Help with grid tie system

[speedracer77]

A good friend of mine is taking advantage of local government incentives to install a grid tie system to his house. He will be on net metering so doesn't require batteries or a charger right now. If I design and install his system for him he will give me some panels which I can use to power my off grid home. I don't have access to the government incentives because I'm not grid tied, so this will be my chance to get into more solar than my 2 40w RV panels and hopefully stop running the generator all the time.

He has 20 480w panels he got a good deal on. I need to choose an inverter and deside how to wire the system. These are the panels:

Do I need a 9,600 watt inverter? I doubt the panels will charge at full capacity often. Also they say max series fuse size is 20 amp. Does that mean I can wire 2 panels in series max, and each of those series can be wired in parallel? I have lots of electrical experience, just not in solar.

 

[MisterSandals]

Do I need a 9,600 watt inverter?

You need an inverter with a wattage rating to handle your loads. If you only need 2000W max, then a 9600W inverter is bigger than you need, and may use more power idling because of its size.

 

[speedracer77]

He wants to sell as much power as he can back to the grid. If I wire the panels into two ten panel series banks can i use this inverter?

 

[DIYrich]

Since he is paying, and you have no experience, get the Sol-ark 15k. Put it between the meter and the main panel, and attach solar. Program it, and you are done. He can add batteries later if he wants to.

Or, get a cheap growatt, and have it push all the power it can through the main panel.

 

[Ampster]

He wants to sell as much power as he can back to the grid. If I wire the panels into two ten panel series banks can i use this inverter?

There are presumably rules from the Authority Having Jurisdiction and from the power company that need to be followed. I know in California there is a site that lists the inverters that qualify. If you list the location of you friends site maybe someone who is familiar with those regulations can assist you. I have had very good luck with Enphase micro inverters. Another alternative is the SolArk as recommended earlier.Both are on the CEC California approved list which many states follow.

 

[1201]

Buy the cheapest 10kw grid tie inverter you can find- probably the growatt

 

[Hedges]

A batteries-optional hybrid would let him have backup in the future.

He wants to sell as much power as he can back to the grid. If I wire the panels into two ten panel series banks can i use this inverter?

No!

"Open circuit voltage 53.61", 10 of those in series would be 536V, and goes up higher in freezing weather.
But the inverter says "100-480 VDC"

Inverter can process 17A per input, 25A max short circuit current.
Panels are 10.71 Imp, 11.266A Isc

You could consider 5s2p into each MPPT input.
That could clip at 17A on most productive days.
But, if you orient 5s toward morning sun and 5s toward afternoon sun, it would make more without clipping.

Or, use single shorter strings, and take the extras for your place.

 

[k490]

I would read as much as you can and watch videos to learn about grid tie solar. Might even want to look for someone local who would be willing to work with you possibly a retired electrician someone has experience understands the electrical codes. You want to figure out a design before buying anything further. Draw up proper design plans to be submitted for permits and his utility to be approved. Once you get all that done then you can start buying what you need.

Micro-inverters give you the fastest ROI because they solve several challenges you will be faced with such as meeting rapid shutdown requirement reducing the number of boxes needed. Micro-inverters clip right on the panel and convert the DC to AC right at the panel gives you a simple design. Then you only have to combine all that wiring in a box then pair of heavier wire will come down to a disconnect. Also with micro-inverters not limited by the number of panels connected to a string where the VOC can exceed the limit.

That disconnect becomes the rapid shut down. Once those micro-inverters are cut from the grid power they all shut down. Also helps with shading if a panel becomes shaded doesn't effect other panels. You could reach out to Greenlancer a company that creates drawings that you can submit to the AHJ for the permits and the utility. I don't know if they create designs for Canadian customers.

