Mountain cabin off-grid

Horsefly · September 2016

Please excuse my lack of knowledge (but maybe I'm in the right forum!). I'm a retired electrical engineer and so I hope I can noodle my way through whatever help you guys provide.

We (my sister, brother, and I) have a cabin in the high country of Colorado. We are somewhat committed to putting in solar and reducing our use of the existing gas generator, but are novice / clueless about the path ahead. Here's what I think is probably the relevant details:

The place is pretty inaccessible for 4-5 or so months of the year. Whatever we do needs to survive on it's own for this time.
Although completely off-grid (many miles to any grid service), we built the place wired for 120V and have had a gasoline generator for the past 40 years (current generator is 9kW).
We do have a few (3) propane wall-mounted lamps for the evening, and a propane refrigerator, and the water heater is propane.
The largest draw of power is the well pump. We have a pressure tank so that the pump only has to run when the tank gets low, or when someone is showering. We think the pump is about 1400W (120VAC), but I'm not sure what the startup surge is. On a typical visit by one of our families to the cabin, the pump causes us to run the generator for maybe 5 minutes, 2-5 times per day.
We probably have at most 15 120V incandescent lights in the house, which we are in the process of swapping out for LEDs.
We do have a small microwave oven (maybe 1500W load), but I'd be surprised if it is used more than 30 minutes in a year. We've visited a few times this year, and never used it all.
The only other things that will draw power (if we have it) are cell phone chargers and laptop chargers.

Our initial calculations allowed for the well pump and the microwave at the same time (unlikely), along with several chargers and all the lights. We came up with 3700W, and my initial take was that was how much inverter/charger we needed.

Although I'm sure I'll have more, my initial questions:

If we can tilt the PV panels enough to ensure they are not covered by snow and they get sun exposure through the winter, are we safe in assuming the batteries can remain sufficiently charged through the winter to not do harm?
We have a sufficient but pretty cheap generator, that probably could never be retrofitted to auto-start based on the needs of the batteries. Aside from the winter when no one is there (see point #1), we may be OK if whoever is visiting can get some indication that they need to start the generator. Is it safe to assume most of the inverter/charger choices have some sort of indicator that can be wired up?
If we do go for the 3700W assumption, it is allowing for the absolute worst case (probably less than 1%) peak draw on the system. Would it be crazy to size it more like 2000W and just go with a rule that (for example) no one should run the microwave (or a hair dryer, etc.) while the pump is running? What happens if the draw exceeds the rating of the inverter?
Although I've looked around, I'm a little unclear on what the temperature will do to the deep cycle batteries. It's pretty certain that wherever we put the battery bank and the electronics, the batteries will get down below freezing, but probably not below 0 deg F. If we maintain the charge in them (see #1 above), will they be OK for 4-5 months?

Like I said, I'm sure I'll have more questions. I've been reading up on this site and others for days now (I currently have about 30 tabs open on my browser!), so I'm learning as fast as I can. Be gentle, but thanks for the advice!

Steve

softdown · September 2016

Thats a lot of info. I'd recommend a 1500-2000 watt high frequency, pure sine inverter. High frequency means smaller and affordable....like $500-600 or so.

The snow will stick to the panels unless the angle is ridiculous. I think a 45 degree angle is good for Colorado panels and the average situation. 22 degrees is best for summer. 52 degrees is best for winter. These figures are for southern Colorado by the way. 37 degrees latitude means best year round production at 37 degrees tilt.

Batteries are fine at any temperature unless they lose their charge to a low level indeed. I'd consider disconnecting them and checking them in the middle of the winter.

How many watts of PV are you thinking? I would think that 800-1200 watts would generally do the job. I'd go MPPT charge controller with over 600 watts. 24 volt system with four 6 volt golf cart batteries ought to do it. You could be up and running for less than $2000 if you work at it.

I tend to think economically. You being an EE....you may want to spend serious money. Very easy to do with solar. What part of the state is the cabin?

Marc Kurth · September 2016

softdown said:

Thats a lot of info. I'd recommend a 1500-2000 watt high frequency, pure sine inverter. High frequency means smaller and affordable....like $500-600 or so.

The snow will stick to the panels unless the angle is ridiculous. I think a 45 degree angle is good for Colorado panels and the average situation. 22 degrees is best for summer. 52 degrees is best for winter. These figures are for southern Colorado by the way. 37 degrees latitude means best year round production at 37 degrees tilt.

