Im having a brain fart, need final advice

[Athens Jim]

Hi all..
after months of evaluating, cost vs objective vs quality etc, im headed towards the growatts, i would love to invest in a LF but i have learned that the HF inverters have become dependable if you dont stress them.. but im going to buy a back up inverter anyway ..

i need some clarification because for some reason i cant get a grip on the calculations.. i mustve blown a gasket or something in my brain.. im worried i wont have enough charging power for the (almost) 60kw of battery storage.. my exaggerated estimated usage will be about 25kw daily, 15-17kw day running whats needed to elliminate battery drain, 8-10kw of it at night..

again, this is being very generous with usage, my current confirmed usage is 7-10kw day, 2-5kw night, not economizing but the house is 1/2 the size..

ide rather have and not need, then need and not have....

and here in lies the brain fart im having..

my parts list ...

4 x 51.2v/280ah-14.36kw lithium packs running SEPLOS bluetooth 200amp BMS in each, possibly buy another 2 units for 80kw storage if feasable??..

36 x Swiss Solar 550watt panels

and getting ready to buy the inverters later this month

i have room to install all 36 panels on 3x flat roof sides of the house, all pointing anywhere thats required..

im thinking>>

3 sets of 1 x Growatt, 9 panels (3 backup for winter connection if needed)

and ofcoarse all 3 connected to the same battery bank

i would prefer to use 2 x growatts and leave the 3rd as a spare, but i cant seem to get my head around the calculations..

maybe install a separate MPPT for a 3rd set of panels?

do i need all 36 panels?
do i need MORE panels?
*********************************************

on to the inverter..
the output load when wired in parallel/triple?, 240v 3 wire, wiring to all 3 inverters will be daisy chained correct??

1=HOT
2=GRD
3=NEUT

inverter 1) 1,2,3 > to house
inverter 2) 1,2,3 > to house
inverter 3) 1,2,3 > to house

not like 3 phase?..

inverter 1) 1,1,1 > to house
inverter 2) 2,2,2 > to house
inverter 3) 3,3,3 > to house

in which setup is the load equally shared umongst all 3 inverters? im thinking in single phase but i could be wrong, ive seen electric motors back in the days change phase load based on direction of rotation, switching amp draw from HOT to GRD, but im thinking old technologies vs new??.. things change


and lastly..
since i have bought the inverters yet, do i have a better option? maybe im missing something..

maybe i should look into 3 phase?

any advice, input would be appreciated

 

[nuke]

I don't really understand your questions

 

[frasere2]

You have a 19.8kw DC system (panels). I'd make sure you have optimizers, I used tigo and they are only $45 or so each for up to 700w panels. Will add 10-25% power per day vs not having them. You only need 2 10kw growatt inverters to match dc to ac size. Do not oversize your panels to inverters as it is a waste. Inverters don't cost that much. Growatt has specific battery requirements, ask them, they will tell you exactly what you need in 1-2 days.

For your panels, you should be paying no more than 33cents/watt. Less if you pick them up.

Also, how are the panels to be placed on the roof? Tilted? Flat? You can get more panels on a flat roof with a 10° East/West tilt, and 15-25% more total power. If you are trying to maximize your power generation, fit the panels to your roof, don't optimize for maximum power per panel. I did my flat roof with 0 roof penetrations and no ballast, using the 10° E/W tilt I mentioned. It is lower cost as the racking is cheaper than a full tilted installation.

 

[DIYrich]

Growatt 5kW off-grid inverter max PV input is 6,000 watts. You have 19,800 watts, so you will need all 3 inverters running.
The Growatt Grid inverters take high voltage batteries, so they are a no-go.

 

[Athens Jim]

You have a 19.8kw DC system (panels). I'd make sure you have optimizers, I used tigo and they are only $45 or so each for up to 700w panels. Will add 10-25% power per day vs not having them. You only need 2 10kw growatt inverters to match dc to ac size. Do not oversize your panels to inverters as it is a waste. Inverters don't cost that much. Growatt has specific battery requirements, ask them, they will tell you exactly what you need in 1-2 days.

For your panels, you should be paying no more than 33cents/watt. Less if you pick them up.

Also, how are the panels to be placed on the roof? Tilted? Flat? You can get more panels on a flat roof with a 10° East/West tilt, and 15-25% more total power. If you are trying to maximize your power generation, fit the panels to your roof, don't optimize for maximum power per panel. I did my flat roof with 0 roof penetrations and no ballast, using the 10° E/W tilt I mentioned. It is lower cost as the racking is cheaper than a full tilted installation.

