Help me expand this system?

Chris Miller · April 2013

Hey everyone,

We're ready to make the leap with our solar. We're currently running 1000 watts of panels and 8 trojan T-105 RE's.

We're going to sell the 100 watt panels and we're looking to move up to around 3000 watts in panels and also add some more batteries too.

At this point, i'm trying to find some good panels around $1 / watt and i'll have to have them freighted in - we're in a pretty remote place.

Any recommendation on the best way to expand this system? I have an FM-80 charge controller so I have to consider it's limitations of 80 amps and 150 volts. I'm currently configured as 48 v battery bank and would like to keep it that way I think.

How many panels? Best wiring configuration? How many batteries to add?

I've also got a 3000 watt wind genny that will be tied to the new upgraded system.

Thoughts?

Cariboocoot · April 2013

Re: Help me expand this system?

Adding new batteries to old is not the best idea. How old are they, and how much have they been used?

Otherwise with one 80 Amp controller on a 48 Volt system you could run a really big battery bank, if you need it. We're talking 800 Amp hours @ 48 Volts for up to 19 kW hours stored power. We're talking 5kW array.

So the question really is: what do you need? No sense buying gargantuan battery banks and humungous arrays if you have lilliputian power requirements. Always design around load requirements.

Chris Miller · April 2013

Re: Help me expand this system?

The batteries are only about 6 months old... hoping adding new ones will be OK.

The thing is, we're only using 7kwh a day right now but our needs are growing. We'll be adding an inverter based mini split A/C that we'll run occasionally and it uses 650 watts. My kids are also getting into rock tumbling and those tumblers run 24/7 and we're looking to add another fridge.

I already ran into this issue where I started with 1000 watts and expanding on that isn't very easy so i'm having to start over. I would rather put in 3000 watts+ and just know that i'll have what I need.

Chris Miller · April 2013

Re: Help me expand this system?

Thanks for the reply by the way...

westbranch · April 2013

Re: Help me expand this system?

so what did your first load analysis look like? Add the tumbler et al to the original analysis and see where you want to get to...

hth

Cariboocoot · April 2013

Re: Help me expand this system?

Chris Miller wrote: »

The batteries are only about 6 months old... hoping adding new ones will be OK.

Should be fine if under 1 year and not abused.

The thing is, we're only using 7kwh a day right now but our needs are growing. We'll be adding an inverter based mini split A/C that we'll run occasionally and it uses 650 watts. My kids are also getting into rock tumbling and those tumblers run 24/7 and we're looking to add another fridge.

Only 7kW hours per day? What's "only" about 7kW hours (asks the man who lives on less than half that)? Another 'frige will plug in another kW hour. Rock tumblers ... give 'em a crank and tell 'em to turn it over by hand.

They're only little motors, but running 24 hours adds up.

I already ran into this issue where I started with 1000 watts and expanding on that isn't very easy so i'm having to start over. I would rather put in 3000 watts+ and just know that i'll have what I need.

What you could get with a 3kW array would be about 6kW hours + using the minimal 4 hours of sun. If you're managing 7kW hour off a 1kW array it's either a miracle or you keep using the generator.

Really if you're going to tack on another 2kW hours of power the 3kW array will not do it on its own. You would be relying on having 5.5 to 6 hours good sun every day. Is that likely?

I'm not being nasty; I don't want to see you get disappointed with your system's performance again.

Chris Miller · April 2013

Re: Help me expand this system?

Ok, here below is what I came up with. We're regularly producing 6-7 KWH per day from the 1k in panels. We are having to run the generator every couple of days though. After looking at this list, we're using a lot more than the 7 I thought. It's probably more like 9 to be honest.

Not exactly sure how sun hours are tracked but our solar picks up the sun and starts charging by 9am every day and the controller doesn't go into "sleep" mode until around 7-8 at night when the sun goes behind a mountain. 79852 is our zip.... LOTS of sun here for sure.

Here is the new load chart with adding in some future loads. We still need to consider a TV for about 2 hours a day but I don't have one to test.

