My Off-Grid Cabin Solar System submitted for your thoughts

[Xplode]

Let me start by saying I have been trying to read everything I can find for the past month, and last summer I did the same thing so I'm not completely new to the ideas but it is a lot of information to take in and I could definitely use some help finalizing some designs for my cabin. It is a vacation property so we are usually only there for 2-4 days at a time, and mostly in the summer. Winter visits are probably as well, but there will be long stretches between so I am hoping the solar system will be able to eventually 'catch the batteries up' in terms of charging.


Requirements:

Mini-Fridge (Used a Kill-a-Watt on my mini fridge at home ~550Wh per day, only up about 50Wh on intial startup if loaded up with already cooled goods)
Lighting - Pot Lights, All LED, 6.5w lamps x up to 19 at a time. Dimmers and grouping of lights limits draw. Having to guess 2hours/day of lighting at about 60W = 120Wh per day
Cell Charger - 3w x 4 hours x 2 devices = 24Wh per day


Estimated Totals: 694Wh, but lets round it up to 800Wh for fun. (plus inverter standby losses)



The Cabin is at 51deg North (In BC Canada).
The kWh/m2 of full sun hours (as provided by Natural Resources Canada) for the area ranges from 6.2H/day in July to 0.9H/day in Jan/Dec (0deg Horizontal Tilt).
The kWh/m2 of full sun hours (as provided by Natural Resources Canada) for the area ranges from 6H/day in July to 1.6H/day in Jan/Dec (36deg Horizontal Tilt).
Altitude is about 3500' above sea level.
-20degC to +30degC Temperature Ranges.

The roof of the cabin, is unfortunately, facing East and only slightly south, at an inclination of about 14degrees. But after looking at the charts for the insolation data, I think I could possibly rig up a tilt to about 30deg southward... Much higher and I worry I'll have to start dealing with heavy reinforcements to hold up to the wind. The storms up there can be quite gusty and strong winds (No I don't currently have actual windspeed data but I can work on collecting that if I go for a tilt)



Planned System (so far)

2x 280W 60Cell Mono Solar Panels (2S Connected)
1x Tracer3210AN 30A MPPT Charge Controller (24V Charging)
4x Crown CR235 235AH 6V Deep Cycle Battery (5.6kWh)
1x AIMS 2000W Low Freq Pure Sine Inverter Charger picoglf20w24v120vr (https://www.aimscorp.net/24-volt-pur...r-charger.html)
#1 DLO Flex Cables with Crimped Lugs (I have access to a hydraulic crimper to assemble my cables)


Concerns:

- The two 280W panels may not be enough to charge the battery up given my roof orientation, especially in the winter. Will my batteries suffer if they take a week to charge back up from 50% DOD? I can add 2 more panels (2S2P) and I think I can still have the same charge controller handle it since the panels will never ever actually output their full value (Tracer max PV array is 1040W)

- The Aims inverter Low Freq series use about 26W IDLE which seems high... It's "search mode" only uses about 12W but won't activate for <50W detected load, which will never happen unless the fridge is running so it'll have to stay in "full on" mode while we are there. There is a 1000W electronic version of the unit but it's only good for 12V and I'm not sure I want to run everything on 12V.... Thoughts?


Notes:

- The AIMS inverter charger has a battery charger built in with auto-transfer switch so I can plug in the little honda eu2000i generator we have to top up the batteries when the sun isn't shining, or if we want to stay longer than the system can keep up to.

- I leaned on the 2000W inverter model at 24V because i want to make sure the inverter will start the fridge compressor. I've seen youtube videos of cheaper units not being able to really support their "surge" ratings as claimed. These AIMScorp units seem to be spec'd fairly well. It will be physically disconnected from the batteries via disconnect switch when we leave site to come home, so it will not be working against the solar panels while we are not there.




Phew - that's a long read, so thanks if you're still here with me!


Looking forward to any thoughts and suggestions you guys have....

[Mike90250]

After 48 hours, if the batteries are below 90% full, they will start to suffer from irreversible sulfation. You could, as you leave the cabin, run the genset for an hour to bulk up the batteries and let the solar do the rest.
You will want to study the self-comsumption specs of the charge controller, and make sure, it can harvest enough power from snow covered panels, to not drain the battery.

[Xplode]

Thanks for the reply.

After only 48 hours? really? I see in most write-ups that people are aiming for 3 days of autonomy (with 50%DOD) so how do they avoid the sulfation you describe? Or is it just an unfortunate part of the off-grid configuration?

I don't mind running the genset for a bit but the whole idea was to try and stop using the genset as much since we prefer the silence (even though the honda units are really quiet) and don't like having to drag gas cans around with us all the time. (It's a large property with 3 cabins on it)

The self-consumption of the charge controller is a good point that I had thought of and since forgotten about. I will inquire with Tracer and see if I can gather that information.

otherwise any major flaws in my layout so far?

[Xplode]

Found the new 3210AN manual specs and it lists self consumption as "<12mA" so worst cast at 24V it's going to be around 7Wh per day.... damn that Wh stuff adds up! but at 7Wh, the system should be stable for months...

[Sunking]

The biggest issue I see is winter. With that said just get a good battery charger to run off the genny in winter when and if batteries get low. You will need the genny regardless to do maintenance and cover your but for those cloudy weekend. Of than that you did a good job of sizing things up and matching components.

[Wilbour]

[QUOTE=Xplode;n379525]



Mini-Fridge (Used a Kill-a-Watt on my mini fridge at home ~550Wh per day, only up about 50Wh on intial startup

- I leaned on the 2000W inverter model at 24V because i want to make sure the inverter will start the fridge compressor. I've seen youtube videos of cheaper units not being able to really support their "surge" ratings as claimed. These AIMScorp units seem to be spec'd fairly well. It will be physically disconnected from the batteries via disconnect switch when we leave site to come home, so it will not be working against the solar panels while we are not there.


