Working to figure out what I don't know.

Denman

So thrilled to have found this forum. I'm reading through threads and hope to find my answers within them. My current system is having some problems, as I see many of us that are new experience.

My battery bank of Rolls Surrettes S-460 is a 48v bank, 2 strings. I've about 2 KW in panel generation with an outback flexmax 60 for a charge controller with a Magnum MS4448 inverter. My backup generator is a Generac 8KW.

My arrogant ignorance led me to order a packaged off grid system that came with maintenance free batteries. I went through those in about 2 years due to not properly setting up the charge controller and boiling them dry. When ordering the double string of Rolls I partnered with the fellow that is their distributor and thought I had this figured out. Thank goodness I've so far been able to afford my mistakes.

I've yet to find a nice spot with the appropriate formulas to apply to my amp charging rates and times for my system, but I'll keep hunting. I see folks here using the formulas for that and I'm betting when I apply them it'll answer a lot of what appears to be magic at this point. I have figured out that my current battery set up (almost 2 years old) should be adequate for me needs with only an 85% draw down rate based on my average daily useage. I'm going to have to bite the bullet and start doing that specific gravity reading thing. I know, I know, I should have been doing it all along but I avoid it like the plague. I see that is one of the very best ways to determine appropriate charged levels and system health. I also see that the apparent weakness in my current might be overcome by bulk charging in the mornings and letting the sun/panels do long absorb charges to help restore apparently lost capacity. My current set up sees mid day charge rates that max out at about 40 amps.

Hey, I'm a powerlineman I figured I could figure this out by trial and error. At this point and investment level I'm thinking it's time to be a bit more detailed and pragmatic in my approach and a bit less wha-hoo.

Thanks for being here, I appreciate the level of professionalism that's brought to bear.

Denny

westbranch

Re: Working to figure out what I don't know.

Welcome, the first thing to do is fill a complete description of all your equipment's settings and specs so we will know where to start point you towards. First thing I didn't see was a Charge controller...
Also post a brief description of where you started and have come to in your problem solving.
go to your profile settings and add it to the Signature line
cheers

Cariboocoot

Re: Working to figure out what I don't know.

Welcome to the forum Denny.

Let's see, two parallel strings of S460's? That would be 700 Amp hours @ 48 Volts. It is not likely a 2kW array will be able to properly recharge that. It's about half the size you'd need in fact. I'm surprised you get 40 Amps from it; you're probably up a mountain in Colorado.

I'd suggest you re-evaluate your power needs and see if you really have to have 16kW hours stored capacity (at 50% DOD). Chances are you don't, if you're not using 8kW hours per day.

Your "85% draw down rate" doesn't actually make sense. I think you mean you're only discharging to 85% SOC, which means you'd be using roughly 105 Amp hours. If so you could have done this on two parallel strings of GC2's (440 Amp hours) for a lot less money and have a much better charge rate.

So maybe when these expensive Surrettes have taught you another lesson that might be what you want to do? Until then Bulk charging with the gen and letting the panels finish the process is indeed the best plan.

Denman

Re: Working to figure out what I don't know.

so from what I'm seeing on the forums and answers my PV is laughably low to recharge 720 ah of batteries at 48v. (57v charging voltage). I'll need to add about 4 KW in panels and change my flexmax 60 to something adequate to handle the loads/charging currents. Am I on the right track? I'm using this answer to base my evaluation on:


*******************************************************************************************
•8,000 WH per day * 1/0.52 system end to end AC efficiency * 1/3 hours of sun = 5,128 Watt array minimum

And if you aim for 2 days of storage and 50% maximum discharge (good cost effective optimum for most people), a 48 volt battery bank would be:

•8,000 WH per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt battery bank = 784 AH @ 48 volt battery bank

And to double check--We suggest a 5% to 13% rate of charge for your battery bank--With 10% to 13%+ being desirable (if you have the room and the money for the panels). 5% rate of charge can work, but mostly if you charge during the day and use the power at night (and typically for weekend/seasonal cabin):
•784 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge= 3,004 Watt minimum array
•784 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge= 6,007 Watt nominal array
•784 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge= 7,809 Watt maximum "cost effective" array

So, based on some quick rule of thumbs design--A 5,128 to 7,809 Watt array would be a good range, with 6,007 Watt or larger array being recommended for a full time off grid home.

