MPPT Controller De-rating Graph

[AzRoute66]

I found this graph in the Specifications Section of a freshly downloaded Morningstar TriStar TS-MPPT-60 Operators Manual. I have tried to figure out what it is telling me but can't quite get it. Intuitively it looks like a statement about 'power', but the numbers don't seem right. I see no mention of it in the text of the manual. Can someone put this graph into words for me?

DeRating.JPG

Thanks in advance.

[max2k]

I found this graph in the Specifications Section of a freshly downloaded Morningstar TriStar TS-MPPT-60 Operators Manual. I have tried to figure out what it is telling me but can't quite get it. Intuitively it looks like a statement about 'power', but the numbers don't seem right. I see no mention of it in the text of the manual. Can someone put this graph into words for me?

DeRating.JPG

Thanks in advance.

I'm no CC expert but looking at the graph alone I say the manufacturer asks to stay within <115V array voltage range. If you feed CC with higher voltage it would reduce its max charging current going to the battery, basically not all available energy from array will get converted. Most likely this is due to thermal requirements- when input voltage goes higher CC probably gets hotter and its internal circuit tries to prevent that by decreasing its max output current.

[Sunking]

It is telling you to keep the PV Vmp voltage at 115 volts or less. Over 115 volts volt you derate the output current. Just like Max said, it is the Controller protecting itself from DIY who do not know what they are doing.

Example if you had a MS TS-60-MPPT on a 12 volt battery with 800 watt panel input, Output current would be up to 60 amps if the PV voltage is 115 volts or less. Now if you wired the panels for say 140 volts which you would never do on a 150 Voc controller, charge current would be limited to 40 amps only using 530 watts from a 800 watt panel.

Here is all you need to know. Follow the rules and manufacturer instructions. When you calculate your panel Voc configuration, the rules require you to derate by 125%. So on a 150 Voc controller means the Voc of the panels cannot exceed 120 volts. 120 Voc on the panels puts the Vmp or working voltage of around 100 volts, and 100 volts is less than 115 volts. Problem took care of itself by following proper design guidelines.

Easy Peasy.

[sensij]

Here is all you need to know. Follow the rules and manufacturer instructions. When you calculate your panel Voc configuration, the rules require you to derate by 125%. So on a 150 Voc controller means the Voc of the panels cannot exceed 120 volts. 120 Voc on the panels puts the Vmp or working voltage of around 100 volts, and 100 volts is less than 115 volts. Problem took care of itself by following proper design guidelines.

Easy Peasy.

The rules = code? If that is what you mean, 125% is the adjustment only when the temperature coefficient of the PV array isn't known. If you have a data sheet for your panel you can perform the calculation and make a more appropriate adjustment for the actual temperatures your system is likely to encounter.

[Sunking]

The rules = code? If that is what you mean,

Nope, two completely different things. Code is bare bones minimum practice. Rules are varying degrees of of Practice. Some more stringent, and some less stringent. From your POV, you push the envelope of safety margins getting away with cutting corners.

125% is the adjustment only when the temperature coefficient of the PV array isn't known

Nope you are dead wrong.Why would I care what the actual coefficient is when I know 125% works ever time unless it gets below -40? Try reading the Code once in a while like 690.7 I don't work in Alaska or Canada.

[sensij]

Is this the code reference you are looking for? Are you capable of reading and understanding it, or would you like it explained?

690.7 Maximum Voltage.
(A) Maximum Photovoltaic System Voltage.
In a dc PV source circuit or output circuit, the maximum PV system voltage for that circuit shall be calculated as the sum of the rated open-circuit voltage of the series-connected PV modules corrected for the lowest expected ambient temperature. For crystalline and multicrystalline silicon modules, the rated open-circuit voltage shall be multiplied by the correction factor provided in Table 690.7. This voltage shall be used to determine the voltage rating of cables, disconnects, overcurrent devices, and other equipment. Where the lowest expected ambient temperature is below -40 deg C (-40 deg F), or where other than crystalline or multicrystalline silicon PV modules are used, the system voltage adjustment shall be made in accordance with the manufacturer's instructions.