QUOTE]


While this doesn't effect your overall requirements, my little dorm fridge pulled over 725w on initial startup. Then settled back down quickly to 50w while running. Perhaps you meant the running wattage was 50w?

[Sunking]

[QUOTE=Xplode;n379525]



Mini-Fridge (Used a Kill-a-Watt on my mini fridge at home ~550Wh per day, only up about 50Wh on intial startup

- I leaned on the 2000W inverter model at 24V because i want to make sure the inverter will start the fridge compressor. [QUOTE]I suggest leaning in another direction. At worse your fridge must pull up to 6 times running current on start up (300 watts), Aims Inverters are about as low quality as they come, , and your batteries are not really large enough to handle a 2000 watt Inverter.

Suggest you consider something like a Samlex 1000-24 Inverter. They are tough and very efficient with Soft Start. To be honest even a 600-24 would do more than you need.

[Xplode]

While this doesn't effect your overall requirements, my little dorm fridge pulled over 725w on initial startup. Then settled back down quickly to 50w while running. Perhaps you meant the running wattage was 50w?

Hi Wilbour - I was correct with my numbers as I was referring to overall system drain in terms of power usage, but you are correct with your numbers as well. My fridge spikes to about 850W for a fraction of a second, then settles down to around 72-78W running. A basic 1000W inverter might handle that, but I was concerned that many inverters over state their capacity, so I didn't want to have the lights on and have it beep and quit, especially if the batteries were starting to get a bit lower.



Hi Sunking. Thanks for the suggestions - I will take a look at the inverters you mentioned. I couldn't find any bad reviews (or many reviews honestly, mostly just on amazon) for the AIMS units, but their numbers seemed alright and I liked that the units actually have a transformer in them. I like that they actually posted durations for the surge ratings they claim, most manufacturers don't seem to do that!

I have googled quite a lot trying to find different options and would probably aim for a 1000W inverter but I have been having trouble finding something in the 24V range that isn't $3k from Magnum or Schneider.... I don't want to be cheap with my system, but I have to find a balance since it's only a vacation property and if I start trying to spend $5k+ on the system, I might as well just use the generator... Also, I'm in Canada so I'm hoping to find most of the parts on my side of the border to avoid heavy shipping and border fees...

When you say my batteries aren't large enough to support a 2000W inverter, why do you say that? Is there a rule of thumb that i'm missing for matching battery sizing to inverter capability?


I Apppreciate the input guys! Very helpful! Thanks!


AFTER THOUGHT - just realized the main difference in features with the Samlex vs the Aims... I settled on the AIMS unit because it has a built in battery charger as well. I'm not the only one that uses the cabin and so I would like to make it stupid simple for the other family members to use the cabin and be able to charge up the batteries if needed. I planned to string up a cord on the back of the cabin to just pull out and plug into the genset if needed. With the inverter/charger combo that means it instantly starts charging and transfers the lighting load to the genset. Are there other brands or models you'd suggest that might meet this feature request, but in a better quality? (or if there's a reason I shouldn't be looking at combo units, I'm all ears)

[Wilbour]

If you are looking at a inverter on only, the Victron 24/1200 peaks at 2200w. I would trust their data sheet.

https://www.victronenergy.com/inverters/phoenix-inverter-vedirect-250va-800va

They do make Charger/Inverters but perhaps the price is out of the ball park for you.

I use the 24/500 inverter and have not had an issue as of yet.

[NorthRick]

Regarding your panel orientation, can you ground mount them? Another reason to do that other than being able to face them south is making the mounting such that you can make them vertical in the winter so snow does not accumulate on them. We have a weekend cabin at about 62 degrees north and there just ain't much sun in December/January. Your charge controller will have a slight draw and between low light and snow cover, the output from the panels is basically zero. As in nothing, nada. Even a very light load with no recharge from the panells will bring the batteries down some if it is weeks or months between visits.

In the winter we pretty much rely on the Honda to charge the batteries back up (only have to listen to it on Sunday). But even then, they may not be fully 100% when we need to leave. You want the panels to remain snow free so the batteries get topped off after you leave.

[Xplode]

Wilbour - those do look like nice products and I tried to find an inverter/charger in their lineup but i only see 230VAC output models. Am I missing something or do you know of a model that outputs 120VAC?

NorthRick - I don't really want to ground mount them since that will significantly up the cost, make them more invasive (in terms of visibility and using up cleared land space near the cabin), and unfortunately, I worry about vandalism/theft. If they're up on the roof, at least they'd have to bring ladders and such. Seems unlikely they'd get stolen but you never know. The thought DID cross my mind that If I wanted to, i could parallel a pair of panels and mount them vertically on the southern side of the cabin... the insolation data provided by NRCAN indicates I could get almost 2 sunhours per day, even in december (weather permitting of course), but I think i may have to clear a few shrubs and trees to avoid shading...


I have wondered about snow accumulation on the panels, but the snow that falls is usually so dry it doesn't even really build up on the lake as the wind clears it all... Now I'm new to solar, so I'm wondering if the panels will warm up during the day and cause snow to thaw, and then freeze as ice on the front of them, which will encourage snow to start sticking... Even if the panels only manage to generate 50Wh/day combined between the two of them, that should be enough to keep on top of the self-consumption from the charge controller no?

[Xplode]

I have circled back to looking at Samlex as a product. I just realized their head office is 45mins from my house so I have reached out to see if they can suggest a good model and place to purchase. If not I'm still looking for suggestions of a product with AutoTransferSwitch and Charger integrated...