Need advice for new system

alter · August 2018

I'm building an off-grid cabin and would like some advice and recommendations for a new solar/battery/generator system that I would use to power the home. I have a lot of questions so thanks in advance.

First off, I had a solar consultant tell me that with the regular usage in my primary house, it would require a 6kw solar system to basically cover all my usage. However, I use Air conditioning, etc frequently and other high draw devices and non-energy-efficient devices which I would not use in the cabin. I am, however, planning on installing 6kw worth of panels on the cabin, as its partially obstructed with tall trees and I want to install a bit more to compensate for partial shade.

The cabin will use propane for the following devices:
fridge
furnace/boiler
stove/oven
water heater
generator for battery bank charging (autostart when below threshold)

For the panels, I'm not sure what type or brand. Just 6kw worth on the south facing roof mostly.
For the charger/inverter, I was thinking the schneider conext XW+ 48v 6.8kw
For the battery bank, I just discovered a new type called "lithium iron phosphate" that appears to be perfect for solar. The one I was considering is the 48v 400 ah Iron Edison. It is expensive but looks like its built to last a very long time.
For the generator, I'm not sure. I see a 15kw Generac Ecogen, that appears it might be good for off grid, however I heard reliability issues about the brand. My priorities with the generator are reliability, minimal maintenance, and quietness.

First question is, does this system sound about right? Any major problems or incompatibilities with this equipment? What about the generator? Any advice for other better or more reliable models? And will the battery work well with the 48v XW inverter? Basically would like feedback or advice on this plan from the experts. Thanks!

westbranch · August 2018

Let's look at this project from a different angle: first you need to define your usage AND life style! that will help you plan the solar and battery portion of the plan... Then you can investigate backup options.. Do not buy any components YET...

Not trying to put you off but to get a GOOD Achievable PLAN...

PS, drop the LPG fridge.... been, there ad still have it for the guest house.... 100# tanks are getting old, me too...Go electric, lots of energy efficient ones now at cheap prices...

alter · August 2018

So, I tried to quantify my usage in my 2nd paragraph. This cabin is not built yet and I plan to have about the same usage in that as I do in my regular house once it does get built, but with more energy efficient appliances, and minus the AC. Please assume that usage won't be more than 6kw.

Why drop the propane fridge? I'm planning on purchasing a brand new, several hundred gallon propane tank which will last for decades. Is your old small propane tank the only reason or do you have other reasons for advising me against it?

MrM1 · August 2018

My SW system install link in my signature. This would give you an idea how to build a system for 3200 Whrs per day.

MrM1 · August 2018

I guess if Ur using the app u can't see signatures. Go to full web view

mike95490 · August 2018

Unless you are an electronics geek, and understand thoroughly, the proper care and feeding of LiPo4 batteries, use a 48v bank of cheap lead acid first, and then in 3 years, as LiPo4 designs settle down, replace the FLA with LiPo4.

Autostart generators, need as much, or more maintenance, than a manual generator. if really off grid, you may want 2 generators, because the generator never, ever, breaks down on a sunny day. And you likely don't need larger than 3-5 kw generator.

I think the break-even point for propane vs electric fridge was about 24 months worth of propane, was worth as much as the extra PV panels needed to run electric, and no funny propane smells, chimney cleaning and such, and much better cooling with electric, which is a bit noisier.

petertearai · August 2018

Yep after a gas fridge then inverter electric ..... definitely electric . No chimney cleaning , no naked pilot flame . .

Estragon · August 2018

A couple of additional details needed; is the cabin a full-time home (vs seasonal or weekend), and roughly where is it located?

alter · August 2018

These are really good reasons to go with electric fridge vs propane, ok I'm convinced there, thanks!

Cabin is in northern Wisconsin its only seasonal.

Regarding the lead acid batteries, my last system used those and I'm not really happy with the experience. They require maintenance, extra precautions regarding the off-gassing hydrogen, rapidly degrade in capacity and have to be replaced every few years. It just seems like the only thing they got going for them is the initial cost but that is deceiving. The reason I'm considering the Iron Edison 400ah 48v Lithium Iron Phosphate is that, it doesn't off-gas, it doesn't require maintenance.. "100% Maintenance Free" according to the company....so as far as the comment about needing to know about proper care and feeding of those batteries, what would that be, for this particular model, that appears to be designed for ease of use and comes with a 10 year warranty. "The integrated Battery Management System (BMS) monitors and regulates each cell in the battery bank to provide perfectly balanced charging and discharging while guarding against over-charge, over-discharge and thermal overrun situations."

mcgivor · August 2018

@alter said

For the battery bank, I just discovered a new type called "lithium iron phosphate" that appears to be perfect for solar. The one I was considering is the 48v 400 ah Iron Edison. It is expensive but looks like its built to last a very long time.

Read this thread, very informative and detailed https://forum.solar-electric.com/discussion/comment/379405#Comment_379405

Refrigerator wise, either DC or AC over propane

Estragon · August 2018

Seasonal in Northern Wisconson - according to pvwatts.nrel.gov you should get 5-6 hours full sun equivalent in summer (I used Eau Claire).

Any shading is bad, so I'd recommend trimming or removing the trees so the whole array sees full sun until whenever you leave in fall. Even minor shading from a few branches can cut output to near nothing. Trimming enough for long winter shadows may be impractical, so I'd assume the array will be in shade and snow covered all winter. As such, the system should be shut down completely in fall.

Lithium will be okay sitting over the winter, but can't be charged in freezing temps. Depending on the length of your season, flooded self-discharge could be an issue, needing a float or occasional charge. AGM or lithium may make more sense for your application.

