How many inverters?

[Aussie75]

My house has two main panels one a 200A and the other 150A. Each has its own direct connection to the meter.

Does this mean I would need two inverters? One for each panel and if so that would mean something like a EG418k or Sol-ark 1K?

Would these be paralleled?

This would also mean careful planning of the panels to make sure each is feed about the same?

 

[MichaelK]

Just looking at the ampicity of your electrical panels is not really a good way to determine capacity. You will be far better off creating an itemized list of electrical appliances and the watts they consume.

I'm assuming you will be building this in Australia? You need a 230VAC 50Hz inverter? Can you go into more detail as to why your home is serviced by two panels?

I consider both the EG4 and Sol-Ark to be low end products to be avoided. Lots of empirical evidence that they can not handle the loads they say they can. For a quality off-grid inverter I'd suggest you go with the Outback Radian. Another good choice is the Schneider XW.

For just run of the mill living, I'd suggest you could get by with just 5kWh of power per day, assuming you want lights, TV/computer, and a refrigerator. Air-conditioning though is the big wildcard that will require LOTS of power, especially if you need to have it running 24/7. What size of air-conditioner would you want to run, and how many watts will it consume? Air-conditioning will be the make or break item that your system needs to handle.

 

[Aussie75]

Gotcha, I want to be able to run the whole house or with grid/battery supplementing.

Its in the SouthEast US. Electric is going to double in price in the next few years.

No idea, it was that way when we bought the house. It has a well pump and use to have 2 heat pumps with electrical coils (with wiring for a 3rd). We switched both over to variable speed ac/heat pump and dual fuel (3 tons). There are also two sub panels off each and we put in a pool which requires 240v.

My biggest issues is I don't want to be locked into like an enphase and have to use their batteries or Tesla.

Appreciate the conversation.

 

[MichaelK]

OK, the Southeast means air-conditioning, which is going to need LOTS of watts. From my own personal experience running a small air-con off grid, you'll need at least 5kWh per room of cooled space. But, I'm not living in the Southeast. For whole home air-conditioning, which is what I'll assume you'll need, you would need a VERY Large system. The other big-ticket item is likely to be your well-pump. Is it 120V or 240V?

You're going to need to make some hard decisions. Do you want to power the well-pump, the air-conditioners, or just keep the frig running and the lights on? The 5kWh of basic power is going to be easy. All of what you are listing most likely not. That itemized list is essential. Flesh that out first, and a realistic wish list of what has to be powered, and what will be nice to be powered. Design/planning comes after that.

 

[Hedges]

Do you want to have power when the grid is down, or just use batteries to shift time from when PV produces to when you power loads? Grid down, your inverter need to supply starting current (about 5x running current for motors.)

Tesla batteries would be pared with fairly wimpy inverters. SolArk has become popular, and apparently performs pretty well. Midnight Rosie will probably be very good, is very new. Schneider is a robust inverter, as is Sunny Island which some of us use. All of these are stackable for more watts and use 48V batteries. Depending on utility requirements, Sunny Island might only serve as a battery backup inverter, with a UL-1741 SA/SB PV inverter.

Don't know if you are planning or grid tie net metering, zero export, or offgrid operation.

 

[Aussie75]

The well pump is 240v

I would like power when the grid is down.

Curious if anyone knows why Duke Energy limits inverter Grid AC Output to 20KW?

Initial thought is grid tie with net metering but I just found out about that inverter limit. So trying to find out more and what my options are.

 

[chrisski]

Curious if anyone knows why Duke Energy limits inverter Grid AC Output to 20KW?

20 kw is a lot of panels, especially since a lot of that will be going to household production and not fed back to the grid

Some places limit you to 15 kw.
======+===
Knowing your kWh requirement helps.

On the hottest days of summer thanks to two ACs, a 5 ton and 4 ton, I use 150 kWh. That’s about 15 to 20 Tesla batteries.

With the grid tied install I’m getting, I decided on some essential circuits. A few lights, refrigerator, washing machine, and a GGFCI circuit breaker. My battery capacity is 10 kWh, and that will easily run those items overnight.

I’m also tying a single 4 or 5 ton AC into this circuit. If it’s summer I should be able to power the AC when the sun shines, and an hour or two after.

A more rational financial decision would be to skip the battery pack and simply install a grid tied inverter with more panels.

 

[Aussie75]

From what I was told its how much you can feed into the grid.
I was thinking why do they put a restriction on the inverter/s output versus the actual output feed into the grid. Why should they care about the size of the system as long as I am only feeding no more than that amount?
I see what you are saying.

 

[Hedges]

The well pump is 240v

I would like power when the grid is down.

Curious if anyone knows why Duke Energy limits inverter Grid AC Output to 20KW?

Initial thought is grid tie with net metering but I just found out about that inverter limit. So trying to find out more and what my options are.

Net metering with export limit could work.
But 20kW inverter should be sufficient for most people.

You need to know starting surge of motors. I expect it to be 5x nameplate running current, while actual running current could be lower due to load. I got the Harbor Freight 1000A clamp meter with inrush.

Good inverters will provide several seconds surge to 2x their continuous rating. So could start a motor that takes 40% of inverter capacity running, e.g. a 2kW motor that needs 10kW surge to start should work with a good 5kW or larger inverter (such as Schneider, Sunny Island, both of which are LF, or Rosie or SolArk which are HF.)

My system has Sunny Island + Sunny Boy. After Sunny Island starts motor, frequency shifts to ramp up power from Sunny Boy to support it. Then Sunny Island's surge is available for another load. Given enough sunshine. You could do 12kW battery + 13kW PV inverter this way, or double that. Other inverters which support AC coupling should do the same.

 

[MichaelK]

The well pump is 240v

I would like power when the grid is down.

OK, that's a start. More details would be better. Is the pump 1/2hp, 1hp, 2hp? Pay close attention to what Hedges just mentioned. Starting surge is very large in most submersible pumps. My 240V 1hp Grunfos consumes 38A at startup, but runs at only 9.5A. My XW+6848 easily handles the startup surge. BTW, I measured the starting surge with a clamp meter that has "inrush current" capability. It's a Uni-T216C. I highly recommend it. I also have a much more expensive Fluke clamp meter. The two match each other to within 1%.

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Its the surge capacity that really separates the good inverters from the junk. Look at SMA, Outback, Schneider, and Victron for serious, quality inverters. If you skip the whole-house air-conditioning, and are not pumping water all day long, I'd say you'd be very comfortable with just 10-15kWh per day, assuming you need ~10kWh for air, and 5kWh for everything else. That would be easy to obtain with a 48V system with ~3000-5000W of panels. You will need a charge controller that can handle 50-80A at 150-200V. A budget brand like an Epever 6420AN or 8415AN might work, though I myself like Midnight's 200V Classic.

Inverters might be divided up into different size classes. Look at Outback's GS4048 or Schneider's SW4048 if your power needs are not that high. Scale up to an Outback 8048 or XW-Pro 6848 to handle the bigger well-pumps, and the air-conditioners. Pay attention to those starting surges to make your decisions.

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