First Solar Power System Build for Cabin

[jwoell]

Hello, first post here so I hope I'm not being too redundant with other threads. Please point me to a similar post if it's already out there.


I have a 1000sq ft cabin that I am designing a solar power system for. I was just hoping for some feedback and possibly some recommendations on equipment or at least recommended online stores.

Cabin is in Minnesota in a location with about 4.4 peak sun hours.

My goal is to have a grid-tied system that could also operate indefinitely off-grid.

Am I in the right ballpark with the rough outline listed below??


Requirements:

1. Grid-tied but able to be disconnected if/when I want to.
2. 120V and 240V output
3. Enough battery storage that it would extremely unlikely to run out of power even after 7-10 days of less than ideal sunlight.
4. Rock solid components that I don't have to worry about failing in the next 15+ years under normal usage.
5. I'm not very concerned about efficiency as solar panels are cheap and I'd rather just go with 50% more panels than I'd ever need and never worry about it.

Enough power to run :

1. oven/stove
2. well
3. lighting
4. refrigerator
5. deep freeze

Current Plan:

1. 6000W 48V Hybrid Solar Inverter
2. 3000 Watts of solar panels
3. (4) 12V AGM 200 Ah batteries

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[Zenithund]

Can I see the house drawings?

 

[SamDeleted]

Enough battery storage that it would extremely unlikely to run out of power even after 7-10 days of less than ideal sunlight.

(4) 12V Lead-Acid 200 Ah batteries

4x 12v 200ah lead acid = 9.6kwh (only 4.8 usable capacity)

5~kwh doesn't sound like enough to get you through ONE dark day, let alone 10 (all depends on your usage of course)

 

[SamDeleted]

Rock solid components that I don't have to worry about failing in the next 15+ years under normal usage.

If it's reliability your after, cheap lead acid batteries are NOT going to do the trick.

If you're going lead acid your best options are either a pack of 2v cell flooded folklift truck battery or flooded tractions (8-15yrs life if well maintained) OR gel/AGM traction batteries (7-10yrs life, no maintenance)

Others here might tell you to go LiFePo4 quoting 1 million cycles and 100 yrs lifespan (yes I'm over exaggerating.....). but none of these claims have actually been achieved in the real world

 

[jwoell]

If it's reliability your after, cheap lead acid batteries are NOT going to do the trick.

If you're going lead acid your best options are either a pack of 2v cell flooded folklift truck battery or flooded tractions (8-15yrs life if well maintained) OR gel/AGM traction batteries (7-10yrs life, no maintenance)

Others here might tell you to go LiFePo4 quoting 1 million cycles and 100 yrs lifespan (yes I'm over exaggerating.....). but none of these claims have actually been achieved in the real world

Oh geez, sorry about that, I stated that wrong. AGM batteries, sorry about that, I'll update the original post.

This is exactly the kind of feedback I was looking for though, thanks for the info.

So here's my philosophy on batteries, right now there is a ridiculous amount of money being dumped into battery tech research for electric cars. That will flow down to long term residential storage as well. Along with this, prices of batteries are dropping like mad and will most likely continue to do so. With that in mind, I'm thinking that I'll be adding more batteries at a later date. With that being said, maybe I should be asking what my long term battery storage capacity should be rather than stating what I already have.

Right now this cabin is grid tied, I'm trying to find a couple of my utility bills to get an actual power consumption value for one or two various months, that'll at least show a ballpark figure anyway, even if it isn't a day to day power usage.

Lets assume for now that my 4 AGM 12V 200 Ah batteries will only be used for emergencies and rarely dropped to a low state of charge. I am wanting to switch over to be fully off-grid though, so this is more about the path to switch over from the current grid-tied cabin to an off-grid cabin.

Thank you guys for your feedback. I'll dig up a couple of utility bills and post again, more to come.

 

[Rednecktek]

Hello, first post here so I hope I'm not being too redundant with other threads. Please point me to a similar post if it's already out there.

