Very large off-grid planning considerations - timing

[jnmit12]

I've learned a lot reading existing threads, but am unclear on a few planning topics that concern my situation..

High-Level: Building a very large 2nd home as a DIY project (with labor help!), Cost of extending electric service makes off-grid solar a no-brainer. Back of the napkin design considerations call for ~40k pv and 160++kwh storage.
As the house is a DIY project, the ramp up of electric demand be slow (diy guest house built after diy pool built after diy kitchen etc) but the home will also be used primarily on weekends, seasonal. Eventually, the house will be used full time - 8+ years away.

While I am still working on structural elements of the main house (lots of concrete and underground elements) I am stick-framing a detached garage with a flat roof. I have a need for "temporary electric" to assist the construction process and to supply the detached garage/ temporary apartment.

I am weighing the pros and cons (cost and time) of purchasing something resembling my final state off-grid system immediately, vs expanding as I need capacity. My situation is tricky because even at my terminal-state, my battery bank will be oversized given our frequency of use. It will be appropriately sized when it is actually in use (think large family gatherings, heated pools etc).

Questions:
-I assume un-used batteries won't degrade in a meaningful way while sitting during the progression of my construction?

-I have not investigated, but I assume I will be able to prioritize consumption from individual battery bank arrays? (so as not to frequently short-cycle the entire bank)?

-If my time horizon for full capacity demand is ~18months, is it foolish to buy most/all now? (My capacity requirements will ramp from 30% to 100% in a step-wise manner) I could buy large chunks of capacity as demand dictates, but I would be creating a new task each time, and potentially adapting to changes in standards and products.

-Stackable Sol-Arks look appealing, but unnecessarily expensive give my off-grid status. Any recommended alternatives given overall capacity requirements and potential need to assign current draw to a portion of the battery bank?

Thanks in advance for any thoughts!

 

[DIYrich]

-I assume un-used batteries won't degrade in a meaningful way while sitting during the progression of my construction?

Even if used, most batteries will calendar age faster than cycle age. In any case, add some now, and more later.

-I have not investigated, but I assume I will be able to prioritize consumption from individual battery bank arrays? (so as not to frequently short-cycle the entire bank)?

Depends upon whether you have net metering, or even a grid connection. If off grid, PV will be used first to supply load, excess to battery, from battery last.

-If my time horizon for full capacity demand is ~18months, is it foolish to buy most/all now? (My capacity requirements will ramp from 30% to 100% in a step-wise manner) I could buy large chunks of capacity as demand dictates, but I would be creating a new task each time, and potentially adapting to changes in standards and products.

Depends. If you ground mount, or flat roof over garage, then adding more later is easy. If you roof mount, then do it now.
Battery capacity is easy to add as you need it.

But, design for your eventual system, and have a plan for expansion. Maybe pre-wire the conduit.

-Stackable Sol-Arks look appealing, but unnecessarily expensive give my off-grid status. Any recommended alternatives given overall capacity requirements and potential need to assign current draw to a portion of the battery bank?

People like the EG4 6000xp for off grid.

 

[1201]

High-Level: Building a very large 2nd home as a DIY project (with labor help!), Cost of extending electric service makes off-grid solar a no-brainer. Back of the napkin design considerations call for ~40k pv and 160++kwh storage.
As the house is a DIY project, the ramp up of electric demand be slow (diy guest house built after diy pool built after diy kitchen etc) but the home will also be used primarily on weekends, seasonal. Eventually, the house will be used full time - 8+ years away.

-Stackable Sol-Arks look appealing, but unnecessarily expensive give my off-grid status.

 

[Brucey]

If I was spending your money and no UL stuff needed then I'd use multiple building blocks of Quattro 10kVA 120V inverters.

1) Single for 120V to get you going. Great surge performance if you have big 120V loads that will tip an eg4 12k or solark 15 into shutdown.

2) Two for 120/240 for the bigger 240V loads

3) Four to double capacity on both legs if required.

MPPTs:
450/200 is good for around 11.6kW of charging. Maybe four of those for 40kWp.

 

[Cronix]

We're in the same boat (building on large property, no utils). We used a Bluetti AC300 with 6 panels and 4 batteries for the 100% of the construction phase. It was easy enough to move around the 3 acres while building various buildings (storage, main house, shop, etc). We won't be using it for our main power (several 18kpv's for that + rackmount batts), but there are many uses for the AC300 and it's portable (enough) that it was worth it to keep them separate.

 

[OzSolar]

It will be appropriately sized when it is actually in use (think large family gatherings, heated pools etc).

High level? A few quick things that you're welcome to ignore.

-Start with your budget and work backwards. EG: How much can I do for this much money vs. how much will everything I want to do cost.

-Best practice is to size your system for the what you're going to do most most the time. Trying to size it for 100% of occasional needs will likely result in twice as much system as you're going to need 90% of the time. You're going to have a generator, this is what it's for.

 

[jnmit12]

If I was spending your money and no UL stuff needed then I'd use multiple building blocks of Quattro 10kVA 120V inverters.

1) Single for 120V to get you going. Great surge performance if you have big 120V loads that will tip an eg4 12k or solark 15 into shutdown.

