Slowly built grid-tie system. First panel, expected results. Second panel, poor results. A little help, please?

[KnightLune]

So, as some background, I am COMPLETELY new to solar in general. So go easy with me. My only real best method of learning is diving right into things myself. I've been trying to keep up with reading and other methods of educating myself, including videos and whatnot, for the past six or seven months. To say I am a little green is an understatement. I am also poor as heck, so dropping money on anything "good" is a bit out of the question for me, though I'd eventually like to upgrade to better equipment. I've been looking for cheap as heck hardware on sale, mostly imported from China, and... yeah, I'm aware this sounds like a train wreck already.

That said, a couple of weeks ago, I decided to bite the bullet and buy a cheap ($40-ish, at the time) 100 watt panel that was on sale on Amazon. Specifically, a WEIZE 100 watt panel as detailed in the attached sticker image. With it, I got a 140 watt Y&H grid-tie micro inverter at another ~$40. Also displayed in the Attachments.



I hooked up the two properly, and ran it directly to the wall to see that under peak hours I was getting roughly ~85 watts from it. This was acceptable for me, and I figured the performance was suffering slightly due to potential angle mismatch, plus the efficiency of the gear in question. Whether this is the case or not is up for debate. If it's hardware-related, please do let me know!

Cool. So, it worked. I was pretty excited since it was my first ever foray into doing something like this, period, and as simple as it may seem for some, was pretty difficult for me, but it worked. Woo!

At this point I decided to snag a deal on a new 190 watt panel from HQST, since I heard good things about their stuff. ~$200 worth of hardware to get this panel and the inverter, plus the cables and everything else that was required. The inverter is from the same brand, but the 180 watt version. Also attached is the info for the devices in question.

Second Panel Info:

• Maximum Power: 190 W
• Open-Circuit Voltage (Voc): 24.3 V
• Short-Circuit Current (Isc): 10.15 A
• Optimum Operating Voltage (Vmp): 20.3 V
• Optimum Operating Current (Imp): 9.36 A
• Operating Temperature: -40°F to 194°F
• Maximum System Voltage: 600 V DC UL
• Maximum Series Fuse Rating: 15A

These two panels are hooked up to an industrial power distribution unit I had laying around from a previous job. The main output from that is connected directly to a plug which is on a separate breaker box with a single 100 amp breaker.

Unfortunately, with these two panels? 170 watt maximum at peak hours on a bright, sunny day. I understand that the inverter is rated for a max of 180 watts, with a max output of 150 watts, but unless I should have failed third grade math, that means that I should, in theory, see 250 watt output with both inverters and these panels. However, most of the time, with both panels connected, I'm lucky if I see 170 watts maximum. So I'm missing out on 80 watts?

Can someone provide some insight here? If I'm missing some details that are required to receive assistance, please let me know. If I'd be better off with another micro-inverter for the second panel, recommendations are welcome. I do have free returns on the inverters for the next twenty or so days, and if I just fudged and bought the wrong stuff... well, my bad. Though at least I learned my mistake.

Looking forward to hearing your responses, but please do go easy on me.

 

[time2roll]

Just to clarify.... there are two panels 100w and a 190w. Are there also two inverters?

How are these wired? Everything should be separate and independent.

How does the industrial power distribution get connected? Does it combine the solar panel DC power directly? I suspect the combiner is the issue as the panels are not matching voltage.

 

[KnightLune]

There are two of the grid-tie micro inverters. The information sheet shows the two different models. One is the 150 watt (on the 100 watt panel) and the other is the 180 watt (on the 190 watt panel).

Each panel is connected to the respective micro grid-tie inverter.

From the AC plug on each inverter, I have these going into the industrial PDU. The PDU is basically just a glorified power strip designed to carry much more power than a standard power strip would allow. There's no reason to use it other than the fact that it was there, I had it, and there's plenty of room for more connections if needed.

So literally I have two independent micro grid-tie inverters essentially going to a multi-outlet which is connected directly to the outlet in the workshop - something I was led to believe is feasible and valid without causing issues. Is this not the case?

 

[time2roll]

That is different than I imagined and sounds like it should work fine.

Have the inverters been plugged in separately to test them one at a time? I would use the same respective connectors for each.