There are a few but all solar setups are unique to the situation so no worries.

I have a 1000sq ft cabin that I am designing a solar power system for. I was just hoping for some feedback and possibly some recommendations on equipment or at least recommended online stores.

That's nice! Let's see if we can get you pointed in the right direction.

Cabin is in Minnesota in a location with about 4.4 peak sun hours.

Is that in summer or winter? I can't imagine there's much sun out there in winter and that's going to be a concern.

My goal is to have a grid-tied system that could also operate indefinitely off-grid.

That's going to complicate things but it's do-able

Am I in the right ballpark with the rough outline listed below??

Let's take a look...

Requirements:

1. Grid-tied but able to be disconnected if/when I want to.

Only certain systems are going to do that very easily, but they're out there.

1. 120V and 240V output

OK, so split phase.

1. Enough battery storage that it would extremely unlikely to run out of power even after 7-10 days of less than ideal sunlight.

That's going to be a metric assload of batteries!!!

1. Rock solid components that I don't have to worry about failing in the next 15+ years under normal usage.

That's anyone's guess. There aren't that many systems out there that have even been around that long to show track history.

1. I'm not very concerned about efficiency as solar panels are cheap and I'd rather just go with 50% more panels than I'd ever need and never worry about it.

That's a good plan, but you might be looking at more than that to compensate for winter.

Enough power to run :

1. oven/stove

!

1. well

! 120v or 240v? How deep/big? That's going to need a significant startup surge support.

1. lighting
2. refrigerator
3. deep freeze

Easy enough

Current Plan:

1. 6000W 48V Hybrid Solar Inverter

You're going to need more than that, start with something in the 12Kw range so you've got 60a on each leg of that split phase to support that stove and well pump kicking on at the same time.

1. 3000 Watts of solar panels

Add a 0 on there at least

1. (4) 12V AGM 200 Ah batteries

Nope, not even close. That's going to be the same energy storage as a single 100Ah 48v rackmount style battery which mmmiiiggghhhttt be enough for a single day, but nowhere near the 7-10 days that you're after.

So here's my philosophy on batteries, right now there is a ridiculous amount of money being dumped into battery tech research for electric cars. That will flow down to long term residential storage as well. Along with this, prices of batteries are dropping like mad and will most likely continue to do so. With that in mind, I'm thinking that I'll be adding more batteries at a later date. With that being said, maybe I should be asking what my long term battery storage capacity should be rather than stating what I already have.

That's going to take some math as you really need to know what you're starting with, then multiply by 10.

Right now this cabin is grid tied, I'm trying to find a couple of my utility bills to get an actual power consumption value for one or two various months, that'll at least show a ballpark figure anyway, even if it isn't a day to day power usage.

That's going to be insanely useful! The more months you can get the better, especially in winter when usage is higher and solar productivity is lower. If you plan your system around your highest bill, then anything above that is gravy.

Lets assume for now that my 4 AGM 12V 200 Ah batteries will only be used for emergencies and rarely dropped to a low state of charge. I am wanting to switch over to be fully off-grid though, so this is more about the path to switch over from the current grid-tied cabin to an off-grid cabin.

The issue with AGM's is that they still suffer from the 50% DoD issues as well as a shorter lifespan. Dollar per watt of power storage out there now a pre-built LFP 48v battery and the same USABLE watts of AGM are almost exactly the same. There's no point in mounting up and wiring multiple hundreds of pounds of battery when a single box will do the same job for the same money.

Just to throw some napkin math at you, a 200Ah AGM battery is about $400 off the shelf roughly and you'd need 4 of them to get a usable 100Ah @ 48v. Now, being in Minnesota you're going to want cold weather protection and heating if possible, so the 100Ah Trophy battery is the Go-To at $1750. That's only $150 savings on the AGM's, but then you're going to have to replace all those AGM's in a few years where the Trophy is plugging right along.

