Grid tied solar to start, future battery, no backup load needed

[DaveNSueM]

Evening all - first post...awesome info here, have not been able to stop reading for past 2 days.

I have planned a 8KW solar (only covers about 40% of annual usage - may expand panel count in future) install (ground mount) using microinverters, grid tied, line side taps, AC fused disconnect...have received permits and interconnect agreement with my Ohio power company. I have a 2 year old generac NG generator feeding critical loads so no need for the system to handle any backup loads.

Talking to a friend recently they mentioned planning for future when net metering phases out and having battery capability to store excess solar for nightime use...seems to make sense and I like to plan ahead when possible. This line of thinking leads me to believe I may pay a premium for the micro's, which also have a proprietary battery system and not nearly the other features of some of the hybrid systems I have been reading about.

I want to start with panels/grid tied inverter only and add battery maybe in a year or so. Seems like so many options to choose from if I go string/hybrid...right now the EG4 18kpv has caught my eye BUT I have seen a few posts where it is mentioned that it may have issues if only setup as grid tied with no battery...is this still true or has EG4 resolved (I will email them directly). Any other systems that could fit this use case? Thanks in advance for any help.

 

[1201]

Forget micro inverters if youre doing ground mount. Waste of money .


Growatt sph10000tl hu-us does not need a battery to operate. It can operate grid tie only and you can add batteries later as needed.

It's also half the price of an 18kpv

 

[SolarFlares]

I agree on ditching the microinverters especially if you plan on adding batteries. Leave the panels sending DC to your inverter. Then when you add batteries down the road you don't incur another conversion loss when going from AC to DC to charge the batteries.

I would look into the 18kpv or a solark 15k and have it wired so it goes from your electric meter > inverter > main panel. This would make it easy to have whole home backup when you add batteries down the road. See this thread for more info on this - https://diysolarforum.com/threads/s...orking-for-peak-coverage-on-solark-15k.85227/

 

[1201]

why 200a passthrough may not be such a good idea

https://www.midnitesolar.com/pdfs/200_amp_inverter_thoughts_(2).pdf

 

[SolarFlares]

why 200a passthrough may not be such a good idea

https://www.midnitesolar.com/pdfs/200_amp_inverter_thoughts_(2).pdf

Lots of valid points. But no critical loads panel makes so many things easier especially for the non-technical crowd. When the power goes out they have to do nothing. I do advocate for a inverter bypass switch as recommended in that thread.

I've been running on a solark 15k in this configuration since the end of 2022 and it has performed perfectly.

 

[1201]

Lots of valid points. But no critical loads panel makes so many things easier especially for the non-technical crowd. When the power goes out they have to do nothing. I do advocate for a inverter bypass switch as recommended in that thread.

I've been running on a solark 15k in this configuration since the end of 2022 and it has performed perfectly.

The two biggest problems I see, and why I wouldn't run it this way

1. Power goes out when loads are more than inverter power. Inverter shuts down and whole house is without power.

2. Power goes out and you dont notice, you're not managing loads- battery runs down quickly.

I personally think it's easier and cheaper to put the true critical loads on a critical loads panel(fridge, lights, etc) and use the CTs to offset the rest of the loads right in the main panel.

 

[wpns]

Really happy with my 18Kpv parallel pair (and sixpack of PP batteries, but those are spendy and prices will only come down). If you know you are going to have/want batteries later, you are much better off planning ahead. As others have said, lose the micro-inverters and get a system that's upgradable to batteries later by just hooking them up. The hard part of adding pairs of batteries to my system will be getting them delivered and getting some help to move them into place with a hand-truck.

Under the Biggest Mistakes thread I listed the two grid-tie inverters I bought less than a year ago that are now decommissioned.

 

[DIYrich]

why 200a passthrough may not be such a good idea

https://www.midnitesolar.com/pdfs/200_amp_inverter_thoughts_(2).pdf

100 amp passthrough only reduces the problem to 100 amps. Instead of "expensive 200 amp disconnect / overcurrent and AC bypass switch device to be required in front of the inverter" you now have a slightly less "expensive (including labor cost) 100 amp disconnect / overcurrent and AC bypass switch device to be required in front of the inverter".

The only real benefit is the 3 smart load ports vs 1 for the 15k. If I had an unreliable grid, having the automation is helpful. Otherwise, once a year having to manage the load on the Smart Load port is not a big deal.