If you are getting a big propane tank and delivery is available, a propane generator may be a good choice. 15kw may be a bit big though. My 4kw diesel goes mostly unused until fall. If I was to replace it, I'd likely look for something ~7-8kw (I have roughly similar size bank as what you're considering. Fuel stability could be an issue, especially with gas and to a lesser extent with diesel.

alter · August 2018

mcgivor said:

@alter said

For the battery bank, I just discovered a new type called "lithium iron phosphate" that appears to be perfect for solar. The one I was considering is the 48v 400 ah Iron Edison. It is expensive but looks like its built to last a very long time.

Read this thread, very informative and detailed https://forum.solar-electric.com/discussion/comment/379405#Comment_379405

OK I read through that article, although most of it was regarding a different type of battery..."Nickel Iron" (NiFe), and not "Lithium Iron Phosphate" (LiFePO4), although those are mentioned a couple times in the article as having beneficial properties.

alter · August 2018

Estragon said:

Seasonal in Northern Wisconson - according to pvwatts.nrel.gov you should get 5-6 hours full sun equivalent in summer (I used Eau Claire).

Any shading is bad, so I'd recommend trimming or removing the trees so the whole array sees full sun until whenever you leave in fall. Even minor shading from a few branches can cut output to near nothing. Trimming enough for long winter shadows may be impractical, so I'd assume the array will be in shade and snow covered all winter. As such, the system should be shut down completely in fall.

Lithium will be okay sitting over the winter, but can't be charged in freezing temps. Depending on the length of your season, flooded self-discharge could be an issue, needing a float or occasional charge. AGM or lithium may make more sense for your application.

If you are getting a big propane tank and delivery is available, a propane generator may be a good choice. 15kw may be a bit big though. My 4kw diesel goes mostly unused until fall. If I was to replace it, I'd likely look for something ~7-8kw (I have roughly similar size bank as what you're considering. Fuel stability could be an issue, especially with gas and to a lesser extent with diesel.

The pitch of the roof will be steeper than normal to facilitate snow to slide off. I'm not planning on shutting it down completely at any point, other than powering off the fridge. The battery bank will be indoors on top of hydronic-heated piping in the floor, which will never fall to near freezing.

Photowhit · August 2018

alter said:

The pitch of the roof will be steeper than normal to facilitate snow to slide off. I'm not planning on shutting it down completely at any point, other than powering off the fridge. The battery bank will be indoors on top of hydronic-heated piping in the floor, which will never fall to near freezing.

Might check LiFePo4's characteristics, unless you intend to run heat through the winter, I think they don't like sub freezing temps.

Estragon · August 2018

My panels are pretty steep (~65° from horizontal), and will get and stay snow covered some years in NW Ontario, which will be similar climate to N.Wi. Maybe a bit colder and a bit less snow? What happens some years is instead of getting cold in mid-Nov, it can stay warmish into the first heavy snows in Dec. The wet snow sticks to even the steep array, then freezes on. By January, there's 2-3" of crusty ice/snow and another 4-5" of fluffier snow on top, so the sun can't get to the dark panels to melt snow until they're cleared manually.

As well as making a trip out in January to clear, I also added some completely vertical panels with the sole purpose of floating the system to offset self-discharge and charge controller consumption.

I assume you'll be using glycol in the hydronic loops. I've never seen a heating system that can't fail. Do you have a local contact who can check on things over the winter?

alter · August 2018

Estragon said:

My panels are pretty steep (~65° from horizontal), and will get and stay snow covered some years in NW Ontario, which will be similar climate to N.Wi. Maybe a bit colder and a bit less snow? What happens some years is instead of getting cold in mid-Nov, it can stay warmish into the first heavy snows in Dec. The wet snow sticks to even the steep array, then freezes on. By January, there's 2-3" of crusty ice/snow and another 4-5" of fluffier snow on top, so the sun can't get to the dark panels to melt snow until they're cleared manually.

As well as making a trip out in January to clear, I also added some completely vertical panels with the sole purpose of floating the system to offset self-discharge and charge controller consumption.

I assume you'll be using glycol in the hydronic loops. I've never seen a heating system that can't fail. Do you have a local contact who can check on things over the winter?

Yep the vertical ones are a good idea. The system really won't be using much when nobody is there so it won't take much to keep them at least above 50%, along with the auto-start generator as backup.

I'll be able to monitor temperature etc remotely with smart thermostat and cameras.

Photowhit · August 2018

What is the temperature range of the LiFePo4 batteries?

alter · August 2018

Photowhit said:

What is the temperature range of the LiFePo4 batteries?

32 degrees F to 113 degrees F

Estragon · August 2018

You may be luckier than me. A couple of years ago, the weather was such that I couldn't find deer, etc., tracks on the ice in my normal early/mid Jan trip to check. If deer aren't on the ice, I'm not keen on breaking trail for them on thin ice, so I aborted. Finally got here in early Feb to find batteries too low to charge with generator (voltage < inverter/charger LBCO), and slushy electrolyte. That was with only charge controller consumption. It looked like panels got covered in mid-Dec. from logs. So far, the vertical panel float thing is working well

With lithium, they might be okay sitting discharged in the cold, which would be a big pro for using them. Personally, I'd want to be sure there was no way they'd charge in freezing temps though, not just by assuming the heat works, but by either/both of the charge controller and/or BMS preventing it.

I can think of way too many ways for things to go pear shaped with auto generator start, especially unattended, to risk it. Lots of people do though, apparently without problems.

Need advice for new system

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