Let's say for napkin math that a 100Ah battery lasts you a day perfectly. The Trophy 300Ah battery is $4700 and 360lb and is one box with 1 set of terminals and wires and lasts 3 days. So for your 10 days that's 3 boxes, 6 wires, and about $14,000 for 9 days of power.

But you really like the thought of AGM, so you decide to go that route. Now you're looking at 4 batts @ 200Ah per day * 9 days = 36 batteries @ 130lb each, 72 wires, and about $14,400 and then you'll get to replace them all in a decade or so. You'll need to build another 100sq ft cabin just for the batteries.

In short, your plan isn't horrible or unmanageable, but your battery situation really needs a re-think. Getting the power bills and planning for the worst of them is going to be a great start as that's going to get your system needs all figured out without having to crunch the numbers on every light bulb in the house.

I suspect that your system will look something like:

One of the 18k-12kw grid tie inverters ala EG4, SolArk, etc.
3x Trophy 304Ah rackmount batteries
20Kw of solar panels

Roughly...

 

[rodrick]

With the price difference between agm and a Lifepo server rack batteries is so minimal unless it’s a environmental issue such as extreme temperatures the cost per Ah is basically the same and you should get more cycles out of the Lifepo battery; a good basic server rack Sok battery runs $1300 at current connected (48 volt 100 Ah)

 

[jwoell]

There are a few but all solar setups are unique to the situation so no worries.

That's nice! Let's see if we can get you pointed in the right direction.

Is that in summer or winter? I can't imagine there's much sun out there in winter and that's going to be a concern.


That's going to complicate things but it's do-able


Let's take a look...

Only certain systems are going to do that very easily, but they're out there.

OK, so split phase.

That's going to be a metric assload of batteries!!!

That's anyone's guess. There aren't that many systems out there that have even been around that long to show track history.

That's a good plan, but you might be looking at more than that to compensate for winter.

!

! 120v or 240v? How deep/big? That's going to need a significant startup surge support.

Easy enough

You're going to need more than that, start with something in the 12Kw range so you've got 60a on each leg of that split phase to support that stove and well pump kicking on at the same time.

Add a 0 on there at least

Nope, not even close. That's going to be the same energy storage as a single 100Ah 48v rackmount style battery which mmmiiiggghhhttt be enough for a single day, but nowhere near the 7-10 days that you're after.


That's going to take some math as you really need to know what you're starting with, then multiply by 10.


That's going to be insanely useful! The more months you can get the better, especially in winter when usage is higher and solar productivity is lower. If you plan your system around your highest bill, then anything above that is gravy.


The issue with AGM's is that they still suffer from the 50% DoD issues as well as a shorter lifespan. Dollar per watt of power storage out there now a pre-built LFP 48v battery and the same USABLE watts of AGM are almost exactly the same. There's no point in mounting up and wiring multiple hundreds of pounds of battery when a single box will do the same job for the same money.

Just to throw some napkin math at you, a 200Ah AGM battery is about $400 off the shelf roughly and you'd need 4 of them to get a usable 100Ah @ 48v. Now, being in Minnesota you're going to want cold weather protection and heating if possible, so the 100Ah Trophy battery is the Go-To at $1750. That's only $150 savings on the AGM's, but then you're going to have to replace all those AGM's in a few years where the Trophy is plugging right along.

Let's say for napkin math that a 100Ah battery lasts you a day perfectly. The Trophy 300Ah battery is $4700 and 360lb and is one box with 1 set of terminals and wires and lasts 3 days. So for your 10 days that's 3 boxes, 6 wires, and about $14,000 for 9 days of power.

But you really like the thought of AGM, so you decide to go that route. Now you're looking at 4 batts @ 200Ah per day * 9 days = 36 batteries @ 130lb each, 72 wires, and about $14,400 and then you'll get to replace them all in a decade or so. You'll need to build another 100sq ft cabin just for the batteries.

