Feed back please

estes53

In your opinion will this get me started?

I say started, because, I am keeping the cost to a minimum, and will probably need to add a couple more panels and another set of 4 batteries, before calling it good.

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Cariboocoot

Re: Feed back please

Welcome to the forum.

Well where to begin?

You have all the panels in parallel, but the specified Vmp is 31.2 which is too low for a 24 Volt system. You would need to put them in strings of two, which eliminates using nine panels.

The charge controller you probably will not be happy with the quality of. Nor is it capable of handling the output from even eight of those panels: that would be about 68 Amps on a 24 Volt system.

The batteries probably aren't 9 Volts each. Four 6 Volts in series gives you 24 Volts. Three parallel strings is not a good idea either, as it can cause current sharing problems. The total capacity of (3 * 370) 1110 Amp hours is very large and would not be well charged by 68 Amps of current. In other words not enough PV for that much battery.

Do you really need 13kW hours of stored power? It's quite a lot for an off-grid system. And if you do need that much you'd be better off going up to a 48 Volt system.

AIMS inverter; do not waste your money. They are one of the worst you can get.

There are no fuses or circuit breakers indicated in the design, and you would need them in several locations.

Power need at the bottom of 6.7 kW hours AC works out to about 657 Amp hours @ 48 Volts. This could be recharged using a single 80 Amp MPPT controller and about 4200 Watts of PV or roughly sixteen of the panels you indicate, not nine.

Maybe you should start with trying to get that power need number down? What exactly are you trying to do? This would not be a cheap system at that level.

estes53

Re: Feed back please

You are right about the battery voltage. It was supposed to say 6Vand I just fixed it.

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estes53

Re: Feed back please

I obviously don't know enough about this.

Could you recommend a web source for some kind of tutorial?

estes53

Re: Feed back please

"Three parallel strings is not a good idea either, as it can cause current sharing problems."

Am I understanding, that it is the uneven number that is the problem, or is it just 3, as opposed to 5?

westbranch

Re: Feed back please

consider that 3 is the max recommended, more starts to cause uneven charging of each string , even 3 can be a problem if the batteries are not all charged evenly to start .

BB.

Re: Feed back please

Because Lead Acid Batteries and the DC wiring has very low resistance, it can be difficult to get parallel battery strings to share current properly. Usually, your first step is to wire each battery string with an equal amount of cable in each string so that the excessive wire length/resistance does not "steer" current wave from the battery string with the longest wiring run. Some examples of what to do:

http://www.smartgauge.co.uk/batt_con.html

Also, there is the issue of checking water levels of cells... When you have a large number of parallel strings, you also have a large number of battery caps to check/add water every month, monitor specific gravity levels, etc.

There are some other issues too (more points of failure, more chances of failure, lead acid batteries, if they become different temperatures will affect their shared charging/discharging current, your really should have a fuse/breaker per parallel string--more costs/complexity, etc.).

Usually, it is better to keep the number of parallel strings down. I personally think one string is "ideal", but some people like two parallel strings (if one cell/battery fails, the second string can carry the loads until the failed unit is replaced). And, again personally, I would suggest that a maximum of 3 parallel strings is about the limit for high current systems and trying to balance current (as well as having to service battery cells/wiring/etc.).

Can you use more than 2-3 parallel strings. Yep, people do it all the time for various reasons. And are happy with the results.

However, if you can 1) look for larger AH cells (instead of two 100 AH @ 12 volt batteries in parallel, you can go with two 200 AH @ 6 volt batteries in series). There are larger 6, 4, and 2 volt high AH capacity cells--And these keeps the cells/batteries light enough that one or two people can scoot them around the battery shed/down stairs to the basement/etc. without needing a hoist or forklift.

Another issue is the total AH capacity of the battery bank. Common large (residential) solar charge controllers tend to peak out around 80 amps or so... If you like a 10% rate of charge on your battery bank (good for full time off grid home), then 10% of 800 AH is 80 amps charging. If you need a larger battery bank, instead of going to 1,600 AH @ 24 volts, you can go with 800 AH @ 48 volts and still use one solar charge controller (and save ~$600 for the second charge controller).

