this application. The simulation is simply wrong.

Cheers

Martin

From the previous posts by "space cannon" including the following from post #11

I guess the bottom line question is; What happens when the input power to an inverter exceeds the the rated input capacity of the inverter for 43 hours out of the year?

So two questions really, one is regarding exceeding of the inverters rating and the other is regarding the simulation software result/posted data which may be calculated incorrectly or expressed incorrectly (resulting in the power mismatch).

Ok, thx guys.

Spacecannon

This is pretty strange. If the inverter output exceeded the inverter capability in a simulation, it means the the load was too high for the inverter. The load, however is simulated, so the remedy is to monitor loads in real life. Inverters are protected against overloads. In any event 43 hours out of a year does not seem significant, particularly because the inverter should be overload protected.

Wattage is not wasted, and does not spill out. Wattage requires a load. No amount of available input will cause an output overload. It's not as if putting a 200 amp circuit breaker in your house causes all the bulbs to glow brighter than when the house had a 100 amp main breaker.

My point also, Mr Bumble, it's a simulation, and I want to know how the inverter can supply 4 times the input power! This is even better than perpetual motion..

This is even better than perpetual motion..

Yes. I suppose that the simulation might be including some storage that the OP has not mentioned. I'd think that, for an installation of this size, the OP might be well served by hiring an engineer... this is a little bigger than a system to keep your sailboat batteries topped up!

Not sure of the specs on this particular inverter, but you can always take a PV string off-line for the particular time of year to reduce input. I can't imagine why there would be an issue on the AC side of the inverter as it can only output up to its rating. On the DC side the MPPT may fault to overload, or "kick out" excess production. With a unit like this it is doubtful it would be damaged by an overload situation.

It doesn't matter what the MPPT does, the poster tells us that there are 1491 panels @169.2W each, that's a maximum of 252.3kW, remember no battery bank here. Unless there's been a recall of the Law of Conservation of Energy (actually momentum, but let's not quibble), it is physically impossible for the inverter to supply more than what is available on the DC side. So once again, how the hell can you get an overload that's more than four times the available power on the DC side?

Easy SC [space cannon] has found a flaw in the simulation software...

Yes. I failed to consider that bit of (crucial) information. Perhaps the program is using listed output instead of actual output of the PVs.

Listed? I can only go by what he posted and assume that the values he plugged into the sim program were the same as he gave here. Even allowing for a increase in output of 10% or so if he were operating the panels in sub-freezing temperatures there's no way you can get a megawatt out of a 250Kw array.

Cheers

Martin

Ahh yes. My critical eye has failed me once again.

But, a 169.2 watt panel is probably listed as a 195-200 watt panel.

Hi Space Cannon

As you have probably noticed there has been some confusion and assumptions made regarding your data. Could you post the manufacturer and model number of your solar panels as well as your panel configuration (number of panels in series and parallel connection, if you know it). Do you have a picture of the calculations from the SAM simulator you could post? Perhaps updated data (Garthh mentions in post #24 a possible simulation error).

A lot of us are keen to figure out the solution to this solar array output power discrepancy.