In short, your plan isn't horrible or unmanageable, but your battery situation really needs a re-think. Getting the power bills and planning for the worst of them is going to be a great start as that's going to get your system needs all figured out without having to crunch the numbers on every light bulb in the house.

I suspect that your system will look something like:

One of the 18k-12kw grid tie inverters ala EG4, SolArk, etc.
3x Trophy 304Ah rackmount batteries
20Kw of solar panels

Roughly...

Wow, talk about a whole lot of good information, that's a long post. Not sure if I can respond to each line item but I'll try to cover most of it.


I think this cabin is going to use much less power than you described though. It's pretty bare bones and there won't be any heating or cooling or anything like that. I'm waiting on some actual usage numbers so we can talk more about that later.

Thanks for all the good info and calculations on batteries too. That is definitely a chunk of change for the full blown off-grid system. Sounds like it will be a bit of a transition from grid to full battery storage. Instead, we may have to start by running calculations for a situation with an average sun day and just having enough battery power on hand to cover the cabin's power needs through the night, with the grid-tie to fill in any spots where we run low on battery power.

I'm definitely not set on any particular type of battery though. I happened to have the 4 AGM 200 Ah batteries already so I just started from there for discussion. I'd want to use the right components and not half-ass it so yeah, not set on those. I had originally purchased them for an experiment where I was going to run just my garage off solar and those 4 batteries. Just to play around with it and get a better feel for real world application. I haven't done anything with that yet though, that's a side conversation anyway.

So here's why I sized the battery needs so small, and it sounds like I was way off. I had read somewhere I while back that even under low light situations, that solar panels might still produce 10% of their rated output power. Is that a true statement or do I need to plan for exactly 0.00 power coming from solar panels on a dark and raining day? I was assuming that I could build the solar array to be big enough that the 10-20% power from it would get my by for a few days if we conserved power. Guess that was way off.

Which brings me to my next point, maybe we could leave the stove/oven out of the equation if it would add that much more complexity. I just thought it would be worth having access to, even if it was only used when there wasn't another option. Maybe we could just replace that with an electric countertop hot-plate or something. For some reason I didn't thing that running a stove burner for like 30 minutes would be a problem. I'm looking at ovens and assuming 5000W maximum, for like 30 minutes or something during the day, thinking that would be offset by the solar array generating power at the same time. Yep, I was way off.


Ok, so until I get those actual kwh usage values, I had a couple other things to talk about then...

We are talking about battery capacity and not wanting the batteries to go outside of a specific state of charge, lets say we want to keep them between 20% and 80% state of charge for the sake of this discussion. My question is, can you set that up on typical hybrid inverters? Specifically, with a grid connected cabin, can I setup a hybrid inverter to charge up the batteries to only a maximum of 80% during the day then run the cabin from the batteries at night until they're down to 20% and then switch back to grid power until daytime when the solar panels will charge the batteries again and run the cabin's immediate power draw at the same time?

As far as solar array size, you listed 20KW of solar power, I'm not opposed to having way way more that I would actually need, I kinda like that idea, but what happens to the power once the batteries are charged? If the batteries are topped off early in the day and then this huge solar array is still generating power, where does that power go? Will it cause deterioration of the solar panels? Extra stress on the inverter that could cause problems? Or is it just dumped to ground or something? This is something that always puzzled me. I'd gladly have a solar array that's 10 times what I actually need, as long as the super-over-extra size wouldn't cause problems to the rest of the system.

I still don't have those actual kwh usage numbers from the utility bill, so more to come, I don't want to get too into it and specific until I have real-world numbers.

Thanks again!

 

[jwoell]

With the price difference between agm and a Lifepo server rack batteries is so minimal unless it’s a environmental issue such as extreme temperatures the cost per Ah is basically the same and you should get more cycles out of the Lifepo battery; a good basic server rack Sok battery runs $1300 at current connected (48 volt 100 Ah)

Noted. It sounds like AGM is not really a thing anymore. Skip that then, lets start talking about a system with LiFePO batteries then. At least in the short term.

