Quote from: Dave Sparks on March 12, 2011, 09:50:05 AM....nightmares about racking systems and panels that don't fit from other forums would shock you.  So as long as you buy nice easy things from them all is well, some of the time...

As well as people being given info that was plain wrong... like being told it was okay to series wire too many panels for the charge controller being used. And people being unable to get satisfactory answers to their questions, so much that they try to get free answers from vendors they never bought from.

I haven't been able to get design info from them, but tend to forget that I already know what to watch for in system design on my own.

Hey Don,

Did you ever solve the keep the cans from freezing problem?

Dave, everything was going just fine with the undersink cabinet insulated and a small transmission oil cooler in a thermosiphon loop using water warmed by the water heater on low. Until the pilot went out. I think the pilot may have gone out because of an issue with an extreme cold snap and issues with drawing propane from portable cylinders. I'm not 100% sure on that, but since it's never happened before am leaning to that theory. I think the propane burner kicked in and the supply tank was low and very cold. It could not supply sufficient propane and flamed out. My theory anyways. I did more propane research and now know I didn't fully realize the issues with cold and propane. We had some below zero weather coupled with a week of heavy cloud cover.

Nothing in cans or jars froze solid but water in PEX lines froze. No problems with any valves or the tank though. I think we were lucky.

I have a new solution in mind for next year that involves a hole in the ground. More on that in a new thread later.

I was running a heat trace to keep my sewage pipe from freezing (to the composting bin for the toilet) but noticed that despite the low wattage (I think it was just 5 watts per foot and I used 6 feet) it was still too much for the 660ah battery bank and 615 watt solar power -- in the winter anyway.

I found my battery bank down to 12.0 volts when I arrived Friday and had to ration light usage despite using CFL's.  We added a freezer which uses about 15-30 watts depending on it's cycle and once the batteries were charged up it ran fine but I can see the need to add at least two more batteries to get me to 880 AH's versus the 660.

At the same time, however, I hooked up my Iota charger (finally) and made use of it for a couple hours and brought the bank back up to 12.5v because the clouds just kept the sun from doing it's job!

I plan to work on the solar power in the near future and might installed another panel and battery just for winter use with the heat trace.  I figure I can install a low voltage shutoff like Don mentioned last year as that ought to heat the pipe and then let the battery recharge and then heat the pipe again etc but I'm working on options still.

We want to add a small fridge too and I feel that it's likely ok to run the freezer and fridge (on low settings) when we aren't there to preserve things and provide cold storage when we arrive but I'm learning I need to get back to the drawing board to make sure the system can handle the usage.  God forbid I wanted to LIVE in my cabin! hahaha  I'd have to do some serious work on the solar (add a couple panels maybe and more batteries) to ensure I didn't have to run the generator very often.

However, in the end, it's just plane cool to have solar power

I had my concerns about that heat tape when you mentioned it.

What kind of freezer, if I may ask?


One of the issues with an unattended system is what will it do when it's cloudy for days on end? I planned for three days minimum of capacity (actually have more than that as things are). This past winter we had five days in a row on two separate occasions with continual cloud cover. The weather station records illustrated that starkly with the watts/m*m column never getting above two digits during those periods. (That is sun watts per sq meter, not the PV power output. Right now, sunny day it is at 766 watt/m*m. Summer it hits over 1000)  That would not be an issue if we were at the cabin; I could start the generator. However, if we were absent and if there was something like a refrigerator operating there could be consequences I'd rather not deal with. For that reason I'd like to have an automatic start generator if we were running a fridge/freezer. Peace of mind insurance.

Quote from: MountainDon on March 14, 2011, 05:12:24 PM
I had my concerns about that heat tape when you mentioned it.

What kind of freezer, if I may ask?


One of the issues with an unattended system is what will it do when it's cloudy for days on end? I planned for three days minimum of capacity (actually have more than that as things are). This past winter we had five days in a row on two separate occasions with continual cloud cover. The weather station records illustrated that starkly with the watts/m*m column never getting above two digits during those periods. (That is sun watts per sq meter, not the PV power output. Right now, sunny day it is at 766 watt/m*m. Summer it hits over 1000)  That would not be an issue if we were at the cabin; I could start the generator. However, if we were absent and if there was something like a refrigerator operating there could be consequences I'd rather not deal with. For that reason I'd like to have an automatic start generator if we were running a fridge/freezer. Peace of mind insurance.