Thanks for the reply..

optimizers.. yah.. thats something that slipped completely!!!

i already bought the panels in bulk, the whole pallet, 36pcs, that cost was $2715 to me door..

as far as mounting, they will be tilted, i shouldve been more specific, the metal frames have already been bought as well.. just not cut to size and assembled, roof dimensions are

1 x 24sqm, 3m elevation, (6mx4m)
2 x 56 sqm 7m elevation, (7mx7m)
3 x 24 sqm but 12sqm usable due to 56sqm elevation hiding 1/2 the roof all day, (6mx2m)

so i have safely calculated for roof 1 and 2 for mounting the panels.. or ALL on roof 2...

so i am safe to run 3 growatts from the panels, but can i run 2 with 12k panels and that be enough to charge the 60kw storage from 60% DOD back up to 95% as expected on our day to day? with a assumption i might be upping to 80kw storage..

im planning on redundant connections for winter use as i have now, adding additional panels during the winter to compensate for losses.. would an optimizer solve this lack of wattage in winter?

but now that optimizers are brought into the mix, i have to recalculate based on optimizer performance dont i?

for comparison..
at the present time, just now, i checked and my system monitor has reported 4.1 - 4.7 kw PV power today on a 10 panel, 5.5kw array, i added an additional panel for winter, during the summer i have 9 up there connected and get all the power out of them, 4.83 - 4.91kw, the 10th is for winter only...

what exactly would a on optimizer do here? pull more power out of the panels for faster charging? would the above indicated 4.1-4.7kw change? or remain the same just be a more efficiate charging process?

ill read up on them ofcoarse, but hands on answers are always better..

 

[MattiFin]

Your proposed system looks like bit of overkill for your consumption but that would depend how often you can tolerate empty battery or need to save on electricity usage. (IE: tolerable for 5 days per year, once per year, once per 10 years)

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html (off-grid, location athens)
18 kWp panels, 60kWh batteries, 20kWh daily consumption, panels tilted to 60 degree for winter sun:

calculated/simulated/statistically 0 days per year with empty battery and even on worst month (december) your system would produce 47kWh per day on average with only 20kWh used.

 

[Athens Jim]

Your proposed system looks like bit of overkill for your consumption but that would depend how often you can tolerate empty battery or need to save on electricity usage. (IE: tolerable for 5 days per year, once per year, once per 10 years)

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html (off-grid, location athens)
18 kWp panels, 60kWh batteries, 20kWh daily consumption, panels tilted to 60 degree for winter sun:

calculated/simulated/statistically 0 days per year with empty battery and even on worst month (december) your system would produce 47kWh per day on average with only 20kWh used.

wow!!... the link you provided has answered alot of guesstimations i had!! but these were the calculations i cant get my head around!!

god bless brother!!! thank you

 

[frasere2]

Thanks for the reply..

optimizers.. yah.. thats something that slipped completely!!!

i already bought the panels in bulk, the whole pallet, 36pcs, that cost was $2715 to me door..

as far as mounting, they will be tilted, i shouldve been more specific, the metal frames have already been bought as well.. just not cut to size and assembled, roof dimensions are

1 x 24sqm, 3m elevation, (6mx4m)
2 x 56 sqm 7m elevation, (7mx7m)
3 x 24 sqm but 12sqm usable due to 56sqm elevation hiding 1/2 the roof all day, (6mx2m)

so i have safely calculated for roof 1 and 2 for mounting the panels.. or ALL on roof 2...

so i am safe to run 3 growatts from the panels, but can i run 2 with 12k panels and that be enough to charge the 60kw storage from 60% DOD back up to 95% as expected on our day to day? with a assumption i might be upping to 80kw storage..

im planning on redundant connections for winter use as i have now, adding additional panels during the winter to compensate for losses.. would an optimizer solve this lack of wattage in winter?

but now that optimizers are brought into the mix, i have to recalculate based on optimizer performance dont i?

for comparison..
at the present time, just now, i checked and my system monitor has reported 4.1 - 4.7 kw PV power today on a 10 panel, 5.5kw array, i added an additional panel for winter, during the summer i have 9 up there connected and get all the power out of them, 4.83 - 4.91kw, the 10th is for winter only...

what exactly would a on optimizer do here? pull more power out of the panels for faster charging? would the above indicated 4.1-4.7kw change? or remain the same just be a more efficiate charging process?

ill read up on them ofcoarse, but hands on answers are always better..

The optimizers will max power per panel not per string. Without optimizers or microinverters, you are limited in power to the lowest producing panel in the string. Not once has any panel in the same plane produced the same power for me. Often as much as 15% difference in the same row (due to dirt, rain, manufacturing differences, etc) or more from row to row (I have 3 pairs of East/west rows). The result being as much as a 25% improvement in power generation, as low as 10%.

As for more panels vs tilting, I'd buy more panels at that price. Max your power on your roof, not the power for each panel. You can get away with 8-10° tilt to minimize rain and dirt residue. If you mount them back to back in an east west formation, you can put 25% more panels than with a 30° tilt as you have to leave room between rows (so panels don't shade each other). If you have a surplus of roof space, then the optimum tilt and appropriate inter row spacing would be best (optimum tilt is your latitude, about 38° for athens). I'm at almost the same latitude, and I can tell you that solar production difference between optimum tilt and 0 degrees is less than 16%. You lose more than that with inter row spacing. For example, this last month, my 15.3kw array produced as much as 45kwh in a single day.

It is hard to determine the optimum setup as i don't know what you panel sizes are (2.2 m x 1.1m???, that would be the same as mine) , the azimuth of your roof, your fire setback requirements (if any) from the edges of the roof, and what angle your racking is set for (if it is preset) or desired.