Brown bear destroyed our yurt powered by Yeti 3000, so I'm designing solar for a cabin & a bit lost

[AlaskanNoob]

Hello all. The wife and I live very off grid in Alaska (helicopter has to deliver stuff) and for the last couple of years we have lived in our 20 foot yurt powered by 16 x 100 watt Renogy panels connected into two separate Yeti 3000s. Even though the yurt location is not great for solar, it has worked wonderfully. In the winter we have had to use a generator for backup not infrequently, but it has worked well. That is the extent of our solar experience though. Few months ago, however, we came back from a trip into town to discover a brown bear had destroyed our yurt. So now we're building a small cabin this summer. Going to mount solar on the two roofs. One section angled for winter will hold 24 x 100 watt Renogy panels and the other roof will hold 30 x 100 watt panels for summer and shoulder season.

I think we want to bite the bullet and purchase three Relion RB300-LT lithium iron phosphate batteries (they take a solar charge down to -4F) as our battery bank but I have no idea what the best solar charge controller would be to charge those batteries and no idea how best to organize the panels into strings. My gut feeling is I should increase the voltage as much as possible by wiring some panels in series in order to keep the wire diameter small but I'm not really sure. One limitation with the RB300-LT batteries is that they may NOT be connected in series, but can be connected in parallel.

I do know during the winter that the winter roof 24 panels will be the only ones to get sun (terrain, trees, and low Alaska sun will keep the other 30 panels shaded).

I'm not deadset on Renogy 100 watt panels but that's what we've been using and they work well for us and are easy to work with, but our experience is limited. The specs are found here (I'm not sure if those specs limit me in any way to how many I can put in series or parallel -- my assumption is that is limited only by the charge controller): https://www.renogy.com/100-watt-12-volt-monocrystalline-solar-panel-compact-design/

I want to make sure we get this system designed right and squeak every bit of juice from the panels into the batteries because it will be powering our electric fence to keep out the bears. My mistake in the yurt was thinking freezing temps meant the bears would be sleeping and so the lithium being unpowered (and thus the electric fence) didn't seem like a big deal. I know better now but I can't afford to learn any more lessons from bears!

Many thanks for any help with my floundering around.

 

[45North]

Hello all. The wife and I live very off grid in Alaska (helicopter has to deliver stuff) and for the last couple of years we have lived in our 20 foot yurt powered by 16 x 100 watt Renogy panels connected into two separate Yeti 3000s. Even though the yurt location is not great for solar, it has worked wonderfully. In the winter we have had to use a generator for backup not infrequently, but it has worked well. That is the extent of our solar experience though. Few months ago, however, we came back from a trip into town to discover a brown bear had destroyed our yurt. So now we're building a small cabin this summer. Going to mount solar on the two roofs. One section angled for winter will hold 24 x 100 watt Renogy panels and the other roof will hold 30 x 100 watt panels for summer and shoulder season.

I think we want to bite the bullet and purchase three Relion RB300-LT lithium iron phosphate batteries (they take a solar charge down to -4F) as our battery bank but I have no idea what the best solar charge controller would be to charge those batteries and no idea how best to organize the panels into strings. My gut feeling is I should increase the voltage as much as possible by wiring some panels in series in order to keep the wire diameter small but I'm not really sure.

I do know during the winter that the winter roof 24 panels will be the only ones to get sun (terrain, trees, and low Alaska sun will keep the other 30 panels shaded).

I'm not deadset on Renogy 100 watt panels but that's what we've been using and they work well for us and are easy to work with, but our experience is limited.

I want to make sure we get this system designed right and squeak every bit of juice from the panels into the batteries because it will be powering our electric fence to keep out the bears. My mistake in the yurt was thinking freezing temps meant the bears would be sleeping and so the lithium being unpowered (and thus the electric fence) didn't seem like a big deal. I know better now but I can't afford to learn any more lessons from bears!

