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New solar and Powerwall install, low production?

sorka

Well-Known Member
Feb 28, 2015
9,516
7,818
Merced, CA

"The problem comes when there is not enough shade to activate the bypass diode. Then power drops and the current through the panel drops with it. This drop in current affects the current in every other panel in the series string.

So although bypass diodes help – they only help when you have the ‘right amount’ of shade in the right place."

Repeated in various articles on the same issue if you do a search.

I'll repeat, I'd never buy a system without either micro inverters or individually monitorable optimizers so that I can tell when something goes wrong with a single panel.
 
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nwdiver

Well-Known Member
Feb 17, 2013
8,882
13,014
United States

"The problem comes when there is not enough shade to activate the bypass diode. Then power drops and the current through the panel drops with it. This drop in current affects the current in every other panel in the series string.

So although bypass diodes help – they only help when you have the ‘right amount’ of shade in the right place."

Repeated in various articles on the same issue if you do a search.

I'll repeat, I'd never buy a system without either micro inverters or individually monitorable optimizers so that I can tell when something goes wrong with a single panel.

The first array I built was from laminates that lacked bypass diodes. So not only did I discover how critical they are I also got to ‘play’ with how much shade it took to trigger them. Not much. Shade half a cell and the bypass diode shunts past the cell group.

What’s a little amusing about this is that Tesla won’t even spend $20 to get string level optimization which is ~10x more worth it than module level.
 
Maybe you'll accept what SolarEdge says. They estimate in one instance at 3.6% advantage to the power optimizer approach and a 7% advantage in another (although one unlikely to occur). They also point out that a string inverter with just one MPPT channel and with multiple arrays in parallel would be at a noticeable disadvantage. For recent Tesla installed 8kW systems, the Delta inverter has 3 MPPT channels, and the Tesla inverter has 4 channels, so this possible advantage for optimizers doesn't apply.

Your initial assertion was that "if a panel on a string gets any shading, it brings the entire string down with it." It's simply not true.

I quite agree that string inverters don't provide individual panel monitoring and there is value in that.
 
So micro-inverters or DC optimizers are still the best options?
Best?
  • If cost per delivered kWh is the criterion, string inverters are the best, and micro-inverters are the worst.
  • If the criterion is individual panel monitoring, then probably optimizers are the best, and micro-inverters (Enphase) do well but at a higher cost. String inverters only allow monitoring at the string level.
  • Ease of wiring on the roof favors micro-inverters. Optimizers are the worst, depending on the RSD requirements.
  • Continued generation even though some part of the system has failed favors micro-inverters, and strings are the worst.
  • Lowest number of electronic items that could fail favors strings.
There's more considerations besides the above. I suspect for most people who already have a system installed, whatever they have will turn out to be their idea of "best".
 
Best?
  • If cost per delivered kWh is the criterion, string inverters are the best, and micro-inverters are the worst.
  • If the criterion is individual panel monitoring, then probably optimizers are the best, and micro-inverters (Enphase) do well but at a higher cost. String inverters only allow monitoring at the string level.
  • Ease of wiring on the roof favors micro-inverters. Optimizers are the worst, depending on the RSD requirements.
  • Continued generation even though some part of the system has failed favors micro-inverters, and strings are the worst.
  • Lowest number of electronic items that could fail favors strings.
There's more considerations besides the above. I suspect for most people who already have a system installed, whatever they have will turn out to be their idea of "best".
You left out the most important criteria, efficiency, particularly in relation to why this issue came up to begin with, shading efficiency. It was that specific criteria I was referencing when I said “best”.
 
If efficiency means kW per roof area, then the panels themselves are overwhelmingly the important item. In that case, the IQ7+ with 290W max AC output would be the worst choice because the premium panels put out too much power.

If efficiency means most kWh delivered during shading, then the micro-inverter will be best. But only if cost is not important. Note though that for most situations, shading occurs when solar production is already low due to low sun angles, and the duration of partial shading is short. The absolute difference in kWh is negligible. If some of the higher cost of module level electronics is spent instead on one more panel, the string inverter is nearly always better.
 
The first array I built was from laminates that lacked bypass diodes. So not only did I discover how critical they are I also got to ‘play’ with how much shade it took to trigger them. Not much. Shade half a cell and the bypass diode shunts past the cell group.