"A more practical approach is to design a battery backup system to power critical loads only: no large appliances such as air conditioning ...". Is that from the 2000's? Today, $7,000 for 28kWh, enough battery to run my house for a day, including the AC. If I turn off my ovens and the clothes dryer, the 15k can easily run the AC. I'll cook on the grill and hang laundry out to dry (preferably away from the grill to avoid the clothes smelling like BBQ). $7,000 to backup a few lights - umm.... I'll pass. $7,000 to run my gas furnace (heat pump if really needed to save the battery) in the winter and AC in the summer - sign me up.

 

[1201]

100 amp passthrough only reduces the problem to 100 amps. Instead of "expensive 200 amp disconnect / overcurrent and AC bypass switch device to be required in front of the inverter" you now have a slightly less "expensive (including labor cost) 100 amp disconnect / overcurrent and AC bypass switch device to be required in front of the inverter".

The only real benefit is the 3 smart load ports vs 1 for the 15k. If I had an unreliable grid, having the automation is helpful. Otherwise, once a year having to manage the load on the Smart Load port is not a big deal.

"A more practical approach is to design a battery backup system to power critical loads only: no large appliances such as air conditioning ...". Is that from the 2000's? Today, $7,000 for 28kWh, enough battery to run my house for a day, including the AC. If I turn off my ovens and the clothes dryer, the 15k can easily run the AC. I'll cook on the grill and hang laundry out to dry (preferably away from the grill to avoid the clothes smelling like BBQ). $7,000 to backup a few lights - umm.... I'll pass. $7,000 to run my gas furnace (heat pump if really needed to save the battery) in the winter and AC in the summer - sign me up.

The grid input is bidirectional. You need 0A passthrough. Why are we even talking about passthrough when it just complicates things?


I don't think you understand how bidirectional hybrid inverters work. As a matter of fact I'm certain of it.

We've had this argument before but for sake of op, with modern hybrids you can leave your loads on the main panel and the inverter will reduce what the main panel is taking from the grid up to its maximum capacity.

If you want loads to be powered during an outage you put those loads on a critical loads panel.

Btw, also for benefit of op, For 7k you can diy almost 60kwh of batteries.

 

[DaveNSueM]

Appreciate the comments - you guys have me thinking dumping the MI's makes sense. Here is an updated pictorial of part of my permit package I created showing 24 panels (panel type is not correct; thinking Aptos 440W bifacial)) along with new EG4 12kpv...I have NOT decided on that yet. Funny enough it dawned on me today that I could actually put the depicted 100A panel on the load terminals...this panel feeds our pool/pavillion and is NOT powered by generator today...not exactly what I would call a critical load

 

[1201]

Appreciate the comments - you guys have me thinking dumping the MI's makes sense. Here is an updated pictorial of part of my permit package I created showing 24 panels (panel type is not correct; thinking Aptos 440W bifacial)) along with new EG4 12kpv...I have NOT decided on that yet. Funny enough it dawned on me today that I could actually put the depicted 100A panel on the load terminals...this panel feeds our pool/pavillion and is NOT powered by generator today...not exactly what I would call a critical load

Sph10ktl-hu-us has 2kw more inverting power than 12kpv and is a grand cheaper.

The way you have your drawing, if you put the CTs at the meter you can offset loads from both panels when the grid is up . This is the simplest way to install it, but you are not powering any loads if grid is down.
Not a problem since you have a gen but it's important to know

 

[DaveNSueM]

Sph10ktl-hu-us has 2kw more inverting power than 12kpv and is a grand cheaper.

The way you have your drawing, if you put the CTs at the meter you can offset loads from both panels when the grid is up . This is the simplest way to install it, but you are not powering any loads if grid is down.
Not a problem since you have a gen but it's important to know

Thanks - that is what I was thinking. Would I need 2 sets of CTs, one for each set of feeders and parallel them OR are the CTs large enough to fit around 2 cables?
Also, I have been researching the Growatt you mentioned and also found the thread where folks are tracking comparison of 3 new inverters.

 

[1201]

Thanks - that is what I was thinking. Would I need 2 sets of CTs, one for each set of feeders and parallel them OR are the CTs large enough to fit around 2 cables?
Also, I have been researching the Growatt you mentioned and also found the thread where folks are tracking comparison of 3 new inverters.