When open-circuit voltage temperature coefficients are supplied in the instructions for listed PV modules, they shall be used to calculate the maximum PV system voltage as required by 110.3(B) instead of using Table 690.7.

Informational Note: One source for statistically valid, lowest-expected, ambient temperature design data for various locations is the Extreme Annual Mean Minimum Design Dry Bulb Temperature found in the ASHRAE Handbook - Fundamentals. These temperature data can be used to calculate maximum voltage using the manufacturer's temperature coefficient relative to the rating temperature of 25 deg C.

and, here is the table. Except in very cold locations, even in the absence of data sheet coefficients you wouldn't use 125% unless you are too lazy to actually look up the right value and are afraid of getting sued.

table.JPG

[AzRoute66]

Never mind. What you all were saying made no sense to me so I read the manual again top to bottom, looking specifically for this, and found it in a list of Protections.

"The TriStar MPPT 150V will limit the solar input current as the solar array Voc approaches the maximum input voltage rating. The array Voc should never exceed the 150 Volt maximum input voltage. See the array voltage derating graph in Section 8.0."

This (solar input current) makes total sense to me. The graph was simply mislabeled on the Y axis.

Appreciate your time.

[max2k]

Never mind. What you all were saying made no sense to me so I read the manual again top to bottom, looking specifically for this, and found it in a list of Protections.

"The TriStar MPPT 150V will limit the solar input current as the solar array Voc approaches the maximum input voltage rating. The array Voc should never exceed the 150 Volt maximum input voltage. See the array voltage derating graph in Section 8.0."

This (solar input current) makes total sense to me. The graph was simply mislabeled on the Y axis.

Appreciate your time.

It's a funny way to say (I'm referring to manual here) that CC won't use the full current available. Y axis is not mislabeled - CC will not produce its full 60A current if you exceed 115V on its input regardless what array is capable in terms of current- it won't simply 'let it through'.

[Sunking]

Is this the code reference you are looking for? Are you capable of reading and understanding it, or would you like it explained?

I was hoping you would take the rope to hang yourself with.

Nope you do not understand what it is telling you. Hell I know the person who wrote the code rule, the intent, and voted it in. My guess is you have is a CA C46 License and really do not know or qualified to work on electrical systems other than limited to Solar. It is very clear you are inexperienced and making rookie mistakes. Example this part is all you need to know:

In a dc PV source circuit or output circuit, the maximum PV system voltage for that circuit shall be calculated as the sum of the rated open-circuit voltage of the series-connected PV modules corrected for the lowest expected ambient temperature. For crystalline and multicrystalline silicon modules, the rated open-circuit voltage shall be multiplied by the correction factor provided in Table 690.7.

So now allow me to explain it to you. All you need to know is 1.25. It exceeds all other requirements and makes life real easy. You will pass Inspection every time with no questions asked.

With that knowledge after you actually do the work a few hundred times, and know what Inspectors are looking for you play the game and the Rules are:

Maximum number of Solar Panels wired is series using X Cell Count Panels with a 150 Voc input limit;

36 Cells 5 or less.
60 Cells 3 or less
72 Cells 2 or less.

That is what any Inspector knows and any good designer. Example if the Inspector sees 6 36 cell panels, you fail Inspection. Then you cry well I used Temp Correction Factor and can do 6. Inspector does not give a damn what you think and gives you two option of either use 3S2P panel Configuration. or a stamped drawing from a PE showing the Calculations and Panel Specs. Take your pick. As for me there is no amount of money you could offer me to sign off on 6 12 volt battery panels wired in series on a 150 Voc controller. I would not risk my career and financial stability for your ignorance.

