Am I on the right track?

System · December 2006

Hello all: I am new to this forum. A friend is building a new home and has asked me to help her with stand-by power. She is 60 years old and her mother lives with her, so they were looking for something other than a generator that needed fuel, maintenance and produced noise & exhaust. I suggested a UPS type system, i.e. batteries that would charge from the grid and kick in to power an inverter during outages. (We were going to use PV, but local building covenants rejected that.)
I am looking at a Xantrex 5548 and about 1400AH worth of AGM batteries. I figured this would run her microwave, refrigerator and a few lights for a couple of days. Am I on the right track?
Thanks for any input.

mike95490 · December 2006

Re: Am I on the right track?

Oldaudio wrote:

(We were going to use PV, but local building covenants rejected that.)

Where is this install located? California has a law overrideing anything else, that alternative energy from PV or hot water collecters, cannot be prevented, as long as it meets safe building codes (and you own the property). Overrules Citys, Homeowner Associations, anything.

BB. · December 2006

Re: Am I on the right track?

You are on the right track... However, batteries and long draws of a few hundred watts over 24 hour period will exhaust even a good-sized battery bank...

For example, a reasonably efficient refrigerator would draw around 1 kWhr per day--if they have an older fridge, it can take 2-3x that amount of power... Your batteries, you would like to not draw them down more than 50% except in an emergency (can drastically reduce their life to months--from years of life--f not done "correctly").

Your suggested battery bank of 1400AH * 12 vdc (assumed) * 50% = 8.4 kWhrs

So, if the inverter is 80% efficient, and assuming that the fridge is the major load (just a few CPF lights and a radio/small TV--say [3 hours/day * (3x17 watt CPF + 100 watt TV) + 1kWhr/day for a fridge]*1kWhr/1,000Whr * 1/80%inv-eff= 1.816 kWhr per day or 8.4/1.816 = 4.6 days fix a couple small errors in typing equation

I would suggest not using the microwave but use a propane camp-stove (or their natural gas stove if available) for cooking. The microwave is a heavy load--but is usually only run for a short time--so it may be OK... But it will reduce battery life by a day if operated a 1/2 hour per day.

Looking at a backup source for charging the batteries and running appliances (like a natural gas or propane generator) would be nice (charge the batteries for a couple hours per day). But it really depends on how long they wish to last without power (hours, days, weeks), what kind of emergencies (earthquake, snow/sleet, heatwave, etc.), what fuels/rules (natural gas, propane, gasoline, diesel, solar), what area (battery, fuel, generator--safe ventilation for battery/generator fumes), and what needs to be run (A/C, central heat, fridge, freezer, stove, microwave, lights, well pump, sump pump,). And, lastly, how much maintenance (fuel/oil, battery replacement, charging in an emergency) they are willing (or neighbor) can perform).

Also, there is a little issue of security (only house on the block with lights and/or a noisy generator can attract attention).

-Bill

System2 · December 2006

Re: Am I on the right track?

I find it so interesting that some people would rather perish due to global warming, than have to put up with seeing the most terrible thing one could imagine - - a solar panel !!
If these people have brains, where do they keep them and why do they have them?
Wayne

System2 · December 2006

Re: Am I on the right track?

Am I the only one who thinks solar panels are"sexy"???? Sorry for the language. They are, aren't they? :-D

System2 · December 2006

Re: Am I on the right track?

I think solar panels in an array are a beautiful sight to behold. Also I
thought the Feds said that solar over rode those nasty CCR's?

brad

System2 · December 2006

Re: Am I on the right track?

mike90045 wrote:

Oldaudio wrote:

(We were going to use PV, but local building covenants rejected that.)

Where is this install located? California has a law overrideing anything else, that alternative energy from PV or hot water collecters, cannot be prevented, as long as it meets safe building codes (and you own the property). Overrules Citys, Homeowner Associations, anything.

Arkansas

System2 · December 2006

Re: Am I on the right track?

BB wrote:

"You are on the right track..."

"Your suggested battery bank of 1400AH * 12 vdc (assumed) * 50% = 8.4 kWhrs"

This would be a 48V battery bank... 48V @ 1400 AH. I think that will require 28 X 12V 200AH batteries in series-parallel.

"I would suggest not using the microwave but use a propane camp-stove (or their natural gas stove if available) for cooking. The microwave is a heavy load--but is usually only run for a short time--so it may be OK... But it will reduce battery life by a day if operated a 1/2 hour per day."