Many thanks for any help with my floundering around.

You might want to take a look at larger panels. 100w used to be the standard but now the sweet spot is 200, 300w or more.
Goal is to cover the same roof area with less handling and wiring and should be cheaper too!
Unless you're looking at used - then I guess you have to take what you can get.

 

[AlaskanNoob]

You might want to take a look at larger panels. 100w used to be the standard but now the sweet spot is 200, 300w or more.
Goal is to cover the same roof area with less handling and wiring and should be cheaper too!
Unless you're looking at used - then I guess you have to take what you can get.

Thank you much for that. I haven't looked in awhile but I was under the impression that a higher wattage panel just meant a bigger panel rather than more wattage for the same square footage. But less framing and less wires makes perfect sense. Of course if it gets too big that's going to make it harder for me to install it way out in the bush with the wife. I will certainly research this though, much appreciated.

 

[45North]

And congrats for living so far north!
And I thought I had snow and cold here at 45!
I'm such a wimp. But at least we don't have bears to worry about. Mostly coyotes and the odd wolf here in the east.

 

[AlaskanNoob]

And congrats for living so far north!
And I thought I had snow and cold here at 45!
I'm such a wimp. But at least we don't have bears to worry about. Mostly coyotes and the odd wolf here in the east.

I don't deserve to have "Alaska" in my screename. I am not cut from the same cloth as the men (and women) who live here. We've only been here a couple years now. I'm just pretending and hoping I don't die on a daily basis from a myriad of things trying to kill us (earthquakes, wildfire, moose, bears, poisonous plants, freezing cold, and most especially my ignorance as I use chainsaws to cut down trees, drive an ATV, etc). I am as sissy as they come but I really respect the locals. There are some really hard working strong people here.

 

[Forbisher]

I think we want to bite the bullet and purchase three Relion RB300-LT lithium iron phosphate batteries (they take a solar charge down to -4F)
**************************
Where is the claim or proof of charging at that very low -4°F
LFP has a 32°F charging cut off and even Battle Born only claims 25°F

 

[AlaskanNoob]

I think we want to bite the bullet and purchase three Relion RB300-LT lithium iron phosphate batteries (they take a solar charge down to -4F)
**************************
Where is the claim or proof of charging at that very low -4°F
LFP has a 32°F charging cut off and even Battle Born only claims 25°F

I could have been more precise. They will take a charge when the outside temperature is as low as -4F by heating the battery cells.

This series of batteries has heating elements inside the battery. When it's below 32F the current the charge controller provides the battery is diverted to the heating elements which warm the battery to above 32F and then the current goes back to charging the battery. That's how I understand it anyway. They explain it with more detail here: https://relionbattery.com/blog/relion-low-temperature-lt-models

When the cabin is occupied the temperature won't be an issue since we'll have the wood stove on. But if we leave the place for a couple days it will get freezing in there. We'll have less of a draw on the system, but we'll still need it to be charging to ensure there is power for the electric fence and the security stuff.

 

[Forbisher]

I could have been more precise. They will take a charge when the outside temperature is as low as -4F by heating the battery cells.

This series of batteries has heating elements inside the battery. When it's below 32F the current the charge controller provides the battery is diverted to the heating elements which warm the battery to above 32F and then the current goes back to charging the battery. That's how I understand it anyway. They explain it with more detail here: https://relionbattery.com/blog/relion-low-temperature-lt-models

When the cabin is occupied the temperature won't be an issue since we'll have the wood stove on. But if we leave the place for a couple days it will get freezing in there. We'll have less of a draw on the system, but we'll still need it to be charging to ensure there is power for the electric fence and the security stuff.

Yeah they have some kind of internal heating to allow low temp charging and the 100Ah battery is over $1200.

Battle Born has an internally heated 100Ah battery now too for maybe a little less?

 

[AlaskanNoob]

I'll check that out, thanks!

