batteries/ cold weather

northshore

Hello, I am looking to install a small pv system at a cabin in northern Minnesota and I would like to know if there is a particular battery that holds up to cold weather better than others. I currently use 3.2Kwh average per month with the highest in the last 12 months at 12Kwh. There were 7 months where I used 0 Kwh. I am tied to the grid but am tired of paying $46 per month for .30 cents worth of power. My battery bank will have to be balanced with whatever size array of pv panels that will efficiently keep the batteries charged. My largest draws are a coffee maker (150watts) and a very small 120v fridge (which is usually shut off anyway because of non-use). It can get -20f easily in winter and the batteries may have to be on the outside of the cabin in a battery box. I have been told by others to just get a generator, however I do enjoy the quiet and since I'm kind of a tinkerer, a small pv system appeals to me more than a genset. I am at the very bottom of the spectrum of knowledge on solar energy so please, I ask that the replies (if any) keep that in mind. Thank you Terry

Steve961

Re: batteries/ cold weather

Hi Terry,

I'm fairly new to all of this, and have just gone through much of what you are looking at. Everyone here has been a great help, and I'm sure you'll get plenty of good advice also.

As far as the battery goes, AGM (Absorbed Glass Mat) batteries are the most resistant to freezing. This being said, even typical flooded batteries should not freeze if kept charged and in an insulated battery box. The only disadvantage to AGM batteries in my opinion is the cost, up to 2X that of flooded. AGM's have another advantage in that they can be stored indoors since they do not release any significant amount of hydrogen gas during recharging. My cabin is in northern Wisconsin, and I have chosen AGM's for my solar system. I liked the fact that I could keep them indoors (theft prevention and warmth), and a little extra peace of mind when I am away for several months in the winter.

One thing you will need to consider is how often you get to your cabin and how long you stay. If you only get there on the weekends, your panels will have 5 days or more to charge your battery bank. And if you only stay the weekend, your battery bank only needs to be sized for 2 days of loads. You can size your system up from this, or just get a small generator for the times you stay more than a weekend. This is basically what I am doing to keep my costs down.

Something else to consider to keep your initial solar investment down is energy conservation. Your two largest loads, the coffee make and refrigerator, can easily be traded for propane appliances. This will drastically reduce your up front costs in solar panels, batteries, and an inverter. I am reducing my electrical needs to just a few lights, a stereo, and a laptop computer. Everything else will be propane. Propane refrigerators are readily available, albeit expensive, though you may be able to score a used one through Craigslist. For the coffee maker, I found the following that has some good reviews on Amazon:

http://www.amazon.com/gp/product/B001K7IDVU/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B002X93MO2&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0BXM3YWPNKJXP3APFD9N

Once you know what your daily energy requirements are, you will be able to get some good system suggestions from several people here.

Good luck.

Steve

mike95490

Re: batteries/ cold weather

I think you really need to have the batteries recharged in less than 48 hours, as sulphation sets in if you are counting on 5 days of solar to recharge. More solar, or more genset runtime to get them bulked to 80% charge.

icarus

Re: batteries/ cold weather

Please read through the basic solar and off grid threads to get some better ideas for system(s) etc.

Bottom line, Flooded batteries will withstand -40 or colder if they are reasonably well charged. A 50% charged battery won't freeze until well below zero F. We routinely keep batteries ~-35-50 and as long as they are kept in float they are fine.

I suggest you read here:
http://www.batteryfaq.org/

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Tony

northshore

Re: batteries/ cold weather

Thanks for the response, Steve, Mike and Tony. All of the information is very useful. Tony, in one of the links you posted it states that at -22f the capacity(ah) is reduced to 50%. I would asume that I should design the battery capacity using those lower temperature values as a guide or would that be overkill. Is there a general rule of thumb for ah capacity to ah used? i.e. "Always go 50% past what you'll use" in ah or if not, what would be the correct method of determining those numbers. It's probably not a plausable question but I'm slowly learning. Steve, I'm more in line with your situation in that I'm only ther maybe twice a month and the AGM batteries sound great but if Mike is right I would be hesitant to pay more because I expect to make mistakes and I would like to make less expensive mistakes in the beggining. This website is filled with so much information that it's mindboggling. Terry

BB.

Re: batteries/ cold weather

The rule of thumb we start with for sizing batteries is 3 days of no sun and a maximum of 50% discharge for long life...

For your place--being only there two weekends a month--I would probably go the other way... Get AGM (if you want) and plan on running them to 20% discharge with no sun.

