Batteryless Off-grid advice

Sethtrosity

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Hello,
I am looking for some advice on a system I have in mind and have a few questions.

The system: Growatt 5000ES (US Model) + 10 250W panels (37.6 Voc, 30.3 Vmp) from santansolar.
I will only be powering 240v loads, using the solar / grid mode for now.
I plan on adding more panels in parallel in the future (10 more).
I would eventually have two sets of 10 in series, linked in parallel.

Growatt 5000 taking input from PV and Grid (PV as priority)
The inverter will then feed a sub panel where my 240V loads will be.
50A Breaker from Main panel to Inverter input.
Inverter output to 50A Breaker on sub panel.

1. Do I need to worry about back-feed into the grid? The 5000ES isn't a grid-tied unit, only uses the grid for input, so I assume no.
2. Should I have a DC breaker on the PV lines coming in before connecting to the inverter? If so, what is the proper sizing or rating I should use?
3. Should I have a PV Quick Disconnect? If so, what is the proper sizing or rating I should use.

I understand that when adding panels in parallel, I should use a combiner box.
I'm just not sure if I need a specific one since the MPPT can handle up to 450 VDC.
Also, if I were to add a DC breaker in-between the PV and Inverter, I'm not sure how to size it.
This would be for protecting the inverter in case over-current happens for some reason.

I have seen the videos on the bond issues, which I made sure to get the US model.
I have also seen the videos on using the transformer to run 110V loads, which I'm not comfortable with.

Any advice is welcomed, thanks!
 

bob.longmire

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Jun 25, 2022
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Hi! Did you end up solving this problem? I'm looking to do something similar and would like to hear what you learned.

Thanks!
 

12VoltInstalls

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Wow. An old unanswered thread ;(
@timselectric will have good thoughts
understand that when adding panels in parallel, I should use a combiner box.
I'm just not sure if I need a specific one since the MPPT can handle up to 450 VDC.
for more than two parallel yes combiner box. At 376VOC a series string will be < 7A but that’s killer voltage so be smart. It shouldn’t go over 435V in extreme cold but that’s a wildhat guess
if I were to add a DC breaker in-between the PV and Inverter, I'm not sure how to size it.
wrll it needs to be DC rated to 450V and if series 8A or 10A would provide a decent disconnect. Cheap DC breakers might be best used for the 4th of July- get a decent one.
 
Last edited:

timselectric

If I can do it, you can do it.
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Yes indeedy @12VoltInstalls

This is the perfect use for this inverter.

Do I need to worry about back-feed into the grid? The 5000ES isn't a grid-tied unit, only uses the grid for input, so I assume no.
Correct, it will not backfeed the grid.

Should I have a DC breaker on the PV lines coming in before connecting to the inverter? If so, what is the proper sizing or rating I should use?
Yes, it's recommended for maintenance and emergencies. It's just a disconnect, overcurrent protection isn't required for less than 3 strings.
My recommendation:
DC Miniature Circuit Breaker, 2 Pole 1000V 63 Amp Isolator for Solar PV System, Thermal Magnetic Trip, DIN Rail Mount, Chtaixi DC Disconnect Switch C63 https://a.co/d/ie091H3
Should I have a PV Quick Disconnect? If so, what is the proper sizing or rating I should use.
Not necessary, unless roof mounted. In that case NEC requires a "Rapid Shutdown" system.

I understand that when adding panels in parallel, I should use a combiner box
Not required. You can just use MC4 branch connectors.
 