2) Two for 120/240 for the bigger 240V loads

3) Four to double capacity on both legs if required.

MPPTs:
450/200 is good for around 11.6kW of charging. Maybe four of those for 40kWp.

Thank you. I had zero'ed in on these (albet with brief/minimal research). Split phase is needed of course, and large loads will be prevalent on the consumption side. Had not considered surge performance - most pumps/motors will be variable speed / softstart, but inevitably I will add something that has a big initial draw. Using variable speed pool pumps, inverter multi-split AC etc.

 

[jnmit12]

We're in the same boat (building on large property, no utils). We used a Bluetti AC300 with 6 panels and 4 batteries for the 100% of the construction phase. It was easy enough to move around the 3 acres while building various buildings (storage, main house, shop, etc). We won't be using it for our main power (several 18kpv's for that + rackmount batts), but there are many uses for the AC300 and it's portable (enough) that it was worth it to keep them separate.

Thank you. I probably should have used this approach before (instead of small generators), but I suppose I'm close enough not to being able to install something closer to a permanent set-up. I've just run 420ft of 4/0 cable between main structure and detached barn... Was originally planning on keeping them seperate, but realized the waste of keeping capacity orphaned in a rarely used barn apartment (in my case).

 

[jnmit12]

Best practice is to size your system for the what you're going to do most most the time. Trying to size it for 100% of occasional needs will likely result in twice as much system as you're going to need 90% of the time. You're going to have a generator, this is what it's for.

I think this is exactly what I'm going to end up with ... Oversized 95% of the time... My thought here is to oversize the batteries and undersize the PV... Very large demand at full use, then we depart and are not concerned with recharge time. No generator in my case - would rather spend the equivalent $$ of extra batteries.

 

[hwy17]

Depending on how leisurely or not the construction timeline is, I would consider not wasting time trying to build, troubleshoot, and operate a temporary or starter system. Just run a generator for your temporary power if you're allowed to.

If this is more like you're living on site in a camper, and building it at your own pace, then it's not out of the question that it makes sense though.

 

[Nobodybusiness]

My thought here is to oversize the batteries and undersize the PV

You have to be able to charge those batteries somehow.
Since you have no grid or generator be kind of hard to do..

 

[NC_hydro]

Hard to go wrong with Quattro's but also consider a Rosie or two or the new Midnite All In One.

 

[Brucey]

Hard to go wrong with Quattro's but also consider a Rosie or two or the new Midnite All In One.

True, Rosie price is a little cheaper than a 10kVA Quattro and 120/240 in a single unit. And made in USA.

 

[1201]

True, Rosie price is a little cheaper than a 10kVA Quattro and 120/240 in a single unit. And made in USA.

Sorry, I don't think Rosie can hold a candle to quattro

 

[upnorthandpersonal]

-I assume un-used batteries won't degrade in a meaningful way while sitting during the progression of my construction?

Assuming LFP.

If you put them at 50% state of charge, and cold, they can stay for quite a while.

I assume I will be able to prioritize consumption from individual battery bank arrays? (so as not to frequently short-cycle the entire bank)?

Why make it complicated. Short cycling LFP is not an issue. You could also just use a shunt and keep the battery between 20% and 80% or something. Personally, I don't bother: I built my place over the course of 5 years, the batteries were always there, and I just expanded over time as needed. That's one of the nice things about LFP: scale as you go.

Any recommended alternatives given overall capacity requirements and potential need to assign current draw to a portion of the battery bank?

I'm biased, I DIY my packs.

 

[Brucey]

Sorry, I don't think Rosie can hold a candle to quattro

It seems to do quite well. Now the Quattro may sustain 20kW for longer than 10 or 15 secs but the Rosie seems to have quite a bit of capacity also:



Post in thread 'Has anybody used the Rosie inverter yet for prime time?' https://diysolarforum.com/threads/h...inverter-yet-for-prime-time.60074/post-741412

 

[1201]

It seems to do quite well. Now the Quattro may sustain 20kW for longer than 10 or 15 secs but the Rosie seems to have quite a bit of capacity also:

I would take the victron over the Rosie for surge as its an actual low frequency inverter but that's only a very small part of the whole system

• Can Rosie ac couple?
• Does Rosie have a portal where the owner can monitor his vacation house from his main house, like victron vrm?
• Can you change Rosie settings remotely? For example if owner needs to change settings on his charge controller?
• Does Rosie have ess capabilities? Eg peak shaving, zero export?
• How much community support is available for Rosie
• Are there any examples of large systems that have been done by Rosie? Eg 60-100kw?
• How does Rosie handle SOC?
• Does Rosie talk seamlessly with other midnite components?
• What is the idle draw of rosie

 

[NC_hydro]

Sorry, I don't think Rosie can hold a candle to quattro

Yeah but I would get a Rosie before a Beta Box (Eg4 anything)

 

[1201]

Yeah but I would get a Rosie before a Beta Box (Eg4 anything)

Fair enough, but any box without remote monitoring would be a non starter for me

 

[shadowmaker]

My thought here is to oversize the batteries and undersize the PV...

PV is so cheap and getting cheaper every day so oversize batteries AND PV if no generator.