Looking for sizing and component wisdom

[tonyandjill]

Hey guys,

I have been collecting info here and other places on solar components and sizing and i have an idea based on my consumption what i think is appropriate. Just want to hear from people here.

My consumption is pretty high even though imo we are pretty conservative with the thermostats. (82F summer, 67F winter). Average from January to october was 1242kwh/mo, 41.4kwh/day. I have a pool and 4 AC units. (I would love to overspec this system so that i can finally turn the temp down in the summer and up in the winter if possible!!)

I'll ideally be adding 2 electric vehicles eventually, but getting rid of one of the 5ton HVAC units and replacing with a mini-split. Possibly doing the same for a 3ton. Together, we only drive about 20-40 miles a day on average so hopefully the cars wouldn't add a huge load.

Also, my roof faces SE and the slope is 45 degrees, which i think is great for my latitude. I also have some room for panels on the ground.

The city i live in only allows 10kw of panels, anything above that and you have to go off grid. i've talked to the power co. and they are adamant. So, my thinking is that if i'm going to do this, 10kw would not be worth it. So if i do go off grid, i need to be sure i never run out of power (wife angry).

So, here are the components im considering right now:

Panels: 30kw of bifacial panels (Philadelphia Solar 400W PS-M108(HCBF), half on the roof, half on the ground - around $8k from inxeption.com

I've been following a guy that bought panels from inxeption. the company seems legit, they just sell a lot of brands ive never heard of.


Inverters: Either two EG4 18kpv inverters - $10,400

The 18KPV's look amazing and i'm leaning that way for sure over the megarevo's. but if there are enough people out there that say the MR's are ok, i might consider them.

- or -

3 Megarevo R10KLNA - around $8k from china with shipping.

(I would like to hear from people that have had good experience with MR, if there are any lol. Ive read a lot of the posts about the issues, there are quite a few.)


Batteries: Either six 5kwh EG4-LL's from signature - $9500

-or-

four 15kwh batteries from china ~ $8k with shipping

There are a few chinese battery companies ive spoken with that are willing to send video of the batteries with their qr codes, serial numbers and a sticker with my name on them (to ensure it isnt just stock footage) and the full capacity of the battery shown on the display. For example, for a 280Ah battery i think the capacity for a new battery should be around 306Ah or something like that. Of course this still doesnt guarantee anything, that's why i'd love to hear from someone that has purchased successfully from CHina.

Anyway, i would appreciate any insight on my sizing and component selection and any other info you want to throw in there. TIA

 

[MisterSandals]

Average from January to october was 1242kwh/mo, 41.4kwh/day

41,400Wh / 3.87h (lowest) = 10,700W of solar

41,400Wh / 48V = 862Ah to store 1 days worth of power

Add in number of cloudy days you want to store power for.

 

[tonyandjill]

41,400Wh / 3.87h (lowest) = 10,700W of solar

41,400Wh / 48V = 862Ah to store 1 days worth of power

ok. so i could keep it under 10kw and stay connected. July-sept we use 2800-3000kwh/mo, so those months i would only make about half the power i would need, but that is definitely a good option. If i set up the bifacial panels optimally, i could potentially get 11-12kw actual output.

would it be worth it to get batteries even if connected to the grid? that way i can use the batteries at night rather than grid power, hopefully, almost never pulling from the grid. They only pay $.04/kwh to buy power back and i think there is a $35 charge just to be connected.

With 4 HVAC units, a pool and eventually, 2 electric vehicles, i would very often be going over the max output of one of the EG4 18kPV inverters. Would it stay active and supply the 12kW while simultaneously pulling from the grid to supplement?

 

[MisterSandals]

would it be worth it to get batteries even if connected to the grid?

That would probably be the only way it made sense, exactly because of the kWh buy/sell numbers you are getting. You have a good grasp of your situation.

there is a $35 charge just to be connected.

$1 a day is reasonable as a backup connection charge for cloudy days or other power shortfalls. If you weigh that against just the cost of buying 2x or 3x the batteries, you may be able to see what makes more sense to your goals. Batteries are expense and don't last forever. But having a lot of battery for emergencies has a value too.

Would it stay active and supply the 12kW while simultaneously pulling from the grid to supplement?

Most do exactly this but check the specs to be sure. I am in the final stages of wiring this up for myself so am looking at what it takes to configure the system to do what i want. There are threads that are dozens of pages long with discussions and trouble shooting so thats a big part of it too. I'd consider ease of use and reliability long before trying to save a few hundred (thousand?) bucks. These are investments to me as I am in this for the long haul and having to mess with it or replace equipment, besides being expensive, is not what i am interested in doing.