Like I was talking about earlier though, I think battery tech is going to change drastically in the next few years, but like they say, "The next battery tech breakthrough is perpetually 5 years away". So who really knows what'll actually play out.

We could always start talking about the idea of getting a junked out electric car and pulling out the battery from that to plug into a person's solar power system. That's a whole 'nother conversation though and I don't want to get too off track.

 

[rodrick]

We are talking about battery capacity and not wanting the batteries to go outside of a specific state of charge, lets say we want to keep them between 20% and 80% state of charge for the sake of this discussion. My question is, can you set that up on typical hybrid inverters? Specifically, with a grid connected cabin, can I setup a hybrid inverter to charge up the batteries to only a maximum of 80% during the day then run the cabin from the batteries at night until they're down to 20% and then switch back to grid power until daytime when the solar panels will charge the batteries again and run the cabin's immediate power draw at the same time?

The inverter can be setup to do that no problem

any excess power from the panels could be used to heat water if you wanted to but if not used it’s not a problem it won’t hurt the panels

 

[Rednecktek]

As far as solar array size, you listed 20KW of solar power, I'm not opposed to having way way more that I would actually need, I kinda like that idea, but what happens to the power once the batteries are charged? If the batteries are topped off early in the day and then this huge solar array is still generating power, where does that power go? Will it cause deterioration of the solar panels? Extra stress on the inverter that could cause problems? Or is it just dumped to ground or something? This is something that always puzzled me. I'd gladly have a solar array that's 10 times what I actually need, as long as the super-over-extra size wouldn't cause problems to the rest of the system.

Or since you're grid tied the excess power will go towards your bill each month.

We are talking about battery capacity and not wanting the batteries to go outside of a specific state of charge, lets say we want to keep them between 20% and 80% state of charge for the sake of this discussion. My question is, can you set that up on typical hybrid inverters? Specifically, with a grid connected cabin, can I setup a hybrid inverter to charge up the batteries to only a maximum of 80% during the day then run the cabin from the batteries at night until they're down to 20% and then switch back to grid power until daytime when the solar panels will charge the batteries again and run the cabin's immediate power draw at the same time?

Inverters can be set easily to change over back and forth, it's a common setting.

So here's why I sized the battery needs so small, and it sounds like I was way off. I had read somewhere I while back that even under low light situations, that solar panels might still produce 10% of their rated output power. Is that a true statement or do I need to plan for exactly 0.00 power coming from solar panels on a dark and raining day? I was assuming that I could build the solar array to be big enough that the 10-20% power from it would get my by for a few days if we conserved power. Guess that was way off.

Yeah, in lousy weather count on 0w coming in and anything that does is going to be eaten by your controllers first before anything gets to your batteries or loads. I've had setups with 300w of panel and couldn't generate 120wh in a day for weeks on end leaving me with dead batteries many, many times.

Which brings me to my next point, maybe we could leave the stove/oven out of the equation if it would add that much more complexity. I just thought it would be worth having access to, even if it was only used when there wasn't another option. Maybe we could just replace that with an electric countertop hot-plate or something. For some reason I didn't thing that running a stove burner for like 30 minutes would be a problem. I'm looking at ovens and assuming 5000W maximum, for like 30 minutes or something during the day, thinking that would be offset by the solar array generating power at the same time. Yep, I was way off.

Still gotta heat food somehow, an electric range is still an electric range, it's just a difference of 5000w now or 500w and 3x as long to cook.

Like I was talking about earlier though, I think battery tech is going to change drastically in the next few years, but like they say, "The next battery tech breakthrough is perpetually 5 years away". So who really knows what'll actually play out.

Even if tomorrow they announced an Unobtanium Perfect Battery made with sea water and CO2 sequestered from the air, it would take years for that tech to hit your hands. Go with what's already proven to work reliably and worry about it in 20 years when you start thinking about replacing your perfectly functional batteries.

