Hey Dave. We were going out the door when you posted that query.

I don't recall the exact model I was considering. It was a year+ ago. What I do remember was I could not readily find the operating temperature range so I emailed Xantrax customer support. I told them my temperature range. They responded with the statement that my location was too cold; it was outside the operating temperature range they recommended.

When I asked the same question of Outback they responded with the answer that their eqipment was rated to -40 degrees. Same on their charge controller.

My installation may not be normal. I wanted both the charge controller and the inverter out in the cold. That's for a couple of reasons. I did not want the hum or the sound of the fan inside. I did not want to give up space inside either, or have the equipment dictate how the space in the one room cabin would be used.


I was aware of the story about the ounding of Outback. I heard it happened some time aroun the time Trace became Xantrex, or shortly after.

It would be great to see charge controllers with a much higher voltage rating. Series strings of PV panels make a lot of sense and panel Voc's keep getting higher.

Cold temperatures can really be the worst enemy of electronics.  My other job is kind of rocket science for a little outfit here in the foothills.  Anyway, we have alot of experience with -135F and it turns out that around 0 F electrical components will crack when they start heating from cold storage.  That is why if you look at the specs most manufactures will list their operational and storage temp specs.  What kills electronics is quick temperature changes.

For instance a charge controller at -5F overnight and a cloudy cold morning and a sudden clearing of full sun.
Full power heating from cold.  No matter who puts there name on the equipment there are only so many times you can do this and sometimes once is enough.  Same scenario with the inverter sitting really cold all night and you start a generator and want to charge batteries, run laundry, and maybe something crazy like pump deep well water all at once. If you do not want to have spares for all this gear let it warm up. If you are storing electronics and batteries where humans are uncomfortable keep this in mind.  Being rated at the temp of -40F is alot different than operational for power devices. Making a reasonable (time) transition is what will keep your electronics operational over the long haul. Good Luck with winter!

Thanks for the insight, Dave.  Good thing I live in mild climate as I am known to abuse equipment.

I think I have finally read over the whole topic.  If I missed something, I am sorry for reposting.

Speaking of the cold I was looking for direction on two topics.
I am building a power shed (4'x4') for a small system (100 watts).
My thoughts were that batteries self discharge faster at colder temperatures.  Battery discharge kills batteries.  Large swings of temperature also can destroy electronics.

  Does anyone know about insulation and ventilation recommendations/requirements for battery banks?

I believe that ideally the batteries would be in a conditioned space. That is, not exposed to high or low temperatures. In practice that can be difficult, the more so if like mine the cabin is left vacant and unheated for a week or more at a time.

Self discharge should not be a problem if the batteries are still connected to the charge controller and PV panels. Of course that would necessitate having the equipment rated for the expected temperature range. True, electronics don't like big temperature swings. Again, ideally you would not have them. I bought good equipment rated for the range that may be encountered. Hopeully that will help. Hopefully the solar gods will appreciate my efforts such as they are.

FWIW, my neighbor in the mountains has a system similar to mine. His golf cart batteries are going into their 6th year. He plans on new ones next year as their performance has dropped noticeably this past summer. They have been abused slightly with occasional deeper than recommended discharges.


Batteries do heat up when "working". So theory says that if in an insulated box that heat will be retained better. In my case the problem I have with that is when we are absent our batteries are sitting there not being asked to do anything. There are no discharge loads other than sel discharge. The charge controller hits them daily with a short bulk charge, then a short absorb charge and then floats them till the end of the day. There is very little heating involved in that. I dn't know that insulating would make much difference.  


If you insulate well then you have to figure out how to ventilate enough to avoid the gassing danger without sending the warm air out and bringing cold air in. One of the last things I want is to be forgetful and blow the battery chamber up, and maybe me along with it. Worse would be an unsuspecting third party.


I know someone who uses a small power ventilator. The charge controller activates a relay that turns it on when the batteries are under charge.


If you have a 100 watt system (Is that the power output of the panels?) I wonder if they is enough electrical energy going in and out of the batteries to actually make a measurable difference to the temperature.

Yes 100 watts is the power of the panels and inverter.  Conditioning would be impossible.  I will make a separate post for the simple system.

My concern was that
"All batteries, regardless of their chemistry, will self-discharge. The rate of self-discharge for lead acid batteries depends on the storage or operating temperature. At a temperature of 80 degrees F. a lead acid battery will self-discharge at a rate of approximately 4% a week. A battery with a 125-amp hour rating would self-discharge at a rate of approximately five amps per week. Keeping this in mind if a 125 AH battery is stored for four months (16 weeks) winter without being charged, it will loose 80 amps of its 125-amp capacity. It will also have severe sulfation, which causes additional loss of capacity. Keep your batteries charged while not in use!"
http://www.progressivedyn.com/battery_basics.html

and

"For instance, flooded cells typically use lead alloyed with Antimony to increase their mechanical strength. However, the Antimony also increases the self-discharge rate to 8-40% per month. This is why flooded lead-acid batteries should be in use often or left on a trickle-charger. "
http://www.vonwentzel.net/Battery/00.Glossary/

IIRC, lead acid batteries can discharge 5% overnight in below zero degree temperature, but I can not find any charts for lead acid discharge rates at various temperatures.  So even two 100 amp 12v batteries could self discharge up to 240 watts a day in below 0 degree weather.  My fear is that a week of cold stormy weather could damage my batteries if left unattended. My goal would be to reduce the lowest temperature swings and discharge, but I run into the gas build up problem when insulating.  Does anyone know if the gas in heavier than air?

