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Inverter selection

Bluedog225

Texas
Joined
Nov 18, 2019
Messages
2,814
I’d appreciate some help narrowing my inverter selection. All off grid.

I’ve got about 15,000 watts of panels (not yet deployed). And 4x sok server rack batteries (100 amp 48 volt). Will probably double this.

I’d like to ground mount the majority of my panels. But I’d also like to have the ability to roof mount some later with micro inverters.

And I’d like to be able to charge from my 7500 watt generator when needed.

My usage will be around 1000 watts continuous in the summer (24/7). Max about 2000 watts at any given time.

What should I be looking at? The need for grid forming narrows it down. Am I reading the Sol-Ark 15k right to believe it would perform all these function? Though it seems like more (capacity) than I need.
 
I'm offgrid (with grid-assist) and talking in that perspective...

I did my system with individual components - which lets me expand as needed. For example, when I add more panels, I add a Midnite Classic controller... and just tie the DC output into the master bus. Similarly when I added a 2nd inverter, I just tapped the master DC buss and wired the AC output.

These days, the all-in-one MPP Solar and GroWatt will do what you want and very well priced AND you can add on more units in parallel. Not sure about ETL/UL but they are very well priced compared to a SolArk.

Take MPP Solar (I have a 3048LV in my trailer) - you feed in AC + DC Solar + Battery and get AC out. Typically the AC input is grid but you could put an ATS in front of that for a generator. When the generator is active the ATS will switch to feed generator AC into the MPP Solar... to meet you're goal of generator charging but have a grid-assist otherwise that's automatic.

Some key things in my mind:
All my stuff in the house is ETL/UL - to make fire insurance claim easier.
Off-grid = no issues with power company / made city permitting easier.
 
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Whichever inverter (S) you decide to purchase, you need to carefully review its solar panel input requirements because you got "15,000 watts of panels". The newer inverters have 500 V dc rated input (older ones like 250 V dc) and about 18 Amps dc rated current (athough it could probably take up to 22 Amps) and a fix Wattage rating. Therefore you need to be under those ratings by 10-15% to be safe. You also want to have the most number of solar panels in series (as long as you don't go above the rated input voltage). Let me give you an example; I purchased twenty 445 watt Solarever panels and an EG4 6.5KW 48V inverter (switched from EG4 3KW). This inverter has 500 VDC, 8000 watt, 18 Amp ratings for its two solar panel inputs, and I will have two strings of 8 solar panels in series feeding its two inputs, in order to stay under its PV rating (445 watts * 8=3560 watts (rated for 8000/2), ~50VOC*8=400Vdc (rated for 500Vdc), and 10 Amps per string (rated for 18 Amps)). As you can see, I can only use sixteen of my twenty solar panels. I cannot either have four strings of five solar panels in series (two 5S2P) because I would go above the 8000/2 wattage rating (445 watts *10= 4450 (rated for 8000/2)). I have heard good things about Sol-Ark 15k but it is very expensive (six times), and it is meant to be connected to the grid (sell power to grid). Your power requirments is very similar to mine (very low) and a 3000 watt inverter would work for you (as long as you don't have loads with large in-rush current), however you will not be able to utilize all of your panels.
 
Thanks. Yes, figuring out my strings is something I’m working on.

I guess looking at some of the strings being on separate charge controllers is a good idea. That is, panels-controller-battery. And think of the inverter requirements separately.

In wonder what the best grid forming inverters in the 2000–3000 (maybe under 5000 watt) range is?
 
, however you will not be able to utilize all of your panels.
Some of that panel capacity can be used to charge batteries regardless of inverter capacity. That is the advantage of a component system vs an All In One design. Also some extra panel capacity can be used in winter when production is lower. To me the inverter should be sized for peak loads (kW) and solar and batteries for overnight cumulative loads and reserve in kWhs.
 
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Why micro inverters on roof? This just complicates the system. If you are completely off grid, keep it simple.
 
I like the safety factor of micro inverters on the structure. No arc faults (ground, series, parallel). Rapid shut down. Traditional AC safety and reliability.
 
I like the safety factor of micro inverters on the structure. No arc faults (ground, series, parallel). Rapid shut down. Traditional AC safety and reliability.
I understand the reasoning. As long as you realize that you are adding a lot of expense. AC coupling changes everything.
 
I’d be interested in hearing more. Off-grid, I thought AC coupling was only going to add the expense of an inverter capable of creating a micro-grid. Is there more? Thanks

edit-and the micros.
 