Batteries are fine at any temperature unless they lose their charge to a low level indeed. I'd consider disconnecting them and checking them in the middle of the winter.

How many watts of PV are you thinking? I would think that 800-1200 watts would generally do the job. I'd go MPPT charge controller with over 600 watts. 24 volt system with four 6 volt golf cart batteries ought to do it. You could be up and running for less than $2000 if you work at it.

I tend to think economically. You being an EE....you may want to spend serious money. Very easy to do with solar. What part of the state is the cabin?

What are the numbers behind these suggestions? What daily load did you use for PV/battery bank sizing?
Do you feel that a 1500-2000 watt inverter will handle the inrush load of a 1400 watt AC motor? (I don't)

I do NOT claim to be an expert, so help me understand the logic behind the suggestions.

Marc

softdown · September 2016

My 1500 watt inverter handles a 3000 watt surge.

jonr · September 2016

Consider getting a non-pressurized water storage tank and a small DC pump. That could allow running the generator only once every few days.

mike95490 · September 2016

The starting surge for the water pump is the main driver. Getting the nameplate off the motor is important. Sizing the inverter to accommodate that is crucial. I can attach a couple charts showing motor size & starting current (LRA - Locked Rotor Amps). Good inverters have a 3 sec or 10 sec surge rating, so you can properly size the inverter, OR install a larger pressure tank and just manually run the pump. Do you have any idea, of when the pump is started, how it lugs the 9kW genset, little, lot, not at all ?
You may want to contact an electrician with a PEAK HOLD AC Ampmeter to capture the 1/2 second starting surge. Standard meters won't read it, peak reading meters are $400, so hiring electrician with one is cheaper, unless you want a new toy, or know how to wire a load shunt to a O-Scope to read and hold, the starting surge.

Image: https://us.v-cdn.net/6024911/uploads/editor/c7/kj40fxmx3gis.jpg

If all your loads are disconnected, even solar glow through snow, should keep the batteries topped off, just fill with distilled before you leave in the fall. -77F is pretty cold !

Image: https://us.v-cdn.net/6024911/uploads/editor/ip/vuy5rjaqym2p.jpg

Horsefly · September 2016

First, thanks for the quick comments so far.

softdown said:

Thats a lot of info. I'd recommend a 1500-2000 watt high frequency, pure sine inverter. High frequency means smaller and affordable....like $500-600 or so.

The snow will stick to the panels unless the angle is ridiculous. I think a 45 degree angle is good for Colorado panels and the average situation. 22 degrees is best for summer. 52 degrees is best for winter. These figures are for southern Colorado by the way. 37 degrees latitude means best year round production at 37 degrees tilt.

Batteries are fine at any temperature unless they lose their charge to a low level indeed. I'd consider disconnecting them and checking them in the middle of the winter.

How many watts of PV are you thinking? I would think that 800-1200 watts would generally do the job. I'd go MPPT charge controller with over 600 watts. 24 volt system with four 6 volt golf cart batteries ought to do it. You could be up and running for less than $2000 if you work at it.

I tend to think economically. You being an EE....you may want to spend serious money. Very easy to do with solar. What part of the state is the cabin?

I haven't gotten to the PV panels part of this. I'm mostly assuming that we can size that as needed once we understand everything else. Hopefully I'm not completely wrong.... I'll have to look into high-frequency inverters, as I don't think I know that term. Same goes for the angles of the panels. The place we are talking about is about one-third of the north in CO (north of Telluride), but since I haven't looked too much at the PV panel stuff, I don't know much about the angles. It sounds like maybe it is OK to allow the batteries to go down some while panels are covered with snow.

softdown said:

My 1500 watt inverter handles a 3000 watt surge.

I have noticed that some of the inverters handle quite a bit of surge. I need to figure out what our pump start-up surge is, and compare some of the inverters that we have looked at.

jonr said:

Consider getting a non-pressurized water storage tank and a small DC pump. That could allow running the generator only once every few days.