That's a good question. For two sets of feeders you would need two sets of cts but afaik, I've not seen any inverter that can use two sets and i seriously doubt a CT would go around two cables. You may be able to find on that does though.

 

[DaveNSueM]

That's a good question. For two sets of feeders you would need two sets of cts but afaik, I've not seen any inverter that can use two sets and i seriously doubt a CT would go around two cables. You may be able to find on that does though.

If I added a 400a disconnect between meter and both feeders I could place CT's on the single feed into the disconnect - would need to talk to talk to my inspector to see if that's even allowed and prob adds $$$ to setup.

In my scenario where I am OK to sell back to grid are CT's required (just leave off) or could I just place on the closest feeder and while some of the reporting may be off the system would function properly? Been digging into manuals for this question but not sure...

I got the CT parallel idea from the Emporia monitoring system instructions as it specifically mentioned 2 sets of feeders BUT I realize that is a different application and may not apply.

Appreciate the input!

 

[DaveNSueM]

Couple more pics to help with visualization of existing conditions - this was installed/permitted about 19 years ago when we added pool and converted overhead utility to underground. Should have added these pics initially so sorry about that

 

[1201]

If I added a 400a disconnect between meter and both feeders I could place CT's on the single feed into the disconnect - would need to talk to talk to my inspector to see if that's even allowed and prob adds $$$ to setup.

In my scenario where I am OK to sell back to grid are CT's required (just leave off) or could I just place on the closest feeder and while some of the reporting may be off the system would function properly? Been digging into manuals for this question but not sure...

I got the CT parallel idea from the Emporia monitoring system instructions as it specifically mentioned 2 sets of feeders BUT I realize that is a different application and may not apply.

Appreciate the input!

a cursory search suggests that you can parallel CTs. so 4 identical cts going into 2 inputs. If this is the case then you are home free.

some of our EEs may know more. maybe @Hedges ?

if not, you dont need Cts for grid tie. the inverters will still power all loads from solar and sell the rest to the grid. the cts are for using the inverter to power loads from battery. since you dont want to sell from battery to grid, the cts measure the amount of load and supply just enough from battery to feed that. for example, at night when the sun is down

 

[1201]

Couple more pics to help with visualization of existing conditions - this was installed/permitted about 19 years ago when we added pool and converted overhead utility to underground. Should have added these pics initially so sorry about that

how much power do you consume per month. If the parallel ct turns out not to be a thing, you could conceivably purchase two sph 10000tl hu-us for 20kw, connect grid input and cts to home panel, so inverter sends power back to that panel, and connect the load output to the outside panel with no need for cts.

or vice versa

 

[DaveNSueM]

a cursory search suggests that you can parallel CTs. so 4 identical cts going into 2 inputs. If this is the case then you are home free.

some of our EEs may know more. maybe @Hedges ?

if not, you dont need Cts for grid tie. the inverters will still power all loads from solar and sell the rest to the grid. the cts are for using the inverter to power loads from battery. since you dont want to sell from battery to grid, the cts measure the amount of load and supply just enough from battery to feed that. for example, at night when the sun is down

Thank you for explanation on the CT function...been trying to wrap my brain around exactly when/how they are used...also thinking a system may give an error code if they do not see them connected at all...and duh...never thought to search forum for the CT question...found a few such as this and will be searching more:

Ok to parallel CT sensors on dual Sol-Ark 15k install?

With dual Sol-ark 15k install and 400a grid service, is it ok to parallel a pair of CTs (per leg) into the master inverter? In other words, my grid line has two 4/0 wires per leg going to the meter for 400a service. Can I put a CT around each of these wires and then parallel them together at the...

diysolarforum.com

 

[DaveNSueM]

how much power do you consume per month. If the parallel ct turns out not to be a thing, you could conceivably purchase two sph 10000tl hu-us for 20kw, connect grid input and cts to home panel, so inverter sends power back to that panel, and connect the load output to the outside panel with no need for cts.

or vice versa

Chart from most recent bill; pool pump and electric pool heater (plus AC) jack it up in summer

 

[1201]

Thank you - duh...never thought to search forum for the CT question...found a few such as this and will be searching more:

Ok to parallel CT sensors on dual Sol-Ark 15k install?

