Tesla Solar inverters

[Garlan Garner]

If your definition of 'tremendous' is <1% then 'yes'. There's a Solar Edge system that's of similar and orientation and size to a String system I designed. They're neck and neck in terms of production. If there's a big benefit to optimizers vs a well designed string system I've never seen it. Optimized systems might be sliiightly more effective but they almost always increase the cost / kWh of production which is why I don't use them in my systems.



The screenshot I posted is from a SMA system equipped with TS4-S rapid shutdown devices that collect module level current and voltage data.

One of these panels DOES have an optimizer and it's not the one you would think... which is why I don't use optimizers

View attachment 316191

Hold on...Hold your horses.

TGIO is DC to DC power optimizers. Thats not a string inverter setup, I've installed those.

A Tigo system is the same as a SolarEdge system in the scenarios we are discussing. TIGO makes DC optimizers that talk the same language as SMA.

What's funny about this is that SMA was originally a TOTAL sting inverter company. They got together with TIGO who makes the power optimizers and said......this is now tremendously more efficient.

 

[Garlan Garner]

Agreed. I generally dislike Optimizers but I HATE micros...

You can dislike both... but you can't argue that a full string inverter beats their efficiency and opportunities.

 

[Garlan Garner]

Read my previous response to your post: I have SolarEdge optimizers. I'm actually supporting your side of the argument.

You are correct....sorry. I replied incorrectly.

 

[nwdiver]

You can dislike both... but you can't argue that a full string inverter beats their efficiency and opportunities.

String inverters beat them on $/kWh.... at the end of the day that's what matters...

If I increase the cost of a system 10% I need to get 10% more energy... not ~1% more.

 

[Garlan Garner]

String inverters beat them on $/kWh.... at the end of the day that's what matters...

If I increase the cost of a system 10% I need to get 10% more energy... not ~1% more.

NO they don't beat them on cost. Not at all. The cost of a power-optimized system is less than a String Inverter Setup.

String Inverter setups require much more expensive cabling as well as a much more expensive Inverter and much more expensive maintenance.

For example....have a pane break in a String Inverter Setup. You are down and out till its replaced. Break a panel in a power optimized scenario....You only lose that panels output.

There are way too many financial upsides to power optimizers. That's why companies like SMA - who used to be exclusive STRING inverter folks have gone the power optimizer route - merging with TIGO.

Ultimately Shading is HUGE ( especially dirt ). Depending on your bypass diodes ratings you can shut down a String Inverter setup with dust alone. I installed such a system in Indian and the customer wanted to know why in the world was is power output down so far on the east side of his home every morning. Answer = condensation on a few panels was killing his String Inverter output.

Don't get me wrong, but having bypass diodes are better than not having them at all, however they kill your system performance on paper.

 

[nwdiver]

NO they don't beat them on cost. Not at all. The cost of a power-optimized system is less than a String Inverter Setup.

String Inverter setups require much more expensive cabling as well as a much more expensive Inverter and much more expensive maintenance.

For example....have a pane break in a String Inverter Setup. You are down and out till its replaced. Break a panel in a power optimized scenario....You only lose that panels output.

There are way too many financial upsides to power optimizers. That's why companies like SMA - who used to be exclusive STRING inverter folks have gone the power optimizer route - merging with TIGO.

7.6kW SMA inverter is ~$1600
7.6kW SolarEdge + 32 optimizers is ~$3200

No; I've seen string systems work fine with a broken panel... not that that's a common occurrence. In 10 years I've only seen one panel break after the install...

The industry is shifting to optimizers because of the new NEC code requiring rapid shutdown not because they make economic sense. An optimized 8kW system is $1600 more expense and generates maybe ~100kWh more per year... that's in no way a reasonable ROI. Take the $1600 and add another kW of solar... cheaper and more effective.

I'm currently designing a 23.7kW ground mount. The inverter portion will cost $3k. Optimizers would add $4k to the cost... That $4k would be better spent adding more panels....

 

[Garlan Garner]

7.6kW SMA inverter is ~$1600
7.6kW SolarEdge + 32 optimizers is ~$3200

No; I've seen string systems work fine with a broken panel... not that that's a common occurrence. In 10 years I've only seen one panel break after the install...

The industry is shifting to optimizers because of the new NEC code requiring rapid shutdown not because they make economic sense. An optimized 8kW system is $1600 more expense and generates maybe ~100kWh more per year... that's in no way a reasonable ROI. Take the $1600 and add another kW of solar... cheaper and more effective.

To each his own.

I don't agree at all with those numbers....however...enjoy your system.

 

[nwdiver]

To each his own.

I don't agree at all with those numbers....however...enjoy your system.

Here's a 7.7kW SMA inverter for ~$1600... show me an optimized ~8kW system for less and I'd definitely buy it

 

[Garlan Garner]

Here's a 7.7kW SMA inverter for ~$1600... show me an optimized ~8kW system for less and I'd definitely buy it

The panels and inverter Aren't the only parts needed for a system.

Show me an String Inverter system that can monitor each panel individually.
Show me an String Inverter system that can MTTP each panel individually. <----- That's HUGE.
Show me a String Inverter system that and shut down to the grid in less than 3 seconds to protect fire fighters and grid installers.
Show me a String Inverter system that requires NO CLEANING of the panels to keep the entire string current up.
Show me a String Inverter system that an have strings of different lengths.

See how the comparison isn't one for one?

Again....enjoy your system. Don't buy anything.

 

[wwhitney]

Optimizers evaluate the voltage of the string between each optimizer - Which is set by the inverter.

