diy solar

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bootlegging a 220 circuit

tomy2

tomy2

escape artist
Joined
Mar 12, 2022
Messages
433
Location
paso robles ca.
I have two solar setups at 110V, and I want to create a 220V circuit for a mini-split that I am adding. The inverters and batteries are at opposite ends of my building. I would like to avoid moving them together, just to get one 220V circuit. This diagram shows the basic setups. If I could find an AC mini breaker with two poles, I could put one leg from each inverter. But would I need to run a communication wire between the inverters? And how can I tell if the two hot legs are 180 degrees different? And would I just tie the neutral wires together at the mini breaker? Any advice would be appreciated.
 

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You need to review the manual for your inverter. It probably has a section labelled something like "Parallel Operation in Single phase" which will describe how/if the inverters can be connected to create a split phase system. If possible, it will involve a special data cable run between the two inverters that would allow them to synchronize and ensure the two sine waves are 180 degrees apart.

If all that seems promising, part you may need to contact support for is to find out whether the inverters can form a parallel split phase system while connected to independent battery banks and whether the length of the data cable will create a problem in your proposed installation. (I suspect those details won't be specified in the manual, but they are critical here.)

As @Shimmy says, you definitely can't just hook the neutrals together and magically expect a split phase system to appear.
 
Personally, I suspect that the distance between the inverters will create a subtle (but maybe irrelevant) out-of-phase effect where the two sine waves will be slightly off depending where in the system you measure - or possibly everywhere as a function of the signal lag over the data cable.

I think it comes down to whether the inverters are smart enough to measure the lag between themselves and first synchronize internal clocks using a protocol sort of like NTP - then align the sine waves to the resulting synchronized clocks. If they just do the quick and dirty version where they expect the lag to be zero, then the length of the cable will directly effect how in-phase the two sine waves are.

If it took 3 round trips of 75' (one way) to synchronize, I think they'd end up about half a degree out of phase just purely based on the speed of light. (Assuming my math is right) Realistically the signal will be much slower than that since it's probably encoded with a serial protocol and there'd be some processing time on both ends too.
 
I just realized that I am paying $8 a day for natural gas from my furnace to keep my house at 66 degrees. The mini-split should only use 4 amps at 220V or 800 watts/hour. If it is on for ten hours a day that equals 8kw/day times .36/kw equals $2.88/day vs. $8./day. So if I just leave the mini-split on the grid, I'm still way ahead.! At $1250. ($300. off by bidding on Ebay}for the unit and a $350. tax credit, itwill pay for itself in one winter.
 
Last edited:
tomy2 said:
.36/kw equals $2.88/day
Click to expand...
36Cents/kWh - ouch!
What is your cost per kWh for site generated solar?
Maybe the short term solution is run MiniSplit on grid, and longer term solution is upgrade the solar to run the mini.
If there are other 240 V loads that could benefit from the 240 power supply located near the mini split, perhaps this would be worth while for other appliances you have?
 
OffGridForGood said:
36Cents/kWh - ouch!
What is your cost per kWh for site generated solar?
Maybe the short term solution is run MiniSplit on grid, and longer term solution is upgrade the solar to run the mini.
If there are other 240 V loads that could benefit from the 240 power supply located near the mini split, perhaps this would be worth while for other appliances you have?
Click to expand...
Hey! it's California.........
 
Shimmy said:
EG4 Seems to insist on a common battery bank for parallel operation, in addition to the paralleling cables.
Click to expand...
This is correct. As well as setting the inverters up for split phase operation. You can't just take two 120v circuits and pair them to get a 240v circuit. Well you can, but you're not going to like the results. :)

I would be interested in what SS has to say about the distance between the inverters. I suspect @Symbioquine may be onto something. It might help to know the exact distance between the two.
 
My system cost about $11k, including $6k for 20kwh of batteries. My 16 panels are rated at 6KW, delivering about 5.2KW this time of year. I just finished transfering 90% of my circuits into solar load ceenters. My PGE account projects my next bill to be $34. down from avg. $250./month pre solar. So the system should be paid for in 4 years. The advantage of living in California is that my batteries are fully charged by 2pm. except for about 30 days a year, when it is cloudy or over 100 degrees and the AC {soon to be all mini-split} is running alot. The new minisplit is arriving this week, and hopefully will live up to it's advertised efficiency ( 26 seer & 13 EER). I installed another smaller minisplit last month in a rental unit and it was a nightmare from day one.
 
$11,000
Collecting 20kWh per day 336 days per year
Say 10-years usable life for the batteries and PV (actually I suspect a lot more than 10 is likely but lets just say 10)
$11,000/(20kWh/D*336D/yr*10yr)
would make your internal cost of site produced electricity around 16-cents per kwh. assuming no major parts need replacement during that 10-years.
You can play with these numbers a lot, or plug in real data from your system, play with how many years.
Compared with the local utility prices, it would seem a good deal to expand the system if needed, and avoid the local utilities as much as you can.
 
