Planning new residential system

EscapedAritst

New Member
Joined
Oct 2, 2021
Messages
4
This is my first solar experience and I'm going all-in on a luxury house. I'm an engineer so I know enough to be dangerous, but I'm a mechanical engineer turned computer programmer so I'm not sure it will help at all with this endeavor. I've studied quite a bit and I'm ready to pull the trigger within the next few weeks. So, I'd like to get some feedback on my thinking process and see if I've gone wrong somewhere or if I'm missing a big piece of the puzzle. First I'll list my parameters. Then spec some options (mostly Will Prowse recommendations). Then expect some of the experts here to tear me apart :)

I am targeting 20KWh to 25KWh daily usage based on filling out many different "calculators" but mostly just looking at electric bills from similar sized/equipped houses (3 bed, 3 split a/c, pool, spa, gas stove/dryer, solar hot water, no need to pump water, etc.)
I will use an LPG generator to charge batteries and supply power when usage outstrips storage plus current solar generation
I only want enough battery to cover for one day (I'll add more if I find I'm using the generator too much)
I want to over-panel a bit for overcast days
I live in Costa Rica on the south west coast and am assuming 4.5 hours of sun average
I want a 48 volt system
I have plenty of space to rack panels and batteries. No tree problems.
I am on a budget...only meaning I don't want to waste money on name brand quality...I definitely want a quality system
I want a split phase 120/240v output to a standard home electrical panel
I would like to be able to connect the system to the grid for a hybrid system one day if they bring the lines close enough (optional if it costs too much to do now)

From studying I am considering the following build options and would love comments:

Battery options (~$12,000):
6 EG4 48v 5.12KWh (favorite option but can't find in stock)
12 SOK 206ah 12v batteries 4s3p to achieve 30kwh storage at 48v (I don't need to protect for cold :)
2 Energy Tech 13.4kwh 48v (not in stock)
3 Energy Tech 10KWh 51.2v 200Ah

Panel options (~$3500):
16 Mono Perc 72-cell 445W panels for 32kwh of avg. daily generation. 8s2p for 320Voc

Inverter options (~$6000):
4 parallel MPP Solar LVX6048 Inverters for split phase 120v - 240v 100amp

Generator (~$6000):
Generac Guardian 24KW generator for charging batteries when the batteries are low and no solar available

Things it would be good to know:

Is there any sense in adding a separate solar for pool pumps...just hook some panels directly to the pump and pump while the sun is shining? Anyone have brand/model ideas? This seems better than adding yet another high power device on the batteries.

I'm assuming the Inverter would be the limiting factor on surge requirements, but think that it is important to understand the batteries play in this. How do I spec the maximum draw the batteries can take in or dole out? I assume the inverter protects both input and output to and from the batteries?

I haven't factored in a peak load because I don't really know what it affects or how to estimate the number. Obviously, you can estimate the number by adding up everything in the house and turning it all on at the same time. But I can't figure any way to lower that without making crazy assumptions.

Should I add more panels for charging and running high power devices simultaneously when the sun is shining?

Where do I buy all this stuff? These are some places I'm sniffing.
https://www.currentconnected.com/
 

svetz

Works in theory! Practice? That's something else
Joined
Sep 20, 2019
Messages
5,110
Location
Key Largo
Welcome to the forums!

...if I'm missing a big piece of the puzzle....

The DIY Checklist might have some steps, or if you spot something missed let's get it added!

I am targeting 20KWh to 25KWh daily
If you have don't have air conditioning or electrical heating that sounds right, but otherwise may be off in winter or summer. (I see you have 3 mini-splits, might want to double-check that usage). In regards to battery, high-altitude/low-humidity locations (e.g., Denver) or super-insulated homes may only need to run the Air conditioning during the day and can "coast" through the night with a "smart" thermostat, that can save a bundle on battery costs.

The 4.5 insolation is probably the annual / average insolation. Take a look at your power use in winter and summer and the insolation for each of those times. Given your location, you may also want to use SAM, for example, my 6.5 summer months also come with a lot of rain, so it might not be reasonable to tilt specifically for summer.


Is there any sense in adding a separate solar for pool pumps...just hook some panels directly to the pump and pump while the sun is shining?
I wouldn't, otherwise you might end up throwing away power that could have been used to recharge your batteries.

I'm assuming the Inverter would be the limiting factor on surge requirements, but think that it is important to understand the batteries play in this.
Surge depends on the motor, it can be really high (figure +15% of the LRA). Mini-splits typically have variable speed motors that start slow and ramp up, so they shouldn't be an issue. Your spa pump, washer, dryer, freezer might be (especially if they all try to come on at the same time). If the spa pump is a problem, you'd probably be best off replacing it with a variable-speed, but you can also get a softstarter.

