new to forum and ignorant as well

[nwmark]

Hello, I am new to using a forum as an informational tool. I don't do social media of any kind. I think most of you assume that if a person finds this site you must know how to post . There are no real instructions or examples to guide me. I have made two posts and can find neither of them anywhere on the forum, so that goes to show I know jack squat about the forumverse. I also think most newbies are not getting their posts replied to. Maybe people have moved on. It seems that most of the replies were done in the height of the pandemic, when people had nothing else to do. The weather is getting nice and people are so done siting in front of a computer answering buffoons like me. Surely the answer you seek is in the volumes of posted replies. Trust me I read every post that I thought might help. There are many posts that are insightful and informative but none have answered my specific issue. I searched the web for solar design
consultants, but they only want to sell me a system they can install. The web directed me to this forum. Are there any certified solar design engineers who use the forum? I am willing to pay a consultants fee if they can help me. I want to do the system myself, so please answer questions, make recommendations so that I might master my small section of the solar grid universe

 

[mikefitz]

How about asking a question? The idea is you present a situation and your goals and folk on here make suggestions.

Mike

 

[400bird]

If you click on your username, then click on it again, it will take you to a new screen where you can find all your posts among other good stuff.

nwmark

diysolarforum.com

What are your specific solar questions? All I see for your post history is commenting on other's posts. Remember, this is a free forum, not every post gets a response. Things like formatting (using paragraphs) and grammar, make the post more readable and more likely to get responses.

 

[nwmark]

How about asking a question? The idea is you present a situation and your goals and folk on here make suggestions.

Mike

thanks for the response. here's my question (s) does each panel need its own mppt device? Can strings of panels have their own mppt ? can three strings with different wattages use a single mppt device ? i.e. String (1) 2520 watts, string (2) 2520 watts, string (3) 2835 watts. I am attempting to install 26 panels in three groups on roof structures. I can give detailed info on panels and string configurations if it will be helpful in answering the question. thank you

 

[nwmark]

If you click on your username, then click on it again, it will take you to a new screen where you can find all your posts among other good stuff.

nwmark

diysolarforum.com

What are your specific solar questions? All I see for your post history is commenting on other's posts. Remember, this is a free forum, not every post gets a response. Things like formatting (using paragraphs) and grammar, make the post more readable and more likely to get responses.

will try that url. I did double click my name and only my profile came up. hopefully those posts are not lost. thank you for tge help

 

[400bird]

thanks for the response. here's my question (s) does each panel need its own mppt device?

All panels need some sort of charge controller (PWM or MPPT, including possibly the charge controller integrated into a inverter)

Can strings of panels have their own mppt ?

Sure, that is the typical usage

can three strings with different wattages use a single mppt device ? i.e. String (1) 2520 watts, string (2) 2520 watts, string (3) 2835 watts.

Not if you want to get peak production out of that larger (3rd) string.

I am attempting to install 26 panels in three groups on roof structures. I can give detailed info on panels and string configurations if it will be helpful in answering the question. thank you

You might be best served by 3 individual charge controllers. It would give you redundancy in case of failure and large multi tracker MPPTs get expensive quick.

When sizing your strings be aware of the max open circuit voltage at temperature compensation. Depending on how cold it gets where you live the VOC can be 10% higher than at "normal" temps.
There are spec sheets and calculators for that.
Victron's is nice if you are going with their products.

will try that url. I did double click my name and only my profile came up. hopefully those posts are not lost. thank you for tge help

Glad to help, once your in your profile, click these tabs.

 

[nwmark]

I live at the 48th parallel and in a valley to boot. During the summer months I lose direct sun around 3 or 4 p.m. , so I don't think the loss of panel efficiency due to high temps will be too drastic.. Conversely in winter months, if I received more panel output due to lower temps it would be more advantageous since my sunlight hours are so drastically reduced. I've watched Will's video about using the six 48 volt batteries into the two inverters to get 240 volts ac. Would something like that work for me ?

 

[Hedges]

Multiple strings can be connected in parallel to a single MPPT input of a charge controller, so long as they have same (or relatively close) Vmp.
Their current can be different, so their wattage can be different.
They can have different orientation. I prefer that, more hours so more watt-hours from the charge controller.
They can function ok with a modest amount of shading on one string, like 10% maybe 20% of the string. If 50% shaded, it fails to contribute because other strings in parallel are higher voltage; in that case separate SCC might work better.

 

[nwmark]

Can you clarify about the loss of production from the larger string in earlier post? If I get three separate charge controllers for my three strings, will I also need three inverters? My ultimate goal is to get 240 ac to electrical panel.