This is a really interesting comment. Is the idea here that a non-pressurized pump is simply gravity driven, and the small DC pump runs maybe more often but not so energy-consuming? If we can reduce the surge of that pump, it can really help our economics.
Again, thanks for reviewing, and thanks for the comments. I'm learning lots from you folks! Steve

Horsefly · September 2016

mike95490 said:

The starting surge for the water pump is the main driver. Getting the nameplate off the motor is important. Sizing the inverter to accommodate that is crucial. I can attach a couple charts showing motor size & starting current (LRA - Locked Rotor Amps). Good inverters have a 3 sec or 10 sec surge rating, so you can properly size the inverter, OR install a larger pressure tank and just manually run the pump. Do you have any idea, of when the pump is started, how it lugs the 9kW genset, little, lot, not at all ?
You may want to contact an electrician with a PEAK HOLD AC Ampmeter to capture the 1/2 second starting surge. Standard meters won't read it, peak reading meters are $400, so hiring electrician with one is cheaper, unless you want a new toy, or know how to wire a load shunt to a O-Scope to read and hold, the starting surge.

If all your loads are disconnected, even solar glow through snow, should keep the batteries topped off, just fill with distilled before you leave in the fall. -77F is pretty cold !

This is awesome info! Thanks for that! I know (from school decades ago) that electric motors draw a ton at start. I'm not sure we can figure out what we have. Truth is, the current pump has probably been there for many years, and we don't know what it is. It's only a 90 foot well (and the pump is only down about 50 ft), so it doesn't have to work hard.

The current generator doesn't seem to strain at all when the pump turns on. The current one doesn't have an automatic governor driven by the generator load. The last one did (we had to replace it last year),it was rated lower (maybe 7kW?), and between the load governor and the lower rating, you could really tell when the pump kicked in.

Getting an electrician up to the cabin will be expensive (30+ minutes each way on a dirt road, minimum) but we may consider that. Like I said, I was trained as an EE - Can I rent one of these peak hold ampmeters?

I like the idea of the batteries being fine through the winter!

Steve

westbranch · September 2016

My thoughts go to having an elevated water tank large enough to handle 3 days (*avg weekend) of use for the max number of people using the place and a generator that is large enough to run the current pump or a Grundfos SQ pump, which should use less power , economics come into play here, and use solar for the other uses of AC power...

BB. · September 2016

In general, like to suggest conservation first--For off grid solar, it is almost always cheaper to conserve energy than to generate it.

Ignoring the well pump... You would get away nicely with as small as a 300 Watt TSW AC inverter. And 2-4 "golf cart" 6 Volt @ ~200 AH batteries for a 12 volt battery bank (200-400 AH @ 12 volts). Running LED lighting, laptop computer+cell phone charger, maybe a small 12 VDC (ceiling?) fan for summer, and a 12 VDC RV type water pump to pressurize the cabin plumbing.

For winter--A fully charged battery bank (lead acid) will not freeze (until something like -70F). And what many people do is put a vertical (wall mounted panel or two) on the side of the building that will float charge the battery bank (call it ~1% rate of charge):

400 AH battery bank * 0.01 rate of charge = 4 amps
4 amps * ~18 volt Vmp solar panel * 1/0.77 panel+charge controller derating = ~94 Watt minimum panel for winter float

In general, a flooded cell deep cycle lead acid battery should be floated (in storage) or recharged ~24 hours every one month at ~75F... If the battery bank is kept below freezing (winter) and it was fully charged before winter shutdown--You can usually get away with no float charging during winter (or live with snow covered panels during deep winter) without much issue (cold lead acid batteries have much lower self discharge rates).

Just to give you an idea (using our basic off grid cabin rule of thumbs) for a 12 volt @ 400 AH battery bank (4x golf cart batteries--cheap and pretty forgiving):

400 AH (at 12 volts) will "reliably" support a maximum of 1 kWatt rated AC inverter (use as small of AC inverter as practical for your needs)
400 AH * 12 volts * 0.85 AC inverter eff * 1/2 days of "no sun" * 0.50 maximum discharge (for longer battery life) ~ 1,040 Watt*Hours per day (balanced system design)
400 AH * 14.5 volts charging * 1/0.77 panel+charge controller derating * 0.05 rate of charge = 377 Watt minimum array (weekend/seasonal usage)
400 AH * 14.5 volts charging * 1/0.77 panel+charge controller derating * 0.10 rate of charge =753 Watt array nominal (full time off grid)
400 AH * 14.5 volts charging * 1/0.77 panel+charge controller derating * 0.13 rate of charge =979 Watt array "cost effective" maximum

You can look at a new/smaller well pump (as recommended by others above) to run from a (hopefully small) solar power system--Or (for example) a cistern that you run the genset 1-2x per week to fill, and use gravity or 12 volt RV pump for pressure.