You way could come up with 6 panels in Series, but no Inspector or designer is going to do that. To add that 6th panel in series would require you to use a Correction Factor of around 1.1 or less. Use 1.25 for every job and you meet the Intent of the Code. Use anything less and you wlil be questioned, and the burden of Proof lies upon you, and unless you are an Engineer with PE, you are not qualified to make any calculations less than 1.25. The only time code will tell you SHALL USE MANUFACTURE TABLES is if the ambient temps drop below -40 degrees. Even then it is not needed because there are no conditions requiring you to use 125% or more.

Hee is a Pro Tip for you or anyone else doing Voc calculation. It is what the Inspector will use

Voc = 27.75 volts for 36 cell panels
Voc = 46.25 volts for 60 cell panels
Voc = 55 volts for 72 cell panels.

Makes absolutely no difference what panel manufacture is, or how cold it gets. Use those numbers and you pass every time. Give it a try rookie. Take an example say a Kyocera 160 watt 36 cell panel. Voc = 22.2 volts and VNOC = .08 volts/= C operating at -40 degrees. Your corrected Voc = [25 + 40 degrees x .08] + 22.2 volts = 27.4 volts all day long. I just wasted my time doing something I already know from experience. If you went through all the tables and calculation you would have come up with 1.23. Who gives a ****, I used 1.25 which exceeds all minimum requirements every time using 1.25. So why do you waste your time and take such risky chances rookie?

[max2k]

...
Hee is a Pro Tip for you or anyone else doing Voc calculation. It is what the Inspector will use

Voc = 27.75 volts for 36 cell panels
Voc = 46.25 volts for 60 cell panels
Voc = 55 volts for 72 cell panels.

Makes absolutely no difference what panel manufacture is, or how cold it gets. Use those numbers and you pass every time. Give it a try rookie. Take an example say a Kyocera 160 watt 36 cell panel. Voc = 22.2 volts and VNOC = .08 volts/= C operating at -40 degrees. Your corrected Voc = [25 + 40 degrees x .08] + 22.2 volts = 27.4 volts all day long. I just wasted my time doing something I already know from experience. If you went through all the tables and calculation you would have come up with 1.23. Who gives a ****, I used 1.25 which exceeds all minimum requirements every time using 1.25. So why do you waste your time and take such risky chances rookie?

hmm- no I'd agree with above logic if we were talking about some generic design regardless of location. In SoCal for example it makes sense to follow code and use manufacturer specified Voc and its temp coefficient to better utilize inverter inputs. OC building department requires such calculation for the lowest temp between -1 and -5C. Actually it goes slightly differently: dept estimated that with Voct = -0.4%/C drop from +25C to -5C is 30 degrees so they came up with equivalent to 1.25 multiplier: 0.004 x 30 = 0.12 therefore it is x1.12 in their permit docs. In case of 600V inverter input it would allow 600/1.12./40.1 = 13 panels per string instead of 600/1.25/40.1 = 11. In case 2 panel difference per string matters. It is actually 11.97 panels, almost 12. In my case 12 panel strings passed without any questions asked.

[Sunking]

hmm- no I'd agree with above logic if we were talking about some generic design regardless of location.

What is the Thread Subject? MPPT Charge Controllers right? What does that have to do with Grid Tie?. You would have a valid point if the OP was asking about a 600 volt MPPT Controller. With 600 volts we have some room to work with that can increase the number of panels wired in series. At 150 Voc there is not a lot of Wiggle Room to shake out an extra panel or two in series.

Great example was a 6-panel system using 12 volt battery panels. You would have to push the limits to put 6 battery panels in series on a 150 Voc limit. Voc adds up instantly to 6 x 22.2 volts = 133.2 volts. To use 6 panels would mean you would have to use a Correction Factor less than 1.25, something on the order of 1.1 or less. To get away with it would require proof and part of that proof is what Temp was used to arrive at a calculation, and what is the panel Voct. Well the only places that could get away with that are quite warm like Death Valley.

