OFF GRID POWER; various thoughts on...

[OlJarhead]

Oh, I understand now OJH.

In that case we need another look. But that charge controller has to go or that panel would cook it.

But before that, what is the amp-hour rating of those batteries? You want two in parallel as I understand it.


OR pick a panel that's smaller.... have to run some numbers.....

Thanks -- I'll check the amp hours (thought maybe it was on the link I gave)...the idea was the I needed to hook up one battery for the camper but figured it would be better to put them both in parallel so the trailer could draw on more reserves if needed (it's used the most).

In the end I figured it might be a good way to break into the world of solar stuff instead of trying to go full force into off grid systems like yours (which I drool over) 

[MountainDon]

The specs didn't come up on the link, but I'll wager a donut that you have group 27's with 105 amp-hours at 12 VDC.

So if you put two of them in parallel you have 210 amp-hours total.
Limit running them down to a max of 50% so that gives you 105 amp-hours of usable power.
Keep in mind the available capacity decreases with cold.
Anyhow 105 amp hours @ 12 vdc = 1260 KwH


I ran two such batteries in our RV for years, when it was a real RV that we drove around in. Those batteries would give us a good day/night of use in cold weather with most of the power being used by the RV furnace blower. I think ours draws about 4 amps.


So if you used up 1200 watts of power and a panel puts out 85 watts, you would need 14 hours to recharge. Not good. It would be best to not use that much power, batteries last longer i not sucked down so much. To regain that sort of power fast you need 20 amps or more going into the batteries. That's about 240 watts.

The 85 watt panel would slowly charge the batteries up over a few days with no use and would definitely maintain the charge over a period of time with no use.

 

[OlJarhead]

The specs didn't come up on the link, but I'll wager a donut that you have group 27's with 105 amp-hours at 12 VDC.

So if you put two of them in parallel you have 210 amp-hours total.
Limit running them down to a max of 50% so that gives you 105 amp-hours of usable power.
Keep in mind the available capacity decreases with cold.
Anyhow 105 amp hours @ 12 vdc = 1260 KwH


I ran two such batteries in our RV for years, when it was a real RV that we drove around in. Those batteries would give us a good day/night of use in cold weather with most of the power being used by the RV furnace blower. I think ours draws about 4 amps.


So if you used up 1200 watts of power and a panel puts out 85 watts, you would need 14 hours to recharge. Not good. It would be best to not use that much power, batteries last longer i not sucked down so much. To regain that sort of power fast you need 20 amps or more going into the batteries. That's about 240 watts.

The 85 watt panel would slowly charge the batteries up over a few days with no use and would definitely maintain the charge over a period of time with no use.

 

Interesting.

I'll have to do some checking to see what I'm using, at the moment with one battery I can drain it over night if it's very cold and we run the heat a lot.  I think we ran the heat one night for about 4 or 5 hours and the battery began to drain (might have been longer) so I killed the heat and we waited 'til morning to kick on the generator and were able to kick the heat on again then.

Bear in mind this is a tent trailer and it was around 5 to 10 degrees outside!  My water in the coffee pot (I always set it up the night before) froze solid!

But most nights we don't have that issue at all.

[MountainDon]

We had issues with running the battery down in cold weather when we had one battery. Those RV furnaces are power hungry. When we went with two batteries it was much better and the last time I replaced the batteries I went with 4 six volt golf carts batteries in a series/parallel set up. That's even better. I never bothered with solar panels as I figured I needed more than I had space for. Plus I didn't want a system for the RV once the cabin was built. I knew I wanted more PV for the cabin and I had also decided the cabin would be based on a 24 VDC system so 12 VDC things like the charge controller and the inverter would not be usable in the cabin.

That's how it worked out for us.

[OlJarhead]

We had issues with running the battery down in cold weather when we had one battery. Those RV furnaces are power hungry. When we went with two batteries it was much better and the last time I replaced the batteries I went with 4 six volt golf carts batteries in a series/parallel set up. That's even better. I never bothered with solar panels as I figured I needed more than I had space for. Plus I didn't want a system for the RV once the cabin was built. I knew I wanted more PV for the cabin and I had also decided the cabin would be based on a 24 VDC system so 12 VDC things like the charge controller and the inverter would not be usable in the cabin.

That's how it worked out for us.

Interesting.

Not sure what the cabin will need or I'll want -- I figure that's a long way off.  But I know the water pump in the well is 12v and my plan has been to put the RV battery (one of them anyway) in there with a solar charger to keep it topped up.  Of course I'd have to build a pump/well house too...but my thought was that once we're done camping in the trailer and staying in the cabin we'd use the setup for the well and start to seriously think about the cabin. 

