A year to figure future storage

[thirteen]

I am a year away from putting in a system. So my question is which is a better system 24v or 48v? I have read do's and do nots.   I have thought of 12v at the start but it works for most things but seeing the way things lean it would be better to go with 24 or 48 to start with rather than try and expand in three years to 24 or 48. I just as well make a good system to start with. The only thing I see is things seem to be harder to get at 48v. I will be using solar for some of the year then micro hydro for the rest. I just do not have enough of either one to run just one system year round.  I will have two battery banks. I will be able to charge either one from the solar or the micro hydro. It will be a manuel switch from one to the other. Everything I have is used and cobbled together so I will be getting all new electrical and new batteries. It works but it's worthless. I will probably cry when I start spending the money but I need something good that will last about 15 years. Then I'll probably be pushing up daisies. So I would like to hear the do's for either 24 or 48 volt system? Just looking for some answers or ideas. 407 days and counting down.

[DanG]

I just as well make a good system to start with

I committed to 48V - but an inspiring battery bank at 48V is big bucks.

Buying one of the industrial tractive-motive 24V banks may be the best bang for your dollar IF you can charge it.

[rossw]

I am a year away from putting in a system. So my question is which is a better system 24v or 48v? I have read do's and do nots.   I have thought of 12v at the start but it works for most things but seeing the way things lean it would be better to go with 24 or 48 to start with rather than try and expand in three years to 24 or 48. I just as well make a good system to start with. The only thing I see is things seem to be harder to get at 48v.

There have been and doubtless will be wars fought over this subject. For some, it's more of a religion than any sort of reality issue.

48V systems are not harder to get.
*SMALL* 48V systems might be a little rare, unless you check out telco-land where 48V is absolutely *THE NORM*
*CHEAP* 48V systems are probably very rare, where "cheap" is in the $100 range.
*NASTY* 48V systems are probably few and far between. I can't say I've ever seen a square or msw 48V system, although they probably exist.

I will probably cry when I start spending the money but I need something good that will last about 15 years.

If you go 48V *NOW*, you won't have to go 48V *LATER*.
If you go 48V *NOW*, you won't regret having spent all your money on a 24V system and just can't afford to replace it, but wish you had gone 48V in the first place.
48V systems are NOT significantly different in price to a similar quality 24V system.


I suspect there will be others belittle my views and attack me for expressing them, but I challenge them to put forward any real, tangiable substantiation to their counterclaims, or just plain shut up

[ghurd]

It depends on where you are?

I am in North America.  My view is 24V sort of splits the difference between 12V and 48V, except it has all the bad qualities of 12V, and few of the good qualities of 48V.

Good 24V inverters are expensive here.  The next step down from good is no-name junk from ebay?
If the junk is ruled out, that leaves good quality expensive inverters.  24V and 48V inverters from a decent company cost about the same.

Available power is measured in watt-hours.  Voltage does not come into it.  10KWH is 10KWH.
Might do OK if there is a local source for decent 24V batteries, especially decent used batteries.  Then again, if decent used 24V batteries are available locally, could probably get 2 sets of smaller batteries and go 48V for the same money?

A small system (Flux says 1KW or less, and I always believe Flux) is OK for 12V.  Over 1KW is better considering 48V if you are in North America.

The UK has more options for decent 24V inverters, or so I hear.
Just 2 cents,
G-

[DamonHD]

G,

Haven't especially noticed 24V stuff other than marked as 'truck' though I note that Maplin (B&M electronics store) stocks a few.

As Ross says and to the best of my knowledge, 48V will be as common as muck for telco stuff, and will probably be a world away from 12V/24V automotive in build quality and price.

When I grow up and take my house off grid (except for export) during the summer I expect to go for 48V for the main power system to minimise wiring losses.  The gel SLAs I bought as 4x12V so I can re-arrange and use those for 48V (or 24V) if I get some round tuits.  My small isolated off-grid system will likely stay at 12V because of the abundance of good/cheap automotive kit and because of my ramshackle collection of 12V-nominal random solar PV.