With dual Sol-ark 15k install and 400a grid service, is it ok to parallel a pair of CTs (per leg) into the master inverter? In other words, my grid line has two 4/0 wires per leg going to the meter for 400a service. Can I put a CT around each of these wires and then parallel them together at the...

diysolarforum.com

oh I didnt even know that question had been asked here. I just did a web search. it looks like they may even have Cts that can fit two large cables. either way, its looking good.

Chart from most recent bill; pool pump and electric pool heater (plus AC) jack it up in summer

View attachment 224980

so if you dont use the pool stuff in winter then maybe primary panel should be house panel. although with paralleling 4 cts you should be able to cover both.

1 sph1000tl hu-us should be enough i think. but it will be working hard in the summer months

 

[Hedges]

CT connected in parallel should report average of the two currents [edit: assuming they are identical and each has a resistor included].

400A service feeding 2x 200A circuits?

You can get CT for 400A, might be large enough to fit around two close cables.
You can get 200A, and smaller.

Some CT are just a coil (and magnetic core), deliver current proportional to current in cable.
Those I think could be paralleled.

Some CT, most we use I think, have a "burden" resistor which converts the current to voltage.
Those can be connected in series, producing sum of voltage proportional to sum of currents in two cables.
I think they could alternatively be connected in parallel, producing a voltage which is average of what the two currents represent.

If sum of currents, that might exceed what power meter expected or would process. But if CT meant for 400A, then it could be 0.333V per 400A, vs. 0.333V per 200A, so sum would produce a scaled down reading.

Parallel CT with burden resistors would produce average of readings, also scaled down.

Scaled down should be fine for zero export, since 0/2 = 0. For limited export, if you want 20A you would tell it 10A, because 20A actual would produce reading equivalent to 20A/2 = 10A.



I may connect one CT (with burden resistor) into two power meters, because I plan to have two AC coupled batteries used for peak shaving. Unless they talk to each other and share an RS-485 power meter.

 

[wpns]

CT connected in parallel should report average of the two currents.

Are you sure? If they are voltage-mode CTs maybe, but current-mode will add the currents (through the burden resistor in the inverter).

 

[Hedges]

Yes, if they are voltage mode, and identical.

Currents from two CT would add. Resistors from two CT would be parallel combination; if same then resistance would be 1/2, so average reading of the two.

(if current mode, no resistor, then parallel would show sum of the two.)

 

[DaveNSueM]

CT connected in parallel should report average of the two currents [edit: assuming they are identical and each has a resistor included].

400A service feeding 2x 200A circuits?

You can get CT for 400A, might be large enough to fit around two close cables.
You can get 200A, and smaller.

Some CT are just a coil (and magnetic core), deliver current proportional to current in cable.
Those I think could be paralleled.

Some CT, most we use I think, have a "burden" resistor which converts the current to voltage.
Those can be connected in series, producing sum of voltage proportional to sum of currents in two cables.
I think they could alternatively be connected in parallel, producing a voltage which is average of what the two currents represent.

If sum of currents, that might exceed what power meter expected or would process. But if CT meant for 400A, then it could be 0.333V per 400A, vs. 0.333V per 200A, so sum would produce a scaled down reading.

Parallel CT with burden resistors would produce average of readings, also scaled down.

Scaled down should be fine for zero export, since 0/2 = 0. For limited export, if you want 20A you would tell it 10A, because 20A actual would produce reading equivalent to 20A/2 = 10A.



I may connect one CT (with burden resistor) into two power meters, because I plan to have two AC coupled batteries used for peak shaving. Unless they talk to each other and share an RS-485 power meter.

wow - thanks for the detail

 

[DaveNSueM]

Forget micro inverters if youre doing ground mount. Waste of money .


Growatt sph10000tl hu-us does not need a battery to operate. It can operate grid tie only and you can add batteries later as needed.

It's also half the price of an 18kpv

The more I read up on this Growatt the more it sounds like a good fit for what I want. Looking at different panels now...short list was Hyperion or Aptos but SS has Adani 530W for what seems like a good price (fairly physically larger than the others)...overall looking to do 24 panels.

Appreciate all of the info you and others have posted on the various inverters - watched most of that presentation you posted recently from Growatt.