Frankly, that is only ~24 uses per year--and even if you assume 200 cycles maximum from the battery bank--that is 8 years of cycling life--and probably the maximum aging life for the battery bank anyway (or even less).

Plan on having a genset (the Honda eu1000i or eu2000i plus a gallon of gasoline or less) can be used to recharge the bank on the second day to 80% charge--then let the solar panels take the bank the rest of the way (if sunny weather is forecast).

Your choice for solar panels can range from wanting to support your daily load (no generator usage) in good weather (pick winter less sun/summer more hours of sun depending on your power needs). To simply planning on using the genset for a few hours every two days--and having just enough solar panels to float the batteries when you are gone (1% of the AGM bank size).

Knowing what your power requirements are will help reduce my "Hand Waving" about your choices and replacing it with hard numbers.

If you are going to make me guess at your needs: $0.43 of power--Assume $0.10 per kWhour:

• $0.43 * 1/$010 per kWHr = 4.3 kWhrs per month = 4,300 WHrs per month
• 4,300 WH per month / 4 days per month usage = 1,075 Watt*Hours per day

That is a fair amount of power usage for a small cabin....

You can see Tony's / Icarus' signature line--Small cabin in the Great White North... He runs on around 600 WH per day (computer, internet, a few lights, etc.).

Solar makes a lot of sense when you are there 9+ months of the year... For cabins that are only used a few days a month--a small generator (plus a battery bank for quiet evenings) can be more cost effective.

-Bill

shortfatguy

Re: batteries/ cold weather

Consider coffee in a tea bag. I keep them in a pot on my wood stove when it's cold or on my gas stove. Remember conserve, conserve and of course conserve even your cooking requirements. Get a generator for backup. I run twice a week for an hour to keep the generator from running gaskets dry and run the vacuum, hard charging odds and ends. Doing any construction I run off the gen too

northshore

Re: batteries/ cold weather

shortfatguy- Do you make up your own coffee in a tea bag or buy them? I always have a pot of water on the woodstove-clever idea.
BB- I do not use quite as much as you guessed. The small REC sends a bar graf of total usage for the previous months going back one year but you were close enough. I will change to cfl's when I go next time and that should make a difference. I talked to the director of operations at the small REC and they are fine with me "idling" my service however, should I decide to reconnect to the grid they"ll charge me one year of fixed monthly rates ($46) plus a reconnect fee. He then said "we usually tell people like you to go buy a generator if your not happy with our service". People like me? I've been a member of that co-op for 12 years and now I'm in the "people like you" catagory. I'm actually kind of proud to be there! Yesterday I went to Interstate Battery and recieved information on their line of equipment but the counterperson did not seem to think any of their batteries would hold up to the cold- he then said why don't you just buy a generator? I am begining to think there is a network of underground Honda generator salesmen lurking across the country. Todays a new day and I am going to include AMG batteries in my search. Thanks again Terry

BB.

Re: batteries/ cold weather

Before you go too far and buy the battery bank (and inverter/solar panels)--You should have a good idea on amount of power you will need... A Kill-a-Watt meter will do a good job of measuring the power--plus you can use it at home and start looking at conservation there too...

To give you a rough idea of how much power you can generate with 1,000 watts of solar panels for use with your AC appliances in Duluth Minn--assuming 0.52 derating (battery bank and AC inverter), fixed array using the PV Watts website (1kW is the smallest array the program will allow):

"Station Identification"
"City:","Duluth"
"State:","Minnesota"
"Lat (deg N):", 46.83
"Long (deg W):", 92.18
"Elev (m): ", 432
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 46.8"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 7.9 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.29, 58, 4.58
2, 4.27, 67, 5.29
3, 5.41, 90, 7.11
4, 4.99, 76, 6.00
5, 5.42, 80, 6.32
6, 5.51, 77, 6.08
7, 5.36, 76, 6.00
8, 5.26, 76, 6.00
9, 4.48, 65, 5.13
10, 3.85, 59, 4.66
11, 2.61, 40, 3.16
12, 2.61, 44, 3.48
"Year", 4.42, 807, 63.75

So, you can get ~40-90 kWHrs per month or:

• 40,000 WH per month / 30 days = 1,333 WH per day
• 90,000 WH per month / 30 days = 3,000 WH per day

If you need less power, just cut the solar array by that amount (1/2 the power, 1/2 the array size).

