Solar priority Automatic Transfer Switch or Contactors

[thejake25]

Hello guys and girls,

Im in the planning stages of setting up a typical off grid solar system with one atypical exception: I would like my inverter/solar power to run through a 150 amp automatic transfer switch or 150 amp contactors which prioritizes using battery bank power first. The idea is to utilize solar as much as possible, and once the inverter shuts down due its low voltage cutoff setting the transfer switch or contactors would automatically switch back to grid power allowing my batteries to charge via solar. Once the battery bank is fully charged the inverter would cut-in and trigger the ATS or connectors to revert back to solar power....

I understand this is not the most economical way to go about solar power so no need to spell out the financial shortcomings of this plan of which there are plenty. My only questions are as follows...

1. Would any generic ATS intended for a generator (baring its rated for the appropriate amperage) be capable of doing this if solar was wired to be the priority? Anyone have any experience with this? If so, what ATS was used?

2. Has anyone used or have thoughts on using two 150 amp contactors to achieve this kind of thing? If so, which ones?

Any and all thoughts are welcome and appreciated. Thanks for your time.

 

[mrdavvv]

I can just talk about my setup, but the hybrid inverters as the LV2424 are programmable in that regard, so you can setup if you want solar, battery or AC mains priority., they are cheap and Will have some videos with them.

You can check if they can work with you in the settings of the user manual: http://www.mppsolar.com/manual/SPLIT PHASE LV/

 

[dashdrum]

A standalone switch could also do this. https://www.amazon.com/dp/B07F12RDZ2

 

[Steve_S]

MPP / Growatt All IN Ones have such facility built in, as do Samlex EVO series Inverters (limited to 120VAC at this time in North America). Victron who is another ier-1 Manufacturer (and gold standard product) also has such capability built in or with additional "modules" depending on teh way you want to go.

You idea is actually the #2 favoured installation that most folks look at and want to implement. Relegating Grid Power to act as Backup to our own Solar & Battery system and using the low Time of Use rate period for charging up batteries if they are low.

 

[thejake25]

Thanks for the response

A standalone switch could also do this. https://www.amazon.com/dp/B07F12RDZ2

This would be ideal but I would need a 150 amp version and haven't been able to find one.

 

[tictag]

I would urge you to consider @Steve_S post because, as he says, this is not 'atypical' at all, you just need the 'right' inverter. Victron has a great white paper on this called Energy Unlimited (available here).

But, to answer your questions specifically,

1. Would any generic ATS intended for a generator (baring its rated for the appropriate amperage) be capable of doing this if solar was wired to be the priority? Anyone have any experience with this? If so, what ATS was used?

Smart switches exist, like the one linked to by @dashdrum that will connect grid power on low-voltage trigger, then disconnect the grid at a recovery-voltage trigger, essentially prioritising solar.

2. Has anyone used or have thoughts on using two 150 amp contactors to achieve this kind of thing? If so, which ones?

Using contactors being driven by voltage sensing relays (VSRs) would be over-complicated and consume a lot of power keeping their coils energised. A smart ATS would be the more optimal solution.

 

[GarrettmDyer]

I just bought the SPF Growatt 3000 LVM - I’ve been having trouble figuring out whether it has a built in ATS...I bought a smart ATS off Will’s site just in case...

 

[JoeHam]

Thanks for the response

This would be ideal but I would need a 150 amp version and haven't been able to find one.

How about three of them?

Put 50 amps worth of circuits on each one.

 

[Hedges]

Why switch at all?

You can get a battery inverter (I think Tesla PowerWall supports this, also SMA Sunny Boy Storage), where the grid, your grid-tie PV inverter, and the battery inverter all connect to the same wires. Nothing gets isolated except in the case of a power failure, in which case you disconnect the grid.

The battery inverter can be programmed to suck down all the PV you generate during some hours, supply all your loads some hours. It just needs to measure power flowing to/from the grid and and adjust it's operation to keep grid current at zero.

The issue with two, 150A contactors is making sure they are never both closed at the same time. Relays sometimes weld shut, so the control circuit would need to know for sure it has fully opened. I had a DPDT relay twist so one half was connected "in" and the other was connected "out". Circuit breakers work, even with a bolted fault! (and 400' round-trip of wire for resistance in this situation.)

Hybrid inverters, or my Sunny Island, just use a single relay to disconnect grid (or generator). The inverter portion is control of solid state circuits. They can be programmed to start a generator (or connect the grid) at some state of discharge.

 

[Hedges]

How about three of them?

Put 50 amps worth of circuits on each one.

Do you realize what happens when you tell all three to switch, and they do so but not at exactly the same instant?

(Oh, not in parallel, but separate his breaker panel in three equal parts? now the poor guy needs a total of four breaker panels. Most people don't even like buying a second one.)

 

[tictag]

Just to clarify, are you talking about 150A AC? As in 18,000W at 120V?

If so, these are industrial-level currents so you might want to check out Schneider or similar. The Alt-E store also has such industrial-level components.
If not, then be advised, an ATS is designed to switch AC supplies, not DC supplies.

 

[JoeHam]

View attachment 18362



(Oh, not in parallel, but separate his breaker panel in three equal parts? now the poor guy needs a total of four breaker panels. Most people don't even like buying a second one.)

To quote the OP:

no need to spell out the financial shortcomings of this plan of which there are plenty.

