Off grid system - NorCal

[mb2112]

Hello. First time posting and hoping to get some feedback from all the experienced forum members.

We recently purchased property in NorCal (affected by the previous 2017 fires). There is a small structure that survived (one car garage with an adjacent living area). Will only need to power some lights for now, but may want design for additional loads over time. Plan on replacing the load center and tweaking the wiring. Structure was built in 1977! We'll only be up there on weekends, boys riding dirt bikes, fishing and just hanging out...

1. Contemplating a 12V or 24V system. Liking the all in one MPP options (1012LV, 2424LV)
2. Seems like I'm stressing too much on the batteries. The more I read, the more I'm all over the map. Looking at Battle Born, Trojan, Big Battery, etc...

LifePo4 LFP Battery 24 volts 5.63 kwh 220 Ah Battery Pack EV Golf Solar with BMS

info@techdirectclub.com

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BYD LFP 24V 5 kwh 200 Ah Battery Pack With BMS 130A LiFePO4

info@techdirectclub.com

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motor vehicle battery - Google Shopping

3. I'll have access to panels. If not, I'll buy some 100w Poly off of Amazon. May have access to some Tesla panels as we are actually having the Tesla roof installed at our primary residence.
4. No immediate plans to grid power or use generators.

I'm very comfortable with all the electronics (being a EE). Always try to follow the KISS methodology (keep is simple stupid) but looking to design a cool little system.

Appreciate any feedback.

Thx

 

[Steve_S]

Welcome to the forum.
1st most important thing here... DO NOT BUY ANYTHING until you have a plan and understand everything. There are ALWAYS DEALS and no such thing as "once in a lifetime". Especially impulse buying... very BAD ! for you, your wallet & marriage !!

FORGET 100W panels ! They are overpriced, underperforming and really only have a place on RV's Boats and sheds... The Solar Charge Controller capacity (how many volts & watts it can handle) is the deciding factor. If the SCC can take 2000W & 200V imagine trying to that with piddly 100W/12V panels... and they cost 2X+ more than standard 60-Cell 300W panels.

NEXT, if you see anything "Renogy" that is the same quality as used toilet paper, avoid it ! They are great are marketing Low Value products with horrible support.

Solar Panels are easy as borscht to get for cheap. We aim a lot of people at Santan Solar for New or Used Panels: https://www.santansolar.com/

Inverter / Chargers / SCC's. The simplest & easiest way to go for a smaller system which can scale is to use some of the All-In-Ones such as MPP Solar or Growatt (GW being a higher grade). These are modular internally & repairable. Most are Stackable (meaning you can add them in-series for increased output) and have management & monitoring capabilities.

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Batteries: It is far cheaper to DIY your own battery packs and it's not hard. We can guide you through that easy enough, there are tricks, quirks & foibles but nothing unusal, as an EE you know .... You can go out and spend large and buy Battleborn or other commercial offerings BUT beware of discount batteries from offshore... WE HAVE EXPERIENCE and many are NOT what they are advertised as.... One consideration as you are only going to be Part-Time... I would not put high end premium goodies up there because it can grow legs, or worse.

24VDC battery pack requires 8 LFP cells, an 8S-BMS and a fuse of course.
Example:
Free Shipping to USA & 8Pcs 3.2V 280Ah Total US $938.36 (DPP Duty/Taxes paid) Link to Lyuan 280s (Xuba Sister Company)
These are NEW, Grade-A Commodity Cells and very popular with many of us here.
A respectable BMS $150 USD +/- depending on features, functions & capabilities.
An MRBF Fuse $26.00 a pop with Block & Fuse: https://www.ebay.com/itm/Bay-Marine...-Single-Fuse-Holder-Kit-30-300A-/174059623226
938.00 + 150 + 26 = $1,114.00 USD plus whatever you decide for a case.
This will give you One Battery Pack @ 24V/280AH/6.72 kWh for $1,114.00 USD

Hope it helps, Good Luck.
Steve

 

[mb2112]

@Steve - Thanks for the feedback. Really appreciate the details on the batteries. That has been the most challenging for me so far.

I'm more than up for a DIY pack but will need to do more research and determine if a 12 or 24v system is more advantageous. Pretty sure I will incorporate an MPP/Growatt integrated.

Alot more research ahead of me...

Marty

 

[creeky]

I go by the size of the inverter. Under 1kw. 12v is fine. Under 3 kw. 24v sure. Over 3kw inverter. 48v.
Lithium for sure. Get a good active balancer. I really love Victron. Its just reliable. And really easy for the DIYer to manage. Plus the history read out on the solar controller and the ease of Bluetooth, wifi reporting etc. Just makes your life much easier.

 

[Hedges]

48V is good for a system that will grow to be 5 kW AC or more.
12V is good if you might later use it as a small portable unit, like in a van charged off the alternator, although higher voltage can be supported with DC to DC.

Lithium? AGM is lower up-front cost for fewer cycles lifetime, and the chemistry provides BMS without any electronics.
With Lithium you can buy 10 years of nightly cycling upfront, and is lighter weight for mobile systems.
AGM might be good for 18 months of deep cycling or 10 years of 15% DoD. I believe in wearing it out quickly to get my money's worth sooner.
FLA gives you more kWh for your $$ but more maintenance.

My suggestion is size an AGM bank for one night's load, use a timer or light sensor to run a refrigerator only while the sun shines. Have a cheap portable generator for multiple cloudy days.

Perhaps some day you will do grid-tie net metering? There are hybrid inverters for that, or battery-less grid-tie inverters that can deliver AC direct from PV while no grid is present.

So you can select some items as short-time use and throw-away, others long-term or planning to re-purpose.

There are some neat used & surplus deals out there, like on eBay a listing for two Sunny Island with Midnight charge controller wired in a box, for $4500. Just add PV panels and batteries. At 12 kW it is far more than you were looking for, but could power a workshop and house.

 

[mb2112]

Keep the input coming. Appreciate all the feedback.

 

[creeky]

One thing people forget when comparing batteries is storage cost. By that I mean the battery requires space and racking. So an AGM battery vs lithium is cheaper to buy. But racking costs more and space is triple. When houses cost 150 sq ft to build, you're extra storage space often surpasses the cost difference.
Lithium is cheaper racking. Cheaper space requirement. Longer life (x10?). Cheaper cycle cost. And you also don't have the cost of swapping batteries out every 3-8 years.