Rgds

Damon

[Volvo farmer]

I went 24V. I thought I would be finding some sort of DC loads to use directly off the battery. I was wrong. The batteries and inverter sit out in a shed and every single load in this house is 120V off the inverter. 

When I was designing my system, I got advice from a guy with 20+ years experience in the field, and he was a real proponent of limiting parallel strings of batteries. He strongly suggested to limit my parallel strings to two (which I did). However, it is my understanding that for the purpose of keeping the cells equal, a single series string is even better than two parallel strings. The guy I talked with even recommended splitting my bank once in a while and equalizing the series strings separately.

So at 48V you can build a moderate sized battery bank with one string of relatively inexpensive T105 type batteries, or you could build a pretty decent sized bank with one string of L16 sized batteries. If you have real dough, companies like Surrette and HUP make 4 and 2 volt cells that could be strung into even larger banks.

At 24V, trying to run a residence off grid, you are almost always going to need to run parallel strings of batteries, especially if you plan on using the less expensive golf cart sized, or L16 sized batteries. For this reason, I vote 48V.

[clockmanFRA]

Hi thirteen.
I came at this from a different angle. What inverter was real good quality and cheap?  Talked to allot of folk and did some research over many years, and my conclusion..... Computer server Uninterruptible Power Supply.

Most companies/business's have these permanently on for their PC,s etc. APC do a fine UPS 5000 at 3.75Kw output. These type of inverters require a 48v DC supply and give a smooth 50HZ 220v AC output.  And when a company updates their computer's  every 3 to 4 years or so, these UPS are skipped/junked. New about £1200, SH and from good source about £300. Slight input mods are required with connection from external batteries, the small internal battires are not used/discarded.
The APC is well made, cold starts, (starts by closing my 100 amp breaker and then pushing the start button) and takes cold and hot weather conditions without any problems, (sits in a cupboard in a wooden open building). Self Shuts down at 40v and has taken 60v input (my turbines in a storm).  I have 5 strings of 4 x 12v at 100 amp batteries, but keep an eye on each, as one battery allways takes a hit in a string, so i do not discharge down below 48v (normally holding at 53.4v).

Trust this helps

[Madscientist267]

However, it is my understanding that for the purpose of keeping the cells equal, a single series string is even better than two parallel strings. The guy I talked with even recommended splitting my bank once in a while and equalizing the series strings separately.

I have to agree with ClockMan on part of this... Two parts to it:

1 - GASP! There's no way a single string has better balancing behavior than parallel strings. When a cell gets slightly off balance, a single string keeps the entire load passing through that weak cell. With parallel strings, the weak string still contributes to the load without having to support the entire drain. Higher discharge rates exacerbate weakened cells, as do higher charging rates; the reverse also happens as well. A weakened cell will reach full before the others, and at higher currents, this will happen faster and faster, straining not only itself, but preventing the remaining cells in the chain from reaching full charge (or at least boiling itself to death during the process).

2 - On the other hand, I agree with you that breaking strings down into smaller chunks for equalization can be beneficial. It also will help you isolate any weakened cells so that you can get rid of them.

On a third, surrogate hand, having multiple (parallel) strings will allow you to disconnect one string at a time for things like maintenance, troubleshooting, individual equalization etc without power interruptions at the output of the inverter (for example) in the process.

This will play more of a role as the size of the system increases. Large banks are expensive, but can be more expensive to keep replacing if they aren't designed right. Gotta do the homework for sure.

Size of system and the like, I cannot comment really on which is best, although I'd shy completely away from 12V (others will strongly disagree, thats fine) for powering an entire building. Just the copper costs alone can offset what you might save on things like inverters.