Battery bank capabilities--You could justify a 7-8 kWatt maximum AC inverter (another rule of thumb ~1kWatt inverter per 100 AH @ 48 volt flooded cell battery bank).

The system is certainly doable--But not small and you would want to get some knowledgeable help if this was your first system--Especially if you have not had much experience wiring a house or large boat/DC power system before.

Also, remember that while your solar array should last 25 years, the batteries may last 7-10 years (you can get 15+ years from Forklift batteries), and the major electronics will have a good life if they last 10+ years between replacements (may need repairs at 5+ years for charge controllers/AC inverters).
***************************************************************************************************

So since my normal loads are on the small side, my well pump and occasionally a larger appliance like a dishwasher, I would estimate that I can continue to use my 4 KW inverter but would need to ramp up the capacity of the charge controller. In the meantime would it be good to do what I saw elsewhere here to charge the bank back closer to health? That being run the generator to bulk and then let the panels charge for 6 hours on absorb?

Gosh there's good info here. I'm like a kid in a candy store!

Denman

Re: Working to figure out what I don't know.

Wow that was a fast reply, so fast I didn't even see it

Denman

Re: Working to figure out what I don't know.

Thanks to both of you. I'll go add info to the signature line right away.

I am, indeed, at 8600 feet of altitude and on the side of a mountain. My daily useage averages about 4500 watts total. We'll hit 6 KW on a weekend if we're really partying hard.

I did indeed mean 85% SOC, the powerlineman in my gets things confused. I like to say you could teach a monkey to do what I do, and it's really fun to learn this stuff.

Good news that I could actually downsize the battery bank, thanks for that tip. My long term plan is to have a complete duplicate system installed on my partners art studio with throw over breakers to backfeed in case of inverter breakdown and other problems. I like redundancy.

westbranch

Re: Working to figure out what I don't know.

that center part of post 4 looks like BB's work ??

Denman

Re: Working to figure out what I don't know.

I'll have to go back and look. I didn't credit properly I think, and error I'll not make again. It was by gww1.

Cariboocoot

Re: Working to figure out what I don't know.

westbranch wrote: »

that center part of post 4 looks like BB's work ??

Yes: you can tell by how long and involved it is; Bill loves to write.

Me ...

70 Amps @ 48 Volts / 0.77 (typical efficiency) = 4363 Watt array.

Your elevation obviously improves the efficiency ratio so you could get away with a smaller array, say 3kW or a bit better. But the FM60 will only handle 60 Amps so yes to make full use of the larger array you'd need an FM80 or Classic 150.

On the other hand 4.5 kW hours a day on a battery system is manageable from a 2kW array in 4 hours of good sun, so again the array size is not so much the problem as the battery bank being larger than needed.

Denman

Re: Working to figure out what I don't know.

Here's a fun question.... given my relatively low useage and overage of battery storage would it be most sensible to divide those battery strings with a switch and charge them alternately? Would that be closer to a proper panel to battery bank ratio and a good solution until I build my next project with it's own system? That would be a 350 ah 48v bank with about 2 KW in solar charging.

Cariboocoot

Re: Working to figure out what I don't know.

Denman wrote: »

Here's a fun question.... given my relatively low useage and overage of battery storage would it be most sensible to divide those battery strings with a switch and charge them alternately? Would that be closer to a proper panel to battery bank ratio and a good solution until I build my next project with it's own system? That would be a 350 ah 48v bank with about 2 KW in solar charging.

I've actually tried the dual battery bank thing myself. Went crazy trying to remember "who's on first?"

But if you think you can keep track 40 Amps into a 350 Amp hour battery is no problem and your DOD would be around 30% which is also no problem.

Maybe you could start building "system 2" around half those batteries?

westbranch

Re: Working to figure out what I don't know.

Lots of issues with 2 separate banks and 1 CC.

IMO since you have the Genset to BULK charge the present setup is good enough for the present until you add/change the CC to handle the max amps... just don't deplete too much, use the gen for those large predicable loads

Denman

Re: Working to figure out what I don't know.