Also, when the average current draw exceeds ~100 amps, you are starting to talk about some very large diameter and expensive copper cables/fuses/circuit breakers. To give you an example of 1,200 Watt @ 12 volt AC inverter that runs at rated load:

1,200 Watts * 1/0.85 inverter efficiency * 1/10.5 VDC inverter cutoff voltage * 1.25 NEC wire+breaker/fuse derating = 168 Amp rated wire+breaker/fuse branch circuit

If you use the NEC, the size of cable would be around:

http://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

1/O to 3/O cable

If you use Boating Association recommendations:

http://www.boatus.com/boattech/articles/choosing-cables-and-terminals.asp

Somewhere around a #4 to #2 cable minimum (watch out for cable length and voltage drop issues)

For 12 volt systems, you can have about ~0.5 volt nominal wiring drop from battery to AC inverter input (11.5 volt minimum battery bus, 0.5 volt drop for operational power, another 0.5 volt drop for 2x current draw starting motors = 10.5 volt inverter cutoff voltage).

For 24 volt systems, you can have ~1.0 volt drop and 48 volt systems ~2.0 volt drop for wiring/discharged battery bank under heavy load.

You have your Battery bank to AC inverter output balanced pretty well for a Lead Acid storage battery bank. ~500 Watt rated output per 100 AH for a 24 volt battery bank (1,110 AH ~5.55 kWatt inverter rating maximum).

However for charging, 45 amps is pretty light. You should be looking at 5% to 13% or so charging current, and if this system is cycled daily, you should be looking at 10% charging current minimum (also, "tall" cased batteries and some brands of batteries recommend 10% rate of charge minimum).

A 1,110 AH battery bank at 24 volts would need an array in the range of:

• 1,110 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 2,090 Watt array minimum
• 1,110 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 4,181 Watt array nominal
• 1,110 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 5,435 Watt array "cost effective" maximum

How much energy do you plan on using per day? Is this seasonal or all year around (i.e., need genset+battery charger), etc.

Off grid solar power is expensive--Anything you can do to reduce energy usage is usually a very good investment.

Remember that you will probably have to replace batteries every ~5-8 years (assuming nothing goes south, depending on quality of batteries, how you cycle them, how they are maintained, any "oops" during usage, etc.), and electronics every ~10+ years.

-Bill

zoneblue

Re: Feed back please

Do you have a real off grid application for this, ie no grid available, or grid connect > 30K?

Thats the first question. Grid 9/10 times is cheaper.

Second, yes the diagram indicates you have a bit to do before you go buying anything. I did document our install somewhat see my sig. Its not necessarily the right way to do it. Done again i would use one of Midnite Solars epanels or MNDC disconnect. This solves all your fusing needs in one tidy cost effective solution. I recomend you download the manuals for those cabinets, as they have great wiring diagrams.

Mostly, just hang around here and read forum posts. Youll pick up a surprising amount in a few weeks if you invest the time. And lets be clear you have two choices, invest the time, or find an installer. Just because it isnt connected to the grid doesnt mean its not dangerous. In fact the opposite applies, all the AC side shock/fire hazzards exist, plus you add high current/DC battery hazzards to the mix.

For off grid the NEC requires you to use a UL1741 listed inverter. That limits you to inverters with 4 figure price tags. Most of us found out the hard way that trying to avoiding that investment is ultimately futile. In my case the chinese inverter died on the thrid day. One way or another serious off gridders end up getting a decent inverter.

If budget is an issue, then you either need to reexamine your goals and prioritys, or downsize the system to a small learning system. Some here have sucessfuly built semi compliant systems on a shoe string. The key there is experience to put together a good design, best practice installation, and undertanding how cheap you can go, ie what brands are good enough to be safe, even if not UL listed. Theres several recent threads on this issue. Welcome and good luck with it, RE can be a sharp learning curve, but also an suprisingly addictive hobby.

westbranch

Re: Feed back please

zoneblue wrote: »

For off grid the NEC requires you to use a UL1741 listed inverter. That limits you to inverters with 4 figure price tags. Most of us found out the hard way that trying to avoiding that investment is ultimately futile. ....... One way or another serious off gridders end up getting a decent inverter.