Right now I'm using PVWatts and hoping it will help me figure out the best way to wire up 54 x 100 watt panels into strings and hopefully recommend a charge controller. Haven't used it in awhile so I can't remember if it does that or not. I seem to recall a tool that did something like that but I haven't looked into it for some time.

 

[Forbisher]

I'll check that out, thanks!

Right now I'm using PVWatts and hoping it will help me figure out the best way to wire up 54 x 100 watt panels into strings and hopefully recommend a charge controller. Haven't used it in awhile so I can't remember if it does that or not. I seem to recall a tool that did something like that but I haven't looked into it for some time.

Wow. 54 100 watt panels is kinda crazy to have to fit into a system.
Do you have a SCC?
12V or 24V battery?

Common SCC are 150V max imput so at 22Voc x 6 panels in Series is 132Voc plus temp compensation to stay under 150V

You could play with the Victron sizing calculator.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

diysolarforum.com

 

[AlaskanNoob]

Wow. 54 100 watt panels is kinda crazy to have to fit into a system.
Do you have a SCC?
12V or 24V battery?

Common SCC are 150V max imput so at 22Voc x 6 panels in Series is 132Voc plus temp compensation to stay under 150V

Thanks for the help with the math. I really appreciate it. I'm trying to work that out now using the Renogy panels which produce 18.9V and 5.29amp. So I'll need to wire them up in series not to bust the voltage limit, and then wire those strings in parallel to keep that voltage without busting the amp limit. Then feed that all into an MPPT to charge the batteries. I'm still working on the math to see if I'll need multiple MPPTs or what not.

Based on your SCC that would mean I could wire up 7 panels in series. Would need to know the amp limit to know how many strings of 7 I could wire up in parallel.

I don't have anything at this point. I'm just going off the roof space I will have available and the size of the battery bank I want to have. I'll need to figure out the charge controller(s) to use. Given the way the sun works here and our terrain, in the winter the sun is super low and the winter roof will have 24 panels facing east to catch the sun just over a mountain range. The panels will be vertical (which should also help keep the snow off of them). This oversized system will hopefully squeak out enough sun for the couple hours of sunlight we might get in winter. The 30 panels of the summer roof won't get any sun during that time unless it somehow bounces off a cloud.

In the summer, however, we will have more power than we know what to do with. But we'll figure out how to use it I'm sure as we eventually modernize our equipment. Running water sure would be cool. And a washer and dryer would be neat.

The battery bank will be 12V. Three 300AH batteries wired in parallel (these LT models cannot be wired in series).

 

[snoobler]

Thank you much for that. I haven't looked in awhile but I was under the impression that a higher wattage panel just meant a bigger panel rather than more wattage for the same square footage. But less framing and less wires makes perfect sense. Of course if it gets too big that's going to make it harder for me to install it way out in the bush with the wife. I will certainly research this though, much appreciated.

It is just a bigger panel with a smaller % of that being the frame. The main driver is price. The bigger panels tend to be a lower $/Watt. It's also less effort to mount. 4 fasteners regardless of panel size for the most part.

PVWatts will not give you SCC recommendations. It just simulates your system for you in terms of annual and monthly solar harvest or usable AC power if you've applied an efficiency factor.

Your SCC is dictated by your charging current, which depends on battery voltage. Your 5400W array would need:

5400W/12V = 450A
5400W/24V = 225A
5400W/48V = 112A

Those numbers are conservative, and you can fall a little short of them. You can also split your array into multiple facings to spread your power more evenly over the day and keep your peak current lower.

 

[snoobler]

In the summer, however, we will have more power than we know what to do with. But we'll figure out how to use it I'm sure as we eventually modernize our equipment. Running water sure would be cool. And a washer and dryer would be neat.

The battery bank will be 12V. Three 300AH batteries wired in parallel (these LT models cannot be wired in series).

Setting your array to the best winter performance makes the summer spike less pronounced.