The idea is to keep the system small--Perhaps you can even cut back down to something like a Honda eu2000i genset--~1,600 Watts maximum with around 4 hours at full load to ~9+ hours at 400 Watt load (or less) on 1.1 gallons of gasoline.

And for seasonal usage--Perhaps you use the off grid solar for "quite time", and the genset for daytime tasks (fill cistern, run shop tools, recharge battery bank during bad weather, etc.).

-Bill

mike95490 · September 2016

Batch up a bunch of thoughts for the electrician and get your moneys worth. Or price out a peak reading meter, expecting to hit up to 60A ac for a couple cycles. You have to make sure the meter responds to measure the true peak that the inverter will see,
The smallest 115V motor in my chart, is rated 29A locked (3335w) and 9A running (1035w) and then there is
POWER FACTOR to consider too, when running off of an inverter.

ramloui · September 2016

On the subject of batteries left alone in winter, I tilt 2 of the 6 panels (500 W out of 1500 W) in my array to almost vertical when I shut down the cabin in the fall. I turn off all of the loads, including the inverter, do an equalize before I leave then turn off the ato equalize option on the CC. When I come back in May, the batteries are full and happy.

Cheers!

Louis R.

softdown · September 2016

Snow will find a way to stick to vertical panels just like it sticks to vertical car windows. The initial snow melts on contact and forms irregular ice...just like your car windows. This forms the perfect toe hold for snow to stick to.

Since you are not planning on using the cabin during the winter, I would not design the panels to operate during the winter...at the expense of summer time operation. 22 degrees is best for the summer. In your situation, I would probably go with ~ 37 degrees....the optimal angle for year round production. There is so much summer sun that the panels do not have to be optimized for summer production.

The larger the inverter, the more energy it consumes to simply operate. High frequency inverters are much smaller and much cheaper. They are great for part time use. Their expected life is possibly ~half that of the large inverters but the costs is ~1/4...or less.

Telluride is getting pretty close to our host in Arizona. I might figure out what I need and make a SUV trip to their store. Shipping large, heavy solar equipment tends to be expensive.

On the other hand, nobody on the planet is qualified to design and install a significant solar set-up without doing a great deal of study. Plenty of books will explain how solar works and make recommendations as well. I never did find a good book for the first installation. I spent months in study and did 99% of the install myself. Hired out the finalization of the connections to a solar pro. He said that I did a "perfect job".

Horsefly · September 2016

Ok, thanks again for all the knowledge being shared here. I am feeling a little more confident about most of it.

Here in CO the snow tends to be a little more dry and fluffy. It doesn't stick much to vertical surfaces except during a driving storm, and then it will melt or otherwise disappear once the storm clears. We do get some deep snow accumulating during the winter, but not on vertical surfaces. So, I like the idea of tilting a panel or two during the winter.

And I'm no longer worried about the batteries freezing. -77 deg F is way below what it would get up there (about 8,800 ft elevation), if we can just get the battery well-charged and maintained before we leave. Even better if we can keep them charging as you guys have suggested.

I figured No AZ Wind and Sun would be in Flagstaff, but I hadn't thought about us driving down there. The drive from Telluride to there is about 5.5 hours, and we'd have to add an hour from our cabin. Might be worth considering. Our base of operations will be Montrose, CO (about an hour the other way), as that is where my sister and her husband live. My sister's husband is really the instigator on this whole project, so he will be doing at least as much as me on this. I think we'd probably want to accumulate the materials there at his house, so we'd be more likely to ship it.

I hadn't been thinking at all about changes to our water system, and I'm guessing in the end we won't want to make major changes there. Gravity feed hurts my head thinking about our location. However, you guys do have me scared about the start-up draw of the pump. I'll need to do some more research on that.

Thanks for all the help. This has been really great. I'm sure I'll have more questions as we get further into it.

Steve

softdown · September 2016

Your thinking is on the right track. On the snow....I live in an alpine desert with very dry snow. It loves to hang unto my 45 degree panels. Scraping the ice off can be pretty tough. I would imagine that super steep panels, like 75 degrees would do pretty well. You do start losing production when you exceed a 52 degree winter time tilt. pvwatts.nrel.gov may tell you exactly what to expect.