To give you a brief taste of real world cases, here is a fairly new thread that I am following as I have very similar equipment:

I need some help with my Schneider System

I have the Schneider XZ+ 6848 with 2 MPPT 80 600 connected to 10 solar panels each of two sets of 5 panels and should see about 300 Volts at 3000 Watts on a sunny day. I also have the Insight Home unit connected but I see no solar PV Volts or power on the displays - what could the reason be? I...

diysolarforum.com

 

[zanydroid]

So if i do go off grid, i need to be sure i never run out of power (wife angry).

Off grid EV for regular mileage is likely to be super painful in the winter. Summer might be ok.

30 miles per day depletes 250 mile range in 8 days. So 10kWh extra per day.

In general I have way too many production systems to take care of for day job for me to want to operate my own grid, which is what off grid may mean. It’s not super clear to me what you mean by off grid. You mean have to cut the cord? Or not allowed to sell back?

 

[zanydroid]

Is your city/state enforcing UL9540 ESS requirements? If so then megarevo/Chinese battery plan is DOA unless you put in the batteries after the initial inspection.

 

[tonyandjill]

It’s not super clear to me what you mean by off grid. You mean have to cut the cord? Or not allowed to sell back?

Yes, cut the cord. They absolutely will not allow me to be connected if i have more than 10kw of panels. I told them I could set it to zero export(?), he just just shook his head.

After I get it all up and running I might add a couple stand alone panels and inverter just for the pool. It's 1hp, runs 8-12h/day sometimes more!

 

[tonyandjill]

Is your city/state enforcing UL9540 ESS requirements? If so then megarevo/Chinese battery plan is DOA unless you put in the batteries after the initial inspection.

I read through all their docs, I don't think so. Seems like all they care about is pv output.

I found docan shenzen (Jennie wu?) They have a 15kwh battery kit for $2800 shipped from USA.

 

[tonyandjill]

Is there any reason why I couldn't add panels batteries and inverters later if necessary? I know it's not great to mix old and new panels but I think i would just put them on a separate mppt.

 

[zanydroid]

I read through all their docs, I don't think so. Seems like all they care about is pv output.

What year of International Residential Code is your state under? That's where the UL9540 rule comes in

 

[zanydroid]

Is there any reason why I couldn't add panels batteries and inverters later if necessary? I know it's not great to mix old and new panels but I think i would just put them on a separate mppt.

All at once saves the trouble / costs of soft overheads like permits, inspections, interconnection application, waiting for approval.

Probably a middle ground is reasonable. Enough in each expansion to justify the fixed overhead. I dunno, like 5-10kW at a time?

 

[zanydroid]

Your state/POCO/utility commission would also be an extreme minority if it has no opinions about what version of UL1741 a grid-tie inverter has (just mentioning grid tie b/c i don't feel an approach has been committed to here).

NEC requires all equipment to be listed (no exception AFAIK in any recent revisions), so you would need at least UL1741 (off-grid flavor)

 

[zanydroid]

Yes, cut the cord. They absolutely will not allow me to be connected if i have more than 10kw of panels. I told them I could set it to zero export(?), he just just shook his head.

What about charging only?

Zero export implies parallel operation where the grid and inverter are on all the time and connected to loads, with dynamic inverter control to zero out the export to the grid.

(all of these are reasonable possibilities, just trying to get the details to figure out how to optimize)

 

[zanydroid]

With 4 HVAC units, a pool and eventually, 2 electric vehicles, i would very often be going over the max output of one of the EG4 18kPV inverters. Would it stay active and supply the 12kW while simultaneously pulling from the grid to supplement?

If you go over the 12kW, I believe 6000XP is "recommended" by EG4 as an affordable helper for the 18kPV. And some forum members have tested it. The tough part though is that cannot be used for grid assist (unless I'm missing something). You can still be grid connected via one or more Chargeverters, which will incur double conversion overhead for any shortfall you pull from grid.

You would also need to upsize the batteries to handle the full inverter AC output of the 18kpv/6000XP stack. ~1-1.5kWh per 1kW of output

 

[tonyandjill]

If you go over the 12kW, I believe 6000XP is "recommended" by EG4 as an affordable helper for the 18kPV. And some forum members have tested it. The tough part though is that cannot be used for grid assist (unless I'm missing something). You can still be grid connected via one or more Chargeverters, which will incur double conversion overhead for any shortfall you pull from grid.

Good to know that that is an option but I think, as long as there are no issues I would just get another 18kpv. As I convert my gas powered heat and appliances to electric and buy electric vehicles (I have 4 adults and 4 kids in the house so potentiality 8 drivers eventually. Although the kids won't be driving tesla's any time soon!) I will probably be adding to the system, assuming something changes with city regs.

Not sure what you mean with the last statement about charge verters and double conversion overhead.