Cost of adding another battery - $1500 for a rack 100Ah 48VDC
Would allow additional 5.12 kWh of solar collection per day, and again lets say 10-years usable life (yes some losses over that time, but to keep it simple we will ignore that for the moment)
local price of energy 36-cents/kWh
Cost for the one additional storage cell (to capture more available solar - "batteries are full at 2:00" - ie missing out on available uncaptured solar)
$1500 / (5.12kWh*336D*10yrs) = cost per kWh 8.7cents. At a difference of 27 cents per hWh your pay back on the one additional rack battery would be about 3.25 years based on that "335 days a year" comment above.
It would seem well worth adding more battery capacity in your case, based on your "the batteries are full by 2:00" meaning you have all the equipment in place to collect more energy, if you just had somewhere to store it.
All that said, I would recommend you install the new A/C and then run the numbers after knowing the load (demand) of this new equipment actually running.
 
OffGridForGood said:
Cost of adding another battery - $1500 for a rack 100Ah 48VDC
Would allow additional 5.12 kWh of solar collection per day, and again lets say 10-years usable life (yes some losses over that time, but to keep it simple we will ignore that for the moment)
local price of energy 36-cents/kWh
Cost for the one additional storage cell (to capture more available solar - "batteries are full at 2:00" - ie missing out on available uncaptured solar)
$1500 / (5.12kWh*336D*10yrs) = cost per kWh 8.7cents. At a difference of 27 cents per hWh your pay back on the one additional rack battery would be about 3.25 years based on that "335 days a year" comment above.
It would seem well worth adding more battery capacity in your case, based on your "the batteries are full by 2:00" meaning you have all the equipment in place to collect more energy, if you just had somewhere to store it.
All that said, I would recommend you install the new A/C and then run the numbers after knowing the load (demand) of this new equipment actually running.
Click to expand...
Thanks for the analysis, not my forte. I don't really need another battery now, these batteries are getting me thru the night almost everyday. Except for those 30 days, and those days in the winter, it is too cloudy for them to get charged and the nights are significantly longer. So I just write off those days. What I need is an EV, I could charge it for free between 1pm and 4pm. of course, I only drive about 500 miles a year, that would be a waste. maybe someday I'll get a renter(I have 3) with an EV. How cold is it there? It has been 23 F every morning this week. At least it gets up to 70 in the afternoon. I hate the cold, like most californians.
 
If you add battery, you might also consider a small 240V inverter connected to one of the two systems. Not sure just how small you could go without starting issues, but it might be reasonable. Or, go for the 120V mini-split and parallel another EG4 inverter with the first one in one of the two spots.
 
tomy2 said:
How cold is it there? It has been 23 F every morning this week. At least it gets up to 70 in the afternoon. I hate the cold, like most californians.
Click to expand...
LOL
Yeah I almost hate to tell you, it has been like we didn't even have winter this year!
While places way further south were in a deep freeze at Christmas, it was above freezing north of the 49th most of Dec-Jan and even when we got some more typical colder weather, it didn't last long. In some ways this is Bad for me, you gotta see the production on a bright sunny cloudless day at minus 25C (-13F) it is Awesome! But with so few cold days, I feel like I missed out on a lot of potential PV-boost over the last two months!
Anyway, I am sure it will change soon enough!
Anyway, it is your system, and your decision what to do with it. If it does what you need, it is perfect.
 
Shimmy said:
If you add battery, you might also consider a small 240V inverter connected to one of the two systems. Not sure just how small you could go without starting issues, but it might be reasonable. Or, go for the 120V mini-split and parallel another EG4 inverter with the first one in one of the two spots.
Click to expand...
Yes, I'm considering getting another inverter. It would be a lot simpler than moving one and the batteries, and upgrading the battery wires for four instead of two, and moving the PV cables in the attic.
 
OffGridForGood said:
LOL
Yeah I almost hate to tell you, it has been like we didn't even have winter this year!
While places way further south were in a deep freeze at Christmas, it was above freezing north of the 49th most of Dec-Jan and even when we got some more typical colder weather, it didn't last long. In some ways this is Bad for me, you gotta see the production on a bright sunny cloudless day at minus 25C (-13F) it is Awesome! But with so few cold days, I feel like I missed out on a lot of potential PV-boost over the last two months!
Anyway, I am sure it will change soon enough!
Anyway, it is your system, and your decision what to do with it. If it does what you need, it is perfect.
Click to expand...
I will pass on that invitation.
 
Well, at 66-degrees room temp, perhaps you have colder 'weather' than I do already! {I like 72F better!}
As you say, no sense adding more battery storage for loads you don't have; this will change when you add the A/C likely.
Hope you post again after you set up for the 240VAC and show us how it all turned out.
 
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