I think the snow would usually melt off by noon if I had the patience. Plus the sun can penetrate through some snow.

jonr · September 2016

Is the idea here that a non-pressurized pump is simply gravity driven, and the small DC pump runs maybe more often but not so energy-consuming?

Either one, although the former requires elevation and is probably harder to protect from freezing.

The Mastech MS2108A claims peak measurement for $40. But I use a clamp probe feeding into a laptop audio card (even cheaper and it produces a graph).

Horsefly · September 2016

jonr said:
The Mastech MS2108A claims peak measurement for $40. But I use a clamp probe feeding into a laptop audio card (even cheaper and it produces a graph).

Good idea. The Mastech one seems so much cheaper than others that claim the same peak measurement, I'm a little worried about it. Can you point me to the kind of clamp probe that feeds into a laptop?

mike95490 · September 2016

ramloui said:

On the subject of batteries left alone in winter, I tilt 2 of the 6 panels (500 W out of 1500 W) in my array to almost vertical when I shut down the cabin in the fall...

Don't those 2 panels make a giant snow dam behind them ?

Horsefly · September 2016

So I'm re-igniting this thread with an idea and a couple more questions. Serves you guys right for being so helpful with my first set.

First my idea: Like I said, our cabin will get effectively no use from about the first of November through the end of February (more likely well into March). For that reason, other than small bit to keep the batteries charged, we really won't need any solar at all during those winter months. After looking at the NREL redbook data for Colorado, I decided we could get better bang out of our PV array if we used a flatter panel tilt, like Latitude-15 deg, rather than the normal tilt = the Latitude of our location. Considering some of the discussion above (except for the snow dam question!), I was also thinking it would be good to be able to have a "winter" setting where we mount the panels so that we could put them almost vertical when we locked up the cabin for the winter, and move it back to latitude-15 deg when we open it up in the spring. I think we can come up with a mount for the array that would allow us to change the tilt between the two angles (maybe with just those two pre-set tilts). Thoughts?

I've been reading some about batteries. My brother-in-law knows more about solar than I do, mostly because he has a small unit on their sailboat. He likes AGM batteries, and my guess is it is partly because it is what he has on the boat. The little bit I had read over the past week had convinced me we'd be best to go with some regular deep cycle FLA batteries. I think I've seen (but can't find now) that AGM batteries cost a little more and don't last as long, but the maintenance free and no worries about gas or acid leaks is a plus. For the kind of system I've described, what other factors should we consider? Do most smallish home / cabin installs still use FLA?
Since we have a perfectly good generator that we can run any time, there is some consideration to not over-sizing everything, but rather going a bit lean on the system capacity. For that to work, we'd need to know when we need to start up the generator. To keep the batteries from going below 50% depth of discharge, do some (most? all?) of the inverter/chargers have some kind of alarm to let us know when the batteries are getting close to 50%? It would even be OK if the inverter just shut down all 120VAC output when it became an issue. Is there something like that as an add-on to either the inverter/charger or the charge controller?

Looking forward to your comments. Thanks again!

Steve

jonr · September 2016

My laptop AC current probe is functionally like this - plugged into the audio jack.

http://www.ebay.com/itm/50A-SCT-013-050-Non-invasive-AC-current-sensor-Split-Core-Current-Transformer-/141906883137

I think I used Zelscope as the software.

Mountain Don · September 2016

Horsefly said: I think we can come up with a mount for the array that would allow us to change the tilt between the two angles (maybe with just those two pre-set tilts). Thoughts?

Steve

With a pole top mount an adjustable system is easy. (These are the best photos I could dig up quickly. ) I left the ubolt nuts on the cross bar mount slightly loose... just loose enough to permit the panel mount to be rotated. Then fabricated a bar and a mount for the bar. The point of adjustment is a 1/2" bolt mounted through the pole. The clip makes it easy to adjust the angle to whatever is desired.

Image: https://us.v-cdn.net/6024911/uploads/editor/b6/bmadfu6oqi9h.jpg

Image: https://us.v-cdn.net/6024911/uploads/editor/zg/ilgb8e9zbmux.jpg

Horsefly · September 2016

jonr said:

My laptop AC current probe is functionally like this - plugged into the audio jack.

http://www.ebay.com/itm/50A-SCT-013-050-Non-invasive-AC-current-sensor-Split-Core-Current-Transformer-/141906883137

I think I used Zelscope as the software.