 

[nwmark]

Multiple strings can be connected in parallel to a single MPPT input of a charge controller, so long as they have same (or relatively close) Vmp.
Their current can be different, so their wattage can be different.
They can have different orientation. I prefer that, more hours so more watt-hours from the charge controller.
They can function ok with a modest amount of shading on one string, like 10% maybe 20% of the string. If 50% shaded, it fails to contribute because other strings in parallel are higher voltage; in that case separate SCC might work better.

The 2 strings @2520 watts each are set up to minimize the effects of shading in the winter months when the sun is low in the sky and casts long shadows. My third string of, 2835 watts, does not have shading issues. If I tie strings (1) and (2) in parallel that will bring the amps of that string to 36 amps. String (3) is 27 amps. Am I getting currents too high to safely work with? Are those levels acceptable as inputs to charge controllers/ inverters ? Are these current levels too high for charging batteries? Thanks for all the help.

 

[Hedges]

"too high" depends on equipment specs. There may be a max Isc input spec. Output is usually regulated by the SCC.

Assuming 48V battery, (2520W + 2520W + 2835W)/48V = 164A

That is a pretty large charge controller. Here is one:

SmartSolar MPPT RS - Victron Energy

The SmartSolar MPPT RS solar charge controllers are Victron's solution for systems with large series connected PV arrays charging 48 V DC battery banks.

www.victronenergy.com

If PV strings are of different orientations, peak could be 0.7 as high in which case a 100A SCC would be only a bit over-paneled.

You'll probably want a couple of charge controllers.
Is the 2835W string 9, 315W panels, and the others are 8?

You have a PV array but no electronics? In that case, options are wide open.
Whatever you connect, have to ensure max voltage is never exceeded, even in freezing weather which raises voltage of panels.
Maybe you will want all 8 panels in series, maybe rewire 4s2p, whatever meets SCC specs.

You don't have to use DC coupled charge controller. There are some all-in-one (e.g. SolArk) which take high voltage PV strings, battery, generator, grid, and feed output.
There are AC coupled systems, like I have. Those use a grid-tie PV inverter, plus a battery inverter that makes a local island grid if utility grid is down.

Decide what functionality and performance you want. Many different choices in system configuration, brand, price.

 

[nwmark]

The string of 2835 watts is made of three series strings. Each one has three 410, watt panels to give 105 volts at 9 amps. Those three tied in parallel will give me 105 volts at 27 amps. I decided to go panels first so I could work on mounting them, while I gained knowledge about the BOS components. Can you opt to oversize the charge controller to avoid exceeding max voltage? The other panels are also 410 watts grouped into four series strings of four panels each to yield140 volts and9 amps. These are then combined into the two parallel strings of 2520 watts. I like the lead to the SOLARK product, which sounds like my final goal. Can you elaborate on AC coupled systems? I will also check out the Victron product you mentioned. My ignorance has diminished slightly, Thank you for the help.

 

[Hedges]

Max voltage is strictly a number on SCC data sheet, your location's record cold temperature, Voc and temperature coefficient from PV panel data sheet.
"Oversize" for watts or amps doesn't count toward max voltage.

Some SCC, like Midnight Classic, have "HyperVOC" where they will survive but not operate with limited over-voltage.

 

[Hedges]

AC coupling. I think SMA invented it.
Imagine a generator running a bit above 60 Hz unloaded, slowing down to 60 Hz under load. AC coupling signals to grid-tie inverters by means of frequency shift, how much power to put out. Battery inverter generates that, or passes grid through a relay, or passes generator through. Works on and off grid, assuming GT PV inverter is designed to respond accordingly.

https://files.sma.de/downloads/SI6048US-DS-en-28.pdf

https://files.sma.de/downloads/SISYSGUIDE-KEN140421.pdf

It is very robust, at least with a low-frequency battery inverter.
Other brand GT PV inverters should be compatible if they support UL-1741-SA and have "frequency-watts" feature.

There are several other brands of battery inverter which support AC coupling, including SolArk, Outback, Schneider. Some of those are high frequency. SMA also makes a high frequency battery inverter "Sunny Boy Storage" which isn't as capable as Sunny Island.

For off-grid, determine what surge current to start motors (A/C, water pump) plus other loads on at same time. Inverter needs to supply that for maybe a second.

 

[nwmark]

I looked at the SolArk and the one that would handle my situation was way too expensive. I think I am going to refigure my PV strings. The only way to get anything close to a balance is to have four strings of six panels in series with 210 volts at 9 amps. Then combine two of those groups in parallel to get 210 volts @ 18 amps. I think the LV6548 by MPP solar will accept these input levels. I looked at the web sites you provided and will do more research before committing. Will update soon. Thanks for the input