There is no natural gas or Propane available in this area. The NG isn't available here and the developer doesn't allow propane tanks. Yes, they can be buried, but the homeowner doesn't want that either. The ground around here is solid rock under 3-12 inches of topsoil.

"Looking at a backup source for charging the batteries and running appliances (like a natural gas or propane generator) would be nice (charge the batteries for a couple hours per day). But it really depends on how long they wish to last without power (hours, days, weeks), pump, sump pump,)... And, lastly, how much maintenance (fuel/oil, battery replacement, charging in an emergency) they are willing (or neighbor) can perform)."

This system is figured for a 3 day outage. The power supplier is a little "country and western" i.e. they are a rural supplier and don't have large maintenance crews. We had 2" of ice just yesterday,
and the response time for restoring power isn't always the greatest.

"Also, there is a little issue of security (only house on the block with lights and/or a noisy generator can attract attention)."
\
Gated community, only about a dozen homes here...crime is non-existent... my window locks are on the outside of the windows, and I live in town.

System2 · December 2006

Re: Am I on the right track?

pioneer wrote:

I think solar panels in an array are a beautiful sight to behold. Also I
thought the Feds said that solar over rode those nasty CCR's?

brad

We may be able to put some PV down the hill in front of the house at a later date. The neighborhood "committee" just did not want the panels up on the roof. "Didn't fit with the architecture"
says they.

BB. · December 2006

Re: Am I on the right track?

That is a seriously large battery system... One suggestion I would have is to not use "small" 12 volt batteries, but to use very large low-voltage cells to reduce the number of interconnects, and not have parallel strings of batteries.

AGM (sealed) type batteries would be nice (very little, if any maintenance required). But you would have ~62 cables connections to make and batteries in parallel can tend to not charge and discharge evenly (slight voltage drop difference between middle and end cells--although differential charging/discharging of parallel batteries and life has been subject to debate here; some have seen little evidence of life issues, others have had manufacturers say parallel connected battery life is 1/2 of series only type banks).

See link for series/parallel discussion here:

http://www.wind-sun.com/smf/index.php?topic=1825.0

However, AGM cells do not seem to be readily available in very large AH ratings that would allow one series string (at least in Concord brand).

AGM batteries are very nice for low (virtually zero) maintenance. Large flooded cell batteries are nice for life and fewer interconnects (example in link below):

http://store.solar-electric.com/batteries.html Wind-Sun's battery web page
http://www.surrette.com/pdf/4ks25ps.pdf Surrette 1,350 AH 4 volt (2 cell) battery
http://store.solar-electric.com/cosuagmba.html (Concorde AGM battery family)

12batteries (4volt@1,350 AH))x2connections each=24 interconnects
28 (12 volt batteries) x 2 connections each+7 banks * 2 connections=62 interconnects

One other possible suggestion for sizing of batteries (and saving some money)... Typically, everyone first looks at the 20 hour battery bank AmpHour ratings... In your case, since you are interested in at least 3 days of service, that would be, on average, a 6 day discharge rate (144 hour, assuming only a 50% discharge)--Looking at the Surrette link above, for example, a 1,350 AH battery at 20 hour becomes 1,990 AmpHour rated at the 100 hour rate... The mathematical formula is known as the Peukert Effect (batteries deliver more power at lower current/discharge rates--search for "Peukert Effect" on this forum for several threads discussing this effect).

One other reason I have liked series connected cells is that (to me it seems) it is easier to isolate a bad battery... With series connections, you simply measure the voltage of each battery and the one with the low(er) voltage is having problems. With parallel connected batteries, you cannot easily measure the current and voltage of any particular cell without disconnecting each battery for individual checking. There are DC current clamp meters that can measure current--but they tend to be pretty expensive to purchase (a Fluke LH2015 is around $500 or so).

The only large battery installations I have seen (telephone type installations) have used very large flooded cell batteries. However, the very good life and low maintenance of AGM batteries, but higher price, is a pretty good reason to use AGM.

Looking around Concord's website, they do have some larger single cell (2 volt) AGM batteries... Upwards of 756 AmpHours at 120 hour rate:

http://www.concordebattery.com/xtender_main.php
http://www.concordebattery.com/xtenderpdf/PVX-6480T.pdf

Wind-Sun does not list them on their website, but they may be able to get you a price on them.