I'll have to check the Freezer model -- my wife bought it at Fred Meyers.  Our plan with the Freezer is to leave it set off unless it's needed.  Once needed a Freezer can usually go without power for short periods of time (even days) if not opened.  However, I am concerned, like you, that it could somehow run without power too long -- something to ponder.

I'm also looking at this fridge: http://www.pcrichard.com/catalog/product.jsp?productId=1533&parentCategoryId=7&categoryId=1104&subCategoryId=1104010020

I was told that getting a fridge without a freezer is the key to using less energy.  I guess I'll be doing some learning!!!

An autostart generator would be very nice to have and I might have to put a small one on the shopping list.

As for the heattape, it does seem to be working nicely but uses more power then I anticipated   I think it's going to be perfect for use when I'm there but will have to be shut off when we leave -- which might be fine.

I may look at a timer to turn it on and off daily though.

Quote from: OlJarhead on March 15, 2011, 11:13:41 AM

I was told that getting a fridge without a freezer is the key to using less energy. 

Hmmm. Where did you hear that? How much less? A top load freezer or fridge will be use less electricity, so if the freezer is a top load that can be very good. I've also read and believe that a top load fridge uses less electricity than an upright. But they are the very devil itself for convenience of use.

Are you aware that residential fridges and freezers are meant for use within a temperature range of something like 60 to 100 degrees. It's obvious that when in a hotter location the unit will consume more power. But it is not obvious, in fact it is counter intuitive, to think that in a colder location (like 40 degrees) the unit may also use more power, not less.

Quote from: MountainDon on March 15, 2011, 12:17:54 PM
Hmmm. Where did you hear that? How much less? A top load freezer or fridge will be use less electricity, so if the freezer is a top load that can be very good. I've also read and believe that a top load fridge uses less electricity than an upright. But they are the very devil itself for convenience of use.

Are you aware that residential fridges and freezers are meant for use within a temperature range of something like 60 to 100 degrees. It's obvious that when in a hotter location the unit will consume more power. But it is not obvious, in fact it is counter intuitive, to think that in a colder location (like 40 degrees) the unit may also use more power, not less.

My neighbor who's been on solar for 30 years told me to look for a fridge without freezer.  Something to do with the cycling/dehydrating/antifrost of the freezer I guess.

The cabin stays VERY cool in the summer (as low as 45 at night and remains cool until well into the late afternoon) so I figured the fridge will not have to work too hard in those conditions.  I also plan to put the freezer on the North side to keep it in the shade 95% of the time (if not more).

I'm not sure I got my point about low environmental temperatures and residential refrigerators made. Refrigerators in cold spaces are not going to run as well as they would in their design temperature range. A fridge in a cold space may not save any power.

The common household refrigerator is not designed to operate at 45 degrees. At low environmental temperatures the internal operating pressure of the refrigerant falls below design parameters. That makes the motor run longer to do the same amount of cooling. So even though the unit might run with less frequency it will run longer than if the room was at 75 degrees. The system does not lubricate as well either and that shortens the expected life. Commercial refrigeration units that have the compressors sitting outside on a roof top have different, more complex, more expensive metering devices in the refrigerant section. They can operate in extremes of temperature without problems and with greater efficiency. A residential use refrigerator could be built to run at lower temperatures and still be efficient. That costs a little money and most people keep their residences at least at 65 - 70 degrees, so the manufacturers of residential refrigerators don't spend the few bucks.

There are refrigerators sold as "garage refrigerators" that are made for use in a cold space like an unheated garage. Expensive though.

My point is do not count on a cold environment making any savings in electrical use. I have some info saved someplace, but I don't know where off hand.

I believe the operating problems are most severe with fridges that have a cooling fan with the condenser. Units with the coils under the skin like many freezers, are more immune to the issues. Something to do with pressure head or something. Low temp = low pressure = low flow = less refrigerant and less lubricant flow = trouble, is what I understood from what I read.

Ok,  here goes.  I have a question which I have been researching.  It is about UL products in the solar setup.  I have to pass a code inspection before a certificate of occupancy is issued.  Based upon my readings of discussions here it appears that all products used in the electric system for a house must be UL approved to pass inspection.  If this assumption is wrong, please correct me.  I have been searching for products to build my system.  There are a lot of products out there from some of the big names, but when I look them up most don't advertise if they are UL listed or not.  I was searching through the Xantrex line in particular and found only 2 products advertised as UL listed and that was for UL 458 - Boats and RV's.    I am particularly looking for this in charge controllers and inverters.  Has anyone else run into this?  Am I missing something?  Also, is there a particular UL listing I should be looking for before I buy a product?