Thanks jonr. Turns out my brother-in-law believes he has the specs on the well pump, including the surge current. Seems most of the inverters we are looking at have a pretty good 5 sec surge capacity, so I'm sure we will be able to come up with something that will work.

Horsefly · September 2016

Mountain Don said:

With a pole top mount an adjustable system is easy.

Thanks Don! Great pics. That is pretty close to what I was thinking about. I was afraid a single pole might not be good enough support in the wind - Seems like the panels act like a sail! Do you not have any problem with wind?

Mountain Don · September 2016

I followed the pole top mount manufacturers instructions for depth of hole and volume of concrete. I don't recall the depth or amount of concrete but at the time I thought it was excessive. However, it has been in place since 2009 with no problems, other than a lightning strike, but that is another story.

But speaking of that please do yourself a favor and install protection. We have both the Midnite SPD and Delta arrestors. At the time of the fatal to electronics strike we only had Delta. Since that we made a few changes and have survived further strikes as attested to by the Midnite SPD having done it job and needing to be rebuilt (they cover strike failure of the SPD under warranty).

softdown · September 2016

My memory is that optimal summer production is ~ 22 degrees for a 37 degree latitude location. You seems to have dug up different numbers.

On the batteries....just buy golf cart batteries. They work very well and and are, by far, the biggest bang for the buck. The odds of killing your first battery bank are excellent. You would rather lose $400 than $1400 I would think.

Good question about when does the inverter shut down and "save" the batteries. Not nearly soon enough. Most are set to turn off at 10.5 volts...this is far too low. Other demonic manufacturers allow the inverter to cruise until 10 volts is hit. These numbers are assuming a 12 volt system of course. Just multiply by two for a 24 volt inverter....which I likely recommend for several reasons. The more expensive inverters tend to have adjustable cut-off points. Another alternative is to wire in a low voltage cut-off. These tend to run around $200. The vast majority of battery casualties are caused by running them too low.

Do you have a roof facing anything close to south? Southeast or southwest works alright. Pole mounts make it easier for criminals to prey upon. A consideration for a cabin that is usually empty. People tend to poo-poo crime...until they get hit. It really hurts in more than just a financial way.

As for shipping from Arizona. They needed about $500 to drop ship (cheapest way) six 32" x 62" panels to Denver last year. You may consider re-evaluating that shipping strategy.

Horsefly · September 2016

softdown said:

My memory is that optimal summer production is ~ 22 degrees for a 37 degree latitude location. You seems to have dug up different numbers.

Actually, I think that is exactly what I'm saying: latitude-15 degrees, 37-15=22!

softdown said:
On the batteries....just buy golf cart batteries. They work very well and and are, by far, the biggest bang for the buck. The odds of killing your first battery bank are excellent. You would rather lose $400 than $1400 I would think.

Wow. That makes it a pretty stark consideration. I may have to lean that way, but I'll need to convince my brother-in-law.

softdown said:
Good question about when does the inverter shut down and "save" the batteries. Not nearly soon enough. Most are set to turn off at 10.5 volts...this is far too low. Other demonic manufacturers allow the inverter to cruise until 10 volts is hit. These numbers are assuming a 12 volt system of course. Just multiply by two for a 24 volt inverter....which I likely recommend for several reasons. The more expensive inverters tend to have adjustable cut-off points. Another alternative is to wire in a low voltage cut-off. These tend to run around $200. The vast majority of battery casualties are caused by running them too low.

That's what I'm afraid of. We can size the system so it is very unlikely to draw the batteries down too far, but most of the time it would be a wasted cost. I'm only worried for the case when someone forgets to turn off something when we leave, or when it rains for the entire weekend while a large group is visiting.

softdown said:
Do you have a roof facing anything close to south? Southeast or southwest works alright. Pole mounts make it easier for criminals to prey upon. A consideration for a cabin that is usually empty. People tend to poo-poo crime...until they get hit. It really hurts in more than just a financial way.

As for shipping from Arizona. They needed about $500 to drop ship (cheapest way) six 32" x 62" panels to Denver last year. You may consider re-evaluating that shipping strategy.