I'm thinking that would be the best way to go. Building system #2 using half the what-the heck-was-I-thinking oversize battery bank. That means I have to put up a building! I'll hunt your site for a nice throwover switch. I'm guessing there's something that will bridge and break loads (like we do in the powerline industry) that I can mount for the throw over and that I'll only have to put it on the positive lead and not both? I'll do that for a while and get my dear sweet wife to work pouring a foundation for her studio. . I'm guessing I can alternate once or twice a week and put a reminder on that silly smart phone of mine. It'll be a good interim solution.

I'm thinking the short-long term solution would be to get a flexmax 80 from the site here. That would probably just swap out with my flexmax 60? That and pick up another KW or so of panels.

Denman

Re: Working to figure out what I don't know.

Thanks. I'll go see what yall in in the panel market here on the site to pair up with my current 220w Trinas (3 parallel strings of 3 series panels).

BB.

Re: Working to figure out what I don't know.

Reads like me...

Start with your desired (winter/summer, daytime vs nighttime, minimum loads you are willing to live with during winter, etc.).

The rest all sort of falls out from that knowledge (assuming you have good sun/no trees/mountains killing your output between ~9am and pm). Batteries tend to be expensive and are a consumable. Very roughly, a 2x larger battery bank will last 2.2x longer--And cost 2x more to replace. So--falling back to 4 times your daily load (2 days of storage for bad weather, 50% maximum discharge) seems to be an optimum for most people.

If you have large surge current, you may need a larger bank. Note that a larger battery bank "forces" a larger solar array, larger backup genset+battery charger etc...

Which comes to the end, which is really the beginning. Know your loads and conservation (insulation, LED lighting, Energy Star Appliances, laptop vs desktop computer, LED TV, turning stuff off when not used, etc.) is almost always a better investment than a larger off grid power system.

You have a working system--I am not a believer in separating the two battery banks, unless one battery string will support your needs and you can re repurpose/sell the other battery sting.

Look at how it is working for your needs. Perhaps a larger array is the answer (it sounds small)--But if you only need 1/2 the battery bank (i.e., 1/2 the bank will support your 25% per day power needs+existing array)--Less is more.

Things like well pumps can have tremendous surge loads (and even running loads). Many utility connected homes have 1-2 HP pump, when a 1/2 HP pump would be sufficient. And there are some very nice pumps (not cheap) that are off grid friendly. Virtually no starting surge, ~600-900 Watt power draw, etc.

Refrigerators, Well Pumps, and fans frequently are what drive the design and over-sizing off off grid power system. If it was not for those two to three items, many folks could get away with a 1-2 kWH per day life style.

With off grid systems, the details matter.

-Bill "it's the narrative" B.

Denman

Re: Working to figure out what I don't know.

So nice to get to read you.

We rebuilt our old modular with massive insulation, all LED lighting and run propane for most large loads. Our refrigerator/freezer is propane as is the on demand water heater and for the winter season we have a gas clothes dryer, energy star. Our large loads are the well pump which is a grundfoss slow start model and an energy star freezer that we keep where it's shady and cool. On my battery monitor on the Magnum ME-ARC control it appears that the well pump draws about 18 amps for less than 4 minutes running time to charge the pressure tank. That well pump is on a timer so that it never runs unless the sun is well up. When we need to use that during a winter evening we fire up the generator. Using my utility experience, we practice a lot of load management. We never run more than one largish thing at a time, the exception would be if the clothes washer is running and kicks on the well pump. We do the laptop thing instead of a desk top, heat with wood exclusively, and love having adjusted our life to as much of a diurnal schedule as we can manage.

My partner has given me the kind head-nod to upsize our panels/charge controller to match our battery bank. Having a longer time between replacements and more of a cushion for cloudy days appeals to us. Now if someone will just hit a pole on a Sunday for that double time .

Denman

Re: Working to figure out what I don't know.

I think I'm getting a handle on which way to go here. Thanks to the opportunity to listen to folks that know what they're talking about.