Having learned on the trailer of course

There is also the likelihood that the camper and the tent trailer will get lots of use still since we hav ea big family.

Anyway, that reminds me, I ought to toss the batteries on the charger for a while.

[rick91351]

With all the concerns with batteries getting too hot and too cold and other components as well having to sit outside in battery sheds and boxes would it pay to build a cellar?  For example into a hillside to house all the components in.  I understand it would have to be vented perhaps with a small fan to carry away hazardous fumes.  That seems as if it would be a good solution to stabilize temps in larger systems that might have one or more banks of large batteries.          

[MountainDon]

I believe that would be a great way to stabilize the temperature fluctuation Rick. One could build a simple cellar set back in a slope for just the batteries. As long as there was a vent tube exiting upwards at the highest point of the enclosure I'd think the H₂ would vent off readily. Some battery chambers have powered vents with the fan being activated only during equalization, when there is the greatest volume of gasses produced.

[Beavers]

Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps.

Any idea how long a "sustained period" is?  Does that mean a couple of hours charging with the generator if the panels aren't keeping up with the charging, is a no go?


I've got a cheap 3500w generator that I've been running tools with while building.  I'm thinking that making one of these lawn mower engine/car alternator generators might work better for keeping the batteries charged.  I'm pretty sure that it would use less fuel, it would be DC power (I could run it right into the charge controller), and I should be able to idle it down to put out less than 26 amps.  Anyone built one of these or have any thoughts on how well they actually work?

http://theepicenter.com/tow02077.html


One last question...

Even the small system that I'm looking at is going to run about $3000, with a pretty good chunk of that being the cost of the panels.
If I started off with just batteries, charge controller, and inverter, I should be able to keep it all charged if I ran the homemade generator 2hrs. a day.  
Within 6 months I would be able to add the panels.

What to you guys think, good or bad idea?


Thanks,
Beavers

[MountainDon]

Good question on what does a "sustained period" mean, Beavers.   I never worried about it as the Iota IQ smart charger I used on the batteries in the RV switched itself beginning with the bulk charge, then absorb and ending in float. With 420 amp-hours of batteries the 55 amp charger was just about perfect.  My generator is a Yamaha 2800i inverter type and it would throttle down as the charger took less current. The Hondas throttle down even better/more.

A note on the Iota DLS chargers. It is possible to 'stack' them in parallel to increase capacity if needed. Same models only.

I believe that if you charge at the C/8 rate you will not be likely to overdo it if you cease the charge when the batteries are full.

If you built an auto alternator based generator I'd think the built in regulator should keep the batteries from being overcharged. A manual throttle control to keep the starting charge rate down to the C/8 rate would work. You'd need a good ammeter to set it. If you were to use an auto alternator charger I would rely on the built in regulator and not try feeding the charge current through a PV charge controller. Most charge controllers are really designed for use with a PV panel input. I've seen discussions on the Outback user forum and the recommendations regarding inputs other than PV are always pointed out to be ill advised by their experts, especially when it comes to mixed feeds. Some charge controllers that have diversion load capability (like you'd need with most wind generators) could likely be used to control a generator output but I don't see any advantages to that. Perhaps some else may have some solid information on that.

Note that the better PV charge controllers have a battery temperature sensor, usually as an option. They are worth it. The charge controller will make adjustments to the charge rate. If the temperature gets too high the charge rate will be reduced. The better sine wave inverter/chargers also have remote battery temperature sensors which is valuable when using them to charge the batteries.


I basically ran a small system with 4 six volt golf cart batteries (series/parallel for 12 VDC) in the RV for 3+ years with no panels. I put something like 700 hours on the Yamaha. I did have a couple small panels hooked up through a cheap controller to keep the batteries floated during our absences, which included 3 - 4 month winter stretches with no visits for the first couple years. 30 watts worth which became about 20 after one panel suffered some damage. They were excellent for that purpose.

So I believe you could get everything but the PV panels and the charge controller and add them later if you can't buy it all at once. I would say that would work as long as you don't have any prolonged periods where the batteries would just sit there self discharging. I would recommend a disconnect switch so you can easily remove all loads when you are gone. Our RV had some phantom load I could never find; the disconnect fixed that when we'd leave.

[Beavers]

Appreciate the info, thanks Don.

I'm just trying to slap something together to provide a minimum amount of power for a few months while I learn more about solar, and come up with cash to pay for a larger system.

I was thinking that I would still need a charge controller, but if the alternator regulator would work that would be great to save the money on the charge controller.

