Tesla Solar inverters

[kodek]

Hi there,

Looking into getting solar for our home, so I'm trying to learn as much as possible .

I had a pleasant conversation with a Tesla solar representative the other day. One thing that caught my attention was that during the conversation, the rep expressed a negative opinion towards micro-inverters.

I did my research after the conversation, and my current understanding is that although most cost-effective, string inverters are technologically inferior to micro-inverters and power optimizers. Unfortunately, I didn't catch the actual type of inverter used by Tesla. I contacted the Tesla rep again, and he said that he can't know what inverter would be used until they survey the property.

Assuming that I'm looking at a ~5.5 KW system (likely to be L-shaped), what sort of inverter would I likely be getting from Tesla? Most importantly, how big of a deciding factor should the inverter type be?

Before confirming the purchase, I've decided to get quotes from other companies. I'm biased towards Tesla, but I ultimately wouldn't mind getting a different company's system. I do hope to get a Powerwall once the solar system is in place.

Thanks!

 

[arnolddeleon]

The SolarCity install I had done a few years ago used SolarEdge inverters and power optimizers. When I looked at the technology I was pretty impressed.

 

[miimura]

Microinverters do two things well.
1. Handle shaded panels well
2. Provide per-panel power/energy reporting.

SolarEdge with Optimizers can do both of those things. If you don't have shading issues, it probably isn't worth the expense of optimizers or microinverters.

 

[Shygar]

SolarCity/Tesla installed a Delta string inverter on both of my installations. I asked about a SolarEdge and basically they said if you don't have shade problems then you don't need the SolarEdge.

 

[kodek]

Sounds like they are able to provide optimizers in some cases.

I don't know if shading will be an issue, but I definitely care to monitor each panel independently. Is this something that customers are able to do?

 

[CA-Gbm84]

If they guarantee the amount of energy the total system will produce, do you really care which panel it comes from?

My understanding is if their designs indicate potential shading, then solar edge and optimizers will be specced (as they need to meet the guarantee) if you don't have shading, no need to pay for additional equipment.

 

[Hank42]

I use Enphase brand microinverters - they have a neat web app that lets you view detailed statistics such as energy usage /produciton as well as lifetime output per panel - useful for warranty etc.. Also, the time-lapse feature is pretty neat - helps identify un-anticipated shading.

It's not really all that useful, but it's included in the cost, and the uptick is not that much more.

 

[miimura]

I use Enphase brand microinverters - they have a neat web app that lets you view detailed statistics such as energy usage /produciton as well as lifetime output per panel - useful for warranty etc.. Also, the time-lapse feature is pretty neat - helps identify un-anticipated shading.

It's not really all that useful, but it's included in the cost, and the uptick is not that much more.

Indeed. I used the Enphase data to convince the installer that there was something wrong with one of the panels on my in-law's house. The installer moved the panel to a different microinverter and position on the roof and found that the problem followed the panel. They got the manufacturer to replace the panel under warranty. It was down to about 50% production in the second year of use.

 

[kodek]

If they guarantee the amount of energy the total system will produce, do you really care which panel it comes from?

My understanding is if their designs indicate potential shading, then solar edge and optimizers will be specced (as they need to meet the guarantee) if you don't have shading, no need to pay for additional equipment.

That’s a good point, but I’d rather not have to wait a whole year to determine if I’m not producing the guaranteed amount. Besides, the compensation amount is less than what I’d pay from the grid, so it’s still in my interest to mitigate issues as early as possible.

 

[NuShrike]

Microinverters do two things well.
1. Handle shaded panels well
2. Provide per-panel power/energy reporting.

SolarEdge with Optimizers can do both of those things. If you don't have shading issues, it probably isn't worth the expense of optimizers or microinverters.

