Am I being bamboozled?

[xerxess]

Good afternoon!

So I recently had solar installed on my roof, but my performance thus far has been below advertised. My specs are below (please let me know if I should post something else). Also realize this is a DIY forum, so if I should go find somewhere else on the internet, fair enough (although any recommendations on where appreciated)!

13 panels @ 370w, 4.81 KW total

AC real/apparent 3.77 kVa

Amperage 13

Microinverters



While this was on the low end of promised production (I had some estimates as high as 6-7 KW), these guys had by far the best price, and the technology / service seemed better. My big issue though is that since we turned it on (about two weeks ago), production has peaked at about 3.8 KW. We've had numerous cloudless days over that period, so I was concerned that the system was producing ~20% less than promised. I called the company, and they said that because it was so hot (~90 degrees many days) that the system wasn't operating efficiently.

Maybe this is true - the folks have been pretty responsive so far, and the explanation sounded fair. But I wanted to verify that if folks could provide feedback. Thanks!

 

[E. Cho]

Yes heat does reduce panel output or efficiency as does the panel's angle, which if the angle is fixed, will be a compromise for the time of day and time of year for the panel angle and for your location. Meaning, fixed panels will rarely meet their advertised specs unless all variables are ideal. Also panel watts rating are for a lower temperature standard such as 25°C, which black panels in sunshine usually over reach.

Keep track and there is a government website that shows the best panel angle for the time of day for your location at different times of year but may not show temperature variables.

20% difference doesn't seem too bad for a compromise of variables. Wait till you get a dark overcast day if you want a shock.

The best electrical efficiency is achieved in cool or even cold temperatures, although LiFePO4 batteries prefer cool or the same temperatures that humans prefer. Plus a byproduct of electron generation is usually heat and too much heat can degrade performance of any electrical component.

 

[xerxess]

To respond to your points, the panels are fixed (roof is approximately 45 degrees) and black. Cloudy day today and max was about 1kw.

Thanks for your thoughts!

 

[wheelman55]

Solar modules are rated at “STC”. That’s “standard test conditions”.

STC is lab conditions. Air temp and module temp is 77F. No wind. Using “full sun”, which is 1,000 watts per sq meter (think pointing you modules directly at the sun at noon).

So your 4.81 kw is unlikely to happen very often. Maybe when the sun peaks over the edge of a cloud you could see 5kw. 3.8 kw seems realistic.

We’ve got a 5.2 kw solar array. On cloudy days we’ll see maybe 500 watts. On full overcast days we can see maybe 250. Full sunny days will give us 4kw to close to 5kw. We are ground mount on a horizontal single axis tracker.

We are off grid.

Enjoy the journey!

Here’s a link to STC:

https://www.alternative-energy-tutorials.com/photovoltaics/standard-test-conditions.html

 

[Tomthumb62]

3.8/4.8=0.79

79% efficiency. That’s pretty average. Wait until the cold of winter (if you get real winter) and you’ll see the efficiency go up due to colder temps. But the production likely will go down due to the short days.

There are online calculators that can help you forecast this. Or just enjoy the journey and keep notes. Not sure if your system has a data logger, but even if it does, writing down some numbers each day might be kinda fun.

 

[ncsolarelectric]

You are NOT going to get 4.8kW of power if your microinverters are limiting it to 3.77kVA. That's the most it can provide. I suspect they sold you 370W solar panels, and IQ8+ microinverters that max out at 299W. The most you can get AC is 13 x 299 = 3.89kW. Anything over that will be clipped and lost. The IQ8+ is too small for a 370W panel, and it reduces the ROI significantly.

 

[Quattrohead]

My two questions are what exact model of micro inverter do you have and when your solar power output peaks is it a flat top, IE the micro inverter has reached its limit.
As NC says above, it sounds rather like your panels and inverters are not a good match.

 

[pvgirl]

As others have stated your system will only produce 3.8kws of power out as built. The microinverters that were selected will only output about 290watts continuous maximum. As others have mentioned 370 watts output from the solar panels, is under ideal conditions, and actual output power will be much less. The difference between the power output of the panels and micro inverters will only limit production on those rare times of peak production, and will likely have a minimal impact on the amount of kwh you produce annually. The extra cost of using larger microinverters vs the minimal extra kwh produced frequently doesn't make financial sense.

You can see estimated production for your system using the free pvwatts site, and you can see what effect different micro inverter sizing will have by tweaking the advanced parameter "DC to AC Size Ratio" your system as build has a dc to ac ratio of 1.275.

 

[ghostwriter66]

"these guys had by far the best price, and the technology / service seemed better." ...

Probably as others have pointed out because they went cheap on the microinverters and honestly - for probably the same footprint (dimensions) could have found at least something in the upper 400W range ...

Also --- are the panels pointing DIRECTLY due south???

I see that your inclination sh0uld be about 38-40 degrees giving maximum tracking for MAR 21 and SEPT 21 ... so you're not to far off there ...

 

[pvgirl]

Doing some rough calculations, assuming Washington DC location panels pointed directed south at 39 degrees, with PVwatts the difference between 1.27 dc/ac ratio(as built) vs 0.97 dc/ac ratio(for the IQ8H micro inverter) is only 5 kwh per year, or about 69 cents per year in additional production, at a upfront cost of around $750(for IQ8H vs IQ8+), not really a good deal.