I have no problem spending other people’s money. ?

 

[Sunny Days]

NONE of the Mpp all in ones can handle 100 amp pass through! So he wont be able to power 100 amps normally from the grid... All he needs is a 100amp or 150amp Automatic Transfer switch, (this can be controlled any way he wants)
Which i personally havent found! I do have one from ebay thats 63 amps but thats as high as ive seen, everything else from china rated at 100 amps is a joke!

The ones available for some reason start in the 1000s $$$ for generators and i wonder if i can retrofit mine with 100amp breakers...?

Or get 6 MPP's, 3 on each phase sharing the laod.

 

[GarrettmDyer]

I

Why switch at all?

You can get a battery inverter (I think Tesla PowerWall supports this, also SMA Sunny Boy Storage), where the grid, your grid-tie PV inverter, and the battery inverter all connect to the same wires. Nothing gets isolated except in the case of a power failure, in which case you disconnect the grid.

The battery inverter can be programmed to suck down all the PV you generate during some hours, supply all your loads some hours. It just needs to measure power flowing to/from the grid and and adjust it's operation to keep grid current at zero.

The issue with two, 150A contactors is making sure they are never both closed at the same time. Relays sometimes weld shut, so the control circuit would need to know for sure it has fully opened. I had a DPDT relay twist so one half was connected "in" and the other was connected "out". Circuit breakers work, even with a bolted fault! (and 400' round-trip of wire for resistance in this situation.)

Hybrid inverters, or my Sunny Island, just use a single relay to disconnect grid (or generator). The inverter portion is control of solid state circuits. They can be programmed to start a generator (or connect the grid) at some state of discharge.

I live in a small cabin in northern CA...it’s all electric - my stove and water heater are 220v , so I won’t be including those in my critical loads sub-label..

My battery bank is 2x 24V lifepo4 battery packs from big battery. 3kwh storage on each...

I use about 7kwh of grid power per day...I’m hoping that I can utilize “time of use” and just use the batteries full storage potential at night.

In the winter when the rains come, it’d be nice to have an automatic transfer switch so grid power would kick in when needed...

I bought an ATS off Will’s sight. It seems that it does exactly what I want...I’m just wondering if it’s a redundancy because the “growatt all in one” would automatically transfer to grid and charge the batteries when they reach the pre-set low voltage anyways...

Growatt has a “solar first” setting that will only charge the batteries if there is no PV available and the batteries have discharged to their low voltage cut off state

Hope that makes sense.

 

[GXMnow]

150 amps is a huge amount of critical loads.

What are you planning to use for an inverter? How much battery storage? How big of a solar array?

My whole house only has a 100 amp panel, and my typical use rarely exceeds 4 KW of consumption even with my A/C running in 100 degree heat. 150 amp on a 240 volt split phase panel is 36,000 watts. Even if it is just 120 volt, it is still 18,000 watts. Have you done an actual power budget on this property? What equipment are you running? 150 amps is certainly not a typical off grid system.

That being said, you could stack 6 Schneider XW+ 6848 inverters and have 40,800 watts available (170 amps of 120/240 volt split phase power), with a surge power of over 70,000 watts. This would require dual 3 unit clusters (two separate essential load panels) and external contactors for the transfer due to the very high current. The internal contactors are rated to 60 amps. The battery bank would need to be huge. How many kilo watt hours of power are you actually using in a day?

My (in progress) setup is going to use just one Schneider XW-Pro 6848 inverter with a 360 amp hour 48 volt (more like 50 volt nominal) lithium battery bank. This will easily run my essential loads for about 2 days. My solar array is 16 panels making about 4 kw of DC and the Enphase micro inverters provide about 26 kwh a day to my home. Running the refrigerator, gas furnace fan and controls, gas stove igniter, PC and internet connection gear, some basic lighting, and my Dish Network and TV, I only use about 1,000 watts average, or 24 KwH in a full day. The A/C compressor needs grid power. That pulls about 3,400 watts. I could not justify trying to run that on batteries. But during the peak sun time while I am on grid, my solar runs the AC and still feeds about 2 amps to the rest of the house. All said, except for the A/C, I could almost run off grid on just the 16 panels. Once I have the battery and inverter all up and running, I will track the consumption and see where it falls. I may add 4 more panels just to help charge the batteries and see how close I can come to zeroing out the grid.

 

[Hedges]

Haven't seen hide nor hair of OP TheJake25 in three months: Last seen Apr 26, 2020


There are some rotary switches that offer 200A at 600VAC, 3PDT:

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That is manual, but you could motorize rotation of its shaft. I think a pneumatic actuator would be good to provide the significant torque required.
It would serve as a snap-action transfer switch for 120/240 VAC 200A, or for 208Y 3-phase, etc.

 

[schmism]

NONE of the Mpp all in ones can handle 100 amp pass through! So he wont be able to power 100 amps normally from the grid...

The growatt's previously mentioned like a SPF 3000TL will support up to 6 in parallel. Giving you 9000w of 220v (18kw) of power. A setup like this will easily allow you to pull 100amp from the grid.

But given the size of this kind of system there are other name brand units I would likely look at first as a system this size with those kind of power requirements is in the $50K and up range. So moving from $4500 chinese inverters to $8000 name brand versions is typically a low enough percentage of the budget as to not be worth the risk of the Chinese inverters.