With my current 9 Trina solar panels @ 220 watts each, I think the best way to go would be the "Kyocera KD255GX-LFB2 255 Watt Multicrystalline Solar Module" that are here on the site. That would mean a generation of 3500 watts and about 65 to 70 amps at optimum sun. Upgrading my current flexmax 60 to a flexmax 80 would handle the current coming in from the panels and make an easy change out on my Magnum inverter. My present input voltage from a series set of 3 Trina panels is 101 to 104 volts at max. Would it be best to get a new Solar Array combiner (currently a Midnight Solar MNPV3) and add the new panels as a 4th circuit into the combiner, or go from 3 panels in series to 4 panels in series? That would make the input voltage somewhere between 135 and 140 vdc. The flexmax 80 has a max input voltage of 145 vdc. I'm guessing it's not good to cut it that close? Another combiner won't break the bank and I can always use the other one when I build my redundant system on another building.

BB.

Re: Working to figure out what I don't know.

There are string calculators on most Mfg. sites... However, it works out that Vmp~100 VDC is about the maximum (standard temperature value from data sheet) for cold climates (works out that Voc-cold is less than ~140 volts). Here is Outback's.

http://www.outbackpower.com/outback-support/string-sizing-tool

You don't need a new charge controller--It is perfectly OK to put two smaller controllers in parallel to the same battery bank. But having a larger single controller is nice too.

Roughly, the "sweet spot" for an MPPT controller is to run the Vmp-array about 2x the battery bank voltage. But the higher voltage you go, the (slightly) less efficient the MPPT controller is. However higher array voltage can dramatically reduce copper wire diameter/costs (2x voltage, about 1/6th the cost of the copper wire--And/or you can have a longer distance between the Array and the Charge Controller/Battery shed).

Do a couple of paper designs and (roughly) cost them out--See what works best for you.

-Bill

BB.

Re: Working to figure out what I don't know.

I should add--You sound like a 3.3 kWH per day system is within your power needs. I cannot think of anything off hand to reduce your electrical loads.

Solar thermal may reduce your wood/propane needs--But deep in the dead of winter, there is little solar RE can do for you.

-Bill

Denman

Re: Working to figure out what I don't know.

I'd love to add wind at some point, that would help out since we get a good deal of it. But I'll wait to tackle learning THAT pile of new info until after I've gotten this deflugelty patched up. I've poured the foundation for some passive solar heating and that'll help a bit in the winter. (we get to -30 routinely). And the future calls for some assist on the incoming water temp for our on demand water heater. This stuff is pretty fun to figure out, as long as I can afford my mistakes!

gww1

Re: Working to figure out what I don't know.

denman

I'd love to add wind at some point, that would help out since we get a good deal of it.

First let me say I like my wind and may even build bigger.

My opinion money wise, You would be better getting a bigger battery and more solar then you would with wind unless you get lots (blow your hat off type) of wind all year.

Why do I say this,
1. If you get a turbine big enough to help it is real hard to control when you get lots of wind. solar is easy it just shuts down and you don't need a way to load it.

2. If you haven't bought stuff yet and you buy solar and a bigger battery then you can run longer during bad times and put less stress on your stuff during good times making it last longer.

3. It is never the turbine that cost but the tower and dumploads and long wire that cost.

I go maby 4 months where I average 0 production and then when it does get real windy for one day I have to find ways to keep a load on the turbine without letting the battery voltage go to high. Solar is pretty cheep and you can mostly plan for it.

I read a post from member chris olsen where he was saying that using a deisel generator was cheeper then doing wind and he has 7kwhs or more worth of turbines and says solar due to overcast doesn't work as well in the winter.

All that said, I still like my turbines cause I had fun building them and can think of worse hobbys. I would have more usable power had I put all the resources towards solar.

If you live in a shady area that you have to cary something heavy all year when you go outside so you won't be blown away, forget all my above statements.
Cheers
gww

Denman

Re: Working to figure out what I don't know.

Given that I am now getting a handle on this sizing thing ..... the wind will be more of a hobbiest exercise and learning experience than good bang for the buck as you point out. We've lived in our middle-of-nowhere for about 4 years now and when we get wind corresponds pretty well with when our solar gain is lowest. In winter it might well blow all night and the next day will often be overcast.