Then the optimizer looks at what its getting from the Panel ( shaded or not ) and THEN matches the voltage of the string by adjusting the current its getting from the panel.

In other words....it says. I see 425 volts on the string....so I'm going to take the 12 or 24 or 36 volts I'm getting from the panel and adjust its current so that I can get to 425 volts. P=I*E

I think the way they work is a little more complicated. Each panel (or optimizer) in a string has to pass the same current. So the control mechanism has to work something like this (figuratively):

1) Each optimizer reports the power its panel can produce for the MPPT at that panel.
2) The inverter sums up the powers to determine the total string power.
3) Dividing the total string power by the target inverter voltage gives the target string current.
4) Each optimizer then adjusts its DC-DC converter output to provide the voltage necessary to match that current.

So the optimizers attached to panels producing more power will be putting out a higher voltage than the optimizers attached to panels producing less power. But the sum of the voltages of all the optimizers in the string will match the target inverter voltage.

Cheers, Wayne

 

[nwdiver]

I think the way they work is a little more complicated. Each panel (or optimizer) in a string has to pass the same current.

That's the electrical benefit to optimizers. They use electrical 'magic' to basically add current instead of voltage, to some extent. With optimizers in a string the current can vary panel to panel. My point is that's not necessary. If you look at the MPP curve there's a fairly wide variation in acceptable current input without significant loss of power. A panel with a MPP of 7A 30v that needs to be at 6.5A because that's the string current will just be at 6.5A and 32v; 208w instead of 210w; Not gonna be a huge loss...

 

[Garlan Garner]

I think the way they work is a little more complicated. Each panel (or optimizer) in a string has to pass the same current. So the control mechanism has to work something like this (figuratively):

1) Each optimizer reports the power its panel can produce for the MPPT at that panel.
2) The inverter sums up the powers to determine the total string power.
3) Dividing the total string power by the target inverter voltage gives the target string current.
4) Each optimizer then adjusts its DC-DC converter output to provide the voltage necessary to match that current.

So the optimizers attached to panels producing more power will be output a higher voltage than the optimizers attached to panels producing less power. But the sum of the voltages of all the optimizers in the string will match the target inverter voltage.

Cheers, Wayne

Of course...but this thread didn't require that data at the time....so I just posted a video and let Solar Edge explain it for themselves.

 

[Garlan Garner]

That's the electrical benefit to optimizers. They use electrical 'magic' to basically add current instead of voltage, to some extent. With optimizers in a string the current can vary panel to panel. My point is that's not necessary. If you look at the MPP curve there's a fairly wide variation in acceptable current input without significant loss of power. A panel with a MPP of 7A 30v that needs to be at 6.5A because that's the string current will just be at 6.5A and 32v; 208w instead of 210w; Not gonna be a huge loss...

Wrong.

Over 10 years....it will be a tremendous loss.

 

[nwdiver]

Wrong.

Over 10 years....it will be a tremendous loss.

1% is 'tremendous'? I'll inform Websters... A $60 optimizer for an extra $5 of electricity over 10 years? Not sure that's worth it....

Also of note is that if power is clipped the loss is 0% because the inverter is maxed...

Seriously... run the numbers... (300w)(5hr/day)(365days)(10years) = 5457kWh

IF a $60 optimizer increases production ~1% that's 55kWh... $60 for 55kWh? Really?

 

[Garlan Garner]

1% is 'tremendous'? I'll inform Websters... A $60 optimizer for an extra $5 of electricity over 10 years? Not sure that's worth it....

Also of note is that if power is clipped the loss is 0% because the inverter is maxed...

Seriously... run the numbers... (300w)(5hr/day)(365days)(10years) = 5457kWh

IF a $60 optimizer increases that ~1%... 55kWh... $60 for 55kWh? Really?

Look ….. My last statement is this:

The reason STRING INVERTER companies are going towards power optimizers for a reason. They sell and they are more cost effective for both SMA and their customers.

AND OPTIMIZERS ARE SELLING!!!

 

[Shygar]

I'm enjoying the discussion here

 

[nwdiver]

Look ….. My last statement is this:

The reason STRING INVERTER companies are going towards power optimizers for a reason. They sell and they are more cost effective for both SMA and their customers.

AND OPTIMIZERS ARE SELLING!!!

Show me the numbers... I'm a numbers guy

I want to believe you... but I gotta see the numbers...

This is why SMA is shifting to optimizers...

Also doesn't help that some people keep perpetuating the myth that string inverters can't handle shade...

Don't get me wrong... SolarEdge makes a fine product... but for 99% of systems the additional expense will NEVER be recovered.

I need to collect data from the 30kW SolarEdge owner and compare that to the 27kW String System I designed. Both systems are ground mounts 180S with no shade. The Data is coming from the actual utility production meter. I'm expecting the 27kW String system to slightly outperform the SolarEdge because the company that installed the SolarEdge system used a 20 degree tilt vs 30 and ran AC lines vs DC. Should be interesting.

.... there is a chance that I'll start using SolarEdge for systems <5kW due to NEC 2017... depends on how much the TS4-Fs cost...

 

[cr0ntab]

I'm enjoying the discussion here

Same, to be fair, it is quite informational.

I'm learning a lot here!

 

[Shygar]

Same, to be fair, it is quite informational.

I'm learning a lot here!

Same

 

[brucet999]

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.

One other thing you are missing is optimizing power output. New panels vary by as much as 5% of their rated output. One low-producing panel in a string will limit the output of all other panels in that string. Your system is therefor limited to the production of the lowest efficiency panel, whereas optimizers (or micro inverters) allow all panels to produce at their individual maximum outputs.