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

[Psyckosama]

True statement. Our property, terrain, and trees make the whole place sub optimal for solar! But the yurt we've been living in is WAY less optimal than this spot and solar was still good enough for the two of us except in the winter when we'd have to run the generator. That was just 1600W of solar panels in a much worse location. This location should be much better especially with so many more panels.

We don't have a lawn, we have a forest. This cabin on the 45' x 60' deck that is elevated 10' above the ground is going to be our best bet. Especially as the cabin will give us some more height on top of that.

When I said lawn I'll admit I meant more "clearing".

 

[AlaskanNoob]

When I said lawn I'll admit I meant more "clearing".

Yeah we don't have any of those either except for where the deck is after I cleared forest. I will probably put up a small ground array optimized for the sun in winter if I can get it up high enough, and feed that into the system at some point. It will have to be taller than the 20 foot or so alders though.

 

[AlaskanNoob]

Somebody had mentioned using Raspberry Pi for the generator auto-start capability. Unless there is an elegant out of the box solution where the system will turn the generator on based on battery SOC and temps, I think I'm going to do something like this guy did. Victron allows its system to be operated on the Raspberry Pi so that's pretty cool. I'm not sure if their software allows for temperature factors for the auto-start logic, but if not it should be easy enough to add a temp sensor to the Pi and some logic of my own. Very cool of Victron to make this available for the Pi.

 

[Q-Dog]

So a few folks here have mentioned that inverters not only invert power from the batteries into AC for the cabin, but also an inverter/charger can charge the batteries too. This guy has a Victron system and has his inverter/charger connected to his generator so when he turns on the generator it supplies power for charging his batteries (I assume in addition to any PV coming in and while also inverting power for his house). Now if I can find an inverter that talks to the SCC and knows when to auto kick on the generator I'll be set.

In a more recent video he replaced his inverter/charger with a Victron Multiplus though. TheColorist has been nice enough to provide me with some great recommendations and he recommended the Victron Multiplus II for our application. I need to study up on that and see if it talks to the charge controllers and can turn the generator on or off. That would be a huge plus if so. Also, it would be nice to turn that inverter off when we leave the cabin so that the 18W draw in idle doesn't deplete batteries that aren't be used while we're away.

https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-inverter-charger-EN.pdf

Yes, the Multiplus has relays that can be used to start a generator. Also has a low power mode that may or may not work for your situation.

 

[AlaskanNoob]

Yes, the Multiplus has relays that can be used to start a generator. Also has a low power mode that may or may not work for your situation.

Thanks. I saw a video from Battle Born where they connect to the software in the Multiplus and I'm assuming that software and the settings therein would allow me to set the settings so it knows *when* to kick the generator on and off (quiet hours, SOC, etc). I'm hoping battery temperature is one of those settings.

 

[Q-Dog]

More than one way to do it, but here is one.

Virtual switch - Generator start/stop [Victron Energy]

www.victronenergy.com

 

[AlaskanNoob]

More than one way to do it, but here is one.

Virtual switch - Generator start/stop [Victron Energy]

www.victronenergy.com

That's a great find, thanks! I don't see any temperature setting in the software but I'll dig a bit deeper. It it doesn't have an option for only starting the generator when the temp is above freezing I'll probably go the Raspberry Pi route.

It seems the "virtual switch" has some option for a temperature alarm but I'm not sure what that's referring to...I think it's the temperature of the Multiplus if it overheats.

 

[A.Justice]

I brought it up largely due to his location being poorly suited to solar enough that secondary options might be useful is all.

I love wind power! I didn't post that link to try to dissuade him from doing it, I just wanted to make sure that if he decided to use wind, that he gets the proper equipment. I would be willing to bet that Alaska has some pretty good areas for wind energy that he could tap into.

 

[AlaskanNoob]

I did the math and came up with a charge controller that seems to fit the bill. But the company is suggesting that a string providing voltage to the SCC that is under the max is still "too close to the max." Why is this? Is my math bad?

Panel SOC is 40.1V. I have three of them in series. 401.V X 3 = 120.3V. I then multiply that by the temp coefficient for my location of 1.23 and the result is 148V. The SCC is a 150V controller. Why is that "too close" to the SCC limit? Is the assumption that the string can produce voltage higher than the 148V and, if so, what's the better formula for sizing an SCC?

 

[Psyckosama]

I love wind power! I didn't post that link to try to dissuade him from doing it, I just wanted to make sure that if he decided to use wind, that he gets the proper equipment. I would be willing to bet that Alaska has some pretty good areas for wind energy that he could tap into.

Righto.

I'm hoping to do an off grid setup myself eventually. I'm going to look into wind as a secondary when I do. Also looking for a place in Vermont which will likely mean I'll be on the side of a mountain. Winds can get pretty heavy up there.

 

[AlaskanNoob]

The company is also recommending a combiner box for each battery bank to reduce the number of SCCs from 2 to 1 on each bank.