For battery bank size, say you want to plan for flooded cell and 3 day of usage + 50% maximum discharge using 600 WH (0.6 kWH) per day on an 85% efficient inverter:

• 600 WH * 1/12 volt battery bank * 3 days * 1/0.50 max discharge * 1/0.85 eff inverter = 353 AH @ 12 volt battery bank.

Insulate the battery bank (watch temperature when recharging)--if you can put in basement (with ventilation for hydrogen gas) / on or in ground it will help keep the battery warm.

Look at using less expensive "training" batteries (perhaps even "golf cart" batteries) for your first bank. Many people kill them with an early death the first time through.

If you are planning on only running small loads, the MorningStar 300 watt (600 10 minute surge) 12 volt to 120 VAC True SineWave inverter is a good start (~$260 + shipping).

Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC

If you are planning on needing more than ~1,200 watts of power--You should think about up-sizing to a 24 volt battery bank. This keeps the DC side of the battery bank wiring a reasonable awg:

• 1,200 watts * 1/10.5 cutout voltage * 1/0.85 inverter eff * 1.25 NEC wiring safety factor = 168 amp wiring and fuse/breaker

I also like to recommend a battery monitor to help monitor your battery bank (just about mandatory for an AGM battery bank). A hydrometer for flooded cell batteries is pretty much necessary too.

Most batteries are killed by not keeping them well charged... Running a battery below ~75% state of charge (days/weeks/months) will sulfate them and kill them in a year or less...

If you get a solar charge controller (and is available for some AC chargers too) get one with the Remote Battery Temperature Sensor Option. Will do a better job at getting your battery bank properly and quickly charged.

A few FAQs to read:

All About Inverters
Choosing an inverter for water pumping
Deep Cycle Battery FAQ
www.batteryfaq.org

-Bill

Kamala

Re: batteries/ cold weather

Northshore,

In your OP you stated that for 7 months of the year you use zero watts. May I assume that this is during the winter months? If so, just make sure that your batts have a full charge at shut down of the cabin, have no loads connected to them and leave them for the season. The cold alone won't damage your batteries. As Tony points out, a fully charged FLA won't freeze until the temperature drops to the 70F range. Self discharge might be an issue but, IIUC, this characteristic of the battery is lessened by low temps. IOW, chemical reactions proceed more slowly at low temps. That is, self discharge should be less per unit time at low temp than it would be at high temp.

If you use the cabin during the cold months, then, yes, you should increase the size of your bank to account for temperature depressed capacity.

HTH

K

niel

Re: batteries/ cold weather

"If you use the cabin during the cold months, then, yes, you should increase the size of your bank to account for temperature depressed capacity."

actually the temperature isn't the big problem, let alone a problem, in the winter for pvs, it's the lack of sun.

Cariboocoot

Re: batteries/ cold weather

I think Kamala was pointing out that cold temps are a problem for batteries, in that the chemical process slows with lowered temps (not to be confused with freeze damage). Ironic, because as Neil points out the PV's love cold temps.

Win some, lose some.

niel

Re: batteries/ cold weather

when the pvs put out power they send it to the batteries and this causes heat to be created. there's less heat produced because of the lowered sun levels and time it's out. if you aren't there then it won't matter as the batteries will just be maintained until when you show up. if you start using them cold then, yes, there could be a reduction in capacity until the batteries warm up and using the battery will start it warming up, but it certainly won't hurt to have a bit more capacity just in case they don't reach a normalized room temperature in time for whatever loads they are needed for.

northshore

Re: batteries/ cold weather

Hello again- I use the cabin the same amount in the summer as winter the difference being the amount of time spent inside. Summers I use it mainly as a base camp for my outdoor forays hence the reason for 0 Kwh's from May through August. I plan on leaving the 120vac refridgerator off and use a cooler ( I do this anyway), there's no running water, no computer or special electronic equipment and no tv's and yes, I do have a 4000w coleman generator. I used it to build the place- it's old, it's loud but I will haul it up there. Now at the risk of sounding stupid ( of which we know that boat has left the harbour) (heads nodding) here is my idea- 2 200 w solar panels (kyocera 210's?) into a mppt CC that can handle the load to 4 6v batteries series wired to 24v to a quality inverter to load center. I would like the CC to be able to handle one more matching panel if possibe (30amp?) and because of the excellent information and guidence on this site I will be installing average or better agm batteries (to be installeed inside) of capacity is still a mystery(to me ) If I kill em, so be it....learning curve expense. (Maybe mk 200ah?) The genset I'll worry about later. Please feel free to critique my idea. thanks Terry

mike95490

Re: batteries/ cold weather

I'd suggest the morningstar 45A MPPT (or the 60A) w/BTS (Battery Temp Sensor)

PV - Unless you are really a self disciplined zen master, start with 3 panels, unless you like listening to your genset.

