Inverter putting out only half of panel rating

[ATSman]

The following is a discussion between myself and the grid-tie inverter supplier I bought from on eBay (read from bottom up
One thing I want to add is if I hook up only one panel (240W) to the inverter I get max of 170W out of inverter.
Anyone have any ideas?

Thanks for your honesty, Ronnie. I am curious to know if any of your other customers are
having a similar problem with their systems.
I do some more research thru forums and discussion groups to try and find an answer,
Let me know if you find out what is going on. I will keep in touch.

Tony
----- Original Message -----
From: Ronnie Freeman
To: Tony Tonon
Sent: Sunday, September 16, 2012 6:19 PM
Subject: Re: Low Power output on Grid Tie Inverter


Hello Tony, Sorry i can't tell you why the inverter is doing this, the only thing i can do is that you ship the inverter back to me and i will send you a new replacement. I don't know the tech aspects of these units, If it just stop working then i could trouble shoot it and try to find the bad part, but when everything is working and doing what its doing i have no ideal. Just let me know if you want to send it back and try another one.

Thanks
Ronnie

Thank you,

Ronnie Freeman @ Using God's Free Energy LLC

visit our website: http://usinggodsfreeenergy.com/ for even better deals!

email: ronnie.freeman@rocketmail.com


From: Tony Tonon <tonytonon@sbcglobal.net>
To: Ronnie Freeman- GTI.co <ronnie.freeman@rocketmail.com>
Sent: Saturday, September 15, 2012 10:08 AM
Subject: Fw: Low Power output on Grid Tie Inverter



Not sure you got this.

Tony

----- Original Message -----
From: Tony Tonon
To: Ronnie Freeman- GTI.co
Cc: Tony
Sent: Thursday, September 13, 2012 7:38 PM
Subject: Low Power output on Grid Tie Inverter


Hi Ronnie,
I though it better to talk to you direct. See attached emails explaining that I am getting only half the power
output from the 600W inverter when the (2) 240W panels are connected.
Please note that I measured 8 amps short circuit (ammeter directly across panel terminals)
It is only when both panels are connected in parallel to inverter does the current drop to 4 amps (1/2 of rated)
I am also attaching the panel spec and pic. I am interested to hear your comments and let me know if you need more info.
Thanks

Tony

 

[BillK-AZ]

I suspect that the PV module is not really UL Listed because if it were UL would not approve a label that does not reference UL1703 and a file number.
Likewise the inverter does not appear to be UL1741 Listed and may be dangerous to use. The voltage and frequency specifications are not that of a UL listed grid-tied inverter.

It seems from the available data that the inverter has an input voltage range suitable for or intended for two SERIES modules, but no specification on maximum allowable open-circuit voltage, so no way to know if it can be used with two modules in series.

Many other questions on your performance tests:

• You will only get the full rated output of the PV module with full 1000w/m? sunshine on the module and a cell temperature of 25?C/77?F. Testing at other conditions requires test translation. Can you do this?
• How are you measuring the power output?
• Have you checked the voltages and currents of the PV modules? if so, please post.
• Sounds like you expect this to be plug-n-play. There are many requirements in making a safe installation.

You are playing with parts that can be dangerous. Please get a licensed electrician to help on this.

 

[ggunn]

This isn't one of those inverters that you just plug into a receptacle in your house wiring, is it? If it is, then all bets are off and you are risking a fire and/or being excommunicated by your utility company.

 

[SolarPro]

Definitely an off-brand PV module, but maybe it's listed. The inverter is the bigger concern, IMO, since it's the interface with the utility. I'm not aware of any listed products that fit this general description. It it's not listed, you're definitely playing with fire. The utility doesn't want you plugging in a non-UL listed coffee maker, let alone a device that exports power back to the grid.

RE: the output power question. The modules could be fine. The products is rated for 240 watts under a very specific set of conditions that you are unlikely to see in the field on a regular basis (irradiance of 1,000 watts per square meter, 25?C cell temperature, etc.) and there are conversion losses through the inverter. If the actual irradiance is 800 watts per square meter and the cell temp is 40?C and the inverter 92% efficient, then 170 watts out of a 240 watt module probably means "everything is okay." (Note that the module power tolerance is ?3%.) The problem is that unless you can measure the instantaneous irradiance and cell temperature, you can't verify whether the actual output power matches the expected output power.