Just doesn't seem to be a lot of info on the to insulate or not to insulate question.

Lead acid batteries lose capacity as their temperature drops. That is, they are unable to provide the same amount of usable power at lower temperatures as they can at 75 degrees F which is a fairly normal rating temperature. Their self discharge rate decreases as well so that is not as big a potential problem in winter as in summer. That's my understanding.


As for the gasses.. the Hydrogen is very light and rises to the battery box top quite readily. Oxygen is very slightly heavier than air. I'd say the H₂ is more of a hazard than the O.


As for the batteries all I can say is that my RV batteries, 4 x 6 volt golf cart types, have sat thru 3 winters in the mountains with nothing more than 20 watts worth of PV panel and a cheap charge controller connected to them. Of course there are no loads either as I pull the disconnect. The charger is connected directly to the batteries. The panels don't get much full sun either. I leave the batteries fully charged and full of fluid in the fall and in the spring they are still charged and the fluid level fine. That goes or the cranking battery as well. It has a small 5 (?) watt panel.

I'd be worried too if there was no input into the batteries, but my experience has been good with the 20 watt panel. Of course, that is no guarantee that everyone will have the same positive experience.


An excellent battery reerence is...

http://www.windsun.com/Batteries/Battery_FAQ.htm#Temperature%20Effects%20on%20Batteries

Thank you.  It is good to hear from someone with experience.  My weather conditions are similar to yours and if you batteries can handle it with 20 watts mine should with 100.  I will unplug the inverter when I come an go.

Don, have you thought about a thermostatically controlled electric heat element inside the power shed?  I'm thinking something like a heated floor set to keep the shed interior at, say 50^o F. 

I've thought of it, but not very seriously. The only electrical power on site is in those batteries and what is replenished by the PV panels. I don't count the generator as it is a manual start. I have 15,000 KwH total storage capacity. That gives me about 3 KwH of useful capacity @ a 20% maximum discharge.

I simply never figured it would be feasible to use my own electrical power for resistance heating of the batteries themselves. A well insulated compartment would be needed to avoid battery run down. That leads to the question of how to safely ventilate without loosing significant heat. Related to that puzzle is the similar question of how to ventilate the charge controller and the inverter. I believe these two items must be isolated from the batteries as they do contain relays that might be able to ignite any hydrogen present. There are also circuit breakers or fuses associated with them. They also must be vented for cooling in warm or hot weather.

It presents many questions to my mind. It might be worth a discussion if anyone has any ideas. One thing to remember is any system should be able to run itself, ideally with little or no user/owner intervention. I don't even like seasonal adjustments such as inserting or removing baffles, insulation panels, or whatever might be thought of. Any system should be forgiving of forgetfulness    and able to run unattended for a few months.

Ideas are welcome!   

Outside low overnight temperatures typically may fall into the single digits down to zero degrees F (possibly a few hours with 3 to 4 hours at a few degrees MINUS), with daytime temperatures possibly only rising into the twenties during the coldest periods, December through February. That said, it is also possible to see minus 20 degrees at some time during snow storms. No, or little, sun at those times.

 

The self discharge is not really noticeable if the batteries are in daily use or have some charge daily.  I even put a small regulator on small systems as it is possible to boil a battery out if unattended. 

I did a one battery horse watering system at a ranch near here.  I have not had to service it since installed.  Likely I should go check the water levels for the customer or hopefully they have.

This is what I say.  If it is part time do most of what you can to take care of the battery system. You are really not totally dependent on it are you if it is part time?  Expect that the battery will not last as long and it is the price you pay.

If you are full time, then all should be done to address keeping the batteries above 40F and below 90F.

I'm just starting to read up on off grid solar stuff.  The more I learn the more I'm convinced that I want my 12x16 house to be off grid.

I've read this whole thread, and have learned a lot!  Also checked out the Backwoods Solar articles, along with Homepower.com.

It's just a ton of stuff to wrap your head around. 

Any recommendations for good how to solar books?  Looking for something that could take me all the way from design to install of a small off grid solar system.

Thanks,
Beavers

No recommendations on any books. I gleaned most of my information from websites.

One that I ound useful is the collection of Codecorner articles by John Wiles of the College of Engineering, Southwest Technology Development Institute at New Mexico State University (NMSU) in Las Cruces, New Mexico. Being in sunny southern NM his focus is on PV power. It's hard to say where one should start the series as the information in many of the older articles have been superceded by later articles that reflect the ever changing NEC in regards to PV alternative power. It can be interesting though to see the progression.