SOLAR USAGE

New Whirlpool Freezer - 1.35 KWH inside building in March
Small Freezer setup as fridge - .25 kwh inside uninsulsted small building

Lizard Heat Lights: 1.69
Lizard UVB Lights 1.118
Bug Zapper: .036
Desk Fan: .1266
Desk Fan: .1266
Bed Lamp: .030.
Bed Lamp .030
Rock Tumbler: .576
Rock Tumbler: .80
Computer: .84
Computer: .84
Bedroom Fan: .40
Ipad: .036
Ipad: .036
Internet: .192
Phone: .048
Answering Machine: .048
Office Phone: .120
External HD: .168
Microwave: .396
A/C: 3.9

13.157 KWH

Cariboocoot · April 2013

Re: Help me expand this system?

13+ kW hours? Ow. You got an oil well on that property somewhere? Gold mine maybe?

So let's say you can get 6 hours of good sun every day and can make use of 'surplus' solar to improve the over-all efficiency somewhat. A 3kW array may still be small: 3000 Watts * 6 hours equivalent good sun * 0.6 over-all efficiency = 10.8 kW hours.

Notice you say you have to run the gen every couple of days. That indicates deficit charging on those solar-only days.

If we use the standard rules-of-thumb and try for the full 13+ kW hours on a 48 Volt system you'd likely have a 1200 Amp hour battery bank (25% DOD). We're talking forklift batteries here or 2 Volt cells. Then you'd need like 120 Amps @ 48 Volts to charge it or about 7480 Watts of panel.

Check the numbers for sun in your area using PV Watts http://www.nrel.gov/rredc/pvwatts/grid.html
It's actually designed for grid-tie, but will give you an idea of what to expect throughout the year.

Cariboocoot · April 2013

Re: Help me expand this system?

You might want to get a battery monitor and wire it in to your existing system and watch the in/out Amp hours over a few days and see how it balances up. It could provide some very valuable information.

Chris Miller · April 2013

Re: Help me expand this system?

Not really sure what I am looking at here:

Attachment not found.

Question for you.... would running a 4000 watt array require a change in batteries or could i just add extra T-105 RE's? We're really just wanting to install as much as we can afford right now and deal with the rest of the stuff later. If we have to make adjustments to our usage then that's what we'll do.

Cariboocoot · April 2013

Re: Help me expand this system?

Problem you run in to with running a bank made entirely of T105/GC2's is that you end up with a lot of parallel strings of batteries. This increases the possibility that they won't share current evenly, and so some will do more work than others with the net result that they all die prematurely.

4000 Watts of array should yield enough peak charge current for about 640 Amp hours @ 48 Volts.

That would be about three strings of T105's or is 675 Amp hours. At this point you should have equal length wires in and to all strings connecting them to a common point (bus bar). It will work, it's just not "ideal". The same three parallel strings @ 12 Volts would be more likely to have trouble as the resistance is lower for 12 Volts batteries than 48, so small changes in wiring resistance have more effect.

With that much battery you would have about your 14kW hours at 50% DOD. Depending on how much load is drawn in daylight (when it can come from panels once the batteries are charged) it could work.

northerner · April 2013

Re: Help me expand this system?

If I was in your situation, I would consider ditching the batteries you have and get larger ones. L16's are a good compromise between what you have now, and fork lift batteries or equivalent. Generally speaking, larger batteries will cost more up front, but will potentially give you a longer life span, with more bang for you buck in the long run.

Also, it appears that you are building a fairly large system, and smaller batteries will lead to more parallel strings and liklely even shorter life. But you must also consider the loss you'd take in selling the T 105's, if you go that route. Hope that helps with your decision, and good luck with your system expansion!

Photowhit · April 2013

Re: Help me expand this system?

I think we are forgetting that he likely has sun and longer days for when he needs the air conditioner. I'll run an A/C during the summer and need roughly the same 13-15Kwh, on a 800 Amphour 24v system.

I think I would shoot for the 4Kwh array and 2 strings of T105's which would be a 450 Amp Hour 48V battery bank. I'd use them 'til they die and then look into replacing with a forklift/traction battery.