 

[ggunn]

Definitely an off-brand PV module, but maybe it's listed. The inverter is the bigger concern, IMO, since it's the interface with the utility. I'm not aware of any listed products that fit this general description. It it's not listed, you're definitely playing with fire. The utility doesn't want you plugging in a non-UL listed coffee maker, let alone a device that exports power back to the grid.

RE: the output power question. The modules could be fine. The products is rated for 240 watts under a very specific set of conditions that you are unlikely to see in the field on a regular basis (irradiance of 1,000 watts per square meter, 25?C cell temperature, etc.) and there are conversion losses through the inverter. If the actual irradiance is 800 watts per square meter and the cell temp is 40?C and the inverter 92% efficient, then 170 watts out of a 240 watt module probably means "everything is okay." (Note that the module power tolerance is ?3%.) The problem is that unless you can measure the instantaneous irradiance and cell temperature, you can't verify whether the actual output power matches the expected output power.

Uh oh.

http://usinggodsfreeenergy.com/shop...xRZiCW8DCE9qjzwUFNLY&shop_param=cid=1&aid=19&

Run away!

 

[SolarPro]

For sure. If you look at the specs, the max power point for the module is just outside the dc input voltage range for the inverter. And the inverter efficiency is only 85%...ouch! Getting 170 watts out of a 240 watt module sounds pretty good, actually.

 

[ATSman]

Series vs Parallel Connection

Series vs Parallel Connection

For sure. If you look at the specs, the max power point for the module is just outside the dc input voltage range for the inverter. And the inverter efficiency is only 85%...ouch! Getting 170 watts out of a 240 watt module sounds pretty good, actually.

Thanks for your input SolarPro.
The voltage input range for the inverter is 28 to 55VDC. What would you say if I connected the panels in series to the inverter?
The connected voltage would drop from 64VDC open circuit to around 62VDC.
Questions:
1. Would the 62V be too high (13% above 55V) and cause damage to the inverter?

2. This would put me at the higher end of the inverter voltage range. Do you think it wold increase the inverter efficiency
versus the parallel connection?

Thanks again.

Tony

 

[SolarPro]

Tony,

I wouldn't put modules in series without verifying the actual maximum dc input voltage. (If this was a listed device, it would include this information.) But if the dc operating range is 28 ? 55 Vdc and you only have one module in series per source circuit, then the inverter is going to hold the array voltage at 28 Vdc under circumstances where the actual maximum power point voltage is lower than that and you'll never get max power out of the array as a result. In other words, the array is not matched to the inverter and the inverter cannot/will not get the most out of the array. Putting two module in series will solve some MPPT problems and create others; the array still won't be matched to the inverter. Even if the array were matched to the inverter, the inverter you have is only 85% efficient, which is extremely low. (The weighted efficiency for the Enphase microinverter, which is a listed device, is 96%.) Since the product you have is NOT listed, I wouldn't use it anyplace in the world where that was covered by the NEC.

My 2 cents....

 

[ATSman]

Module V x I curve and spec

Module V x I curve and spec

Tony,

I wouldn't put modules in series without verifying the actual maximum dc input voltage. (If this was a listed device, it would include this information.) But if the dc operating range is 28 ? 55 Vdc and you only have one module in series per source circuit, then the inverter is going to hold the array voltage at 28 Vdc under circumstances where the actual maximum power point voltage is lower than that and you'll never get max power out of the array as a result. In other words, the array is not matched to the inverter and the inverter cannot/will not get the most out of the array. Putting two module in series will solve some MPPT problems and create others; the array still won't be matched to the inverter. Even if the array were matched to the inverter, the inverter you have is only 85% efficient, which is extremely low. (The weighted efficiency for the Enphase microinverter, which is a listed device, is 96%.) Since the product you have is NOT listed, I wouldn't use it anyplace in the world where that was covered by the NEC.

My 2 cents....

see attached

 

[SolarPro]

Right. That's the I-V curve at STC, which assumes a cell temp of 77?F (25?C). Put the array in the sun and at least 6 months out of the year the cell temperature will be above 25?C. (Cell temp is usually ambient temp plus 10–15?C.) This means the I-V curve shifts to the left. Now your MPP voltage is lower than the inverter input voltage. Putting the modules in series puts you up against the high operating voltage limit of the inverter. And if the array voltage is too high on a cold day, then you smoke the inverter.

None of this magically turns the inverter into a listed unit though...