In a full system the generator hookup is through the inverter, and then back into the batteries?  Looking at inverters it looks like only the higher dollar inverters are set up for generator use.  So with a cheaper inverter you still need a charger like the Iota to have a generator backup? 

[MountainDon]

In a full system the generator hookup is through the inverter, and then back into the batteries?  Looking at inverters it looks like only the higher dollar inverters are set up for generator use.  So with a cheaper inverter you still need a charger like the Iota to have a generator backup? 

Depends on where you draw the line for becoming a higher dollar inverter, and how much power and what wave form you want/need.

Xantrex, for example does have a square wave inverter/charger, 1500 watts inverter, priced at something like $800. To me that's not cheap, nor is it overly expensive; model TR-1512 (also in 24 VDC models I think). A unit like that has three stage charging and an equalization charge setting. I looked or quite some time for a stand alone charger that had equalization capability and never found one that made economic sense. It was better to go with a combination unit, IMO.

You should have an equalization setting if you are using flooded lead-acid batteries. If you go with AGM batteries you don't need equalization capability, AGM's don't like the higher voltages.

I had some other thought rolling around and it got away on me... maybe I'll be back in a bit.      

[MountainDon]

Oh!

It was simply to note that inverter/charger units operate in a pass thru mode, when the AC generator power comes online. When generator input is sensed, the inverter section switches off basically, and the generator power is passed thru to the house/cabin power circuits. At the same time the battery charger section will accept incoming generator AC power and begin to charge the batteries.

If a big AC load in the cabin comes on the generator input into the charger may be reduced until the AC load is removed. I only mention this as I found it interesting. I've watched the generator power automatically split and change between charger and AC use on my Outback Mate monitor, as Karen used the toaster or microwave while the generator ran.

Since my generator is smallish I have my inverter/charger programmed to accept only up to 20 amps generator input. The inverter on the other hand can pump out 30 amps continuous. I've seen the situation where all 20 amps (2400 watts) from the generator goes into the cabin AC loads and the inverter supply an additional 800 watts from the batteries. Then with the big AC loads removed the inverter/charger goes back to charging.

[MountainDon]

Arizona Wind-Sun has excellent information on batteries available.

Beavers, you've seen it, but I mention this for others. According to them "At approximately -22 degrees F (-27 C), battery AH capacity drops to 50%. At freezing, capacity is reduced by 20%."

My battery bank was sized taking this into account. I also thought long and hard about insulation.   In the end I decided against the bother of insulating. I may have mentioned my reasoning before; I don't recall. So will the reader please forgive me for boring them if I am repeating myself.

My cabin is seasonal use. Mid-May through August we are up there virtually full time. In winter (December through March) the cabin may sit for 2 to 3 weeks (hopefully never longer   ) with nobody there. My collected data shows that in periods of inactivity the PV system puts 300 watt-hours maximum into our 15,120 watt-hour total rated capacity battery bank. That may change upwards as the batteries age. That is so little input I seriously wonder there would be any measurable warming effect? I believe it is so insignificant an amount that there would be no benefit to the trouble and expense of insulating while still providing ventilation. That's how I see it. Others may have differing opinions.  

If, on the other hand, our cabin was used continuously through the winter months there would be much more power flow in and out of the batteries; with the resultant internal battery heating byproduct, it would most likely be worth the effort involved to provide insulation. As with so many things regarding homes and cabins there is no "one size fits all" answer.



One thought I have had is that it is a shame to be wasting all that solar power when the system sits idle. It would be cool to be able to use that excess power in the manner of a diversion load as used in wind generation. The excess power could be used in a resistance heater to either warm the batteries or perhaps to keep the temperature inside the cabin from falling as low as it does. The Outback FlexMax charge controller has an auxiliary function that I'm sure can be used for something like that.
other brands may have similar features. I have not taken time to check it out. If anyone has any thoughts on that I'd be happy to hear about it or carry on a discussion.

[OlJarhead]

In our cabinets in MNN we installed battery blankets.  These are DC powered blankets that are designed to keep the batteries from freezing in serious sub zero weather.

I'm wondering if something like your ap Don, would benefit from that?  specially since it could be used as a diverter for the unused power

[MountainDon]

Something like that would help keep the battery temperature up with the excess power. It would be akin to Glenn's use of excess power being used to pump water.

[OlJarhead]

Something like that would help keep the battery temperature up with the excess power. It would be akin to Glenn's use of excess power being used to pump water.