12VoltInstalls

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DC Miniature Circuit Breaker, 2 Pole 1000V 63 Amp
I use that for a disconnect between Epevers and batteries.
China Taxi :)
I use a 10A version on the two strings but they will never trip from the panels- 8A fuses in MC4 holders probably can’t trip either as 4S keeps them at < 6.xA
Most PV Combiner Boxes these days have a DC disconnect switch and a contactor for Rapid Shutdown compliance
I’m not sure ‘most’ is the case. Specific requirements are not inherent in the $100 boxes or the $300 boxes
 

ncsolarelectric

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I use that for a disconnect between Epevers and batteries.
China Taxi :)
I use a 10A version on the two strings but they will never trip from the panels- 8A fuses in MC4 holders probably can’t trip either as 4S keeps them at < 6.xA

I’m not sure ‘most’ is the case. Specific requirements are not inherent in the $100 boxes or the $300 boxes
Correct, the stuff you get on Amazon and for off-grid systems does not comply with NEC requirements. I don't recommend that stuff to anyone and if you're putting solar panels on the house, a rapid shutdown should be installed even if it's not a grid-tied system.
 

ncsolarelectric

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It depends on what version of the NEC is being followed. A simple contactor would not be compliant for 2020.
True, 2020 went a little overboard but I do have access to Hoymiles panel-level RSD devices, cheap! However, I prefer their microinverters with the 16 - 60V input range, and 1440W output. Nice!
 

timselectric

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I don't need panel level monitoring, with a string inverter. I want low cost compliance. (Solid state relays would be low enough cost, I believe)
 

timselectric

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Mosfet control should be very low cost.
Might have to just make my own. Could be a fun little project.
 

ncsolarelectric

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Mosfet control should be very low cost.
Have you ever tried to get UL Listing on a product? Large or small, low-cost or not, it's damn expensive, it takes a lot of work and a long time for the company to recoup that investment. IMO, a DIY RSD is not a good idea. The extreme temperatures involved do not make adding silicon MOSFETs or SSRs practical for DIY. Even the best engineers with $$$ backing them, usually don't get it right the first time. Doing it wrong can start a fire rather than prevent one.
 

timselectric

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I don't need it to be UL listed. Just want to protect my local firefighters, if the need for them arises.
The current alternative is no rapid shutdown. And a sign that says, "let it burn". lol
 

ncsolarelectric

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I don't need it to be UL listed. Just want to protect my local firefighters, if the need for them arises.
The current alternative is no rapid shutdown. And a sign that says, "let it burn". lol
If you can get a permit without UL Listing, more power to you. I wouldn't even try.
 

Sethtrosity

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Hi! Did you end up solving this problem? I'm looking to do something similar and would like to hear what you learned.

Thanks!

I'll just put a little update here.

I have 22 panels, in a 11S2P combination with two fused mc4 connections on the main positive leads.
They feed directly into my house, to a DC Breaker, and then to the inverter. The inverter is powering a sub-panel.

I went with the Growatt 5000ES from signaturesolar. Had nothing but issues with the unit, and with their customer support.
Long story short, the inverter wasn't using solar to power the load even though it showed that is was in the reports.
You can read about my experience here if you'd like: https://diysolarforum.com/threads/my-signature-solar-experience-not-good.40669/

I ended up going with a custom MPP 6048: SunGoldPower TP6048
It was more expensive, but I haven't had any issues with it since I installed it. Also, I am still running the system without any battery.
 

Larry Oswald

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Jun 7, 2022
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Relays would be very unreliable. They arc, they weld, they would not pass code. It has to be solid-state with protections. Now they even have panel-level monitoring. This is what you want.
The link needs emphasis. It goes here

The electrician is totally educational and entertaining in all his videos highlighting rules, regulations and techniques.
 

OnGrid

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Sep 11, 2021
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I'll just put a little update here.

I have 22 panels, in a 11S2P combination with two fused mc4 connections on the main positive leads.
They feed directly into my house, to a DC Breaker, and then to the inverter. The inverter is powering a sub-panel.

I went with the Growatt 5000ES from signaturesolar. Had nothing but issues with the unit, and with their customer support.
Long story short, the inverter wasn't using solar to power the load even though it showed that is was in the reports.
You can read about my experience here if you'd like: https://diysolarforum.com/threads/my-signature-solar-experience-not-good.40669/

I ended up going with a custom MPP 6048: SunGoldPower TP6048
It was more expensive, but I haven't had any issues with it since I installed it. Also, I am still running the system without any battery.

Did you put your panels on the roof? If so, do you have the Rapid Shutdown?
 
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