UL listed or ETL listed satisfies NEC.  All Outback charge controllers, inverters and power panels are listed. Ditto on the Xantrx C series controllers; probably all their major inverter/chargers.

I noticed that the printed matter I have on my Outback inverter shows ETL clearly. Hidden is the fact that it is ETL listed to UL1741 standards. And if I remember rightly the label on the unit shows the UL symbol. Not everyplace I've seen the unit offered for sale makes mention of any approval.  Reading the manufacturers manual seems to always mention UL or ETL listings.

Depending on how knowledgeable or "by the book" the inspector is it may be the little things that catch you up. Automotive wire and standard welding cables are not UL listed for example. Black wire is not suitable for a negative DC conductor. Run of the mill terminal connectors are not UL listed. The common RV / race car battery disconnect is not UL listed. Some PV modules sold as blemished or seconds may not have UL labels. (sometimes that is because the cells may be placed too close together to pass the high voltage test. Sometimes it may be because of the connecting wires not having UL labels. Sometimes it may be just that they never paid to get the right to use the label).


My battery cables are not UL-Listed. But I used white tape on the ends of the negative cables just like NEC calls for. I did not invite the inspector. There is a break point, above which white tape is accepted and below which it is not.


Side note: When looking at things like breakers and switches, for example, sometimes you come across things with a UL recognized label. These are for components that are used in devices. The entire device can get the UL listed label, but any components with the UL-R symbol are not approved as individual items. Clear? I had found some circuit breakers classed as UL-R. Good price. But by themselves they were not UL-listed. They needed a UL-Listed enclosure as well. Probably more than you needed to know.

Very nicely done Don!  If you are going to be inspected then talk with the local inspector about any quirks he has! Do the best you can about what Don has said. Yes all of the Xantrex high end gear will work for code as well as Outback. The Outback gear came from Xantrex guy's who went out the back door BTW.
Magnum as well and anything from Midnite also! Good luck!

Thanks Don .  I didn't know about the ETL.  I found that the outback flex controller was, but it was not readily available.  I had to go and pull the user manual for the product to get the information.  After much searching I was able to find an owners manual for the C series from Xantrex to find that it is UL certified on page 23 out of 100.  What a real PITA it is to find this information.  With the cost of testing and the necessity of the certification to pass code, you would think this would be more prominently displayed.  The Xantrex website no longer has any links to any of the C series products.    Morningstar charge controllers also seem to be certified, but again, I had to dig through the manual, product by product to get the information.  Very time consuming. I spent a long time on just three controllers.  I can't imagine how long it would take for all the different inverters.   Does anyone know if there is a reason for this?  Is there just a general assumption that major brand names are certified?  Or do inspectors just not usually check?

My view is that the local hardware stores and electric supply sell the UL wires and other parts I would need, but not the off grid components. Education and design of the electric system is the next step for me.

Thanks Dave.  Inspection is certified by any licensed electrician.

Aw shucks    Thanks Dave. 

Quote from: Squirl on March 16, 2011, 09:46:40 AM

My view is that the local hardware stores and electric supply sell the UL wires and other parts I would need, but not the off grid components.

Don't forget that common everyday UL listed AC parts (disconnects, switches, breakers...) are almost always not safe to use on the DC side of the system.

Quote from: Squirl on March 16, 2011, 09:49:22 AM
Thanks Dave.  Inspection is certified by any licensed electrician.

Actually that depends on the county, state, ect. You can do it yourself if you are the homeowner in most places.

to MPPT or not MPPT?  That is the question.