 

[AlaskanNoob]

It is just a bigger panel with a smaller % of that being the frame. The main driver is price. The bigger panels tend to be a lower $/Watt. It's also less effort to mount. 4 fasteners regardless of panel size for the most part.

PVWatts will not give you SCC recommendations. It just simulates your system for you in terms of annual and monthly solar harvest or usable AC power if you've applied an efficiency factor.

Your SCC is dictated by your charging current, which depends on battery voltage. Your 5400W array would need:

5400W/12V = 450A
5400W/24V = 225A
5400W/48V = 112A

Those numbers are conservative, and you can fall a little short of them. You can also split your array into multiple facings to spread your power more evenly over the day and keep your peak current lower.

Thanks so much for the help! I have to admit I'm pretty happy with the smaller panels because I'm the guy having to lift and install this stuff and it's tough to get help out here. Nobody just drops by where we're at which is a good thing until I can use a hand.

If I understand you correctly, since my battery bank has to stay a 12V system (a limitation of the Relion LT batteries) then the charge controller I get has to be able to handle AT LEAST 450amps? I don't know much about charge controllers or if one that can handle that is the way to go, or if I should get multiple charge controllers instead. A real solar plan is a whole lot harder than our Yeti 3000... My gut feeling is that I will need multiple MPPT charge controllers to handle multiple panel strings to overcome that 450 amp limitation, and I think multiple MPPT can be tied into the same battery bank and all charge it at the same time, but I have no real knowledge and no experience with that.

I think I'd like to make my winter panels into their own array separate from the summer facing panels, just so the summer panels aren't dragging down the whole system in the winter (although the winter panel strings being wired in parallel with the summer strings should avoid that I *think*). I'm not quite sure how to do that...I would assume the charge controller would have to take inputs from those two arrays separately? Or, instead, just use multiple MPPT as mentioned.

For whatever reason, I was thinking a single MPPT that could take a super high voltage and high amps would be able to charge the battery bank more effectively because it would have more power options to choose from when charging. But I don't know if I'm thinking about that correctly.

Using the Midnite solar design tool (and assuming I did it correctly) it would appear I would need to purchase 6 of the CLASSIC 200/LITE charge controllers to handle 8 strings in parallel of 7 panels wired in series. I have no idea what it would take to connect 6 MPPTs to the same battery bank but some stuff I've read suggests a "follow me" mode is required to get the MPPTs to coordinate on charging.

Once I get all of this figured out I'll also try to figure out how to wire my backup generator into the charge controller in case the charge controller thinks it's needed. I got a generator that has a kit to allow for that, but haven't messed with it yet.

 

[snoobler]

Our 330W panels weight about 50#. Pretty easy for my wife and it to install. Would be pretty tough with one person, but do-able.

If you're stuck with 12V, then yes, you need 450A. The highest are 100A, and they are very expensive. You'd need about $4000 in charge controllers.

Simulate your two arrays in PV Watts. Panels you have that aren't being used in Winter are a waste. Winter solar is horrible, and you need all the help you can get.

Concerning super-high voltage, the only value there is if you have to run long distanced. IIRC, there are some 600V SCC that only run at about 80A for around $1300. You'd need 5 of them.

You don't wire a generator into a charge controller. Charge controllers need DC. Generators produce 120VAC and/or 240VAC. You wire them into your inverter/charger that can take the generator output and charge the batteries.

 

[AlaskanNoob]

Our 330W panels weight about 50#. Pretty easy for my wife and it to install. Would be pretty tough with one person, but do-able.

If you're stuck with 12V, then yes, you need 450A. The highest are 100A, and they are very expensive. You'd need about $4000 in charge controllers.

Simulate your two arrays in PV Watts. Panels you have that aren't being used in Winter are a waste. Winter solar is horrible, and you need all the help you can get.

Concerning super-high voltage, the only value there is if you have to run long distanced. IIRC, there are some 600V SCC that only run at about 80A for around $1300. You'd need 5 of them.