Micro-inverters also handle different tilts, azimuths extremely well. So basically you can have panels facing optimally almost randomly, and so you can add-on panels anytime -- something you can't do with inverters. Remember, shading includes cloudy days -- optimizer/micro-inverter strings don't collapse power-wise because of partial shadowing via clouds. Also, no dangerous high-voltage lines anywhere beyond 240v.

Inverters handle system maximum output better (with a properly sized inverter), than micro-inverters, where you can exceed rated performance.

Personally, I would never install without either optimizers or micro-inverters.

 

[Garlan Garner]

The SolarCity install I had done a few years ago used SolarEdge inverters and power optimizers. When I looked at the technology I was pretty impressed.

I have SolarEdge inverters and power optimizers. They are by far the best because everything is DC on the roof.

Micro Inverters ( made by Enphase ) require AC on the roof. AC is a lightning magnet if not properly grounded AND AC on the roof often times requires a much more complicated permit and multiple inspections which are costly.
Lastly...I replaced 2 microinverters in my first 2 years whereas I've never replaced a power-optimizer. AC is a beast to maintain ON A ROOF.

I installed both on my roof - first micro inverters....then I removed that setup and installed power-optimizers...

Check out my progress below over the past 4-5 years. Its ALWAYS LIVE

 

[cmaster]

I used microinverters. Attached to each panel.

Microinverters do two things well.
1. Handle shaded panels well
2. Provide per-panel power/energy reporting.
.

 

[Az_Rael]

Hi there,

Unfortunately, I didn't catch the actual type of inverter used by Tesla. I contacted the Tesla rep again, and he said that he can't know what inverter would be used until they survey the property.

I had asked about power optimizers when signing with Tesla, and thought that was what I would get as my system had panels on two different roof surfaces, one facing east, the other south. Our rep certainly implied they use power optimizers. However, I ended up with two Delta inverters, which I guess are the string type. The design sheet I got after the survey did not specify what type of inverters I would be getting, and I didn’t think to ask at that point.

In the end, if you care about exactly what equipment is going to be installed, do not use Tesla Energy. We had a big fiasco with them installing the wrong panels on our roof, as they had subbed out a different panel the day before install. We did get them to switch out the panels, but it took another month and it just added to the numerous delays we experienced.

I am not super happy about the Delta inverters, but in the end, we don’t have shade issues, and we rarely get cloudy days being in the desert, so I guess the only benefit I am missing is being able to identify bad panel(s) in the array. It kind of stinks to pay top dollar for the system and not get exactly what you wanted, but unfortunately, we didn’t discover what a PITA Tesla Energy was until we were in too far to back out. I trusted the Tesla brand more than I should have when choosing them over other installers.

 

[miimura]

One more thing to note is that many string inverters can be fed by different strings of panels with independent MPPT channels. This allows sections of panels facing in different orientations to still operate properly. You definitely don't need micro inverters just because you have panels facing different directions.

 

[nwdiver]

SolarCity/Tesla installed a Delta string inverter on both of my installations. I asked about a SolarEdge and basically they said if you don't have shade problems then you don't need the SolarEdge.

Glad to see this; One of my pet peeves is perfectly sited systems with zero shade issues with micros or optimizers. I just think 'There's $0.40/w you're never gonna get back'; Sure, module level monitoring is cool... but is it really worth $0.40/w?! If you have 8kW that's $3200!

Weird that Tesla is using Delta inverters... I've always thought they were a tier 2 company as opposed to tier 1 companies like SMA, Fronius, Solar Edge and Enphase... maybe things have changed...

Micro-inverters also handle different tilts, azimuths extremely well. So basically you can have panels facing optimally almost randomly, and so you can add-on panels anytime -- something you can't do with inverters. Remember, shading includes cloudy days -- optimizer/micro-inverter strings don't collapse power-wise because of partial shadowing via clouds. Also, no dangerous high-voltage lines anywhere beyond 240v.