 

[Hedges]

I hooked up the two properly, and ran it directly to the wall to see that under peak hours I was getting roughly ~85 watts from it. This was acceptable for me, and I figured the performance was suffering slightly due to potential angle mismatch, plus the efficiency of the gear in question. Whether this is the case or not is up for debate. If it's hardware-related, please do let me know!

This part is exactly as expected.
The panel produces 100W under "STC", standard test conditions (which are described on the sticker, including spectrum, 1000W/m^2, panel at 25 degrees C.

In operation, it is usually heated by the sun which reduces output power. And your sunshine and haze may vary.
85% of STC rating is typical. A few panels do worse.

Sometimes "PTC" performance test conditions output is also quoted. Elevated temperature and a cooling breeze.

As for your less than expected performance with both panels/inverters, As Time2Roll asks, how do each perform? Your results are about what we expect from the larger one by itself.

PDU? Is it anything other than just conductors? Control and measure circuitry, perhaps?

How do you measure wattage out?

 

[KnightLune]

I was hoping to get a chance to test out the performance of each panel individually today, but it just remained too cloudy and too sporadic to get any good results. I'll have to test isolating them some other day when the sun is actually out. Kind of hard to judge when I'm getting an average of 40 watts for the day with slight few-second-long bursts of ~130 to ~180 watts.

In regards to the PDU, it's a 4u rack mountable one with energy monitoring per port. Aside from that, no fancy bells or whistles. Using a simple smart plug with energy monitoring before or after it provides no different results, so I doubt the extra hardware there is causing any issues. Even ignoring the PDU and smart plug and just using a standard Kill-a-Watt device at the wall outlet provided identical (+/- 2W) readings.

Just a sanity check for the 190W panel with the 180W inverter, here. Given the spec sheet I posted and the listed specs for the panel itself, is this a good match, or did I just mess things up and get something that's hampering its ability to produce the rated production of the panel?

I'll report back tomorrow when I can get some decent results. Hopefully the sun will cooperate.

 

[Hedges]

I think numbers for 190W panel and 180W inverter line up.
New panel, you said, so don't expect defect or degradation?
Could try new panel with 140W inverter. Hmm, not on the spec sheet. Different model?
Does the 180W inverter need communication to start? Some require additional electronics. Try 100W panel on it.

 

[KnightLune]

Okay, so I had some time to mess with the panels, isolating each panel and trying a single one with their respective inverters.

With the 100W panel, and the 150W inverter, I'm getting roughly 85-90 watts during peak production hours. As stated before, this is to be expected, and I'm glad to be getting that from the cheapest of the two panels.

With the 190W panel and the 180W inverter, I'm getting anywhere from 115W to 125W. I have not seen it budge from that point. For the heck of it, I decided to throw the 100W panel's inverter onto the 180W panel and I seem to be drawing the same maximum that the 100W panel does.

I'm really not sure what to take away from this. Could there be something wrong with the panel itself? Is the problem with the inverter? Is there any way I can quickly check this out? If the problem is indeed with the inverter I can quickly get that replaced, but the return window is closing on that and I wouldn't really know of any other cheap alternatives that would work, so suggestions are welcome at that point.

Thanks for your patience and help up until this point, guys. It has been greatly appreciated!

 

[Hedges]

Have you tried 100W panel on 180W inverter?

It is possible for a panel to put out reduced wattage.

Voc is easy to measure with a voltmeter.
Isc can be measured with a meter, if it goes high enough. I would turn panel away from the sun while making/breaking connection, to avoid arcing. (Or I use a suitable DC rated switch.)

More difficult is Vmp, Imp. I did some math and connected multiple electric radiator heaters to get a V(load), I(load) close to that. With multiple panels of same model, I could compare and spot outliers.

Bad cell and bad diode are possibilities. But you said "new", so don't expect that.

 

[KnightLune]

I would try putting the 180w inverter on the 100 watt panel but the 100 watt panel has a lower operating voltage that wouldn't allow the inverter to even function.

That said, upon reading the spec sheet and consulting with other people using the 180 watt inverter I have, it operates with a maximum output wattage of 150W under optimal conditions, and often times runs much lower than that. So the inverter I'm using is essentially going to see roughly 120-130 watts unless it stays in a very cool environment, which I just don't have. Bummer.

I suppose I should look for a replacement grid tie micro inverter here, unless I'm just looking at things wrong? Willing to take recommendations for something that'll fit the following panel specs, just so I have some other heads checking me out, here.