What’s a little amusing about this is that Tesla won’t even spend $20 to get string level optimization which is ~10x more worth it than module level.
Not sure I understand what you mean by "Tesla won’t even spend $20 to get string level optimization". What string level optimization are they foregoing?
 

sorka

Well-Known Member
Feb 28, 2015
9,516
7,818
Merced, CA
So micro-inverters or DC optimizers are still the best options?

If I could choose it would be micro inverters as it removes all single sources of failure...mainly the monolithic string inverter. I'd rather chance a single panel module going out and having to wait several months for that to get fixed vs a 100% outage for several months during peak summer production.

Tesla has never offered this as an option and the $1.50 installed after the 26% credit was half the cost of any other micro inverter choice from any other installer.
 

nwdiver

Well-Known Member
Feb 17, 2013
8,882
13,014
United States
If I could choose it would be micro inverters as it removes all single sources of failure...mainly the monolithic string inverter. I'd rather chance a single panel module going out and having to wait several months for that to get fixed vs a 100% outage for several months during peak summer production.

Tesla has never offered this as an option and the $1.50 installed after the 26% credit was half the cost of any other micro inverter choice from any other installer.

Micros are generally ~$0.40/w more than a string inverter. For Tesla this is probably close to $0.45/w since they produce their own in house now. For a 8kW system that's ~$3k. Is it worth $3k to have that level of redundancy?
 

sorka

Well-Known Member
Feb 28, 2015
9,516
7,818
Merced, CA
Micros are generally ~$0.40/w more than a string inverter. For Tesla this is probably close to $0.45/w since they produce their own in house now. For a 8kW system that's ~$3k. Is it worth $3k to have that level of redundancy?

No. For my sized system, $1500 was basically the cutoff for me which was about the difference between hardware hardware costs when I was going to self install my own system buying from Wholesale Solar in Shasta. Then Tesla offered that $1.99 installed before the tax credit which was just about what it was going to cost me to buy just the hardware and all the trimmings.
 
No. For my sized system, $1500 was basically the cutoff for me which was about the difference between hardware hardware costs when I was going to self install my own system buying from Wholesale Solar in Shasta. Then Tesla offered that $1.99 installed before the tax credit which was just about what it was going to cost me to buy just the hardware and all the trimmings.
How did this end up? I had my install today for same system size and they ran two strings in parallel to the inverter. They are coming back tomorrow to install the power wall and I'd like to know if I should make a stink.
 
Still in limbo waiting for PTO. Never got a response about low production.

I did get txt a few days ago saying: "I apologize for the delayed response while we are currently working hard to keep up with our heavy demand. We are still working on submitting your application for PTO. Currently, our timelines for application prepping, submittal and the utility approval are taking longer than usual as we are working through a high demand for the products in your area. We really appreciate your patience through out this entire process."
 
Quick update, maybe TSLA social media workers will take notice...

NOTHING has happened since the original post. I did get a new project advisor assigned and emiled them again about my concerns, and they said the inverter will be fully functional after PTO, which sounds to me like it's operating in some kind of reduced/limited/limp mode until it gets the software unlock from Tesla.

I do get texts every Sunday evening saying they're working on PTO, but that gets old week after week.
 
Time for more updates.

8/6/21 - Got email from SCE that application was filed for PTO
8/9/21 - Got email from SCE that application needed engineer to review
8/9/21 - Got email from SCE saying engineer approved and application sent for final review
8/16/21 - PTO approved!

So 4 months for PTO after inspection passed. Still gotta figure out the low production problem though.
 
Updates...

8/23/21 - Tesla website account no longer shows contact info or project advisor. Only option is to chat. Started a chat to tell them system production is still low even though before they told me before it would be normal after PTO. Person told me system will start working properly after 4 weeks of PTO during a "commissioning" process./period I didn't believe them and they gave me phone number to call. Called, spent an hour on hold, talked to a real human being and told them the problem, they were able to see that my actual production was low vs what estimates they had on their end for daily production, and said they'll look into it.

8/28/21 - Got an email saying my system has been analyzed and is indeed underperforming.

8/29/21 - Telsa App shows service is required and to make appointment, but shows no appointments available.

8/31/21 - Call support number again, spend 40 mins on hold, appointment made in 2 weeks for service.
 
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