If I ever have an install with those issues I'll definitely use optimizers... 10 systems so far... nothing like that yet. From an equipment perspective current is far worse than voltage. I'd rather have 8A 400v going through my attic than 18A 240vac. In terms of safety the new rapid shutdown requirement means that the lines are dead until the inverter is energized using a Tigo TS4-S or something similar.

 

[Garlan Garner]

One more thing to note is that many string inverters can be fed by different strings of panels with independent MPPT channels. This allows sections of panels facing in different orientations to still operate properly. You definitely don't need micro inverters just because you have panels facing different directions.

Just because panels are facing different directions? No. you don't.

However a more prominent reason for "power optimizers" is shading. String Inverters can't tackle anything concerning shading. Even the shadow of a pencil can degrade the entire string of a string inverter.

 

[nwdiver]

String Inverters can't tackle anything concerning shading. Even the shadow of a pencil can degrade the entire string of a string inverter.

Not true. Bypass Diodes compensate for shade just fine. 1 String per MPPT is just as effective as 1 Optimizer per panel. The top row and bottom row are separate strings on independent MPPTs. The 43w and 44w panels are shaded... unshaded panels not affected. The 2nd panel from the left on the bottom has an optimizer... no benefit noted.

 

[Garlan Garner]

Not true. Bypass Diodes compensate for shade just fine. 1 String per MPPT is just as effective as 1 Optimizer per panel. The top row and bottom row are separate strings on independent MPPTs. The 43w and 44w panels are shaded... unshaded panels not affected. The 2nd panel from the left on the bottom has an optimizer... no benefit noted.

View attachment 316181

The graphic you posted is obviously NOT signifying the OUTPUT current of a string. That graphic is totally incorrect in indicating the string current. That graphic might be indicating what the panels could potentially produce, however there is no way one panel in a string is outputting 43 watts and the one next to it outputting 67 wats when they are connected in series.

I built panels by hand. Panel diodes do nothing of the kind.

I dare you to shade a panel in a string and NOT have it affect the entire string. Its like having a dead battery in the string of good batteries. There is nothing the good batteries can do if current is limited by the bad one.

Every panel is connected in series in a string inverter setup...not parallel. There is one Negative and one Positive lead in a series of panels and the electrons flow in a nice neat straight line ( which denotes the name STRING ).
There is no way for electrons to jump over a panel in a string. That's just not physically possible.

 

[nwdiver]

I built panels by hand. Panel diodes do nothing of the kind.

I dare you to shade a panel in a string and NOT have it affect the entire string.

Every panel is connected in series in a string inverter setup...not parallel. There is one Negative and one Positive lead in a series of panels and the electrons flow in a nice neat straight line ( which denotes the name STRING ).
There is no way for electrons to jump over a panel in a string. That's just not physically possible.

I built panels too... that's how I learned about bypass diodes. If they don't let electrons jump over a panel what do they do? The screenshot I posted IS 7 panel in series on the top... the electrons ARE 'jumping' over part of each shaded panel at ~44w.... how else would the other panels in the series be unaffected and maintain ~66w?

So... Dare accomplished... panels 4 and 7 are shaded... the rest of the string is not affected....

Here's another screenshot in the evening... shading the 5th panel... unshaded parts of the string not affected. Why would they be? The bypass diode is bypassing current around the shaded portion... hence the name.

 

[Garlan Garner]

I built panels too... that's how I learned about bypass diodes. If they don't let electrons jump over a panel what do they do? The screenshot I posted IS 7 panel in series on the top... the electrons ARE 'jumping' over part of each shaded panel at ~44w.... how else would the other panels in the series be unaffected and maintain ~66w?

So... Dare accomplished... panels 4 and 7 are shaded... the rest of the string is not affected....

The diodes on a panel are in series with the solar cells. They prevent backflow current. A diode will only let current flow in one direction. This keeps shorts from happening in each panel. That's the ONLY thing a diode does.

The diagram below has one blocking diode, however each panel can have its own - which is common.

This is more like the diagram would be with only 1 panel.