The point is Inspectors and designers have a method to their madness. They have done it so many times, they have patterns memorized. Example they know if they see X amount of panels in series what the limits are. In this example 150 volts. You know 5 is a pass no questions asked. You see 5 panels, smile, and make a check mark in the inspection forms. Cross the line at 6 panels and now a Red Flag is raised and here come the questions and a Frown with a sinister grin on his face that says Gotcha. He knows had to use something less than 1.25 and what he considers how cold igt gets at night is not your number. In other words the burden of proof now rest on the Contractor or Installer to come up with proof, an din many cities require a PE to certify so if something happens, the city is not liable, that goes to the PE who pushed the limits.

However if in the permits, the calculations are shown and certified by an Authority already has the answer why he used 6 panels in series. At 600 volts, you have more room to work with and economics shift where the added cost of certification is beneficial and lowers the end price. Say $500 for certification to save $2000 in equipment and labor. Works on a house size project.

It is not worth the time and money spent to change 6S wired panels, to 3S2P. Use 3S2P and there are no questions because you are not pushing the limits or raising Red Flags. Use something less than 1.25, you had better be prepared to Prove it and that cost real money and time. There is nothing to be gained pushing the limits of a small scale

[sensij]

Sunking. What world are you living in? max2k has actually worked with his city's inspectors. I've worked with mine. Using 125% blindly is probably a big red flag indicating a designer who is clueless, or an engineer in over his head. The calculation applying the temperature correction to STC Voc is simple, required by code (if you read the 2nd paragraph, which you chose to ignore in your novel). The accepted source of temperature information, listed in code, is freely available.

You write like sometime who has read bunch of forum posts about inspections, but never actually experienced one. Real world inspectors don't say "gotcha"... They look at the calculations in the permit paperwork, which already passed plan check, and say, "looks like you built to the plans, nice job". (Except when it comes to grounding. Then all hell breaks loose).

[SunEagle]

Sunking. What world are you living in? max2k has actually worked with his city's inspectors. I've worked with mine. Using 125% blindly is probably a big red flag indicating a designer who is clueless, or an engineer in over his head. The calculation applying the temperature correction to STC Voc is simple, required by code (if you read the 2nd paragraph, which you chose to ignore in your novel). The accepted source of temperature information, listed in code, is freely available.

You write like sometime who has read bunch of forum posts about inspections, but never actually experienced one. Real world inspectors don't say "gotcha"... They look at the calculations in the permit paperwork, which already passed plan check, and say, "looks like you built to the plans, nice job". (Except when it comes to grounding. Then all hell breaks loose).

Using the 1.25% multiplier might be on the conservative side but it would be accepted 100% of the time by all AHJ's. It isn't a flag indicating a designer who is clueless but someone that understands the code and does not push the envelope to save a few pennies.

Using a lower multiplier could be accepted by a % of the AHJ's but unless there is a critical reason to push the voltage into the CC why take the chance of getting a red flag by the AHJ or over loading the CC?

I am sure you can find a good reason for getting the perfect calculation, but based on the hands on experience per Sunking and myself (on the electrical power side at least) being more conservative makes things go more smoothly and quickly when it comes to project planing and installations.

[Wy_White_Wolf]

Using the 1.25% multiplier might be on the conservative side but it would be accepted 100% of the time by all AHJ's. It isn't a flag indicating a designer who is clueless but someone that understands the code and does not push the envelope to save a few pennies....

Nope. Wyoming code is 150%. Most off-grid here is in mountainous areas that can easily see -40F so the state upped the derate.

WWW

[SunEagle]

Nope. Wyoming code is 150%. Most off-grid here is in mountainous areas that can easily see -40F so the state upped the derate.

WWW

So I stand corrected that 100% of the AHJ's will not accept the 1.25% multiplier.

The code is a guidance to follow to meet safety levels. Being more conservative (while more expensive) is not a bad thing to do. If based on real time data the Wyoming officials want to be more conservative then I applaud their actions to keep people and equipment safe.