 

[frasere2]

1) Get the electric line diagrams done online. Cheap, quick, and permittable. It should not cost more than $150.
2) Get the growatt 10k inverter (as others have said). Cheap and works great. 2 strings of 10 panels each. This inverter will accept up to 4 strings. I currently have 2 strings of 9 panels at 540w each going to this inverter.
3) Add optimizers for $45 per. Will increase solar power by at 10-15% and they also work as rapid shutdown. I'm averaging +13% for the first 2 months this year, better on sunny days (up to 25% increase).
4) You didn't mention if this is a ground mount or roof mount or if the panels are bifacial? There is some discussion of mounting bifacial panels vertically in snowy areas (lookup the setup in Finland in this forum) as that will produce well when it snows, plus it keeps the snow off the panels.

Best way to maximize ROI is to minimize spending up front.

 

[BigTXSun]

1) Get the electric line diagrams done online. Cheap, quick, and permittable. It should not cost more than $150.
2) Get the growatt 10k inverter (as others have said). Cheap and works great. 2 strings of 10 panels each. This inverter will accept up to 4 strings. I currently have 2 strings of 9 panels at 540w each going to this inverter.
3) Add optimizers for $45 per. Will increase solar power by at 10-15% and they also work as rapid shutdown. I'm averaging +13% for the first 2 months this year, better on sunny days (up to 25% increase).
4) You didn't mention if this is a ground mount or roof mount or if the panels are bifacial? There is some discussion of mounting bifacial panels vertically in snowy areas (lookup the setup in Finland in this forum) as that will produce well when it snows, plus it keeps the snow off the panels.

Best way to maximize ROI is to minimize spending up front.

I was tracking your comment #2 -- "2 strings of 9 panels at 540w each going to an inverter. " the OP is putting in a smaller system but for someone looking for a Grid Tie like his friend with 20 480w panels, how would this work?

Those 20 panels will either exceed the maximum DC input in series, or if he breaks them up and parallels the strings to hold down the voltage the amp will increase and exceed the inverter inputs. So what is the option if no batteries are used strictly on the on the grid?

 

[BigTXSun]

 

[BigTXSun]

Sorry, I tried to get the data sheet in with the post, but it did not work. I am in the same boat as the OPs friend. looking at a 11.4KW system -- approx 20 panels and pushing it a long distance approx 400-450 feet. I want to stay at a high voltage to run the distance for wire cost, but the initial calculation on the 2 strings of 10 panels is 550ish volts, and when tied together, 22 amps. unless I am doing the math wrong. If I am correct, both exceed the limits of the controller. I guess I could push each string to a dedicated controller, then combine them going into the meter. that is more costly, and in this case, there is no room to expand without adding another controller, or, I guess, the actual term is inverter.

 

[1201]

Sorry, I tried to get the data sheet in with the post, but it did not work. I am in the same boat as the OPs friend. looking at a 11.4KW system -- approx 20 panels and pushing it a long distance approx 400-450 feet. I want to stay at a high voltage to run the distance for wire cost, but the initial calculation on the 2 strings of 10 panels is 550ish volts, and when tied together, 22 amps. unless I am doing the math wrong. If I am correct, both exceed the limits of the controller. I guess I could push each string to a dedicated controller, then combine them going into the meter. that is more costly, and in this case, there is no room to expand without adding another controller, or, I guess, the actual term is inverter.

They have 4 mppts so you can do up to 4 individual strings to get amps below 13

 

[RGSCAN]

I would read as much as you can and watch videos to learn about grid tie solar. Might even want to look for someone local who would be willing to work with you possibly a retired electrician someone has experience understands the electrical codes. You want to figure out a design before buying anything further. Draw up proper design plans to be submitted for permits and his utility to be approved. Once you get all that done then you can start buying what you need.

Micro-inverters give you the fastest ROI because they solve several challenges you will be faced with such as meeting rapid shutdown requirement reducing the number of boxes needed. Micro-inverters clip right on the panel and convert the DC to AC right at the panel gives you a simple design. Then you only have to combine all that wiring in a box then pair of heavier wire will come down to a disconnect. Also with micro-inverters not limited by the number of panels connected to a string where the VOC can exceed the limit.

That disconnect becomes the rapid shut down. Once those micro-inverters are cut from the grid power they all shut down. Also helps with shading if a panel becomes shaded doesn't effect other panels. You could reach out to Greenlancer a company that creates drawings that you can submit to the AHJ for the permits and the utility. I don't know if they create designs for Canadian customers.