 

[zanydroid]

Not sure what you mean with the last statement about charge verters and double conversion overhead.

Chargeverter is an AC to DC charger.

Suppose you are prohibited from grid tying because you AC connected 18kpv, and 2x 6000XP together. You cannot direct AC connect to grid, because this is anathema when you have off-grid inverters in the mix like the 6000XP.

Instead you can go Grid AC -> Chargeverter -> Battery DC bus. You don't let the 6000XP cooties touch the public grid with this setup.

Double conversion. The path is:
Grid AC->Chargeverter -> Battery DC bus -> inverter -> AC output -> house

AC -> DC -> DC ->AC, which is probably a ~15% wastage.

(The Chargeverter would invalidate UL9540 FWIW because it's not an approved accessory for any UL9540 system)

 

[tonyandjill]

ok. thank you guys for that info. it was very helpful. I have a couple more questions.

Mounting: Just wanting confirmation of my reasoning and anything i mightve missed:

1. Roof: 45degree slope, SE facing with a relatively complex roof surface. i can fit about 30 panels on the best parts of the roof but i would be limited by the city anyway to only 25 (400w each). This is not ideal since the roof faces southeast AND i wouldnt be able to take full advantage of the bifacial panels if mounted to the roof.

2. Ground mounted panels along the perimeter of the property. one string would face SSE and one would face SSW. One string would start about 90ft away from the inverter and the other would start about 150ft away. I like the ground mounts bc i can clean and service them and also increase the albedo around them. Recommended wire size is 13awg for copper, and ive never seen that, so i guess 12awg. I know that the copper coated aluminum is not recommended, but is straight aluminum wire ok? Supposedly it's cheaper. What extra steps/costs are there with AL?

Also have a question about the PV input for the EG4 18kpv:

I know this is pretty basic but nominal MPPT input voltage is 360vdc with an input range of 100-600vdc.

So, should i aim for 600vdc (or slightly less than this) at my max expected output per string?

The Voc per panel is 37.15v. would that scale up with the bifacial gain, or no?

 

[MisterSandals]

i would be limited by the city anyway to only 25 (400w each).

This is not ideal since the roof faces southeast

How many panels could you fit on the 2 SW facing roof sections? Maybe 6 or 8? Th sunlit top left in your pick i guess.

That would spread 25-35% of your array to afternoon.

I don't have a clue how to best use bifacial panels so i did not comment about that (sorry).

 

[zanydroid]

This is not ideal since the roof faces southeast AND i wouldnt be able to take full advantage of the bifacial panels if mounted to the roof.

Use PVwatts to estimate the output.

Ground mounts will cost more than roof mount. Need to see what the % improvement of bifacial and more optimal angle will be vs the more costly racking.

Recommended wire size is 13awg for copper, and ive never seen that, so i guess 12awg. I know that the copper coated aluminum is not recommended, but is straight aluminum wire ok? Supposedly it's cheaper. What extra steps/costs are there with AL?

Take whatever document or webpage that suggested #13 and burn it.

CCA is very new and probably not easy to find. I don’t even know if it is available in PV compatible wire.

Most likely MC4 connectors only work with copper.

Aluminum is fine if it is available in a wire type approved for solar (insulation and voltage). You also need to confirm that terminals are dual rated for Al and Cu. Otherwise you need to use splicing methods rated for both. PDB, terminal block, Polaris style, Ilsco Mac, dual rated splicer, dual rated split bolt, …….

I haven’t heard of many people using aluminum on this forum for small conductors like #8 (which is equivalent to #10 copper). Aluminum can be a massive savings over copper for long runs at high ampacity. Problem with smaller conductors is that it’ll be hard to find aluminum that small.

So, should i aim for 600vdc (or slightly less than this) at my max expected output per string?

No you may need to be rather below 600vdc since Voc increases with lower temperature. Exactly 600vdc will smoke your MPPT in 90% of climates. You need to adjust down based on the temperature coefficient on spec sheet and your worst case winter lows. Note this also means the turn on voltage needs a buffer for warm weather

The Voc per panel is 37.15v. would that scale up with the bifacial gain, or no?

No bifacial gain is on current. (Voc and Vmpp will change but not meaningfully as long as you stay below the smoke threshold for voltage and above the turn on voltage).

The circuit ampacity needs to be adjusted. I am not sure what the adjustment is. You might want to create a post asking for the bifacial adjustments.

You need to paste the whole panel specs (ideally with a screenshot for less room for error). There are at least 4 numbers needed probably. Piecemeal makes us ?

 

[tonyandjill]

How many panels could you fit on the 2 SW facing roof sections? Maybe 6 or 8? Th sunlit top left in your pick i guess.

I don't have any sw facing roof sections. The second pic with the ground mounts hows the true orientation of the house.