What are your loads? Ice chest not fridge, no electronics gear. Whats the solar going to power? Coffee pot, microwave, toaster, bug zapper, electric blanket?

I'd skip the AGM, and make a simple bank of 4, 6V golf cart batteries, and abuse them. If you get past 4 years, graduate to AGM.

System Meter & Shunt, (Battery state of charge meter) to log amps in and out, you are in learning mode, and it's usefull to get a feeling of what's going on.

Start with 12V system, unless you know you are running more than 1KW of AC loads. (more choices of chargers and inverters).

Just my thoughts.

BB.

Re: batteries/ cold weather

If you can qualify your loads and design your system "up front"--you will save coming back 4 years later and trying to figure out going from 12 volt to 24 volt bank (new inverters and chargers), or staying with a small system (spouse makes you start the genset and vacuum, etc.).

Cheap batteries now and good batteries later is not a bad plan... Most people are very successful in torturing their first battery bank to an early death (including yours truly)--Usually by over discharging (deficit charging)--and sometimes by overcharging/lack of watching the electrolyte levels.

Depending on how you want your system configured--many of the components (charge controllers, battery monitors, etc.) can work with a 12/245/48 volt battery bank. Solar arrays, get "standard voltages" (alternate sources) to make easier to upgrade more panels later (if needed). If you ever plan on a 48 volt bank--watch the "high voltage" solar panels (Vmp around 50-70 volts)--with current MPPT controllers it is not possible (for most locations) to configure a 1x panel (too low of voltage) or 2x panels in series (too high of Voc in cold weather).

I would suggest designing "two systems"... A minimal first pass system. And a second one that would represent your ideal system. Pick as many components that can be moved over to the "eventual system" to keep out of pocket costs low.

-Bill

northshore

Re: batteries/ cold weather

Hello- Thank you for your input, it's more helpful than you may realize. I figured on 24v because there is always the possibility of using over 1Kw a day, hopefully not likely, but never say never. Power is for coffee maker (15 minutes in morning then the coffee goes into a thermos, a couple of 13w cfl's and not much more. I will be bringing the Baby George Forman grill home and there is a microwave but I honestly can't remember the last time I used it (it's used as clock). My reasoning for Agm batteries are inside installations (as the cabin warms, so will the batteries) and not as much maintenance. I'm looking for a system that is dependable as I am not inclined to be the type who will be constantly looking at a monitor wondering what the system is doing, however I know basic maintenance will be required. In other words, put in a good small system up front, let it do it's thing and I'll be fishing. I cook using a gas grill on the porch and I cook stews and such in a Dutch oven suspended over a fire pit by a tripod so none of that aspect is a problem. Looking at the parameters of my idea, do you think that 200ah for batteries will be sufficient or should I increase the ah. PS- I will by no means neglect this system as I take extremely good care of everything I own and the wife does not like it there because there's not enough shopping. Terry

Cariboocoot

Re: batteries/ cold weather

northshore wrote: »

Hello- Thank you for your input, it's more helpful than you may realize. I figured on 24v because there is always the possibility of using over 1Kw a day, hopefully not likely, but never say never. Power is for coffee maker (15 minutes in morning then the coffee goes into a thermos, a couple of 13w cfl's and not much more. I will be bringing the Baby George Forman grill home and there is a microwave but I honestly can't remember the last time I used it (it's used as clock). My reasoning for Agm batteries are inside installations (as the cabin warms, so will the batteries) and not as much maintenance. I'm looking for a system that is dependable as I am not inclined to be the type who will be constantly looking at a monitor wondering what the system is doing, however I know basic maintenance will be required. In other words, put in a good small system up front, let it do it's thing and I'll be fishing. I cook using a gas grill on the porch and I cook stews and such in a Dutch oven suspended over a fire pit by a tripod so none of that aspect is a problem. Looking at the parameters of my idea, do you think that 200ah for batteries will be sufficient or should I increase the ah. PS- I will by no means neglect this system as I take extremely good care of everything I own and the wife does not like it there because there's not enough shopping. Terry

I 'bolded' the bad things to run off grid. You're probably already aware of them! BTW, I have a microwave and use it - sparingly.