To compare costs:

12x Surrette 4 volt 1,350 AH (20 hour rate) batteries at $904.76= $10,900 (plus $hipping)
24x2 Concord 2 volt 648 AH(24 hour rate) batteries at ~$230 = $11,000 (plus $hipping)
28x Concord 12 volt 212 AH (24 hour rate) at $1,580 per 4 batteries = $11,060 (plus $hipping)

Price/size of Concord string can probably be reduced... They warranty their batteries to 80% deep discharge (instead of the 50% discharge I suggested above)... So you can use fewer/smaller Concord batteries to achieve your AH ratings...

http://www.concordebattery.com/otherpdf/sunextenderbatterysizingtips.pdf Concord Battery Sizing Recommendations

Well, this appear to be a tough call for me... Surrette's are very good, long life batteries in one series string. Or two similar types of Concord batteries (two different voltage configurations 2volt/12volt--7 parallel strings of 4 batteries vs 2 parallel strings of 24 batteries). Prices are all virtually the same.

The Surrette string could be made smaller (cheaper) because of the 50% discharge cycle spread over 144 hours... The Concord string could be made smaller because of the 80% discharge level vs the 50% level generally recommended for flooded cell lead acid.

The Surrette's, appear to be, designed for, roughly, twice the life:

Surette: DESIGN CRITERIA: 10 YEAR WARRANTY, 3300 CYCLES, 15 YEAR LIFE

Concord: 1 year full warranty, 4 year pro-rated. (from one of Wind-Sun's Concord pages)

I will leave it to other here with more experience with home power battery systems as to how they would design the battery bank and what batteries to use.

Should be an interesting discussion...

-Bill

System2 · December 2006

Re: Am I on the right track?

Bill: Thanks for your reply. Yes, your suggestion about using larger cells is a good one. One consideration for me was shipping costs. We have a fairly large regional battery distributor about 10 miles up the road. The best I could come up with from them was the 12V 200AH AGM types. I think the shipping on anything else will kill me. And, they do fit the client's requirement for little or no maintenance.
Yes, I have a Fluke clamp meter.
In my personal system I use 160AH block cell NI-CD. Most of my experience has been with the large flooded type cells. Formerly, I was a communications technician with the Canadian National Railroad. We had large systems every 25 miles or so to power microwave communications installations. In 2003 we switched to fiber and the current requirements were less. We then went to AGM types.
I will spend tomorrow perusing your suggested links.
Thanks for all the replies.
Durff

BB. · December 2006

Re: Am I on the right track?

Durff--You sand-bagged me! :-o

You probably have more large battery bank experience than 99% of the people here (obviously, including me). :evil:

-Bill :-D

crewzer · December 2006

Re: Am I on the right track?

A friend is building a new home and has asked me to help her with stand-by power… they were looking for something other than a generator that needed fuel, maintenance and produced noise & exhaust. I suggested a UPS type system, i.e. batteries that would charge from the grid and kick in to power an inverter during outages… I am looking at a Xantrex 5548 and about 1400AH worth of AGM batteries. I figured this would run her microwave, refrigerator and a few lights for a couple of days. Am I on the right track?

Oldaudio,

The basic concept will work, but there are options. It’s often less expensive in the long run to buy energy efficient appliances that it is to generate, store and distribute the energy. Accordingly, it might be worth buying a new, energy efficient fridge and spec’ing a smaller backup energy system.

For example, a modern Sears Energy Star 21 cf fridge is rated at 432 kWh/yr, or ~1.2 kWh/day. Assuming a microwave rated at 1,000 W (= ~1,400 W load) for 1 hour/day (= ~1.4 kWh/day) and seven 14 W compact fluorescent lamps for 10 hours/day (= ~1 kWh/day), the net daily energy requirement would be ~3.6 kWh/day.

Assuming 90% inverter efficiency, the gross energy requirement would be ~ 4 kWh/day. Assuming three days of backup and not discharging the batteries below a 40% state of charge (OK for occasional back-up applications, I would think), the battery bank would need to be rated at 20 kWh.

For a “48 V” system operating at ~50 V in mild ambient temperatures, that would be a 48 V battery bank rated at 400 Ah, so let’s make that 500 Ah to allow for cold ambient temperatures. That would require eight size 8D 12 V AGM batteries wired in series-parallel to configure a bank rated at 48 V x 500 Ah. So, I think a 48 V x 1,400 Ah bank would be expensive overkill.

I also think you have some options for the inverter/charger. Frankly, I believe that a unit rated at ~2,500 W or so would suffice. The Xantrex SW Plus 2548 ($1,839) is rated at 2500 W continuous at 40 C, and the Outback FX3048T (~$1,750 including the optional Mate) is rated at 3000 VA continuous at 25 C. Either should be able to simultaneously handle the fridge's short start-up load, the microwave's continuous load and the lights.