The company is suggesting I re-do my setup (attached) as such:

For the 12 volt battery bank I recommend going with 1 250 Volt 85 Amp charge controller, and wiring 2 strings of 3 panels in series with a combiner box. The 148 V is very close to the maximum and we could break it up into 2 strings of 3 to only use one unit.

For the 48 volt battery bank I recommend going with 1 450 Volt 100 Amp charge controller with 2 strings of 5 in series and 3 in parallel with a combiner box. Again, the 247 Volts is very close to the maximum.

The question I have about his recommendation on the 12V bank is it appears he's suggesting I keep the panels wired as they are with two strings of 3 panels in series, but instead of having 2 SCCs, use a combiner box and then go with only one SCC. But if I did that wouldn't I lose half of the amps that could be used to charge the battery with only one SCC instead of two? Each set of 3 panels would provide up to 80 amps for the SCC to charge the battery with, for a total of two SCCs and 160 amps. But if I cut it to a single 250/85 SCC then it would only be able to charge with 85 amp.

Same concern with the 48V bank. It seems I'd be going from two charge controllers that could supply 200 amps to the bank down to one charge controller that could only supply 100 amps to the bank.

Am I thinking about this correctly?

The company confirmed my issues (should I cut my 160 amps available to charge the batteries down to only 85 amps available because my three panels will produce 148V and that is too close to the "limit" of a 150V SCC???):

yes we will limit the charge current ability by only having one 85 amp charger. But by pushing the limit on the input voltage of the 150 Volt charge controller you run the risk of damaging the unit, which is my reason for pointing you in that direction.

The 150 Volt Option may work here but I am wary of encroaching on the maximum input voltage for the unit.

The strings consist of 3 panels in series. Each panel has a VOC of 40.1V. If I take 40.1V x 3 that's 120.3V. If I then multiply that by the temperature coefficient for my area of 1.23 that equals 148V. Is this calculation I've done not conservative enough for sizing the SCC? Is it possible the string (without going into historic low temps) would produce more than 148V and thus damage the 150 volt SCC? I honestly don't know. Is there a better math formula for sizing a SCC?

To confuse myself even more, I just used this calculator which also takes into account "temperature coefficient of VOC" (which is -.29%/C for my panel) and its calculator (for the temp I used several degrees cooler than the coldest recorded temp in my area) and it came out to only 141V produced rather than 148V. Weird. But if their math is correct that's even less reason to worry about a 150 volt limit on the SCC.

Solar panel maximum voltage calculator - How to work out the max voltage

To get the maximum solar panel voltage you should expect from your solar panel, use our solar panel maximum voltage calculator.

gold-coast-solar-power-solutions.com.au

 

[AlaskanNoob]

The company got back with me and confirmed the 150W SCC will work so no need to cut amp production in half. And they provided a formula for calculating string voltage that jives with the Aussie calculator from above so that's really nice to have.

I redid some math on my end and also came out with an answer of 141.23 Volts for 3 of these panels in series.

The formula is:

(Standard Test Condition temp – low temp) x temp coefficient % VOC x VOC + VOC = VMax


25 - (-35) = 60 * 0.0029= 0.174

0.174 * Open Circuit Voltage at Standard Test Conditions (40.10) = 6.9774

6.9774 + 40.10 = 47.0774 Volts *3 = 141.23 Volts

Based on these calculations the 150 Volt charge controller will work here.

 

[AlaskanNoob]

The company was helpful with the generator auto-start solution:

For the generator auto start situation: I recommend using a SmartShunt with a Cerbo GX for each battery bank. The SmartShunt can be directly connected to the Cerbo via a VE Direct Cable. Then, Relay 1 on the Cerbo GX can be used to program a generator auto start/stop based on a number of conditions. State of Charge, Battery current, battery voltage etc. The information from the SmartShunt can help us kick on the generator depending on certain conditions that would not be dependent on the temperature so you could run your generator at cold temps. For example, we could set the generator to autostart at 40% state of charge and run until 99% SOC.

If we use the Temp Sensor on the auxiliary input of the SmartShunt. You will need the Temperature sensor for BMV. Product # ASS000100000 .

Low temperature alarm is available if the Aux input has been set to “Temperature”. When enabled, the alarm will activate when the battery temperature falls below the set value for more than 10 seconds. The alarm will deactivate when the battery temperature rises above the clear value.

So it appears if the low temp alarm is on, that will cancel any command to auto-start. the generator which should give me what I'm looking for on the 48V system (on the 12V system I'll just let the generator kick on since it will be going to an LT battery).

 

[AlaskanNoob]

So now I'm going to focus my research on:

1. DC optimizers for the panels
2. Fuse/breakers to make this system as safe as possible and to prevent a fire
3. Wire selection

 

[k3nny]

So a few folks here have mentioned that inverters not only invert power from the batteries into AC for the cabin, but also an inverter/charger can charge the batteries too. This guy has a Victron system and has his inverter/charger connected to his generator so when he turns on the generator it supplies power for charging his batteries (I assume in addition to any PV coming in and while also inverting power for his house). Now if I can find an inverter that talks to the SCC and knows when to auto kick on the generator I'll be set.