I went to 24 Volt, but I have a water pump (850 Watts about 6 mins a day) and digester pump (900 Watts about 30 seconds a day) to feed. Otherwise I would have stayed with 12 Volts. Really, 12V is fine for continuous loads that remain below 1200 Watts with the occasional draw up to 2000 or so. At minimum system Voltage 1200 watts is about 120 Amps on the DC side and 2000 would be ~200. Both can be handled under normal circumstances.

There are advantages to 12V is you're out in the remote; availability of 'repair' parts from Auto/RV dealers and the 12V equipment that exists. But there are disadvantages also. In general, if you're going for the small capacity off-grid system then 12V would probably be better suited. There will be those who disagree with me, of course.

But you should also always plan for the future. How will things be 10 years from now or even 5?

I'd skip the AGM's at first. Their advantages will not off-set the added cost per Amp/hr in my opinion.

You can't really determine an Amp/hr rating for your battery bank without having firm info about the loads.
I'd be more worried about the wife not liking it there. That sounds like trouble!

icarus

Re: batteries/ cold weather

Any resistance heat unit, coffee pot, hair dryer, heater, toaster etc. is bad news for any small off grid system. Consider that there are all kinds of alternatives. For example, Coleman makes a great "Mr Coffee" maker you put on the stove top. Works just like the plug in type, only uses no electricity. We make toast on a small propane catalytic heater, works great. (hard to find the right one however!) Butane/propane hair dryers are available, but why in the world you need to dry your hair is beyond me. Propane/butane, or heat on the stove irons also work well if you really need to iron something.

Just for example, your 1500 watt coffee maker, running 15 minutes/day will use ~375 wh/day,, nearly half of what we use all day.

All that said, I bought Susan a heated mattress pad for Christmas. Draws ~150 watts, but only for ~30 minutes (75wh) a day. Pretty sweet to jump into a warm bed when the room in ~45f and it is -40 out!

Tony

PS, as I am always suggesting, loads always grow! With the bed warmer, a couple of extra lights, another paddle fan, and a hand held cuisine art and we now use closer to 1 KWH day!

Kamala

Re: batteries/ cold weather

I agree with those that suggest using FLA instead of AGM. If I were building a "stationary" system, I would use FLAs and find some way to vent any outgassing. The reason I went with AGMs in my tiny trailer is that they are installed under the bed about a foot from the propane water heater.

You'll spend significantly less money on the FLAs and spend a little more time on them. That time spent could be considered an investment in knowledge or experience. Though I've never maintained a FLA, I don't think it is as esoteric as some posts here would suggest.

All cooking is done over flames... except coffee! I'd fix that for sure!

K

mike95490

Re: batteries/ cold weather

Kamala wrote: »

All cooking is done over flames... except coffee! I'd fix that for sure! K

Even a can of sterno works pretty well, for 1 or 2 people.

northshore

Re: batteries/ cold weather

Hello Thanks for all the input and suggestions. I am now going to take the information and ideas that I've gathered and do a prelimanary cost analysis including comparisons of like components,brands etc.(similar, I believe to what BB suggested-two system design). Once that is complete, I will do a final cost analysis using the components I have selected, along with an ROI for the project( which is important but not the driving factor) ($13.14Kwh is what my last year's grid average was, that shouldn't be too hard to beat). Final tally will then include the 30% tax credit available. Cariboocoot- I would like to look out 5 or maybe 10 years to see what my needs might be, but at my age that scares me! I've always proceeded on any projects I do with with a timeline (I don't like the term deadline because of the negitive connotations plus it takes some of the fun out of it) so I've set July as a good time to start the install for obvious reasons (warm weather). I am quite impressed with this website and the help everyone has offered so when purchase time rolls around, NAWS will be given top consideration for those components. By the way, just to clarify, my wife likes it up there- she just likes to shop more! ciao for now Terry

dagr51

Re: batteries/ cold weather

Are you sure you meant $13.14 per kwh? As in thirteen dollars?

northshore

Re: batteries/ cold weather

That's my average for two years back. The last 13 months goes like this: $598 while using 42Kwh for that thirteen month period ($14.23). The REC had an "operation roundup" where they would round up your bill to the nearest dollar and gave it to those who couldn't afford their services (I wonder why!) and on three occasions, I gave more( in cents) than I actually used. My bill came today for my primary residence and I used 454Kwh last month and it cost me less than using NO Kw's at my cabin! Almost criminal. Terry