Solar Basics?

[Redbearded]

Hi All,

Working on understanding the finer points of basic solar... let me know if I have anything incorrect

<putting power in>
Panels - provide power to the (can be series, parallel, or some combination) (higher voltage= smaller wires and less losses)
MPPT - charge Controller, which Charges the 
LiFePO4 prismatic battery array (at either 12,24, or 48 volt nominal)
If shore power then hybrid charger?

<taking power out>
if DC= simple as long as batteries don't undervolt
if AC= Pure Sine Inverter (can be included in a Hybrid charge controller)

<safety parts>
Fuses protect against shorts and too high of a current draw (emergency)
BMS (optional if bottom balancing?) (auto balancing=spendy)
Heating mats to protect from low temp charging (32.deg power draw is OK, charging can damage cells)
Properly sized wires 
Simple low and high voltage disconnects (for cell safety)

Any glaring errors? Or missing subtleties?

My main goal is to figure out what components I need to research to have a safe and whole system. So far I know I need panels, MPPT charge controller, batteries, inverter, high and low voltage disconnects, and the accompanying interconnects fuses and switches. The hybrid charger/inverter is less useful for me (I think...) as I wasn't planning on plugging in anywhere and just going solar only (system will be in a converted cargo trailer and fully independent).

Thanks for the assistance

 

[jonsun]

Sure if money is not a factor its fine. You could build a significantly cheaper system with as much power.

 

[GotSmart]

That is making a two wire system complicated. 

How much power do you need?

 

[tx2sturgis]

My main goal is to figure out what components I need to research to have a safe and whole system.

Redbeard, that's not really a 'goal' per se. It should be the desired result tho.

Example: I can build a 'safe and whole' system for $25 but it wont power very much. Or I can spend $25,000 on a 'safe and whole' system but it sure wont fit on a small trailer. 

You need to either:

Figure out your budget (space and/or cost) and build to that level, OR,

Figure out what you want to power and build to THAT level, with cost as secondary.

Middle ground for most of us is about 200 to 400 watts of solar.

 

[bigskybob]

I would change battery to regular GC.Modified sine wave is much cheaper and works fine for everything except MW.Thge MW will still work,but it complains.I recommend 2 watts input for every amp of storage.Get a 30 amp mppt cc.You WILL want to expand later on.Keep things as simple as you can.

 

[jimindenver]

The most solar I have seen in person on a cargo trailer is 945w in t. Three 315w panels. He is adding some hinged to the sides too. That was a cargo trailer like I have seen at the RTR or other gatherings. Bigger cargo trailers can take more, there are some really big ones on you tube.

 

[bigskybob]

What is "bottom balancing"?Also never heard of using a heat mat under batteries.

 

[John61CT]

The LFP is what's unusual there.

5-7 times more expensive than lead per nominal AH capacity, so let's say triple even with the higher usable percentage.

Yes that's just a higher up-front investment, **if** you take good care it **may** end up cheaper than lead over say decades' POV.

But it takes a fair bit of knowledge to put the right infrastructure together, most experts advise against laymen DIY, and of course lots of other risks.

So, are you sure you can/want to invest thousands in this when maybe hundreds will do?

How many AH per day do you think you'll need?

 

[John61CT]

> What is "bottom balancing"? Also never heard of using a heat mat under batteries.

LFP specific stuff.

 

[Redbearded]

One of my concerns is weight of lead acid. I would actually go with Li-ion out of a crashed tesla or volt if I wasn't freaked about those damn cells, lol. I figure LFP is a good middle ground.

I'm looking at 8 180AH LFP in a 24v system with a usable 70% discharge capacity of 

180AH*24V=4320WH*.7= 3.024 KWH

I figure the batteries will run about 2k and the whole solar power system under 5k. I'm planning on being full electric and I have all kinds of stuff, like a server, tv and home theater, chest freezer (running as a fridge), induction plate, maybe even a small electric scooter or something. The goal is also to not have to plug in at all. I'm pretty handy with stuff and want to learn the specifics (I actually love learning the specs).

Cash isn't such an issue at the moment and I'd rather just do it once and be done with it. Plus the more I spend the bigger my tax credit will be (30% of the cost of the system, including batteries and everything else). The plan is to eventually, when I find a place to settle down (if that happens) use the system in the house for offgrid.

 

[John61CT]

Must be nice!

Add shipping and the compression plate/strapping to the $2,000.

Why 24V?

Post that follows is a generic summary from my notes

 

[John61CT]

Bare cells: ​Winston/Voltronix, CALB, GBS, A123 & Sinopoly

Systems: OceanPlanet (Lithionics, not in Oz, just FYI), Victron, MasterVolt, Redarc

Note **every** vendor, also of hardware touted as "LFP ready", gives charging voltages **way too high** for longevity.

My theory is they would prefer their cells get burned out in under 10 years.