 

[xerxess]

So I must have missed all of these responses - my bad!

So to clarify - as noted, it's maxed at the 3.9 kWh, regardless of weather, day, etc. Panels are perfectly south facing, good tilt, etc.

My confusion is that I was repeatedly told it was a 4.81 kWh system, and no mention was ever made of a 3.9 kWh max. Is this worth complaining to the company about? I hear folks saying it might not make a big difference - fair enough - but it certainly feels dishonest perhaps?

 

[xerxess]

You are NOT going to get 4.8kW of power if your microinverters are limiting it to 3.77kVA. That's the most it can provide. I suspect they sold you 370W solar panels, and IQ8+ microinverters that max out at 299W. The most you can get AC is 13 x 299 = 3.89kW. Anything over that will be clipped and lost. The IQ8+ is too small for a 370W panel, and it reduces the ROI significantly.

This is exactly right. With that being said, I hear pvgirl's point - that apparently it wouldn't make that much of a difference? This surprises me somewhat, as I'm hitting 3.9 kWh every day, so I'd think it would be able to go higher on some days than others. But I also don't know what the hell I'm talking about, so will defer to the forum's expertise.

Again, thanks!

 

[Hedges]

kW, not kWh.
What did they put in writing?

 

[Quattrohead]

They sold you a mustang / Camaro / I don't know my Dodge vehicles LOL with 13 inch wheels.

 

[mvonw]

Gosh, reading these posts, I feel pretty good that my totally self designed/installed newbie/moron 20kwp array regularly produces at 20 Kw for extended periods. So far this fall, it’s been really cold and my system has been cranking at 25kw, when there is sun, that is. Mine point directly south and are at 45 degrees for snow sloughing.

 

[OffGridInTheCity]

I use PVWatts - https://pvwatts.nrel.gov/pvwatts.php - which provides local location weather to estimate future PV. In my case, I get about 80% of what it predicts overall but then I have partial shadows till 11am and last hour of the day.

My point is, run it for you're location as an independent metric and see where you are month to month relative to this. If you don't have ANY shadow or issues like that and future weather is similar to past weather, I'd expect you to get within 90% of what it shows. Even if you're within 80%, you've not likely been 'taken' and might ease you're mind on this.

PV is quite variable!

 

[ghostwriter66]

So I must have missed all of these responses - my bad!

So to clarify - as noted, it's maxed at the 3.9 kWh, regardless of weather, day, etc. Panels are perfectly south facing, good tilt, etc.

My confusion is that I was repeatedly told it was a 4.81 kWh system, and no mention was ever made of a 3.9 kWh max. Is this worth complaining to the company about? I hear folks saying it might not make a big difference - fair enough - but it certainly feels dishonest perhaps?

Unless its CLEARLY in writing on the contract with them stating that the minimal will NOT drop below XXXX then you have - just liked 10's of 1000's of other people - been honestly scammed ...

They quoted you results the verbally told you were probably for June 21st (summer equinox) with no clouds -- and then when you price out all the equipment they actually gave you - you will see that probably 80% of the cost went to Labour and not hardware ...

Calling the company they already have a circular argument script that they give people that leave you more confused then before you call ... OF course sometimes they may have simply just hooked things up incorrectly -- BUT I am going to assume they tested it before they left and got exactly the results that THEY (not YOU) were expecting ... and moved on to the next house ...

sorry about that ---

 

[xerxess]

Unless its CLEARLY in writing on the contract with them stating that the minimal will NOT drop below XXXX then you have - just liked 10's of 1000's of other people - been honestly scammed ...

They quoted you results the verbally told you were probably for June 21st (summer equinox) with no clouds -- and then when you price out all the equipment they actually gave you - you will see that probably 80% of the cost went to Labour and not hardware ...

Calling the company they already have a circular argument script that they give people that leave you more confused then before you call ... OF course sometimes they may have simply just hooked things up incorrectly -- BUT I am going to assume they tested it before they left and got exactly the results that THEY (not YOU) were expecting ... and moved on to the next house ...

sorry about that ---

Well, what they quoted me appears to be an impossible figure - i.e., my system could NEVER produce 4.81 kWh because the inverters can never support above 3.9. I'm also hearing that it is likely that the difference is rarely going to matter, and that it would have cost more to get higher inverters. But still seems like misleading advertising, no? I get that clipping is a thing, but why advertise it as a 4.81 system if it's ALWAYS going to get clipped mid-day?

 

[McKravitts]

They say misery loves company and you have a lot of company out there. There are many web sites exposing the fraudulent actions of solar companies, particularly the salespeople. Here's one article.

One of the biggest lies I've heard several times is that a solar system causes your electric meter to run backwards. Most salespeople don't even know the difference between an off grid and a grid tie inverter and they know nothing about the net metering devices that electric companies install.

I'd say all in all you're pretty lucky getting what you are. I know a guy who paid in excess of $30,000 and was told his payback period was a mere 12 years.
After a few months of collecting data he calculated his payback at over 100 years.

There are many smart people on this forum who can help you beef up your system for a small fraction of the cost a "professional" installer will charge.