Advice and Expectations

[Vic]

I meant to also state my latitude last time but I'm at 40 degrees north but instead of the mid-west I'm closer to the eastern seaboard in Roxbury NJ. Thank you for the time plots, I'll need that info soon enough in other considerations.

For right now I need to clear my mind on this last bank plan while I'm getting it wrapped around my load requirements. Basically from what I can tell my biggest worry is a load created by a 25K btu window a/c. That runs 24/7 only in the summer months with optimal sunlight. I would venture to say at best with lighting overall another 200 watts intermittent only at twilight, refrigeration ~ 4-500 Watts 24 hour period, another 125 Watts max for consumer electronics.

Thanks Mike for info on your location.

YES!!  That A/C  is a very large load.   It will need 2500 - 3000 watts to run,  and will have a very large starting current,  which  will require a stout Inverter,  and battery bank.   And,  when running from the battery,  will need about twice that amount of power for every hour it ran on battery to recharge it -- this is a large burden.

Often,  the designer of  Alternative Energy back-up systems will choose to run only basic loads,  and run a small A/C,  for example,   to cool only one or two rooms during Grid outage.

Also there are very efficient A/Cs available now that will reduce the start and run current vs BTU output,  but of course,  this requires a fairly large investment.

The little Honda generator that I mentioned earlier will not come close to being able to start or run your existing 25K BTU A/C.

You have a lot to study and digest.   That process will help the system that you design meet your needs and expectations.

FWIW,  my opinions.     Vic

[dgd]

Michael,

That battery diagram you posted shows two 6v 225h cells in series to give 12v at 225Ah. Then to reach a bank with capacity you think you will need you have proposed five  more of these 12v 225h strings all paralleled together for 12v at 1350Ah.
This would be the completely WRONG way to go. Charging parallel strings is problematic and individual cells can soon become stressed due to strings trying to balance the state of charge between individual cells. This is because all cells are not exactly identical and some charge faster/slower than others and some maintain a slightly higher charge (voltage) than others.
The solution is NOT to have parallel strings of cells.
Design your bank to use only one string of cells.
e.g.
So your designed 1350Ah 12volt bank is about 16Kwh capacity
The same capacity at 24volts would be 625Ah and 48volts would be 312Ah
To make a single string 48v bank the nearest cell size would be an L16 (6v at 380Ah to 425Ah depending on exact model), having eight of these in series would achieve a single string of cells with capacity about 19 to 20Kwh.

Designing a battery bank based on multiple small capacity cells usually means parallel strings.  A single string design usually needs higher capacity individual cells and higher bank voltage.

dgd

[vtmaps]

The solution is NOT to have parallel strings of cells.
Design your bank to use only one string of cells.
<snip>
To make a single string 48v bank the nearest cell size would be an L16 (6v at 380Ah to 425Ah depending on exact model), having eight of these in series would achieve a single string of cells with capacity about 19 to 20Kwh.

Actually, the OP will need 24 large 2 volt cells in a 48 volt configuration to handle his stated loads (over 20 kwh per day).   At least $20,000 of batteries.   The OP will need at least 180 amps of charging current and will have significant daytime loads.  The OP will need a 15,000 watt solar array and a 15,000 watt generator.

Michaeld,
you need to rethink your loads.  It will be much cheaper to conserve a watt than to produce and store a watt.  This means new windows, better insulation and tighter construction to reduce air conditioning.  It means a more efficient air conditioner.  etc

You are over-thinking the design of this system... no sense thinking about it at all until you come up with a kwh per day number that represents your needs.   The next step will be to pick a battery capacity and system voltage that can handle the load.  The next step is to figure out how much solar panel and generator you will need to charge those batteries. Then finally you can start choosing inverters, charge controllers, and balance of system.

--vtMaps

[michaeld]

Somewhere along the line I have unquestionably given incorrect data on the load factor. I have seen more than a few install video's that the guy's were pulling volts/amps out of their hats with the same batteries albeit in a higher voltage and half the amps. But there are more than just a few running 250 dollar max Harbor Freight kits with and including a 15K btu a/c unit I am aware they're draining the cells down to the inverter min cut-off level.

I already figured the 24 hour period to be 0.902 Kw, I now need to find the relationship from that 24 hour period to find what recovery I'm be able to manage in the few hours of peak solar charge available on days which are productive. Two volt cells in a 48 volt supply is a bigger bank than the old telco offices used when they were running 1920's step switching.

Yes they were using unregulated shunt chargers but like them I only need to run 24/7 in the period of complete grid failure. When a line transformer blows it's back online in 15 to 18 hours flat. When the whole grid fails it can be one to two weeks it could even be longer if something more destructive occurs.