I have done some looking into the idea, as I intend to be completely off grid one day, and the conclusion I came to is that my system will be a 48V deal. Currently, I'm learning on a 12V system, and also have a 24V system (that is not RE powered) for backing up my servers. That system was 12 originally; had to upgrade it to keep up with the demands of the load. Luckily it was small enough at the time, it didn't cost me that much to do so. I can easily imagine that I would NOT want to have a sizeable 24V system and have to upgrade to 48. That could get very expensive very quickly (in terms of overall cost).

Everyone's needs are different. And as pointed out, availability in your location for a given price plays a role as well.

My $0.02

Steve

[Volvo farmer]

1 - GASP! There's no way a single string has better balancing behavior than parallel strings. When a cell gets slightly off balance, a single string keeps the entire load passing through that weak cell. With parallel strings, the weak string still contributes to the load without having to support the entire drain. Higher discharge rates exacerbate weakened cells, as do higher charging rates; the reverse also happens as well. A weakened cell will reach full before the others, and at higher currents, this will happen faster and faster, straining not only itself, but preventing the remaining cells in the chain from reaching full charge (or at least boiling itself to death during the process).

Well, if the connections between parallel strings are not of equal length, or become corroded and increase their resistance over time, then there is a way that a single string might have better balancing characteristics than multiple parallel strings.

However, I had not considered that with a couple of parallel strings, one could limp by on half a battery bank if a cell goes bad, and with only one string, you might be kind of screwed until you replace the screwed up cell(s). 

I suppose there are advantages and disadvantages to each way of doing things. I have neither the background nor the experience to make any conclusions of my own, so I sort of lean on those who have been around and have been doing this a while. Even so called "experts" can come to wrong conclusions though.

[rossw]

However, I had not considered that with a couple of parallel strings, one could limp by on half a battery bank if a cell goes bad, and with only one string, you might be kind of screwed until you replace the screwed up cell(s). 

There are photos somewhere on this board (well, there used to be, there may or may not be any more) photos of my setup.

I have three strings, each of 24 x 2V/500AH cells. Each string has its own 200A fuse and a 500A DC Isolator switch. From there, two short cables to the inverter. This lets me parallel all three strings for "normal" use, but to isolate one exactly as you say, for special treatment or investigation.

Works very well. (And before you complain about the cost: I picked up all the cells second-hand for around 20% of their new price)

[DamonHD]

Ross,

What special things do you do before *reconnecting* a string into the main bank, if any, to avoid fireworks?

Rgds

Damon

[rossw]

Ross,
What special things do you do before *reconnecting* a string into the main bank, if any, to avoid fireworks?

Nothing terribly exotic.

I measure the voltage of the remaining "main" bank, and of the isolated bank about to be returned. If they're less than a volt or two apart, I put my clamp-meter over the busbar that will join them and throw the isolator to "on". I expect the current to spike to 50 or 60 amps, but within a second or so its usually back down to a few amps only, at which point I remove the ammeter and leave it be.

If the voltage difference is more substantial, I use the biggest 12V incandescent lamp I can find (150W) and put that between the isolated bank and the main bank and leave it for a while to see if they'll come close. If they do, its as above. If not, it depends which is high and which is low. I'll either wait until the sun goes down and the main bank has discharged until it's "close enough" to the isolated string, or wait until the sun comes out and the main bank is charged up enough to be close to the isolated string.

[DamonHD]

Interesting that 1V is "close enough"; I was worried about ~0.1V given the milli-ohm internal resistance of the batteries.

And I like the idea of letting the mountain come to you if the gap is too large.

(And almost the only incandescent I own is a 12V car bulb bought for this purpose, used while wiring up my new 4x100Ah 12V bank...)

Rgds

Damon

[rossw]

Interesting that 1V is "close enough"; I was worried about ~0.1V given the milli-ohm internal resistance of the batteries.

Yeah, that was my original thinking too. The reality is that 1V across the bank is 0.04V per cell, which is really not much. If you look at the difference in voltage of your banks going from charging at 10A, to discharging at 10A, there's a substantial difference - and thats how I get away with it.