I'm not sure where the maximum array size is for the FM80 with out much clipping, I would think you could get close to a 5Kw array and you might find you need it, but if you have little concern for the panels matching, you might start with 4 Kw.

Are you in the south western US?

northerner · April 2013

Re: Help me expand this system?

Photowhit wrote: »

I think we are forgetting that he likely has sun and longer days for when he needs the air conditioner. I'll run an A/C during the summer and need roughly the same 13-15Kwh, on a 800 Amphour 24v system.

I think I would shoot for the 4Kwh array and 2 strings of T105's which would be a 450 Amp Hour 48V battery bank. I'd use them 'til they die and then look into replacing with a forklift/traction battery.

I'm not sure where the maximum array size is for the FM80 with out much clipping, I would think you could get close to a 5Kw array and you might find you need it, but if you have little concern for the panels matching, you might start with 4 Kw.

Are you in the south western US?

Even without the a/c, he claims to be using over 9 kwh per day, which is quite significant. I have an equivalent amount of storage, although, currently only have a 1.4 kw array, and find I am running into the problem where, when the sun is shining, I just don't have the storage capacity to take advantage of the extra production. I only have about 1 1/2 days of storage, and I use less than 7 kwh per day on average. I live in a fairly sunny place, yet find that I still need more storage.

Photowhit · April 2013

Re: Help me expand this system?

northerner wrote: »

Even without the a/c, he claims to be using over 9 kwh per day, which is quite significant. I have an equivalent amount of storage, although, currently only have a 1.4 kw array, and find I am running into the problem where, when the sun is shining, I just don't have the storage capacity to take advantage of the extra production. I only have about 1 1/2 days of storage, and I use less than 7 kwh per day on average. I live in a fairly sunny place, yet find that I still need more storage.

I think your still new yet and don't understand that you must have waste with an off grid solar system...
...sorry for being blunt, but it's hard to sigh or shrug your shoulders on a forum.

I wouldn't have him throw out his batteries now, if he is in an abundant sun area he will likely use 20-30% of his load over night...

If my solar array isn't producing more energy than I can store, my system WILL FAIL!

northerner · April 2013

Re: Help me expand this system?

Photowhit wrote: »

I think your still new yet and don't understand that you must have waste with an off grid solar system...
...sorry for being blunt, but it's hard to sigh or shrug your shoulders on a forum.

I wouldn't have him throw out his batteries now, if he is in an abundant sun area he will likely use 20-30% of his load over night...

If my solar array isn't producing more energy than I can store, my system WILL FAIL!

What you say is true, there will be waste with an off grid system, and I'm well aware of that. Also, you don't have to feel sorry for being blunt. After all, it's all in good fun, and that's something I'm having with my system.:D

However, I'm running into a problem where I don't have enough storage to get me beyond 1 1/2 to 2 days, which is not enough for my usage of less than 7 kwh per day. I often find that my batteries drop down to a 50% to 60% state of charge by morning. I also get plenty of sun where I live, but there are also cloudy stretches, where solar output is reduced significantly. Of course one could try to counter the lack of storage by either allowing for more generator run time, something I prefer to minimize. Other option is to have a large enough solar array, to help get you through the cloudy stretches. In my case, I will be doubling my array size, which will certainly help, but I also still plan to add another bank of at least 4 batteries.

So it's important to look at the options to find the right balance. More batteries put you in a better comfort zone, meaning less daily DOD and longer battery life. On the other hand, batteries are currently the most expendable part of the system, which have a finite lifespan, and adding to a solar array is a relatively cost effective method to consider as well.

westbranch · April 2013

Re: Help me expand this system?

northerner wrote: »

However, I'm running into a problem where I don't have enough storage to get me beyond 1 1/2 to 2 days, which is not enough for my usage of less than 7 kwh per day. I often find that my batteries drop down to a 50% to 60% state of charge by morning.

So tell us just what is running at night and what the SoC is before retiring for the night? ie can you do any load shifting?

vtmaps · April 2013

Re: Help me expand this system?

northerner wrote: »

More batteries put you in a better comfort zone, meaning less daily DOD and longer battery life

Not necessarily... If your battery bank is large enough to give you 3 or 4 days of autonomy and you have multiple sunny days in a row, you may find yourself with very shallow overnight discharges. This is not good for batteries.
From the NAWS battery FAQ:

a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film.