Besides the electrical there are also mechanical and financial considerations. Just to charge a massive supply like that it would take a quarter the area of Nellis AFB just to mount that many 6 foot by 5.5 foot panels! My south facing is on the eve end of the house, four to six panels tops on no options there.

I am footing the cost out-of-pocket no energy rebate here on off grid systems probably not in any state for that matter, I don't know? If the recommendation is in fact correct going from a $250 concept to 10K hey I'm a sport. $20K just in batteries in not only unfeasible it's downright insane. There would be no ROI at least in my lifetime.

I'll continue to track this window unit and pick up another watt meter on my way home while reading up on the specs of the 12 volt cells over the weekend. I should have my ducks in a row by Tuesday I also need to re-read these suggestions attempt to find where I'm getting off-track. Get it off-track, little solar humor there. Yes very little! If I ever get On-track, my luck I'll have a stroke or something? But Thanks Guys! Hope you all have a great weekend!

Best
Mike

[Vic]

Hi michaeld,

Regarding the window A/C;  a 24/25K BTU A/C  will just have to run on 240 VAC,  so,  a Kill-A-Watt meter will (probably) not be able to measure it ...  unless there is a new model now available.   A Clamp-On AC Ammeter/Multimeter should be able to measure its current.   A manual that came with that A/C should mention its power or current needs.   Also may be able to find that info on-line for your exact A/C,  or one similar.

And there is a surprising amount of "information" on the Internet that is flat-out incorrect,  misinterpreted,   half correct,  out of context,  etc.   The exact details of well-engineered systems DO matter,  and often in short videos,  all of these details are often omitted,  or glossed over.

A back-up generator might help you in the your situation.  Normally such a whole-house style generator would need a considerable amount of fuel.   Usually,   these units run on Nat Gas or LP Gas.   Nat Gas might not be available in a large-scale emergency.   This is something that you might want to think about,  if you are unable to pare your AC  power needs significantly.

More opinions.    Good Luck,   Vic

[michaeld]

I was able to find my neighbor on his way home for lunch and got him to stop by he just txt me the model of the a/c and I looked up the spec for an LG1511ER, it's 115 volt and two summers old and purchased while the central air compressor was replaced at the time. It's worked so well we've left the breakers off saving considerable energy not really sure on the large one's rating either TBH.

The window unit is actually 15K btu (and the hey it works video I guess he was actually running 5 or 6K btu). This one says 115V, 1380W, 12 Rated Amps I guess that rated must mean a maximum start current load. It is on it's own 15 amp single socket plate not a minutes headache with it so far.

I believe I have the wiring plan for a 48 volt supply. I'll fiddle with this an see if it let's me add it to this message for critique. You can tell from the last message I was thinking it was already Friday that usually only happens on Wednesday or Thursday. heh heh heh. Been a long two weeks finding the Pro's. Google hides you pretty good if you don't know exactly what your hunting for.

let;s see how this works.that was rather quick.

[vtmaps]

Somewhere along the line I have unquestionably given incorrect data on the load factor.
<snip>
I already figured the 24 hour period to be 0.902 Kw, I now need to find the relationship from that 24 hour period to find what recovery I'm be able to manage in the few hours of peak solar charge available on days which are productive. Two volt cells in a 48 volt supply is a bigger bank than the old telco offices used when they were running 1920's step switching. 

If your average draw is 902 watts, that is 21.648 kwh every day.  Your battery bank should store about 80 kwh so that your daily use is about 25%. 

80 kwh ÷ 48 volts = 1666.7 amphours at 48 volts

A 1600 ah, single string, 48 volt battery bank will set you back about $20,000. 

Your last diagram showed three strings in parallel. But you have been advised repeatedly in this thread to avoid parallel batteries.  Why are you so determined to do it wrong?

Parallel batteries are never the optimal solution.  If you find yourself (in a less than optimal circumstance) with parallel batteries, there is a right and a wrong way to interconnect them.  BTW, your diagram show a wrong way.

--vtMaps

[Vic]

   ...   My south facing is on the eve end of the house, four to six panels tops on no options there   ...

   ...   I'll continue to track this window unit and pick up another watt meter on my way home while reading up on the specs of the 12 volt cells over the weekend. I should have my ducks in a row by Tuesday I also need to re-read these suggestions attempt to find where I'm getting off-track   ...   But Thanks Guys!   ....
Best
Mike

Hey Mike,

Well,  seems that you have the room for 4 - 6 ea PV modules will give some clarity on the maximum size of a system that might fit on your property.   Sometimes a Ground Mount for PVs can also work.