• Maximum Power: 190 W
• Open-Circuit Voltage (Voc): 24.3 V
• Short-Circuit Current (Isc): 10.15 A
• Optimum Operating Voltage (Vmp): 20.3 V
• Optimum Operating Current (Imp): 9.36 A
• Operating Temperature: -40°F to 194°F
• Maximum System Voltage: 600 V DC UL
• Maximum Series Fuse Rating: 15A

 

[Hedges]

Is it? GMI180L says 16 to 25V
Panels says 18.78Vmp; I'd rather have more headroom for hot weather, but should operate.

What you do have to watch is not to exceed 30Voc max rating of the inverter. "12V" panels are OK, but most larger panels are "24V", and exceed 30Voc

 

[KnightLune]

Seems like the inverter did in fact work with the 100W panel. No difference in performance, though. 100W panel still provided an average of 75-85 watts at peak hours. 180W panel averages 110-120 still with the same inverter.

Using a multimeter, the 190W panel seemed to provide pretty accurate numbers to what was advertised. So it doesn't SEEM like the panel itself is causing any issues. So is it just the 150W max output that the inverter provides that's the issue, or am I looking at something else on top of that? Because I still only see a hair, at most, higher than 120W max out of this 190W panel.

 

[Hedges]

Using a multimeter, the 190W panel seemed to provide pretty accurate numbers to what was advertised.

Which numbers, Voc and Isc?
It is possible for a panel to perform well on both of those, yet deliver reduced power. I had a couple that did.

Measuring PV panel performance

I suppose I could buy a solar panel tester like Will reviewed, but that doesn't feel DIY enough to me. Besides, I'm a cheapskate, and I try to do things in the most difficult (and expensive if the equipment wasn't on hand) way. I'm presently working on an underperforming string of Sharp 165W...

diysolarforum.com

But since yours is new, that shouldn't be the case.

The panel may have output reduced more under operating temperature or illumination conditions than the other panel.

Could be something about the inverter. 150W rated, 160W max. Maybe needs more voltage to hit that wattage?
Oh, efficiency is about 90%. Figure panel actually puts out 85% of rating at best.
190W x 85% x 90% = 145W
You get 120W, 18% below expectation. Maybe illumination getting through whatever moisture and dust is reduced that much.

Do you have panel aimed directly at the sun, at noon?

 

[McKravitts]

Can someone provide some insight here? If I'm missing some details that are required to receive assistance, please let me know. If I'd be better off with another micro-inverter for the second panel, recommendations are welcome. I do have free returns on the inverters for the next twenty or so days, and if I just fudged and bought the wrong stuff... well, my bad. Though at least I learned my mistake.

Looking forward to hearing your responses, but please do go easy on me.

Like you, I'm new to solar and had a similar experience.
My issue stemed from the fact that most cheap chinese made inverters are built more for foreigen markets which for the most part don't have split phase. I'm not sure if this applies to you or not, but for what it's worth here's what I discovered.

I connected my cheap chinese Y & H grid tie inverter to my 240 split phase line and at first thought I wasn't getting full power. I loaded one leg with know loads and it appeared that I was only getting 1/2 the power I expected.
After taking some measurements I discovered that half my solar power was going into one leg and half into the other regardless of the load on either leg.
I'm not sure where you live but my power company is on a mission to punish roof top solar owners. They changed the meters such that you get charged the same for providing power to the grid as you do for using it, unless you have them install a new net metering meter.
This net metering meter gives two readings and they credit you about 1/5th the cost per KWH you supply as what they charge you per KWH. I still use the original meter.
So for the brief time I was doing my test I was paying the power company to give them half my power.
I'm experimenting with solar to liberate myself from the monopolistic power company, but to do it by playing by "the rules" isn't easy.
Once I learned all this my cheapscape nature made a U turn.
I purchased a sperate stand alone inverter, a 4.8 Kwh battery bank, transfer swithches, battery monitor etc.
I built a simple circuit that monitors the loads and whenever my output exceeds my usage, it auomatically switches to battery charging.
It's a bit of a pain at this point to keep my batteries soc at a point where it is available to accept the charge, but I'm working on automating that as well.

Good luck with your solar experimenting. Just remember, the more you learn, the more expensive the habit becomes.