The Renewable Energy Handbook by William H. Kemp IS amazing, full of info, and explains it for any skill level, he even starts with the basics of how electricity works, but don't get me run, he goes into details for a pro to

Thanks,

I'll check out Amazon for the Kemp book.

I did read a few of the Codecorner articles, seemed like good info to know.  I've just scratched the surface of the Homepower website, there is just so much info there!   

I have not gotten through all of the Kemp book, but I found it to be rather preachy.  Seemed out of place and offputting if his intent was to expand the number of people using renewable energy.  (Not everybody approaches solar as a genuflection to Gaia!)  

Edited to add:  The Dummies book on solar was a good overview, but it only has a single chapter on off-grid applications.  Maybe you can find it at the library. (Do they still have libraries?) 

Quote from: Pritch on November 24, 2009, 12:44:43 PM
(Do they still have libraries?)  

yes, at least we have a good one     The best thing about the library is it's free to read their books. Ours has a suggested purchase program. They don't always take my suggestions but if they do I have first dibs on the book.



Regarding the Kemp book, Amazon.com has reviews that cover the gamut, excellent to poor. The reviews are one thing I like about Amazon.com. 

I have the kemp book.  I have read it twice (there is some stuff that I skip over like hot tubs biodiesel).  I will say that it was helpful. It has some good ideas, but I found it lacking on the technical side.  I'd say it is good for primer to mid level stuff but it wont get you all the way there.  The nice thing is that it is mostly dedicated to off grid.  It is preachy.   I wish I could suggest a better book but have not come across one yet.

Wow, the Sun 100 watt panels are at $1.74 a watt at sunelec.com  Has anyone ever seen a price that low? 

Thanks for the book reviews guys.

While I'm ordering books, I'm want to order a copy of the NEC.  Is there much change from the 2005 to the 2008 version, as far as solar stuff?  The 2005 edition is way cheaper.

The NEC 200x Handbook is more valuable to most DIY'ers as it contains the entire NEC plus explanations and diagrams that do not appear in the code itself.

As for which version to get/use, what does your locale use? That's what I'd use. If they use 2005 note that there are over 300 changes. Some are big, like the requirements for AFCI and some are small, like renaming self threading screws to be known as self cutting screws. Go figure that.  

You might want to read a free download by John Wiles, entitled Photovoltaic Power Systems and the National Electrical Code: Suggested Practices. To quote from the NMSU website...

This guide provides information on how the National Electrical Code (NEC) applies to photovoltaic systems. The guide is not intended to supplant or replace the NEC; it paraphrases the NEC where it pertains to photovoltaic systems and should be used with the full text of the NEC. Users of this guide should be thoroughly familiar with the NEC and know the engineering principles and hazards associated with electrical and photovoltaic power systems. The information in this guide is the best available at the time of publication and is believed to be technically accurate; it will be updated frequently. Application of this information and results obtained are the responsibility of the user.  Be mindful that it is still based on the 2005 NEC, but there may have been some updates.

That guide may be found at...
http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/PVnecSugPract.html


I used the NEC in the public library (reference only, no check out) for some research as well as a lot o John Wiles information. As well I have a small handbook that covers in simplified form the basics of regular house wiring.


I also have seen a paper from the STDI, where Wiles works, PV INSTALLATIONS, A PROGRESS REPORT Only 50% of the systems surveyed passed all provisions of the NEC.

There's also a Code Corner article, #108, that goes through some of the 2005 to 2008 NEC changes.

http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/codecorner.html

Quote from: Mike 870 on November 24, 2009, 04:04:47 PM
Wow, the Sun 100 watt panels are at $1.74 a watt at sunelec.com  Has anyone ever seen a price that low? 

I get a solar industry mag that says there is a glut on them now.  This could be a good time as who knows what the future will bring.  Lack of profits may close some of the manufacturers if it doesn't get better.

I have some that were from them for $1.98 a watt which was the best I had seen earlier.  Still haven't installed them though.

Thanks Don, I really appreciate the help!  I'll be sure to check out the links you gave.
Nebraska uses the 2008 NEC...makes sense to get that.  

I used the load calculator at the wagonmaker site the other night.
I think it's all starting to click, but would like to run it by you guys to see if I'm close to being on the right track.  

This is all based on using propane and no electricity for heat, cooking, refrigeration, and hot water heater.

My total connected watts = 192

Watt hours = 1188

Adjusted Daily AH Load (24v) = 58.28

So with 5 peak sun hours I would need 279 watts of panels minimum.

For three days of storage I would then need 437 AH capacity if I only discharge to 60%.

Using Trojan 6v T105's I would need 8 to get 450 AH of capacity.

Am I looking at this right?  


With a 24V system and 6V batteries the number of batteries in the bank have to be a multiple of 4?

With charge controllers is it best to go with the most amps you can afford?

As far as converters for a small system, will a $300 Samlex, or Exeltech type converter be just fine?  A $3000 Outback converter can't really be necessary for a small system, can it?