See: http://www.xantrex.com/web/id/43/p/123/pt/25/product.asp
and: http://www.outbackpower.com/Backup.htm

So, the new fridge, the smaller inverter and the smaller battery bank will cost ~$4,200. The SW Plus 5548 ($2,800) and a 1,400 Ah AGM battery bank will cost ~ $8K or so, both plus the usual shipping, taxes and misc. hardware.

In summary, I think that a new fridge and a smaller system will meet the requirements provided, cost less to procure, require less storage space (especially for the batteries), and the new fridge will be also be cheaper to run from the grid. Also, I believe the new energy efficient fridge may qualify for a federal tax credit.

Finally, no matter which way you go, you'll need a whole punch of parts to tie the grid, the inverter, the batteries and the load distribution center together in a code-compliant manner. If you chose the Outback solution, the E-Panel from Midnite Solar may be a simple and cost-effective solution.

See: http://www.midnitesolar.com/MidNite-Products.html

HTH,
Jim / crewzer

System2 · December 2006

Re: Am I on the right track?

BB wrote:

Durff--You sand-bagged me! :-o

You probably have more large battery bank experience than 99% of the people here (obviously, including me). :evil:

-Bill :-D

Bill: No sandbagging intended...my apologies. I must admit, that the systems I was working with were designed and in place long before I came along. So, most of my experience was testing and maintaining/replacing them. I had a 100% solar home about 15 years ago. Small scale... (only 110W PV ), DC only, wood heat & solar hot water. I did not have an inverter on that system, so I really have no experience with residential inverters running things like MW, referigerators, and freezers.
Durff

System2 · December 2006

Re: Am I on the right track?

Crewser said:"...
For a “48 V” system operating at ~50 V in mild ambient temperatures, that would be a 48 V battery bank rated at 400 Ah, so let’s make that 500 Ah to allow for cold ambient temperatures. That would require eight size 8D 12 V AGM batteries wired in series-parallel to configure a bank rated at 48 V x 500 Ah. So, I think a 48 V x 1,400 Ah bank would be expensive overkill.
...
In summary, I think that a new fridge and a smaller system will meet the requirements provided, cost less to procure, require less storage space (especially for the batteries), and the new fridge will be also be cheaper to run from the grid. Also, I believe the new energy efficient fridge may qualify for a federal tax credit.
...
Finally, no matter which way you go, you'll need a whole punch of parts to tie the grid, the inverter, the batteries and the load distribution center together in a code-compliant manner. If you chose the Outback solution, the E-Panel from Midnite Solar may be a simple and cost-effective solution.

See: http://www.midnitesolar.com/MidNite-Products.html

HTH,
Jim / crewzer"

Jim: Thanks for the reply. I will pass your suggestions along to the homeowner, as she hasn't purchased any appliances yet. And I agree, any load savings in the planning stage will be an all around benefit in the long run.
I will print out your post and study it today. I had a gut feeling that the 1400AH batt bank was overkill. I was using the Xantrex worksheets and that's what I came up with. I may have hit the wrong button on the calculator....
Thanks to all for your inputs.
Durff

BB. · December 2006

Re: Am I on the right track?

Durff,

Just having fun! :-D Asking questions is never a cause for apologies.

I tended to be on the design side of engineering, so asking what was happening in the factory and the field was always a great source of knowledge and education for me (and made for better product too). It was surprising how many design engineers I worked with (in the US), could not even be bothered with factory and field problems.

-Bill

crewzer · December 2006

Re: Am I on the right track?

Bill,

Yeah, "design for manufacturability" and "design for maintainability" are sometimes foreign concepts to design engineers. However, the field guys have their quirks too. One of the strangest things that ever happened to me was when I was approached by a rather irate fellow at a party one night and his barrage went something like this:

"Hey, you're crewzer, aren't you? Well, I've got a bone to pick with you! You know that equipment that you and your engineering pals designed and built for my department? Well, unlike the old stuff we had, yours never breaks, so now we have to work all day -- thanks a lot!"

Oh, well... :roll:

niel · December 2006

Re: Am I on the right track?

don't you just feel so sorry for them jim. do i hear a bunch of little violins playing? :-)

System2 · December 2006

Re: Am I on the right track?

Would a couple of these do the trick? http://www.xantrex.com/web/id/218/p/1/pt/30/product.asp

Am I on the right track?

Comments

Categories