I could very likely safely do it with several volts difference - I just haven't had the need/balls to try it.

And I like the idea of letting the mountain come to you if the gap is too large.

Yeah - if it was desperate - like main bank was nearly flat and isolated was full, I might do it - but I might do it for a transition only and then isolate the "flat" main bank too. Dunno. Cross that bridge if I ever need to.

(And almost the only incandescent I own is a 12V car bulb bought for this purpose, used while wiring up my new 4x100Ah 12V bank...)

They're great. Using them like this, you can't blow them up. They completely safely limit current, and display that they're doing so all at the same time

[Madscientist267]

Well, if the connections between parallel strings are not of equal length, or become corroded and increase their resistance over time, then there is a way that a single string might have better balancing characteristics than multiple parallel strings.

This is very true, and I thought about it after I posted yesterday. But when the connections are properly designed (and clean), the balancing is superior to a single string.

Interesting that 1V is "close enough"; I was worried about ~0.1V given the milli-ohm internal resistance of the batteries.

This varies depending on the size of the bank. With small batteries (<50AH), 1V isn't really that big of a deal. With 1000AH (for example), I'd be a LOT more inclined to have them MUCH closer.

Steve

[B529]

I can't see a reason to go 24 or 48.

48, smaller wire$, less battery strings....

All the off-grid systems I've installed have been 48, including ours.

Did a few upgrades to a few 24 systems. They too like Volvo Farmer intended to use 24vdc, but don't.

I know you are over a year away, but you may consider trying to buy batteries sooner than later. Batteries as well as everything else are going up in price.

[rossw]

This varies depending on the size of the bank. With small batteries (<50AH), 1V isn't really that big of a deal. With 1000AH (for example), I'd be a LOT more inclined to have them MUCH closer.

My banks are 500ah each, so with one isolated it's 1000 + 500.

I was also quite "timid" first time I did it. I used a small nippy-clip (cliplead) as a sacraficial link. I quite expected it to disintegrate in a puff of smoke. Those things are hard pressed to carry more than 5 amps, perhaps 20 for a few seconds. It got warm, but it didn't give up.

I'd ask you (or anyone else for that matter) - tell us what battery voltage you have with a modest charge current. (Say, something like C/20 or less) - 10, 20 amps sort of current I'm thinking.
Now with a similar state of charge in the batteries, take the charge off and see how far it falls. And now put a similar DISCHARGE current and measure volts.

I think most people will find a surprising voltage difference with even these fairly small currents. I believe that you can apply the same thing to adding strings in parallel. Whatever the voltage difference is between charge and discharge for a current YOU consider to be "acceptable", is what you can safely bring another string online at.

[ghurd]

My banks are 500ah each, so with one isolated it's 1000 + 500.

I was also quite "timid" first time I did it.

I'd ask you (or anyone else for that matter) - ...

Gosh Ross, you should invest in some full-size batteries!

"timid".  Me too, and I still am.  Typically I deal with maybe a pair of 85~120AH class 12V that are not mine.

I have an #1156 tail light bulb (2.2A 12V) with wires soldered on it.  Only takes a minute or 2 to get the batteries very close to the same voltage.
Might take a several minutes if one is nearer to flat, but in that case I put the more 'deader' (is that a word?) battery on the (solar) charging system alone for a day.
If I am in a hurry, I put the deader one on the solar by itself, let its voltage climb a bit while the fuller battery voltage drops, then connect them.
So yes I agree, it does not take much drain in one, with the other charging, to get them at the same voltage.
G-

[fabricator]

The one piece of advice I will give is IF you decide to go with anything BUT a 48 volt system, DO NOT post about it here, your system will be labeled third world, clunky, etc, etc, 48 volt is the party line.

[Madscientist267]

Come on, yall.

What is with all the urination competitions about system voltages around here?

It's simple, really. Use what works for you. Why should ANYONE discriminate against someone else for their choice of system voltage? I just don't get it.