The mounting is a fun challenge for me, and this is where my power company connections come in well. A couple years ago, for fun, I set a couple 60' poles on our place and have access to junk parts for steps and mounting hardware that I can adapt for mounting the turbine. Being able to use the excess capacity in resistance heating would take some of the load off my direct vent propane heater that keeps my battery enclosure/utility building at 62 degrees F. It'll give me a good excuse to grab my hooks and check things out once in a while .

With our redundant system in another building also supplying a ready back up on the solar side I think it might be a fun experiment. I much appreciate the advice and will use it to approach this in a more conservative light, choosing to spend more of my available funds on the redundant solar set up.

And I think I'm going to order parts today.

Denman

Re: Working to figure out what I don't know.

I have a breaker sizing question for the upgrade of my current system.

The breakers for the new midnite solar combiner box are pretty easy to figure. I'm wondering if my current 63 amp breaker in the magnasine MS4448-PAE, on the input from the combiner box will be sufficient. I currently get a max of 39 amps from my Trina modules and the new Kyocera panels should supply in the range of 16 amps based on the historic efficiencies I see. That should be good since it will be around 55 amps. In my industry (powerlines) we usually oversize our fusing a bit, but at the same time we know that supplied fault current has to be in excess of the rated breaker size to cause the breaker to blow. This is what has me wondering.

Oh and I finally figured out that signature thingy. Pesky error messages, apparently I'm too wordy.

BB.

Re: Working to figure out what I don't know.

As I recall from years ago... The Outback (and Midnite?) 63 amp breaker is an anomoly compared to the rest of the US/NEC/UL breaker world.

The 63 Amp Outback breaker is design to run at 60 amps (or maybe 63 amps) of rated load. All other breakers are designed to "trip" at rated load (eventually), and should be derated by 0.80 for continuous current if you want 60 amp branch circuit:

60 amps * 1.25 NEC derating = 75 amps (rounded up to 80 amps) breaker/fuse requirement.

Find the specs. for that breaker to confirm.

-Bill

Denman

Re: Working to figure out what I don't know.

Perfect. In that case the two breakers in my Magnasine panel will now be upgraded to 80 amp breakers. I've found them and though a bit pricey figure the safety is worth it, not to mention the part about getting it all put together and then having to tear it all apart due to tripping breakers bit. Personally I'd prefer to only do this upgrade/repair/reconfigure thing once. Thanks again.

BB.

Re: Working to figure out what I don't know.

Of course, you have to make sure the AWG of the branch circuit wiring meets code for 80 amps too.

-Bill

Denman

Re: Working to figure out what I don't know.

Yes sir, because a frying wire is really just a long stinky fuse.

Denman

Re: Working to figure out what I don't know.

Hey! No one hit a pole but some underground primary went bad. That little pile of double time means I just ordered all my parts!

Denman

Re: Working to figure out what I don't know.

I just figured out something else I didn't know. You can't just mix new panels with panels that have been up for 4 or 5 years. Back to the drawing board for me.

westbranch

Re: Working to figure out what I don't know.

who says? You can if you match the output within about 10% of Voltage on the same wattage or more if in parallel.. The combined out put will be at the lowest rated panels output... eg a 130W and 140 would give you ~ 260W. Does that make sense?

Cariboocoot

Re: Working to figure out what I don't know.

westbranch wrote: »

who says? You can if you match the output within about 10% of Voltage on the same wattage or more if in parallel.. The combined out put will be at the lowest rated panels output... eg a 130W and 140 would give you ~ 260W. Does that make sense?

Even this is not exactly correct as panels are a current source. On a PWM controller if the Voltage is within 10% the current will be Imp + Imp (parallel connection). Even on an MPPT controller the Voltage differential does not cause significant losses above 10%, and it's still better than not adding the extra PV.

The old idea that panels lose some high amount of capacity over time has largely proven to be a myth, as many quite old panels are still producing within spec.

The biggest problem with adding panels later is finding some that are specification compatible with the older ones. My 175 Watt Sharps, for example, are no longer made and other panels with a Vmp around 35 are now not that common. But they do exist.