Batteries have a maximum C-Rate, make sure you're well under that for normal draw and surges shouldn't be an issue, more on that in the battery FAQ.

Growth
You can get inverters with a "parallel" feature that allows multiple to be connected together, the big advantage to that is it lets you grow rather than fork-lift; the downside is they usually need to be equally paired so if you get a 5 and discover you need a 6 you might decide to fork-lift anyway). Mincroinverters are the cats meow for expansion, but they can be expensive as you end up not being able to mix/match batteries yet (e.g., dependent on a single vendor), see Ensemble (solution might just be months away though).

How do I spec the maximum draw the batteries can take in or dole out?
The max is provided by over-current protection (aka circuit breakers/fuses). You size those to the wires and then control underneath that by turning stuff off.

I assume the inverter protects both input and output to and from the batteries?
The inverter will "trip" if it can't supply enough power. Some will auto-reset, some require a manual intervention.
Be sure there's a low-voltage cut off to protect the batteries, preferably something you can adjust so you're in control of your batteries life-cycle rather than what the factory believes is best for you.
 
Last edited:

mrzed001

Voice of reason
Joined
Apr 10, 2020
Messages
743
Location
Hungary - EU
Battery options (~$12,000):
6 EG4 48v 5.12KWh (favorite option but can't find in stock)
12 SOK 206ah 12v batteries 4s3p to achieve 30kwh storage at 48v (I don't need to protect for cold :)
2 Energy Tech 13.4kwh 48v (not in stock)
3 Energy Tech 10KWh 51.2v 200Ah
If you want you can DIY a battery bank for half the price
2x 16x EVE 280 (or CATL 302Ah) cells $5500 (28.8 kWh) + 2 JK Heltec BMS &450

Panel options (~$3500):
16 Mono Perc 72-cell 445W panels for 32kwh of avg. daily generation. 8s2p for 320Voc
You have 4 inverter, you can have more. The sun is not always shines at max :)


Inverter options (~$6000):
4 parallel MPP Solar LVX6048 Inverters for split phase 120v - 240v 100amp
Good choice. Sol-ark is Nr1 but expensive


Generator (~$6000):
Generac Guardian 24KW generator for charging batteries when the batteries are low and no solar available

Things it would be good to know:

Is there any sense in adding a separate solar for pool pumps...just hook some panels directly to the pump and pump while the sun is shining? Anyone have brand/model ideas? This seems better than adding yet another high power device on the batteries.

MPP Solar has batteryless solar pump invedter.


I'm assuming the Inverter would be the limiting factor on surge requirements, but think that it is important to understand the batteries play in this. How do I spec the maximum draw the batteries can take in or dole out? I assume the inverter protects both input and output to and from the batteries?
Max charge and discharge at 0.5C.
2x 280Ah = 560Ah ... /2 = 280A
This is the max charge and discharge for your LFP battery.
So you can have 280A x 48V = 13.4 KWp solar panel.
Also your consumption should be less than 13.4 kW
If you double the battery this values double too

I haven't factored in a peak load because I don't really know what it affects or how to estimate the number. Obviously, you can estimate the number by adding up everything in the house and turning it all on at the same time. But I can't figure any way to lower that without making crazy assumptions.

Should I add more panels for charging and running high power devices simultaneously when the sun is shining?

Also if EV then best charged directly from sun :)

Where do I buy all this stuff? These are some places I'm sniffing.
https://www.currentconnected.com/
 

EscapedAritst

New Member
Joined
Oct 2, 2021
Messages
4
Damn, what a great bunch of info you guys just dumped on me. I'm just digging into the meat of it. Between the SAM software and the DIY Checklist, I'm into a major study session again. I just wanted to thank you all for responding!! I'll be back shortly after I've digested this new information.

On question immediately for mrzed, if I do my own batteries, is there a tutorial you know of that gives the best practices? And, what container would you use for those?
 

mrzed001

Voice of reason
Joined
Apr 10, 2020
Messages
743
Location
Hungary - EU
Damn, what a great bunch of info you guys just dumped on me. I'm just digging into the meat of it. Between the SAM software and the DIY Checklist, I'm into a major study session again. I just wanted to thank you all for responding!! I'll be back shortly after I've digested this new information.

On question immediately for mrzed, if I do my own batteries, is there a tutorial you know of that gives the best practices? And, what container would you use for those?