We could always start talking about the idea of getting a junked out electric car and pulling out the battery from that to plug into a person's solar power system. That's a whole 'nother conversation though and I don't want to get too off track.

That's part of the Advanced Class.

 

[jwoell]

Or since you're grid tied the excess power will go towards your bill each month.



Inverters can be set easily to change over back and forth, it's a common setting.


Yeah, in lousy weather count on 0w coming in and anything that does is going to be eaten by your controllers first before anything gets to your batteries or loads. I've had setups with 300w of panel and couldn't generate 120wh in a day for weeks on end leaving me with dead batteries many, many times.



Still gotta heat food somehow, an electric range is still an electric range, it's just a difference of 5000w now or 500w and 3x as long to cook.



Even if tomorrow they announced an Unobtanium Perfect Battery made with sea water and CO2 sequestered from the air, it would take years for that tech to hit your hands. Go with what's already proven to work reliably and worry about it in 20 years when you start thinking about replacing your perfectly functional batteries.


That's part of the Advanced Class.

Thanks again for all the info.

I found an electric bill for the cabin. In July it used 598 kwh of electricity. That was with a dehumidifier running 24/7 as well.

Google says that an average dehumidifier uses about 300-700 watts of power. So 7.2 - 16.8 kwh per day since it was running 24/7. Lets still include this in the calculations for now.

So given that number, a ballpark would be around 20 kwh per day. I know it's not linear but for the sake of this discussion we could start with that. Lets also assume it was only used half of the month, so 15 days out of 31 got us to the 598 kwh.

So in the end lets just say it would require 50 kwh per day. That's a nice round number. (And quite a bit more than I expected)

If the peak sun hours are an average of 4.4 at this latitude, I'll go with 4 hours per day of sun.

50 kwh ÷ 4 peak sun hours per day = 12.5 KW

So a 12 KW hybrid solar inverter with a decent number of extra panels would be a good place to start I'm thinking, perhaps 20 KW.

***Note that if the dehimidifier was left out of the conversation this could be reduced 25-30% I'm thinking. I'll be adding a watt meter to that to measure the exact numbers.


aaaaaand I'm totally irritated with 'Rednecktek' right now because he was spot on from the beginning. ?

​

You mentioned earlier that you would recommend "One of the 18k-12kw grid tie inverters ala EG4, SolArk, etc.". I've been casually browsing through plenty of random inverters from a bunch of different companies, just so I have some idea of the kind of stuff is out there but I haven't come close to picking out anything specific. Is there any place in particular you look at to get these things? Not sure if there are a couple good websites that sell this stuff or if it's just direct from the manufacturer or whatever google happens to pull up?

Is there kinda a go-to hybrid inverter model that is considered ideal for this sort of thing? I'll start by looking at the EG4 and SolArk listed above.

As always, any other thoughts would be greatly appreciated as well.

 

[Rednecktek]

And you're looking at about $18,000 for inverter and batteries for a 1 day supply...

 

[jwoell]

And you're looking at about $18,000 for inverter and batteries for a 1 day supply...

I keep seeing this 10KW hybrid inverter from Sun Gold Power show up in my searches. Is this something I should avoid? It keeps popping up in my searches and I'm trying to figure out if I should even pay attention to it.

Better yet, I'll look around on this site for a hardware review section...

10KW 48V Split Phase Solar Inverter

Highlight: ★ All in one unit: 10KW Pure Sine Wave Solar Inverter Combined with Max 200A battery charging, 2 MPPT Solar controller inbuilt, Max.Voltage of Open Circuit : 500VDC, Split phase (120V/240V) or Single phase (120v) output. Wifi module is included, which allows the user to view the...

sungoldpower.com

 

[Rednecktek]

Everything I'm hearing is that people are shunning the 10k in favor of the 18k's because you get more power, more array, and more features for the same price.