Ok, here goes for discussion.  I am looking to upgrade components of my small portable solar setup to slowly expand more towards a cabin sized system.  These will be UL for a future electrical inspection.  The first component I have settled on is the charge controller.  Some advertisements seem to boast an up to 30% greater efficiency.  Here is the breakdown of my understanding and factors that I used to come to my conclusions.  The first factor was price.  I will use similar devices for comparison (60 amp).  The minimum price non-mppt charger I could find was a Xantrex C60 for $150.  The minimum price MPPT chargers I found were the Outback FM 60 and the Xantrex XW-60 for $500.  So what do you get for that extra $350?  My understanding from some books and articles the MPPT technology has 2 main advantages.  First it takes voltage over the necessary amount for the battery bank and converts it to current.  An example if your panels are putting out 17v and the charging volt of the batteries is 14v the 3v difference would be lost if it were a non-MPPT charger.  So on cold sunny days this would be most pronounced.  The second advantage is that this conversion of volts to current can match higher voltage solar arrays to lower voltage battery banks.  This can be a real advantage by not having to pick you panels as closely and mixing and matching panels.  This can also have an advantage if you want to run the DC solar line a long distance (like don did), because you can use a higher voltage, lower amperage line and just let the charge controller do the work of matching the voltage.  Did I miss anything?

So let me break this down into dollars and my system. 

First, my I don't plan on running long DC lines.  My hope on integrating passive solar into my home means I will have a clearing for solar access around the house.  If I do run a line, it will be 120v AC.

Second, I believe I can shop and match panels in 12 and 24 volt and connect them in series or parallel to match the voltage of my battery bank of 24v to 48v depending on sizing and expansion.  I will reconsider this if I find a great price on an only 12v inverter, but the cost difference in 12 and 24v inverters would half to be over $200 for MPPT to start to have consideration for this factor.  I also would have to find an large difference in price between the panels that put out 100v and at 1 amp and the ones that put out 25v.

So the last factor was the power efficiency gain per $ spent.  The efficiency gain seems to be largest for systems at 12v rather than higher voltage. The panels seem to come in average voltage ratings of 17, 26, 35 Vmp.  So the tolerance of power lost seems to be greatest at the 12 v. level.  I will go with this for maximum dollar differences.  So if I have a 500 watt panel array at 12v, a 30% gain in efficiency (highest advertised gain) would be an extra 150 watts.  This compares to that I can get a 150 watt panel for $300. So with weighting the greatest panel difference and greatest average gain, it is still cheaper to get an extra panel.  This seems to change as you go for larger systems and more panels.  Then the power gain from a $350 additional cost MPPT charger is greater than the percentage gain from adding more panels.

So for simple small to medium sized systems it seems cheaper just to add an extra panel rather than going with an MPPT charger, and for a medium to larger system the additional cost is worth it. 

What did I miss/ get wrong?  I would appreciate any critiques.

I have the Outback FM60. The FM60 has a maximum open circuit voltage (Voc) rating of 150 volts. That means if the incoming voltage from the PV array e\xceeds 150 volts the unit may toast. My Sharp panels have a Voc or 36.1. Three in series equals 108.3 volts. However, in winter with clear blue skies there can be a cold weather induced peak. It doesn't last for long but can still damage the charge controller. I have recorded readings of 141 volts on several occasions.

The maximum Voc of the Xantrex C60 is 55 volts. That is going to severely limit any series connections with PV modules. Voc from the panels should probably not exceed 36 volts. 


Outback generally has a operating temperature range that goes to lower temperatures than many other charge controllers.

To add to the Voc notes above.

I used the string size calculator that Outback has online. It has sliders for maximum and minimum temperatures. It comes up with recommendations for maximum number of panels in series and parallel. There is an extensive list of PV module data to choose from. You can also enter your own data for panels that may not have made it into their database yet. Using that calculator the maximum voltage my three panels should produce is 127 volts (three in series). Looks like I hit 12% more than that. Could have been extra cold or extra bright (8800 feet altitude has less atmosphere to screen the PV modules.).

I believe Xantrex has a similar tool; I know SMA (grid tie inverters) does.

I also believe that when running the numbers to keep everything on the up and up with NEC that there may be another safety factor percentage that needs to be considered. Another 25%, BUT I am not certain of that. So that is only mentioned as a caveat, something to be checked on, no guarantees one way or the other. I may be confused. That may apply to sizing breakers or wires. Darned if I recall for certain.

Maybe Dave Sparks can set us straight on that.

Squirl have you planned out how much battery capacity you will need when all is said and done?  I think that is the place to start and then from that data work out array capacity and from that charge controller size.