You don't wire a generator into a charge controller. Charge controllers need DC. Generators produce 120VAC and/or 240VAC. You wire them into your inverter/charger that can take the generator output and charge the batteries.

Thanks so much for the info. I'll look into those 330 watt panels. 50 pounds should be workable for sure and that might prove to be a nice way to go. Plus I would assume that would make it less expensive to add DC optimizers to them which is something I am considering for the winter roof panels given that the sun pokes up over a mountain range that almost always has clouds over the top of the mountains.

Your charge controller math checks with what I just ran on the Midnite Solar website. Pricey.

We have some challenges with winter and our low sun over a mountain range about 20 miles away from us doesn't help. What's more, our property and terrain doesn't help. Our cabin (well it's just a deck at the moment but soon to be cabin) is on a hill that slopes down to the east. So we have a pretty good unobstructed view of the east, the mountains that run north-south, and the sun poking above them during winter and shoulder season sunrise. But to the south we have rising terrain above us that obstructs the sun completely in the winter. So our winter roof will be panels that are straight up and down hoping to make hay from that winter sunrise and reflection off the snow (an hour or two of sun a day tops). If we put all our panels facing that direction, they'd miss out in the summer and shoulder season on quite a lot. More importantly, our summer roof isn't angled for the winter because of its slope used for dumping snow off the deck, so it's not an option to have them facing east (and our property doesn't see the sun when it's in the south during winter due to terrain).

Thanks for correcting my understanding of the generator wiring into the system. I'm definitely going to need the generator in the winter, but not nearly as much as at the yurt where our 1600 watts of panels never see the sun during winter!

 

[AlaskanNoob]

Setting your array to the best winter performance makes the summer spike less pronoun

Any idea if DC optimizers will allow delivering optimized power to SCC(s) for charging the battery bank? Or do DC optimizers only work with inverters?

From the little I know and from reading some of the threads in this forum, I'm leaning toward making smaller strings and wiring them in parallel for use with more, but smaller and cheaper, SCCs. So that way I accomplish some of the shading protection by splitting up the system that way. But I think the SCCs are supposed to coordinate with each other to charge the battery bank, so I'm not sure about that part.

 

[snoobler]

If you have 4 panels in series and one is shaded, it will decrease the performance of all 4 panels. Optimizers will minimize this effect. The 4 optimizers in series would analyze how to best handle the shaded panel and attempt to deliver the maximum power.

It sounds like your winter solar is almost nonexistent. Winter and summer arrays make more sense now.

Are any portions of your property accessible that have more favorable winter exposure?

 

[AlaskanNoob]

If you have 4 panels in series and one is shaded, it will decrease the performance of all 4 panels. Optimizers will minimize this effect. The 4 optimizers in series would analyze how to best handle the shaded panel and attempt to deliver the maximum power.

It sounds like your winter solar is almost nonexistent. Winter and summer arrays make more sense now.

Are any portions of your property accessible that have more favorable winter exposure?

Yes, the area where we're building our greenhouse has more favorable winter sun. But we are not building our cabin there and giving up the amazing view we have in our desired living spot. Besides we already built a 45' x 60' ten foot high deck in that spot last summer so that train has left the station.

You got me thinking last night and so I have swapped the location of our "summer panels" to another spot that will get some low angle glancing sun in the winter during sunrise. This spot will also produce in the summer, with the only downside to the spot being that it will be shaded some in the afternoon during the summer, but that's no big deal and likely worth the gain in the winter. I can always add a few more panels to the original "summer" spot and they will produce like crazy in the summer with our long days of sun.

I think your winter approach made sense so I think I'm going to go with that. Besides, if it works in the winter during sunrise then it will definitely work during summer sunrise. If it can keep us from running the generator in the winter that will be a real score.

 

[snoobler]

Are there ways you can incorporate panels into the deck?