I could look for who the manufacturer was if your interested.  We use them for Cellular backhaul sites where we've got SONET transport nodes and MW transport gear 

[MountainDon]

cool.  see if their are 24 VDC models. Thanks

[Beavers]

   

This place is a great source for info, and I really appreciate the help!  But man...the more I learn the more I realize how much I don't know!

I got my copy of the NEC in the mail today, and after skimming through it, I realize I have WAY more to learn than I thought!

Oh well...a year ago I didn't know the first thing about building a house, but with a lot of studying and the help of this forum, I've managed to figure it out. 

Guess it's time to get serious with studying up on the NEC first.

[OlJarhead]

http://www.watlow.com/literature/specsheets/files/heaters/colfrzs0407.pdf

Comes in 12vdc, 48vdc, 120vac and 240vac


But at 12vdc you might be able to work it no?

Check them out

[MountainDon]

Those guys have a whole world of available heaters. They would be able to supply whatever was needed by the looks of it. Whether or not their equipment would be cost effective is the thing.    

This will need some more thought and research.


The first step will be to come up with a realistic estimate of how much excess PV power there is in summer and winter......   more to come.


I'm going to park this link to those guys website here as a handy thing.

http://watlow.com/products/heaters/ht_flex.cfm

[Pritch]

Well Don, now you have to start planning your battery box insulation retrofit!   

[OlJarhead]

Those guys have a whole world of available heaters. They would be able to supply whatever was needed by the looks of it. Whether or not their equipment would be cost effective is the thing.    

This will need some more thought and research.


The first step will be to come up with a realistic estimate of how much excess PV power there is in summer and winter......   more to come.


I'm going to park this link to those guys website here as a handy thing.

http://watlow.com/products/heaters/ht_flex.cfm

We use them to keep the batteries from freezing when it's -40 in MNN    But they do work.  I'd also like to check and see what the cost is (I ought to find out who our rep is -- *chuckle* maybe I can get a deal on some )

[MountainDon]

Well Don, now you have to start planning your battery box insulation retrofit!   

something to think about over the winter.   

[MountainDon]

Okay, if anyone has been holding their breath on this "excess PV power" idea you may as well take a breath now. This has become very low priority for me right now. I've done some research and more thinking. Here's my reasoning....


First let me say that the procedure to setup the Outback inverter to use the excess power is straightforward. Matching the load to the available excess would be the main trick. Too large a load would have the system continually cycling the diversion load on and off too much.

Standard Test Conditions (STC) in the PV industry are based on an irradiance of 1000 watts/ square meter. In summer we get 6 - 8 very good hours of sunshine a day with 2 to 3 hours over 1000 watts/m*m, the balance over 700 watts/ m*m. In summer I don't have much use for that extra power. We could use it in winter, though and that was what I was hoping to do.

In winter we get about three real good hours of sunshine, 11:30 AM through 2:30 - 3:00 PM. Real good in winter meters out at 450 to 550 watts/m*m. Much less than summer.

Let it be noted there are three stages in charging the batteries, bulk, absorb and float. During the bulk stage all the power from the PV panels is used to charge the batteries, assuming an MPPT charger. In absorb and float there is waste, some power from the PV panels is wasted. On a day after typical loads the day/night before, it takes until 1 to 2 PM for the bulk stage to be completed. This past weekend we didn't even make bulk on Sunday; very cloudy.

So if I say the winter maximum output is about one half that of the summer, that would be approximately 624 watts total rated panel capacity x 50% = 312 watts.... round that up to 325 for good measure.  325 x 3 hours is 975 watt/hours, lets call it 1 KwH. That's like running one of my electric heaters on medium for an hour. Not much warmth for the trouble. 1000 watts = 3412 BTU


In summer though there may be enough excess to run something like two of these pads:  12 volt / 30 amp / 370 watt  from solarseller.com ....  scroll down the page about 2/5 the way.

http://solarseller.com/diversion_load_heating_air_water_wind_hydro_solar_loads.htm

They could be wrapped on the water heater tank and the foam insulation replaced. I'd have to do some calculations to see if it would be practical or not; cost vs benefit.

Thoughts welcome.

[rick91351]

Don: I am tossing a dream or two but if you went to a tracker system.  How much more output do you feel you would see from your panels?  The literature I am seeing is all over the place everywhere from 25% to 50%.  25% would hardly be worth it cost wise I would think.  However if you could achieve even 35 to 40% that would really be getting into the more doable lets take a look at this would it not?  Especially if it were in more of a every weekend to full time residence application or say a remote pumping application? 

In your location do you have any problems with ice accumulation on your panels and cutting down your output that you have noticed?  I would think they would be dropped down now to almost no chance unless you have a lot off freezing rains mixed with snow.

 rlr