Everypanel I looked at had a 25-26 Vmp, but the Voc was around 30.  And all the 17 Vmp ones had a Voc of 23.  The Xantrex C60 can only go 12v and 24v systems.  The C40 can go up to 125 Voc, which should be more than enough if I want to go from a 24v to a 48v system.  My understanding was any voltage differences from over 2-3 above the battery bank would just be lost if I didn't get the MPPT charger.  That is just what I could glean from a few articles on it, not 100% though.

So for $100-$125 I could go for a C40 or TS-45 and a slowly expand a 24v system up to 960 watts, and if I went bigger I could switch to wiring in a series to 48v  up to 1920 watts.  If I went with a system over 1-2kw, then that it would probably be time to upgrade to an MPPT charger.  I would probably have to run the cost/benifit ration if my system was over 1kw.  So if you get 25% more power (average high advertised rate) it would be worth the additional cost at around 1kw.  Although, I distrust the advertised improved rate.  It seems like this would only be under certain conditions and would not apply some or most of the time. So if in reality, if over the life of the product,  it gave you a 15% real world gain, it would become cost effective closer to the 1.5kw range. This of course is with distance run not being a factor. These are just my thoughts so far.  

So operating temperature should be another factor to check.  The Xantrex C series is 0 degrees C.  The morning star and outback are -40 C.  That and the warranty seem to be more brand specific than between the MPPT technology/ cost difference.

Does the FM60 have diversion control for use of excess energy?

Don,
A building department or inspector could calculate that you are overvoltaging a controller from temp data and make you rewire an array. I doubt they would...  As far as safety, the wire is 600vdc, the breakers are 150vdc, and so if you overvoltage the controller it will record that and probably have problems, or will soon. Same with the breaker. The point here is it will not harm anything except your budget. Electrically the controller just stops working or internal circuit protection takes over. Some internal protection is one time only!
One of the extremely nice things about a 600vdc hi voltage controller is that you widen the design range. Also the issue of long distance and small easy wire gages for ease of use is very tempting, as long as one has the wallet!

Ok is the NEC 25% buffer down or up? Example if you have a 45 amp controller at 24v then it has a maximum rating of 1080 watts. A 25% decrease is 1080x.25 = 270 watts  or a panel array of (1080-270) =810 watts.  As opposed to X x 1.25 = 1080. Or an array of 864 watts.  Either way, it is around the panel array size were MPPT technology becomes a cost effective alternative.

I have an idea on size, but there is a lot of time and money before this is all finished.  I currently have a 100 watt 12v. single deep cycle marine battery system now.  It is great for lights and a little bit of charging.  I figure I can add a panel or two and keep it 12v, but I will need a new controller.  As I spend more time there, I figure I will expand it.  I would like to reach around a 500 watt 24v system with four T-105's by around when it is time for the electric inspection.  This would give me 5400 watt hours, and around 2kw hours production per day in the summer. Good for a weekend, but not quite full time.  If/when I am there full time, I would probably want up to 11000 watt hours capacity and maybe a 750 watt panel array.  My estimate is around 1.5-2kw hours a day (what I have used in the past).

Since I am on the very top of the mountain, I figure I will want to add a small wind system eventually.  I have read that the power output of these can vary from a little too extremely high.  I think I would give it its own charge controller.  I will probably install this type of system after I get a certificate of occupancy.  Between the two systems I have an average estimate of 3-4 KW hours per day, which is less than my current electric usage.

This lead me to kicking around the cost/benefit of MPPT technology, so I thought it would make a good discussion topic.

on the NEC rules...
It's volts or amps.

(1.25 x 1.25 is 1.56, so rather than go through n * 1.25 * 1.25, I use n * 1.56)

Example. Sizing a circuit breaker to be used between the PV modules and the charge controller.

Take the short circuit current rating (Isc) of the PV module you plan to use and multiply it by 1.56, then select the next higher breaker size. So Isc = 8.13 x 1.56 = 12.68, probably use 15 amp breaker.

If the Voc is 36.1, then 36.1 x 1.56 = 56.3 volts, so the DC voltage rating of the breaker should be at least 56.3 volts.


More thoughts on selecting, or not selecting MPPT, later.


PS I never overvolted anything. I came close on two days but since it was during the coldest temperatures recorded in some sixty years it's not normal. The next highest recorded voltage was 127 which is very well within the 150 maximum. I know it would only take once.  If I get concerned I have a choice of a higher volatage controller or a cold weather panel cut out. I have toyed with the thought of a cut out. 

I meant "you" in the same sense as "one".