Rule of thumb is that higher capacity (EDIT) lower voltage systems get less and less efficient as power goes up. Copper, switching, conversion losses? All go up. More current flowing = more waste heat. Costs therefore can go up in an effort to compensate for this (thicker wire, etc).

But there are reasons (some very valid) for staying with a lower voltage system if that's what works. Sometimes it is because a system was originally designed as a smaller system where 12V worked just fine, and has been added to over the years. It wouldn't necessarily make sense to change over to a higher voltage system 'just because'. Sometimes, it's 'cheaper ta keeper'.

Others design their system around what is available that meets their needs, for the best cost.

There really isn't a such thing as a 'right' system voltage. It's a matter of preference, availability, ease of maintenance, cost of ownership/operation, reliability, upgrade costs, power levels, wiring/conversion efficiency, versatility... blah blah blah

The list goes on and on. And NOBODY is either RIGHT NOR WRONG. There are RULES OF THUMB, but that's IT.

The entire thing is completely subjective and depends heavily on a balance of variables that are too grand in scope to give a 'religious' answer to.

So please, keeping in mind that I am not taking ANY side here, personally I'd appreciate it if the topics about this stay on a factual level. IOW, Quitcha Bitchin'!

I'd hate to think that there is a third category that people just can't talk about without a fight breaking out. It's bad enough it's already politics and religion.

Do we really need to add 'RE nominal system voltages' to this?

Steve

[TomW]

The one piece of advice I will give is IF you decide to go with anything BUT a 48 volt system, DO NOT post about it here, your system will be labeled third world, clunky, etc, etc, 48 volt is the party line.

fabricator;

Just knock it off. We all know you and your side kick are just trying to pick a fight so stop it.

Thanks.

Tom

[ChrisOlson]

My house ran on 12 volt from June of 2002 to November of 2009 when I bought a slightly used Xantrex XW6048 inverter.  I rewired my bank 48 volt and thought I had made a big upgrade.  Three months later it had become evident that the efficiency of that pure sine wave inverter was so horrible compared to the 12 volt units I had previously, that I was putting more hours on the generator than I ever had before in the previous 7 years.  In February 2010 after waking up to the house being only 48 degrees inside due to a dead battery bank and my furnace blower had quit, and the generator failed to start, I put all my 12 volt equipment back online.

I recently bumped my system to 24 volt to accommodate the output of my 12 foot turbines and I have been happy with the 24 volt system.

A kWh is a kWh is a kWh and it don't matter one bit what voltage it's supplied at.  You have to put in what works for you and gives you the most bang for the buck.
--
Chris

[rossw]

What is with all the urination competitions about system voltages around here?
It's simple, really. Use what works for you. Why should ANYONE discriminate against someone else for their choice of system voltage? I just don't get it.

Couldn't agree more mate. Not everyone shares your consideration and acceptance however.

There really isn't a such thing as a 'right' system voltage.
NOBODY is either RIGHT NOR WRONG.

What gets my wick is when someone, having determined what suits them, then goes about a character assassination of anyone who doesn't share their views, and indicates that anyone who doesn't do it *their* way is a pretentious pratt with more money than clue. Hopefully that attitude can be weeded out before it infects any more threads.

[ChrisOlson]

But there are reasons (some very valid) for staying with a lower voltage system if that's what works. Sometimes it is because a system was originally designed as a smaller system where 12V worked just fine

Steve makes a good point here.  The voltage doesn't matter one bit.  If you have 4 batteries and you're pulling 1 kW, every battery in that bank has to deliver the same identical amps whether it be 12, 24, or 48 volt, to make the 1 kW of power.  The people who claim there's a big savings in copper with higher voltage systems tend to skip over this.  But the fact is, if you have four 12 volt batteries wired series for 48 volt, and you pull 480 watts for easy figuring, every battery has to deliver the full 10 amps of the load.  If you wire those same four batteries parallel for 12 volt, now you need 40 amps to make that 480 watts, but each battery is still delivering the same 10 amps.