Some here have successfully built semi compliant systems on a shoe string. The key there is experience to put together a good design, best practice installation, and understanding how cheap you can go, ie what brands are good enough to be safe, even if not UL listed. .

Also you can assemble a system with good quality components but not have a combined Inverter/Charger (a pricy bit of kit).
The combined units are usually a bit more than the price of 2 separate units.
Some are worried about failures in a combined unit and being without a whole unit when only one part of the system needs to be fixed.
Your choice.

hth

Photowhit

Re: Feed back please

I think most of what I would say has been covered, curious where you are located and if this needs to be off grid? This can give information about the needed reserve and available sunlight.

Motivations for off grid can vary tremendously, Off grid are more expensive and time consuming than grid tied systems, but perhaps you are not in the US or have other reasons for being off grid, are you a prepper? ...not a dirty word around here, but more to your reasons for being off grid.

I have no problem with Non UL1741 inverters, at least 2 of the ones I use are not compliant and one of the ones I use that does have ul1741 can't realistically be made compliant. Many systems that pass inspection aren't up to code. And code often doesn't apply to off grid structures (not connected to the grid) or is not enforced. I like to focus on a safe system. That said we have seen many people who have had issues with Aims inverters and there are other options that are nearly as inexpensive with out being cheap(the rep for Aims).

Asking here isn't a bad place to start for information, there are some threads here about information and I'll hunt up some links for you this evening. So more information please, Lookss like you have a moderately sized system, My system would have benefitted from going to 48 volts, which I would have done, but I had already purchased the battery for a smaller system and it should last quite a while.

Info on the array and panel voltage could be gleaned from many of the threads here, might suggest reading through the beginner threads.

CDN_VT

Re: Feed back please

estes53 wrote: »

I obviously don't know enough about this.

Could you recommend a web source for some kind of tutorial?

I have been reading here & 2 other sites for over 10 years . Plus this is somewhat one of my trades . There is so much to learn & still within , they do have Voo-Doo , Or as some other forums say VMM :-) ..

Best thing is to read all the posts here as they are posted or go back an just read other questions being posted & follow the links that the replys put up. I's amazing what you will gain .
Get the Power circle (Attached ) and work it through as you read & re-figure what the replys are posting .


After a while the AC/DC stuff will make more links here & sense.


VT

PS the replys on this thread are the norm folk here who do most of the replys EX -Me .

No worries we all started below " You must be this tall tooo"

zoneblue

Re: Feed back please

And code often doesn't apply to off grid structures (not connected to the grid) or is not enforced.

Unfortunately this is not true, not here, and im also pretty sure that the US NEC does also not discriminate between grid connected and off grid. I think thats a common fallacy that people like us off gridders, who dont like rules, tell ourselves to make us feel less like lawbreakers. However the reality is that electricity is electricty, and safety is safety.

I posted recently about a recent example of a large fine levied on a badly wired motorhome, here... http://midniteforum.com/index.php?topic=2114.msg20742#msg20742

Im NOT saying everyone necessarily has to do things to code, thats a personal choice, like whether you believe that speeding increases your risk of car accidents. Our system isnt inspected, and likely never will be, however its a personal goal to get it up to local NZS standards. The value of rules i think is that they help us understand the point of them. That can only lead to better practice and safety. Its my view that anyone who is not a qualified electician, undertaking electrical installations, assumes a responsibility to learn to do things safely. And those rules help with that.

Now that the NEC 2014 is freely available theres another good reason to better understand the rules. https://archive.org/details/nfpa.nec.2014

Theres no longer that barrier between those that have access to the code, and the rest of us. Article 690 goes into PV systems extensively, and its interesting reading. Here the codes are still 200 bucks a pop.

The trouble with codes, is that the difference between complying and not is clear to everyone, but the difference between almost complyng (follwoing the spirit) and grossly non compliant is so open to interpretation that you tell someone here that the code doesnt matter and next thing you know you have really shocking installations going in all round the place.

What was the OP about again? Oops.