Here is a link to a high quality PV module that is fairly high in efficiency:
http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/hiposopa/solarworld-sunmodule-sw280-monocrystalline-solar-panel.html

There are many vendors,  but have quite a lot of experience with this vendor.

This PV is about 66" X 40",  outside dimensions -- fairly standard for the common 60-cell units.  Six of these PVs have an STC rating of 1680 watts nominal.   The normal de-rating for PVs is to about 77% of the STC watt value -- so one would expect about 1300 watts from an array of six of these modules.   And from the data that you  mentioned for your 15K BTU A/C,  these six modules would not quite run that A/C with NO other loads whatsoever,  except on a cold day,  when A/C might not be needed at all.

Looking at battery configurations may be educational,  and interesting,  however,  you really get to decide how much maximum power that you need,  the average power,  how much of the power needs to come from a battery,  and just what the PV modules can provide directly when any battery that you might have is charged,  and so on.

Would strongly suggest that you look at a residential Back-up Generator,  and study what type of fuel that such a unit would need.  This,  by far,  will be the best bang for the buck for a Grid back-up system,  that you appear to need.  It is possible that a small battery-based system could supply some modest loads.

Electric Heating and Cooling appliances need to do a lot of work.  Work requires POWER.  Large power demands from battery based PV systems are generally expensive.  Off-grid PV systems are VERY expensive,  and batteries wear out,  requiring more expense down the road.

If you have Nat Gas,  and are willing to take the chance that Nat Gas will not always be available in a wide-spread emergency,   several thousand dollars spent on a back-up generator  could be money very well spent (especially if you find a generator that could run for a week or two,  almost continuously.  Your local Zoners MIGHT permit an LP Gas storage tank at your location.   This could be a fairly good alternative,  as it would probably survive many of the risks that could impact the availability on Nat Gas (if you have it at your location).

Sorry for being a bit redundant,  just trying to make a point that you might want to consider.

Since your 15 K A/C  runs on 120 VAC,  the Kill-A-Watt should just be able to measure its running demand (not the start current).   And the K A W  is able to store the total power consumed over any period of time that you choose.  This is very helpful when designing power systems.

EDIT:  OH,  and there IS a Federal 30% Tax Credit even for much of the items that make up a fully off-grid power system,  ending in TY 2015,  I believe ...   Consult your Tax advisor,  and so on ...

Will let you digest some of this.   Good Luck,    Vic

[michaeld]

Points taken Vic thanks! I was huffed to hear Tom had run all that gear. I was wanting something with a small footprint and was googlin the gear in his sig last couple of days. 2 volt cells came out to almost 3 ton of battery and the clock is ticking on those just sitting on the pallet.

I got in touch with a farm implements rep locally, it's not his regular product lines but said he'd contact Cummings and GE see if they made anything on the small side.  Our heating/cooking is LNG here. I can bury up to 750 gal double wall fiber tank a small diesel would require a small engine house. There is no current regs on wind, but is still a risk since no regs there is no grandfather either.

Just for the halibut and experience still going to build a cheap HF or HD kit just to see what it can do. If it can keep portable hand tools topped off it'll be worth it Just out of curiosity were you suggesting L16RE-2V cells in that 20K string vt?

[vtmaps]

Just out of curiosity were you suggesting L16RE-2V cells in that 20K string vt?

L16 is a case size.  Based on your stated load I was estimating 2 volt cells with 1600 ah - 1800 ah.  I guess those would be a bit larger than an L16.

--vtMaps

[Resthome]

Mike.. Digest all the information the folks have given you. They are right on the money. You really need to forget running that a/c on solar for any given period of time, unless you have a huge amount of solar and a very large battery bank.  Those spec are AC specs. When you take that 1380 watts and run it off an inverter at 12v that inverter will be pulling approx. 115 Amps out of the batteries. That in itself is a huge load. So as everyone has been telling you get you real required loads. Good Luck with the project, just understand what folks are telling you. They are all very knowledgable on the subject.

[RossW]

I've lived totally off-grid for 10 years here in regional Australia, at 36 degrees south.
My system was 48V right from day 1. Until recently I was using conventional lead-acid cells, around 1000 amphours capacity.
I have a 5KW inverter and 3600W PV on tracking arrays which provides me between 30-50% more watt-hours per day than fixed arrays.
I run the whole house (a large house) with two home offices, a bunch of equipment running 24/7. We burn through around 20 kWh/day. (Considering that has to run the full effluent treatment plant, water pressure pumps and a whole slew of computers, it's not so bad). Here's my install a few years ago.


