Defective Inverter?

nbaker

I have six 100 watt mono panels, wired for 36V.  I have this wired into a cheap 1000 watt grid tie inverter (all over amazon/ebay etc).  Just finished my system setup and turned it on yesterday.  Monday was semi clear skies and no shading and I saw a 500 watt measurement on the AC side around 2PM.  I was OK with that.  Today was a different story.  Cloudless sky, no shading, around noon and I was only measuring 280 watts.  Seemed low to me so I pulled out the multi-meter and measured 43.3V (panel's VOC) with 13.3A right at the DC input to inverter.  By my calculations, I should have seen at least 460 watts on the AC side, and that's even being conservative with 20% inverter loss.  Are these inverters really that inconsistent with their MPPT or are my calculations off since I was measuring before any load.  I'm already looking to return this inverter and spend more money, so any inverter recommendations are welcome.

Photowhit

Sorry, not a lot of time, I copied this from a post I did earlier;

Solar panels rated vs actual output.

Solar panels have a name plate rating. these ratings are based on Standard Test Conditions (STC). In the real world they will produce less. Some now come with Normal Operating Cell Temperature values (NOCT) They are generally about 75% of the name plate.

These means you can expect about 75 watts out of a 100 watt panel. This is what you can expect when the panels are warm/hot. You may approach Standard Test Conditions(STC), in very cold fall days with good direct sun, but it will be rare.

Here are some example of panels ratings, Note the differences between NOCT and STC;

nbaker

Understand that and I'm not expecting to see the full 100 watts per panel. Just not making since between what I measured with my multimeter and what the inverters output was.

wellbuilt

I have a string of 3 295 watt panels and I see 750 watts on a hot day between 10 and 200 pm . 

 If you are charging battery’s and they are full the panels will put out less power . 

wellbuilt

I reread your previous post , and it says you have battery’s in the system , so if you are in absorb and your battery’s are getting full your solar panels won’t show all the power . 

  You can put a 600watt load on the system and the charge controller will put out full power to meat the load . 

 I have 4424 watts of solar and when the battery’s are in float I see 275 watts , if I pull the trigger on 2 saws the system jumps to 3200 watts . 

 I can get 3500/ 3750 watts on a clear day so not so bad

nbaker

wellbuilt said:

I reread your previous post , and it says you have battery’s in the system , so if you are in absorb and your battery’s are getting full your solar panels won’t show all the power . 

  You can put a 600watt load on the system and the charge controller will put out full power to meat the load . 

 I have 4424 watts of solar and when the battery’s are in float I see 275 watts , if I pull the trigger on 2 saws the system jumps to 3200 watts . 

 I can get 3500/ 3750 watts on a clear day so not so bad

I have batteries however they have no connection to this cheap grid tie inverter.  I have a DC switch to completely bypass the charge controller and battery (since I know the bank is full).  I was reading the low wattage directly out of the grid tie inverter, directly feed from the PV.  Im at a loss because my multimeter measurements showed decent wattage (A * V) on the DC input side while the AC inverter output was very low.

mcgivor

Where exactly is the inverter placed? From experience I've seen inverters placed beneath the panels themselves, this in turn  increases the operating temperature of the inverter itself significantly, this may be causing the inverter to reduce its output to protect itself if so positioned.

softdown

mcgivor said:

Where exactly is the inverter placed? From experience I've seen inverters placed beneath the panels themselves, this in turn  increases the operating temperature of the inverter itself significantly, this may be causing the inverter to reduce its output to protect itself if so positioned.

Seem like there is a need for "10 Rules for Solar Success". People keep making the same mistakes over and over and over again. I've seen so many failure directly related to heat issues. Especially regarding batteries.  

It would not be hard. We could start with the  regulars posting up their "Top Rules".

nbaker

mcgivor said:

Where exactly is the inverter placed? From experience I've seen inverters placed beneath the panels themselves, this in turn  increases the operating temperature of the inverter itself significantly, this may be causing the inverter to reduce its output to protect itself if so positioned.

The GTI is in my basement next to the service panel.  Its 68 degrees down there. Its a 60 ft run from the PV to GTI, and I lose about 0.3V during that run.

I have one of those blue (Ecoworthy) GTI's with the LCD screen ordered.  I'm hopeful this has better efficiency since is double the cost.  Yes, I am aware the payback on that extra $100 will take years at 600 watts PV.  I'll comment back once I receive and can compare the output of each.

nbaker

New inverter arrived.  Very little addition in output.  I was measuring the voltage on the DC input without a load so I was seeing the VOC voltage, that's how my numbers were inflated.  Newbie lesson learned.