By design, the front of the cabin faces a beautiful view of the San Juan mountains (south), and the sides (the pitch of the roof) face east and west. So, mounting directly on the roof is a no go. You have certainly scared me about the shipping. Maybe a trip to Flagstaff won't be so bad!

Horsefly · September 2016

Mountain Don said:

I followed the pole top mount manufacturers instructions for depth of hole and volume of concrete. I don't recall the depth or amount of concrete but at the time I thought it was excessive. However, it has been in place since 2009 with no problems, other than a lightning strike, but that is another story.

But speaking of that please do yourself a favor and install protection. We have both the Midnite SPD and Delta arrestors. At the time of the fatal to electronics strike we only had Delta. Since that we made a few changes and have survived further strikes as attested to by the Midnite SPD having done it job and needing to be rebuilt (they cover strike failure of the SPD under warranty).

I have to admit I know so little I don't even know what you are talking about with the arrestors. I'll add it to my list of things I need to get smart on. Thanks!

Horsefly · September 2016

softdown said:

People tend to poo-poo crime...until they get hit. It really hurts in more than just a financial way

I forgot to respond to this thought. We're always a little concerned about trespassers, but someone would have to actually work to get to our cabin. It's a couple of miles from any marked road, and a mile or so past a locked gate. You're right that we should think about it, but I have a hard time thinking someone is going to come in and be deliberate enough to take apart a solar array.

Mountain Don · September 2016

FWIW, our place in the NM mountains is also at 8800 feet, is part time and is snowed in Dec thru Feb/March, but we snowshoe in once a month. I installed a set of golf cart batteries in 2009; 24 volts. Still running the same set of batteries. We do not overstress them and they are kept full by the PV system. The charge controller maintains them well. Auto EQ is turned OFF. The inverter and all loads are disconnected. We have mostly sunny days and the panels seldom stay covered by snow. Our snow is mostly powder and readily slides off.

Lightning kills people and more often kills electronics. Midnite SPD, Delta. There are DC and AC versions. Some believe both types should be used. I do. They use different approaches to lightning protection and lightning can be a strange thing. A few dollars more spent up front might help prevent replacing charge controllers and inverters later.

Our mountains have a lot of lightning. I have experienced some of the same in the mountains of CO. You should research protection before installing, IMO. If lightning is prevalent you might also consider looking into an air terminal (lightning rod) system. We did but in retrospect, we should have read the handwritting on the wall (so to speak) and acted before our strikes killed pretty everything with a chip in it. {handwriting on the wall = a good number of old charred trees in the neighboring forest}

softdown · September 2016

22 degrees is optimized for the summer solstice on June 23rd (this year). We get ~16 hours of sun that time of year. There is rarely a need to optimize summer production unless air conditioning is used. Right now 37 degrees is the optimum angle due to coinciding with the fall solstice. This also holds true with the spring solstice.

I don't know your cabin usage patterns of course. Just thought I'd drop that tidbit of data in. Plus....light bulbs are not used nearly as much during the super long days.

Making the panels an adjustable tilt is cool if you can pull it off for a reasonable cost without compromising the strength of the assembly unduly. Since there is no winter usage, I would not bother. I would possibly recommend a permanent ~30-40 degree tilt. This yields the greatest production throughout the year. 37 degrees being the magic figure (on paper) as you have seen.

I used 45 degrees here and would do that again. I have to break out the generator about 1-2 days a year so this array does pretty well even during the winter solstice on December 23rd. December is a solar production death warrant. Short, cloudy days with extensive use of light bulbs. Lucky you don't have to worry about winter time production.

You have come along way in a short time. I could not have done it without advice from this board.

ramloui · September 2016

mike95490 said:

ramloui said:

On the subject of batteries left alone in winter, I tilt 2 of the 6 panels (500 W out of 1500 W) in my array to almost vertical when I shut down the cabin in the fall...

Don't those 2 panels make a giant snow dam behind them ?

Yes, of course. However, the shed is built to support that load. And even if the snow covers all of the other panels, the 2 tilted panels are all that is needed to keep the batteries on float till the spring.

The other benefit of tilting the panels almost to vertical, is that, at least at my lattitude, the sun is very low on the horizon. Coupled with the fact that the snow acts as a giant reflector, the 2 panels are plenty while I'm away for the winter.

Mountain cabin off-grid

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