Over at BatteryFAQ.com they make a similar statement, but consider that even 10% discharges are harmful.

northerner wrote: »

I don't have enough storage to get me beyond 1 1/2 to 2 days, which is not enough for my usage of less than 7 kwh per day. I often find that my batteries drop down to a 50% to 60% state of charge by morning.

2 days of autonomy sounds very balanced. It's not so bad to drop down that low. Deeper discharge cycles may (over the lifetime of the battery) actually yield a better ratio of dollars spent to kwh stored and released. Many industrial battery manufacturers suggest 80% DOD per cycle as the most cost effective... the battery won't quite last twice as long at 40% DOD per cycle.

Of course, in those situations there are no partial (or mini) cycles which are inevitable in a solar RE system.

--vtMaps

northerner · April 2013

Re: Help me expand this system?

westbranch wrote: »

So tell us just what is running at night and what the SoC is before retiring for the night? ie can you do any load shifting?

I can't do a whole lot with load shifting. The majority of my usage is either needed all the time (ie fridge, furnace fan, other phantom loads that need to be on, etc...), or is at night and in the morning. Part of the problem is that my current solar array size is just too small. But, even after fully charging the batteries, it's a little disturbing to see how fast they run down. I'm usually at about a 75% state of charge when I retire, and as mentioned, often drops down to about 50 to 60% by the time the sun comes around. Of course, the arrival of summer will bring more production, with less consumption. My furnace fan is the single biggest overall user in the cooler months, which tends to run more at night, despite turning down the thermostat to 15C.

The combination of a larger solar array and more storage will largely solve my problem. But I can see that if I were to just expand the array, I would still be regularly running it tight with the batteries! I think another bank of 4 will put me in a better comfort zone. Ideally, I would like to double my storage capacity. If batteries had a longer cycle life, I would definitely be doing that.

northerner · April 2013

Re: Help me expand this system?

vtmaps wrote: »

Not necessarily... If your battery bank is large enough to give you 3 or 4 days of autonomy and you have multiple sunny days in a row, you may find yourself with very shallow overnight discharges. This is not good for batteries.
From the NAWS battery FAQ:

Over at BatteryFAQ.com they make a similar statement, but consider that even 10% discharges are harmful.

--vtMaps

Good point vtMaps! But I was thinking of getting closer to dropping 20 to 30% on a regular basis. I didn't think about going to the other extreme and going too shallow!

The other down side about dropping to 50% on a regular basis, is there's little room for future expansion, if that's a concern? If your loads or needs increase over time, perhaps expanding a family, etc..., then it would be difficult to increase storage at a later date. Something for others to consider when designing their system. Going down to 70 or 80% on a regular basis put you on daily comfort level, and also allows for future expansion.

Of course new battery technology could eliminate this limitation with lead acid batteries, but there isn't an alternative, yet.

NorthGuy · April 2013

Re: Help me expand this system?

northerner wrote: »

Going down to 70 or 80% on a regular basis put you on daily comfort level.

That's true. But money that you have save by going regularly to 50% SOC instead of 70 to 80% SOC can add to your comfort level too

northerner · April 2013

Re: Help me expand this system?

NorthGuy wrote: »

That's true. But money that you have save by going regularly to 50% SOC instead of 70 to 80% SOC can add to your comfort level too

That's right!;) Depends on your point of view and circumstances.

Also, that brings up an extra question. How much extra life can one expect out of a set of batteries as they age and their capacity is reduced? If you use them regularly down to 50%, as they age that will bring them even lower. If you have the extra capacity, would you not expect more life out of the set with the reduced capacity? Or do they deteriorate fairly quick once they get more and more sulphated due to age???

Cariboocoot · April 2013

Re: Help me expand this system?

Regular deeper discharge = shortened cycle life, everything else being equal.
Curiously, so can insufficiently deep discharge (as in kept floating most of the time).