EV usage is very different from much gentler House bank cycling. Most EV people talking "lithium-ion" mean other chemistries not as safe as LFP, much shorter lifetimes, and with completely different setpoints and behaviors.

My charge settings for LFP: 3.45Vpc which = 13.8V max for "12V".

Either stop when voltage is hit, or if you want another couple % SoC capacity, stop when tailing amps hits .02C, or 2A per 100AH.

If you can't "just stop" then Float at 13.2V, but may shorten life cycles.

Don't need to fill up all the way at all, as far as the cells are concerned, in fact it is bad for them to sit there more than a few minutes, so do so only if loads are present, ready to start discharging right away.

Store cool at 10-20% SoC, or higher if not getting topped up regularly (I would monthly), letting them go dead flat = permanent unrecoverable damage. 

Same with charging in below freezing temps.

Persistent heat also drastically shortens life.

Charging at 1C or even higher is no problem, as long as you wiring is that robust, vendors spec lower out of legal caution.

Going above 14V won't add much AH capacity, but will shorten life cycles dramatically.

The point is to look at the SoC vs Voltage chart, and avoid the "shoulders" at both ends, stay in the smooth parts of the curve.

Following these tips, letting the BMS do active balancing is unnecessary and potentially harmful, just look for LVD / OVD and temp protection. Multiple layers if a very expensive bank, don't rely on any one device to work.

Check cell balance say monthly to start, then quarterly, finally every six months if that seems safe to you.

This thread is long but informative
http://www.cruisersforum.com/forums/sho ... hp?t=65069 , give Maine Sail your close attention.

Also his summary notes here
http://www.pbase.com/mainecruising/lifepo4_on_boats

**Everything** at that site is worth reading, very valuable. He also has great articles in Practical Sailor.

 

[Redbearded]

One of the perks of being in CA is I'm close to the distributors so the batteries are in stock
I know someone who has a solar install company and I'll have him get me the panels, I'm sure he will cut me a deal

Actually I think I read your notes last night, Good summary and I like the link to the boating site.

Also there is a great video "LiFePO4 Battery 101" on youtube that has tons of good info!

 

[John61CT]

Feel free to post additions, questions or comments if your LFP research brings up evidence from credible sources that any of the above is not correct.

 

[jimindenver]

Red

I do not see how many watts you plan on having up top. I have slightly under 1200w and have produced over 50,000 Ah's since February so your plan is feasible. Most of my big ticket items like the A/C use less power than the solar puts out and I choose each with that in mind.

With the bank you are looking at a 1-1 ratio of watts to Ah is going to be 1440w of panel. 1-1 is a rule of thumb I do not agree with. In practice it can be painfully slow bring up a depleted bank in good conditions. During the short days of winter it can take days to do the job and that's if you are not still using power.

I also do not see a back up means of charging. I have only used my generator for charging once in 5 years of running solar but I believe it is a essential part of a long term plan. Believe me when I say I can count the number of long sunny days that I have seen here in Colorado on my fingers. Quartzsite was cloudy much of the RTR and it can be hard to find sun in forested areas like Prescott and Flagstaff with all the trees.

 

[John61CT]

Other threads on LFP, maybe PM other knowledgeable members a link to here asking them to contribute to our collective quest for knowledge

https://www.google.com/search?q=site:cheaprvliving.com+lfp

Also, Maine Sail may well be willing to do some paid consulting via email (or here in public!) as long as you assure him

1. You won't use your DIY system on a boat

and

2. You release him of any liability

Might only be a couple hours' worth, and I imagine his rate isn't more than $200 an hour as long as you don't set any tight deadlines.

If that's interesting to you

RC (Rod) Collins [email protected]

and put "consulting" in the Subject field


But likely he'll turn you down. 8-(

 

[John61CT]

> 1-1 ratio of watts to Ah

Since CAR with LFP is pretty constant, way over 2-3C

every AH produced by the panels gets accepted by the bank

No "excess" production after 80% SoC.

I suspect that changes lots of "rules of thumb" out there based on experience with lead.

Bottom line is, just put back in what you take out, averaged out over time. Bigger bank gives lots more time to catch up.

No need to get back to Full, in fact should not unless you're going to start using it right away, is another big paradigm shift.

As with, no harm going down to 90% DoD, long as you don't ever risk getting to 0% SoC, instant and permanent death.

 

[John61CT]

With a decent alt/vr setup, just going for a drive for an hour or two can contribute many days' power usage to an LFP bank.

May not be cheaper than a little inverter genny, but one less thing to carry, get stolen, carry fuel for if TV is diesel. . .


And note that LFP means no solar at all is required if you know you'll be driving say 5-10 hours per week, even less if your needs are more conservative than OP's.

 

[tx2sturgis]

Dude, we just went WAAY past solar 'basics'....

 

[John61CT]

Well, his friend with the solar company can cover that part.

May re-title the thread "Big-budget LFP system, starting from scratch"