15kW Grid Tie With Battery Backup Planning

goldenfab

New Member
Joined
Oct 16, 2021
Messages
7
I'm trying to plan out a solar system for a house I'm not yet finished building. I have no experience with solar but I have wired my workshop/guest house and the main house I'm building. I'm wanting to start purchasing things sooner than later so I'm not stalled out by any supply chain issues. The attached drawing is mostly to scale which shows I where I want the ground mounted PV array in relation to my existing panels. I've found some 310W REC panels available locally I can pick up and avoid shipping costs for $140 which sounds like a really good deal but I can't figure out what inverter(s) I should go with. I've been reading up a lot on here but I just keep going around in circles.

My first thought was to backfeed with IQ7 micro inverters into the 200A subpanel in my workshop since it would be the shortest wire run. Is there any reason you can't backfeed into a subpanel that's located in a different structure than the main service panel? If not is there any reason would not be able to put a grid tie inverter w/ backup batteries up in the main house interlocked into the main 400A panel to create a micro grid for grid to get the grid tie inverter(s) to turn on in grid down situations? I would prefer to have all the inverters and batteries located at the PV Array however I don't see a way to interlock it so I don't backfeed the grid when its down. For grid down operation I don't want to mess around with critical loads panels, I would rather just interlock or transfer switch the whole house and be smart about not drawing more power than my system can make.

My primary reason for being interested in solar is to be prepared for long term grid down situations and to hedge against rising energy costs. I'm in sunny AZ and right now power is very reasonable compared to other places, off peak is $0.0523 and on peak is $0.08683 per kWh. Right now living in my workshop/guest house over the last 2 years the highest usage so far has been 78kWh in a day and I average closer to 50kWh when its cold which is when I use the most power with electric heat pumps. I think my power usage will be similar when I finish the main house so I'm thinking for my peak sun hours of 6 I should go with a 10kW array that could be expanded to 15kW.

I have a very well insulated house with hydronic electric heat pumps for heating and cooling and I'm planning on adding large water tanks so they can store heat energy during sunlight hours so my electric loads during the night when PV isn't producing would be typical household needs less HVAC. My water heater and cooking range is gas but my clothes dryer is electric (have gas hookup) and my oven is electric.

If I go AC coupled I need less wire because I think I can backfeed into the workshop subpanel but then I need to spend $ on grid forming inverters since they have to match the capacity of the grid tie inverters which seems like a waste to me since I don't need/want very much battery capacity.

Next thing I looked at was Victron and Outback inverters but all the ones I'm seeing are max 48V DC input so running 15kW/48V = 312A over 295ft seems cost prohibitive with the price of wire right now.

Should I be looking at high DC voltage inverters? Should I go AC coupled? Or are there other options I don't know about?
 

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goldenfab

New Member
Joined
Oct 16, 2021
Messages
7
For a big system take a look at http://store.evtv.me/products.php?cat=3
30kw inverter http://store.evtv.me/proddetail.php?prod=sandi30kw

355v battery pack, 75kwh http://store.evtv.me/proddetail.php?prod=model3pack

add a high voltage solar charge controller
Thanks for sharing. I would rather stay away from single point failures like one inverter. Not such a big deal when I'm on grid but I would really like the peace of mind that if the grid is down for very long and an inverter goes I can still make reduced power until I can get new parts. Also I really don't need/want to invest in very big batteries. I'm thinking 2kWh to maybe 4kWh at most.
 

dougbert

Solar Addict
Joined
Sep 20, 2019
Messages
346
For a big system take a look at http://store.evtv.me/products.php?cat=3

Thanks for sharing. I would rather stay away from single point failures like one inverter. Not such a big deal when I'm on grid but I would really like the peace of mind that if the grid is down for very long and an inverter goes I can still make reduced power until I can get new parts. Also I really don't need/want to invest in very big batteries. I'm thinking 2kWh to maybe 4kWh at most.
no problem just giving options

this product line has been used on some Caribbean Island resorts for operations and guest power use - no grid out there

just a customer of their battery control modules

I went totally NO NetMetering - I produce it here, store it here and use it here.

I now use the Grid only for backup power, with the aim of 5-7 days of battery backup power - at 50kwh now, goal of 100kwh. Currently with 7300 watts of panels, hoping to reach 12,000+ on my current design

build thread in Show and Tell
 

EB3DESIGN

New Member
Joined
Mar 25, 2022
Messages
1
I am looking at buying a pallet of (30) SunPal 645~670w $200 panels - HERE in CALIFORNIA Sell off the excess

Im looking to build the following systems. Both max out my South Facing 23deg Sloping Roof 4mi from beach...


10kw 48v (15 Panel) Grid-Tie with Backup on a Duplex like to be able to power both at 5kw or one unit at full 10kw
I want to sell back used power to SCE
- (15) SunPal 645~670w ($200)
- (2) 5kw Growatt ($600)
- (4) EG4 Gyll 48v LiFePO4 battery ($1499)

3kw (5 Panel) 48v Grid-Tie with Backup on a Tiny House, to be able to power with RV plug-in or off Grid

I would to completely off-grid, or feed back host house thru RV Plug
- (6) SunPal 645~670w ($200)
- (1) 5kw Growatt ($600)
- (1) EG4 Gyll 48v LiFePO4 battery ($1499)

Any thoughts or recommendations how o best build these TWO Systems for the best results at the best price?
 

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iamrich

Photon Sorcerer
Joined
Dec 17, 2020
Messages
1,010
Location
Elgin, Texas
If my fuzzy mm to inch calculation is correct those are 8 feet by 4 feet, 74 pound panels. Not exactly DIY friendly.

I would check with your power provider to see what they will approve. It might make your choice much for you. I don't your provider will allow choice 1 above.
 

Biasjo

Renewable energy user - North Carolina
Joined
Dec 19, 2021
Messages
577
I am looking at buying a pallet of (30) SunPal 645~670w $200 panels - HERE in CALIFORNIA Sell off the excess

Im looking to build the following systems. Both max out my South Facing 23deg Sloping Roof 4mi from beach...


10kw 48v (15 Panel) Grid-Tie with Backup on a Duplex like to be able to power both at 5kw or one unit at full 10kw
I want to sell back used power to SCE
- (15) SunPal 645~670w ($200)
- (2) 5kw Growatt ($600)
- (4) EG4 Gyll 48v LiFePO4 battery ($1499)

3kw (5 Panel) 48v Grid-Tie with Backup on a Tiny House, to be able to power with RV plug-in or off Grid

I would to completely off-grid, or feed back host house thru RV Plug
- (6) SunPal 645~670w ($200)
- (1) 5kw Growatt ($600)
- (1) EG4 Gyll 48v LiFePO4 battery ($1499)

Any thoughts or recommendations how o best build these TWO Systems for the best results at the best price?
Dang those are big panels…
 
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