The only place there's any difference is from the bus to the inverter.  You might have to feed a decent sized 12 volt with dual 2/0, a 24 volt with a single 2/0 and a 48 volt with maybe a single 1/0.  Otherwise there is not one bit of difference.

When I bumped my system from 12 to 24 volt recently, I found out my solar panels perform better on 12 volt than they do on 24.  7% more watts on 12 volt vs wiring the panels series for 24 volt.  So I split my array into two parallel strings and feed each 12 volt half of my four bar bus with the two strings of solar panels.  It was either that or spend another 500 bucks on a MPPT controller to get more power out of those panels on 24 volt.

Some people will call this "cobbled together crap".  But you have to do what works within your budget, not what all the self-proclaimed "experts" tell you you SHOULD do.
--
Chris

[rossw]

But you have to do what works within your budget, not what all the self-proclaimed "experts" tell you you SHOULD do.

I knew you'd say something I could agree with, if I waited long enough

[MagicValleyHPV]

From a layman's perspective, my system was guided by limited PV mounting space, expected usage and versatility.

1. Motorhome - limited roof area for modules
2. All DC usage - make do with NO inverter
3. Ability to charge 28v 10Ah lithium EV (my 'gofer' vehicle and soon to be my only, daily wheels when the RV is parked)

My first purchase was a Sunsaver 15L MPPT controller. This allows me to configure and charge either 12v or 24v systems from any source up to 75v input.... efficiently. My second purchase was originally, 3 sets of Harbor Freight 45w kits - but after testing for two weeks and seeing noticeable voltage variations between modules, I took'em back for a refund. Not a week passed and I scored a new, Sanyo 186w PV for less than $3/watt shipped. I'm planning a second module soon.

I decided to wait until the last moment for batteries - idea was to assemble all the pieces first, then the batteries could be put to immediate use... taking maximum advantage of the warranty, and not be forced to grid-feed them while waiting for other components.

My backup charging is a home brew mix of a 120a Leece-Neville alternator coupled to a 9hp Kawasaki OHV (soon to be fed LPG, which is also what my RV runs on).

My EV has 28v lithium so I needed a balancing capable charger with, ideally, 24v input. That requirement was met last week when I ordered a HYPERION EOS 1420i 20 AMP capable balancing charger.

So far...

PV  $550
4 x 6v GC batteries (estimated 175-200Ah) $330
SS 15L controller $200
EV charger $180
I already had most of the mounting hardware and cabling so N/C

Part of the beauty of this system, is the ability to drop back to 12v if I should lose a battery, or even two batteries. I just swap a few cables and keep going. Even the EV charger will function on 12v (at a reduced capacity of course).  

 



          

[ghurd]

The large wire cost difference is from the generation points to the battery.
10' turbine on a 60' tower 250' up the hill,
500W hydrro 350' down the hill,
1000W of solar 150' behind house?

The diference gets substantial from 12V to 24V to 48V.
G-

[Volvo farmer]

When I bumped my system from 12 to 24 volt recently, I found out my solar panels perform better on 12 volt than they do on 24.  7% more watts on 12 volt vs wiring the panels series for 24 volt.  So I split my array into two parallel strings and feed each 12 volt half of my four bar bus with the two strings of solar panels.  It was either that or spend another 500 bucks on a MPPT controller to get more power out of those panels on 24 volt.

I have never heard of this phenomenon before. I always thought a volt was a volt, an amp was an amp when it came to solar. Do you have any theories as to why your panels performed so much worse in series than in parallel?  Did you try this experiment with matching pairs of panels? or are they mis-matched?

[ChrisOlson]

I have never heard of this phenomenon before. I always thought a volt was a volt, an amp was an amp when it came to solar. Do you have any theories as to why your panels performed so much worse in series than in parallel?  Did you try this experiment with matching pairs of panels? or are they mis-matched?