Hi there,
Just wondering if you could recommend a source of literature for a grid tie system with details. I'm at the beginning of a grid tie journey for my home and want to get it right?

Tx
Ray

 

[BigTXSun]

They have 4 mppts so you can do up to 4 individual strings to get amps below 13

So each MMPT is separate, but you still can not go over the maximum total voltage max of 550 for the operating voltage total for the inverter?

I was looking at the mission solar panel MSE425-SX6W (MSE PERC 72 415-425W) and based on my temperatures of -5, the lowest ever recorded, although this happens rarely if it gets to 10F, that is a bad winter. a string of 10 likely would not work; 8 panels would push me below the 500V mark. I used the calculator on this site to figure. https://www.photonik.solar/string-voltage-calculator.

If I understood 1201 post, the 4 MMPT would allow for 4 strings under 13 amps, but the 8 panels would be the maximum based on max volts unless that is a specification for each MMPT, My common sense tells me that is the answer; otherwise, the inverter only supports a minimum number of panels regardless.

 

[1201]

So each MMPT is separate, but you still can not go over the maximum total voltage max of 550 for the operating voltage total for the inverter?

I was looking at the mission solar panel MSE425-SX6W (MSE PERC 72 415-425W) and based on my temperatures of -5, the lowest ever recorded, although this happens rarely if it gets to 10F, that is a bad winter. a string of 10 likely would not work; 8 panels would push me below the 500V mark. I used the calculator on this site to figure. https://www.photonik.solar/string-voltage-calculator.

If I understood 1201 post, the 4 MMPT would allow for 4 strings under 13 amps, but the 8 panels would be the maximum based on max volts unless that is a specification for each MMPT, My common sense tells me that is the answer; otherwise, the inverter only supports a minimum number of panels regardless.

You can have 4 individual strings up to 600v, 13 amps.

If 8 panels will be close to 600v at your coldest temp then you can have 4 strings, or 32 panels total

On my inverter I have three strings of 14 panels each, total 42 panels

 

[MisterSandals]

MMPT is separate, but you still can not go over the maximum total voltage max of 550 for the operating voltage total for the inverter?

You can have 4 individual strings up to 600v, 13 amps.

Thats 600V, 13A for each MPPT. It wasn't clear to me you got the "each MPPT" part.

MMPT

MPPT as in maximum power point tracker.
This functionality occasionally varies the amps to volts ratio to locate the maximum output (watts) from the array, and then maintains this ratio until the next cycle (i think about every 10 minutes, maybe less).

 

[1201]

Thats 600V, 13A for each MPPT. It wasn't clear to me you got the "each MPPT" part.


MPPT as in maximum power point tracker.
This functionality occasionally varies the amps to volts ratio to locate the maximum output (watts) from the array, and then maintains this ratio until the next cycle (i think about every 10 minutes, maybe less).

Oh definitely less than every 10 minutes. I'm sure it's in seconds

 

[Hedges]

Constantly dithering to find slope of W/V curve and say at the peak.
But some units periodically do a full sweep to see if there is a higher local maxima. That could be minutes apart.

Consider a single series string of half-cut panels, which are internally wired as 2p3s. If one section is shaded, at full voltage the panel only puts out 1/2 current, 1/3 power. That is a local maxima, and slightly reduced voltage reduces power so MPPT remains there. Pulling down to a lower voltage it activates one bypass diode, putting out 2/3 voltage, full current, 2/3 power.

 

[BigTXSun]

Thats 600V, 13A for each MPPT. It wasn't clear to me you got the "each MPPT" part.


MPPT as in maximum power point tracker.
This functionality occasionally varies the amps to volts ratio to locate the maximum output (watts) from the array, and then maintains this ratio until the next cycle (i think about every 10 minutes, maybe less).

Got it. that was what I was looking for. I found something similar in a YouTube video, but it was nice to hear it again from a different source. I know Growatt or a DIY solar help store could have answered just not ready with all my questions to call them just yet.