I recently replaced my lead-acid batteries with smaller, lighter LiFePO4 cells and although it's only been 6 months, they have met or exceeded my expectations in most regards. I would not however (at this stage) suggest LiFePO4 cells to a beginner!

I have a 14 kVA home-brew generator that runs off propane for those periods where the sun and wind don't provide what we need. In summer, it can go for a month or two without running. In winter it's rare for it to not run once a day, although this winter with the LiFePO4 cells we've managed 3 or 4 consecutive days without the generator running several times. (In previous years I don't think it ever made a day without a run. Many days it had to run two or three times).

I agree with the views expressed above.
1. REDUCE your consumption.
2. Have REALISTIC expectations.
3. DO NOT go the "cheap route, for now". It WILL cost you much more to re-do later.
4. Size properly, install properly, operate with awareness and flexibility.

Use power when you have it, and conserve it when you don't. That means not running heavy loads (washing machine, dishwasher, airconditioner) at night when you're running entirely on your battery reserves.

DO factor in a generator. Even an inexpensive generator that you can throw away after a year or two, will cost you FAR LESS than increasing the size of your battery bank to carry you for 2 or 3 days, and running the genset when your batteries are low will extend their life. Flogging batteries to pieces simply because you want to watch TV or need the lights on, is a VERY expensive exercise. $2 worth of fuel and a $100 genset is probably the cheapest "battery insurance" you can make.

[michaeld]

Hi John Hi Ross, thanks for your contribution. I greatly appreciate those points to take into consideration. Also a picture is worth a thousand words.

-vtmap after seeing Ross's setup I owe you an apology for doubting your expertise. Along with my ignorance of the subject in general coupled with some sleep deprivation, all the W, KwH, Voc, Imp, Amps, Volts, strings and banks. There was no sugar plum fairy dancing around in there. He was more like an evil leprechaun with a wrist rocket flinging walnuts at me while suffering a bad toothache.

So looking at that picture I know you all have been there. One other piece of info that made me skeptical till now is how it's never been so apparent to me that times have certainly changed and this is not political it's meant to be funny about how we live today and Where we live. Some of you are more free'er than some of us. So if it's not funny just scratch out my comment and leave the rest because I need this advise later please!

Okay not bashing my state in any way. But where I live you can't buy fireworks on holiday's or any other days either. You can't find an Estes model rocket in a dimestore to save your life if you had to. A Daisy BB gun here is considered a firearm. The Red Rocket model not just the hi-tech air pumps they have out now days. Paint Ball is big now with the older kids but those might be regulated too as far as I know?

My point with all that is, since the only two super battery marts in the entire County here sits all by themselves in an area where retail land prices are at an astronomical figure there is a reason for that that don't meet the eye straight out.

Even if I had a nice a construction an setup as Ross's if there ever was an electro-mechanical failure. It would not just be one problem but two or three, New regulations enacted miraculously just the day before the day of the incident would be flying out at me faster than I could reach my hand out to receive the violation summons.

So all that general bla bla bla together is why I thought the little a/c couldn't be the problem also now that I got a good eight hours rest I switched out of the what little tech mode back to the what little common sense I got.

I realize that the 30K complete system I saw was a grid tie system and not stand alone like I need to come up with. In that system he had either 37 or 38 panels on his roof. It must be a home/business it was the guy from Texas video. I'm not sure if I could get that many panels in every square inch of property I got. Much less try to make something aesthetic looking.

The town library has six on their roof I don't know what it can power or what the use is. I could ask an see though. After going to HF site it looks like they got out of the solar business. I went to bed then. I'm much better today! Ross I do have two of the wheel type generators from the local big box store.

They are great but really loud and if I happen to not be around, she won't be able to keep an eye on the fuel level. But for the mean time they kept up with the demand on them.

[Robin]

Michaeld, I don't know if you have acted on this system yet. Vic and the others have given you some great advice. Listen to them. They are Pro's.
Here are some quick off the cuff thoughts I have from skimming this thread.
Do not even think about Harbor Freight panels or anything else from Harbor Freight.
Samlex may not be the best choice for this installation. I would go with a battery based grid tie inverter. SMA Sunny Island, Schneider XW or Outback. Magnum makes good stuff too, but they are not grid tied.
24 or 48V is a must. Do not make a 12V system. It will be a waste of money.
Don't expect to be running that air conditioner. Didn't I see that this is only for power back up during utility outages? Skip the air conditional and save yourself $20 to $30K.
$20K for batteries is ridiculous for this system.
Keep asking questions and listen to the pro's. They have been there and done this.

[zoneblue]

And stay away from youtube, its 99.99 percent garbage on the subject of RE. Ryan and the power time videos excepted of course.