This is the reason for fudging things in the right direction, aka building in margins.
Round up usage figures, and figure the whole day's worth will come from the batteries (some will come direct from panels if you do this right). Base the battery capacity on that (25% DOD is preferable).
Figure out battery bank size, round up to the nearest available capacity.
Based the array on that number, round up to the nearest available units.
You have to be able to figure the amount of sun available too, and size accordingly (less sun = more panel).

Then over time even though the real capacity goes down the system will stay working. By the time you start running short of battery power they'd need to be replaced anyway.

A sure fire formula for getting into trouble is to try and shave everything to precise numbers. No one's usage, equipment, or weather is that consistent: such a system will fail sooner rather than later.

NorthGuy · April 2013

Re: Help me expand this system?

northerner wrote: »

If you have the extra capacity, would you not expect more life out of the set with the reduced capacity? Or do they deteriorate fairly quick once they get more and more sulphated due to age???

If you look at the manufacturing cycle life charts, you can put slightly more AHs through the battery if you cycle it deeper, but the difference is not big. So, from this viewpoint you don't save much money by cycling deeper. You save some energy because deeper charging is more efficient.

I've read somewhere that there's an aging process which kills batteries over time because of slow corrosion, regardless of the use pattern. If that's true, you want to get the whole cycle life out of your batteries before they die of old age.

northerner · April 2013

Re: Help me expand this system?

NorthGuy wrote: »

I've read somewhere that there's an aging process which kills batteries over time because of slow corrosion, regardless of the use pattern. If that's true, you want to get the whole cycle life out of your batteries before they die of old age.

So positive grid corrosion is the usual way deep cycle batteries die over time, providing one maintains them well? I always thought sulfation was an equally bad problem? I take it is dependent on your charging and usage patterns, and the size of the deep cycle battery. Bigger and thicker plates won't corrode as quickly as a one with thinner plates, but also have less surface area.

Cariboocoot · April 2013

Re: Help me expand this system?

Batteries are like people:

They start dying the moment they're born.
They're made of different components yet all have basically the same functions and needs.
Some will die sooner than others due to accident or misuse.
Some aren't made that well to begin with.
Others will suffer accidents, get repaired, but will not be quite the same afterwards.
Some are inherently more robust than others.
You can't expect them to be 100% interchangeable for any given job.
Over time they will lose strength, no matter what.
Eventually they die and no one can change that.
The best you can hope for is to look after them well, treat them suitably, and enjoy them while you have them.

/bizarre philosophical mode

NorthGuy · April 2013

Re: Help me expand this system?

northerner wrote: »

So positive grid corrosion is the usual way deep cycle batteries die over time, providing one maintains them well? I always thought sulfation was an equally bad problem?.

According to this, sulphation is much bigger problem.

However, as I understand, you can control sulphation by properly maintaining your batteries, or you can even reverse it. But you cannot stop or reverse corrosion.

northerner · April 2013

Re: Help me expand this system?

NorthGuy wrote: »

According to this, sulphation is much bigger problem.

However, as I understand, you can control sulphation by properly maintaining your batteries, or you can even reverse it. But you cannot stop or reverse corrosion.

There is a company that claims they can control corrosion.

http://www.batteryvitamin.net/

Does anyone know of or have experience with this approach, or is it a scam?

NorthGuy · April 2013

Re: Help me expand this system?

Cariboocoot wrote: »

Batteries are like people

Batteries need vitamins too

...

Cariboocoot · April 2013

Re: Help me expand this system?

Sulphation and corrosion are both chemical processes that begin the minute the battery is activated (plates "formed"). You can't stop either one, you can only slow them down to the point where they are a serious detriment to lifespan. There is a difference between "hard" sulphation that ultimately coats plates and prevents them from functioning and "soft" sulphation which is a normal part of battery operation (reversed with proper recharging).

When you put the components together the chemical reaction begins. You can speed it up, slow it down, even reverse it to a degree (recharging) but you can't stop it and still have a functioning battery. If you could it would be a "perfect" battery and not possible under the known laws of physics.

Beware the snake oil salesmen.

Help me expand this system?

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