Yes, I figured out why it was happening.  The open voltage of my panels is about 17 volts.  The difference between that and a floating 12 volt battery bank is 3.5 volts.  When I wired them series the open voltage is about 35 and in direct sunlight it goes to 40.  I do not know why I get more open voltage from the panels in series to an extent that's out of proportion from what a single one has for open voltage.  Perhaps somebody here who knows more about solar panels could explain that.  They're 123 watt Sharp modules.

At any rate the 24 volt bank floats at 27 so there's a huge difference between the "clamp" and the open.  The solar installer where I bought the panels said I'd need an MPPT controller to operate the panels at higher voltage for the 24 volt.  It was $500 for that controller so I did it the "cheap" way.
--
Chris

[madlabs]

Wow, never realized how attached folks can get to a voltage.

Me, I went with 12V for two reasons:

1)- plentiful and cheap used/new gear. Everyone is going to higher voltages, so 12V stuff is for sale cheap. I got a Trace 2512 for free.

2) My panels, batteries and inverter are all located very close to each other, so the larger wire cost isn't so bad. I have a shpping container that has the panels on the roof and the batteries and inverter inside. So my panels need less than 25' of wire to get to the batteries.

If I had a 3 story house the wire cost might have changed my mind. It does bum me out a little with my windmill, over 100' total run. I have a tiny mill right now, but if I go for a real mill the wire ain't gonna be cheap.

Jonathan

[ghurd]

Typically, the series amps (proportional) will increase a small percentage.

If the amps decrease it would be due to 'the weakest link'.  Matching the individual panels for output amps at 17V working voltage would help considerably.  Connecting panels so the pair (or 4 for 48V) is seeing the same conditions helps... like if the lower portion of the rack gets some shading when the upper portion does not, then series then so shaded PVs are with shaded PVs, and full sun PVs with full sun PV.
It is the same reason PV name brand manufacturers assemble PVs with matched cells.

The open voltage is almost always more than 20V.  ~17V is typical peak power voltage.  When the 17V open was measured, there must have been an anomaly.
G-

[ChrisOlson]

The large wire cost difference is from the generation points to the battery.

Yes, but I got around that for years by using short runs and multiple input sources consisting of three small turbines and using the 10 AWG spools of wire that came with my solar panels to run five parallel positives and negatives from my 1,230 watt solar array to the solar combiner panel, and then a #4 battery cable from the combiner to the bus, which is only about 2 feet long.

When I replaced the turbines with the 12G machines I ran into an issue with 130 amps from one turbine.  So I bumped my system to 24 volt to accommodate that, which basically only involved replacing the three smaller inverters with one big one and rewiring my bus.  When I did that I did change my controllers out with a Morningstar RD-1 because I needed more precise load control with the higher-capacity system.  That RD-1 cost me another 130 bucks but I've been really happy with it.  I could sell my 12 volt inverters, and I'm going to sell one of the 3 kW units.  But I'm gong to save the other two for spares in case my 24 volt would ever go down because I can switch the whole system back to 12 volt for an emergency in about 30 minutes if I had to.
--
Chris

[ChrisOlson]

When the 17V open was measured, there must have been an anomaly.

Glen, I didn't actually measure that.  I just remembered that's what it said in the papers that came with the panels and maybe that was the "rated voltage".  I did measure the open on the series connection when I found out I was not getting the power from my panels on 24 volt that I had gotten previously on 12.

I"m not sure I totally understand what you said in the rest of your post there.  Are you saying sort of what the installer told me where I bought the panels?  Which is basically that I needed a MPPT controller.

My panels are never shaded.  Except for one anomaly where I screwed up.  In the spring and fall from about 9:30 to 10:30 or so in the morning, one of the turbines throws shadow flicker from the blades on that array.  When I put all that in there it was summer and the sun was straight up.  I forgot that the sun heads down to the Caribbean for the winter and on it's trip down there, it causes this problem for an hour everyday.
--
Chris