In a more recent video he replaced his inverter/charger with a Victron Multiplus though. TheColorist has been nice enough to provide me with some great recommendations and he recommended the Victron Multiplus II for our application. I need to study up on that and see if it talks to the charge controllers and can turn the generator on or off. That would be a huge plus if so. Also, it would be nice to turn that inverter off when we leave the cabin so that the 18W draw in idle doesn't deplete batteries that aren't be used while we're away.

https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-inverter-charger-EN.pdf

Grew up in AK now in AZ ( miss AK though ).

Your Victron gear can handle the generator. It will know the bank State Of Charge (SOC) and can be configured to fire up the genny to charge the batteries. For example, you can have it fire up on a schedule and run for 30 minutes ( to keep the genny healthy ) as well as keep the bank charged based on the parameters you set.

I'd add a Cerbo GX to the mix. You don't need the screen, you can mange it from a phone. Not sure of your lat/lng (Fairbanks vs Nome vs Valdez vs Southeast, if north of Fairbanks ?) or if you have internet out there but you may be able to get Starlink and mange the system remotely.

What kind of generator do you have or plan to have?

 

[RStone13]

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.

So sorry for your loss, not fun! Cabin build should turn out great with lessons learned from yurt living.

 

[AlaskanNoob]

Grew up in AK now in AZ ( miss AK though ).

Your Victron gear can handle the generator. It will know the bank State Of Charge (SOC) and can be configured to fire up the genny to charge the batteries. For example, you can have it fire up on a schedule and run for 30 minutes ( to keep the genny healthy ) as well as keep the bank charged based on the parameters you set.

I'd add a Cerbo GX to the mix. You don't need the screen, you can mange it from a phone. Not sure of your lat/lng (Fairbanks vs Nome vs Valdez vs Southeast, if north of Fairbanks ?) or if you have internet out there but you may be able to get Starlink and mange the system remotely.

What kind of generator do you have or plan to have?

Thanks for the reassurance! Great point about putting the genny on a schedule to make sure it stays healthy and lubed up, that's another great advantage to this system.

Victron also recommended the Cerbo GX so that's going to get added to the list for sure.

We have the Starlink order done and we're told we might get it in 2021 I think? That will be super nice especially since the dish will self heat and melt the snow.

We have a Honda eu3000 that will go to our 12V bank and then a Honda eu7000 that will go to the 48V bank. Being from Alaska you know about redundancy I'm sure...

 

[k3nny]

Thanks for the reassurance! Great point about putting the genny on a schedule to make sure it stays healthy and lubed up, that's another great advantage to this system.

Victron also recommended the Cerbo GX so that's going to get added to the list for sure.

We have the Starlink order done and we're told we might get it in 2021 I think? That will be super nice especially since the dish will self heat and melt the snow.

We have a Honda eu3000 that will go to our 12V bank and then a Honda eu7000 that will go to the 48V bank. Being from Alaska you know about redundancy I'm sure...

Perfect. I have two of the Honda eu3000 deployed on a project for the Army. They work great and you can remote start them. I'm sure the 7K is the same. You will have a very capable system once you have it all sorted out. Kinda amazing if you think about it. We were lucky to run a lightbulb back in the day at the flyout cabins. A maglite was high-tech.

If you haven't already take look at kilovault batteries for the AK climate.

Also, DavidPoz helped out with a DIY heated battery box up in Maine.

You could save some money going this route but given that is AK it may be worth it to have both solutions to keep the battery bank temp happy.

 

[AlaskanNoob]

Perfect. I have two of the Honda eu3000 deployed on a project for the Army. They work great and you can remote start them. I'm sure the 7K is the same. You will have a very capable system once you have it all sorted out. Kinda amazing if you think about it. We were lucky to run a lightbulb back in the day at the flyout cabins. A maglite was high-tech.

If you haven't already take look at kilovault batteries for the AK climate.

Also, DavidPoz helped out with a DIY heated battery box up in Maine.

You could save some money going this route but given that is AK it may be worth it to have both solutions to keep the battery bank temp happy.

Thanks I'll check that out. Thinking about the RELiON LT for the cold battery bank but I've already changed a bunch on my system plan from what I've learned in this thread so we'll see after more research.

 

[AlaskanNoob]

One potential issue I may have discovered given Will's video. If I'm understanding him correctly, given our 48V battery bank, the panels we use need to have a VOC higher than 48V. But it sounds like since we'll have these panels in series (some series of 3 panels, some series of 5 panels), we'll produce a higher voltage and so shouldn't have issues charging the 48V bank. So I think we're good on this score but I'm not quite sure yet.