Ohhh there is a lot of video on YT:
Off-grid garage:

The Digital Mermaid:

And you can always ask us.
We even know what they did wrong or not ideal 😄

Most use a simple shelve system.
Some use the boxes that is made for trucks.
I want mine to be perfectly water resistant so IP65 cabinet.
Some topic here:


 

EscapedAritst

New Member
Joined
Oct 2, 2021
Messages
4
If you want you can DIY a battery bank for half the price
2x 16x EVE 280 (or CATL 302Ah) cells $5500 (28.8 kWh) + 2 JK Heltec BMS &450
I'm finding that pricing is only "half the price" if purchased off Alibaba. I can't find anything less than about $25/watt
You have 4 inverter, you can have more. The sun is not always shines at max :)



Good choice. Sol-ark is Nr1 but expensive




MPP Solar has batteryless solar pump invedter.



Max charge and discharge at 0.5C.
2x 280Ah = 560Ah ... /2 = 280A
This is the max charge and discharge for your LFP battery.
So you can have 280A x 48V = 13.4 KWp solar panel.
Also your consumption should be less than 13.4 kW
If you double the battery this values double too



Also if EV then best charged directly from sun :)

If you want you can DIY a battery bank for half the price
2x 16x EVE 280 (or CATL 302Ah) cells $5500 (28.8 kWh) + 2 JK Heltec BMS &450
When I look at the prices the only way I can get a half price battery system is to order from Alibaba. Is there a place where I can buy cells in the US?
 

wattmatters

Photon Sorcerer
Joined
Apr 16, 2021
Messages
1,077
Is there any sense in adding a separate solar for pool pumps...just hook some panels directly to the pump and pump while the sun is shining? Anyone have brand/model ideas? This seems better than adding yet another high power device on the batteries.
Off-grid? No. Just use an efficient multi speed pump and run during the day when there is ample solar to cover the pumping cycle needs.

I have a 48V 4kW clone Voltronic PIP inverter and it runs my pool pump without concern. The pump has a very soft start. Ramps up to ~900W over about 30-seconds, stays there for 5-min before dropping back to all day running mode of ~320-340W. The solar PV easily covers that.

My old single speed pump used to suck 1200W all day. Seriously, modern efficient multisided pumps are way better and cut down your energy supply requirements by a lot.
 

mrzed001

Voice of reason
Joined
Apr 10, 2020
Messages
743
Location
Hungary - EU
I'm finding that pricing is only "half the price" if purchased off Alibaba. I can't find anything less than about $25/watt



When I look at the prices the only way I can get a half price battery system is to order from Alibaba. Is there a place where I can buy cells in the US?

Check this thread (and others). I think Amy (or Basen) has a warehouse in the US (so it is still Alibaba, but from local warehouse).

 

l00semarble

New Member
Joined
Jan 1, 2022
Messages
12
Hey EscapedArtist. I'm in a very similar situation building a new house in Uvita. I just joined this forum and just posted my own questions about overall system design:

https://diysolarforum.com/threads/b...r-grid-assisted-off-grid-in-costa-rica.33426/

Where is your house?

I'm a bit of a n00b myself but I do marine electrical work as a living including all kinds of alternative energy and batteries/inverter etc.

One thing I noticed in your specs is that you seem to be planning for 100% efficiency from your solar:

445 watts * 4.5 hours * 16 panels = 32 kwh per day

My understanding is that you can only expect about 75% efficiency to allow for imperfect angle, temperature, dust on panels, Toucan poop, wiring losses, etc. One quote I saw from a Costa Rican solar company had a 64% efficiency factor applied to the total PV wattage. That sounds low but certainly 100% efficiency is virtually impossible.

My planned house sounds very similar to size/specs as yours. Largest load is the pool pump and we will have mini-splits which we won't use regularly but we may use for humidity control if we lock up the house. We won't have electric water heater or well pump. I am debating about electrical cooking. Propane costs money and is a hassle to hump the bottles up and down the mountain. But electric cooking can take a lot of power.

Anyway - I'm still working my spreadsheets and considering system topography. My first rough ideas were a minimum of about 10kw of PV, maybe about 12-15kw inverter with higher surge capacity, and min 30-40 khh batteries. In comparison your initial cut is 7.1kw of PV, 24kw inverter, and 30 kwh battery. If you derate your solar as I suggest we are pretty close on PV too.

24kw of inverter would be necessary for 24kw continuous and surges above that. That is a lot of power. Really necessary?
 
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