I thought AC coupling was only going to add the expense of an inverter capable of creating a micro-grid. Is there more? Thanks
I know your question was directed at @timselectric but I will give you my perspective. I will be curious what he has to say as well. I think AC coupling is a good way to leverage a hybrid inverter because GT inverters are less expensive than additional hybrid inverter capacity per kW. Also micros are about the same as other devices to get the RSD functionality needed for the roof of my home.
My hybid is only 5kW of inverter capacity and I have added 7kW of AC coupled micros on my roof. More are planned. The 5kW is adequate for my needs but I need more solar capacity to charge my 42kWh pack and keep it near the top in case we have a multiday power outage with little solar. I run my hybird inverter in Self Consumption mode which means I run on batteries and use the grid as backup.
 
Seems that everyone is in love with the all in one inverter/charger/charge controllers units. I admit, they are cheap, you get a lot of bang for your buck. They also suffer from one problem—their all in one design—means if the charge controller becomes fubar, you have to take the inverter off line for repair or replacement. Ditto the same thing if the inverter section would go up in smoke. While more expensive, I prefer an inverter and a separate MPPT charge controller. But that's just me.
 
Short and sweet.
When AC coupling. You have the added expense of the micro inverters. And a more expensive inverter, equipped to handle AC coupling. And also utilize battery storage.
Not saying that it can't be done. It most certainly can.
But, I prefer simple and cheap.
 
Thanks. That what I thought.

In reality, I’ll probably get some midnite classics to charge the batteries. I’ll have strings at various places, one optimized for winter.

This just leaves me with the need for a smallish (3000 watt) inverter capable of grid forming. Preferably one that could handle generator input. Though, I suppose I could have a separate charger.
 
I know your question was directed at @timselectric but I will give you my perspective. I will be curious what he has to say as well. I think AC coupling is a good way to leverage a hybrid inverter because GT inverters are less expensive than additional hybrid inverter capacity per kW. Also micros are about the same as other devices to get the RSD functionality needed for the roof of my home.
My hybid is only 5kW of inverter capacity and I have added 7kW of AC coupled micros on my roof. More are planned. The 5kW is adequate for my needs but I need more solar capacity to charge my 42kWh pack and keep it near the top in case we have a multiday power outage with little solar. I run my hybird inverter in Self Consumption mode which means I run on batteries and use the grid as backup.
Micro inverters make sense for you. Because you have a grid tied system. But for off grid, it's just an unnecessary added expense. In my opinion.
 
Not particularly directed at you times. There seems to be a lot of resistance/hostility to micros from the guys who came of age in the the string inverter world. The guys at midnite are the same. Esp when it comes to rapid shut down requirements and thoughts related to direct current safety and arc fault avoidance.
 
I'm fairly new to solar. Only heavily into it for the last year. But, I have done a lot of research in what would work best for me. You have to do the same for yourself.
If it meets your needs and fits in your budget, that's really all that matters.
 
But for off grid, it's just an unnecessary added expense. In my opinion.
Like everything, it depends. As I mentioned earlier if someone is adding solar to a dwelling they presumably have the added cost of RSD then micros can be competitive. It also depends if there is additional capacity on the existing off grid inverter or it's charge controllers. If more inverting capacity is required micros may be less incrementally especially if adding just a few kWs. As you mentioned, one has to do the math to see where the trade off actually is finanicially.
 
Like everything, it depends. As I mentioned earlier if someone is adding solar to a dwelling they presumably have the added cost of RSD then micros can be competitive. It also depends if there is additional capacity on the existing off grid inverter or it's charge controllers. If more inverting capacity is required micros may be less incrementally especially if adding just a few kWs. As you mentioned, one has to do the math to see where the trade off actually is finanicially.
I completely agree. Each situation is different. Depending on many factors.
Whether you are starting from scratch. Or adding to an existing system. If adding to existing, you have to decide if it is more cost effective to work with your existing system. Or possibly start over , and reuse whatever can be re purposed. If starting from scratch, you should plan for future expansion.
I've learned over the years (lots of years lol), that bad planning is very expensive. So, do all of the homework. Before you start spending money.
 
Ampster-I don’t understand why the existing off grid inverter would need more capacity. Would you mind expanding on that?

I thought I‘d size the inverter to the planned load. And the micros “plug” into the main to supply load instead of drawing from the battery (through the inverter).

Why would the inverter need capacity?

Edit-or do I need an inverter that can take the AC generated and charge the batteries? In addition to the DC charge controllers.

Edit 2-of course it does. Sorry. Disregard.

Thanks
 
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