diy solar

diy solar

Solar configuration

@Daxo I’ve wondered about running the system with a large enough solar controller to carry the 800 watts of pv or having 2 smaller solar controllers that were sized to 400 watts pv each. It’s pretty close to the same price, one larger, or 2 smaller. Under the larger solar controller I would connect either 400 or 800 watts of pv depending on my camping situation. With the 2 smaller, one would just set idle disconnected.
 
@Camp20144

I'm not familiar with a CPAP, did a quick search for it, is this a machine for sleep apnea?

If so, it is the single most determining factor in this system design. Knowing your cpap machine power supply specifications would be invaluable.

What does it use, DC or AC for power supply? Wattage?


Other than that, I can see multiple reasons why this should be a 12V system in my humble opinion.

Yet again, cpap power supply will determine all the tiny bits and pieces of what goes and what doesn't.


Best,
D.
 
@Camp20144

I'm not familiar with a CPAP, did a quick search for it, is this a machine for sleep apnea?

If so, it is the single most determining factor in this system design. Knowing your cpap machine power supply specifications would be invaluable.

What does it use, DC or AC for power supply? Wattage?


Other than that, I can see multiple reasons why this should be a 12V system in my humble opinion.

Yet again, cpap power supply will determine all the tiny bits and pieces of what goes and what doesn't.


Best,
D.
Yes, a cpap is for sleep apnea (a must have for me).

I have the 12 volt power supply cord for my cpap that connects to a battery with a “cigarette lighter” power outlet. At home I use the 110 volt power supply. The 110 volt power supply, is a 110 volt ac to 12 volt dc converter. It outputs 6.67 amps @ 12 volts. That 6.67 amps is enough to power the cpap, the heated humidifier and heated hose. I have the ability to shut the power off to the humidifier and the heated hose. I figured a worst case power use scenario is 6.67A, or 80 watts/hour, 7 hour night 560Wh.

I have 2 100Ah Battleborn batteries, BMV-712 smart meter and shunt, fuse block, and female “cigarette” socket. I’m ordering the wiring and fuses to get those connected so that I can run my cpap off battery to get actual Watt hours using the BMV-712.
 
@Daxo Thank you for your assistance.

I was looking through the Resources section and it looks like at 800 watts of solar I’m in the could be 12 volt or 24 volt. What I see as an issue with 24 volt is I have to then drop the 24 volts back down to 12 volts. It appears that subjects me to efficiency losses that I shouldn’t have to deal with. Some have mentioned 24 volts for expansion of the system. After thinking about it, I don’t foresee expanding this system. If I pursued a larger system in the future I would start that larger system from scratch. I will always have use for this size system. So at this point I think it would remain intact at 12 volts and 400 or 800 watts pv.

Thank you,
Mark
 
@Camp20144

I read the whole thread again just to have all the details fresh.

I try to take each and all of the specifics and run them all simultaneously against each other, such as design goal, budget, components, how things work, cost, performance, and so on and on till finding the system design golden middle between any and all of the given specifics.

With that said, not certain but this time reading, I've noticed you aren't looking for the cheapest SCC but rather are more interested in the best option for your needs. Is that the case? This might come into play later.


The following is merely my take on your solar build, a mere suggestion or food for thought if you will. Hopefully, you find some of it useful.

Yet, since you are the one who will build, operate and maintain this system, it's mandatory to take the time and learn all the ins and outs of a solar panel system, as your safety is entirely in your hands from the get-go. Ask questions, ask a lot of questions here and in other places such as FB groups etc.

Always triple-check anything and everything anyone, myself included, suggests to you. Run the ideas by other folks in multiple places.



The system voltage part;

Since you already have two 12V 100Ah LiFePO4 batteries and your primary use of this system is to power a CPAP device whose native voltage is 12V, having two batteries in parallel(12V system voltage) is preferable in my opinion. In fact, a system redundancy where possible is a must.

Why?

If you use 2x12V 100Ah in series to get to a 24V system voltage 100Ah capacity, if, for whatever reason one of the batteries stops working your entire system is down. With a CPAP device, I believe this is a big no-no.

Also, on top of that, you would be dealing with either an additional device to keep the two batteries balanced or additional maintenance every 6 months.

With the two 12V 100Ah batteries in parallel to get a 12V system voltage 200Ah capacity, you gain battery storage redundancy where if one of the batteries fails, your system will keep running the device. That's a (y) in my book.


At this point, things are getting better and better because you could use MRBF fuses now, including for the SCC, Inverter, and even as a main battery terminal fuse.

MRBF is reliable, practical, and compact, but also cheaper than say a class T fuse as a terminal fuse. It has an acceptable Arc breaking capacity @12V/ 10 000A. Heck, If it's safe to be used on boats 100 miles out at the sea, I guess it must be pretty darn safe and reliable altogether.

The nice thing about having 2x 12V batteries in parallel is if you use cables of the same length to connect to a common busbar for both batteries separately, the positive and negative battery terminals, you can fuse each battery separately by a factor of 1.25x max current the battery can deliver. (take BMS rating for reference) See the diagram below.
common busbar.png

In doing so, you can use the same gauge wire for these connections, at the same time make sure the charging and load current are equally distributed, and above all, you gain a battery storage redundancy where if one fails, the other keeps running. Also, if one of the batteries stops working, you can take the bad one out till you get the replacement and obviously, keep your system running at half the storage and a reduced inverter capacity in the meantime.

Again, this would not be possible in a 24V system using only two 12V batteries.

Now, the nice thing about the 24V system is that you are dealing with half the amps across the board than you would be at the 12V system. Yet, up to 1500W AC(post-Inverter efficiency losses and cutout voltage calculation), amps should be very manageable at a 12V system with 200Ah capacity.

More specifically, you've said previously that your biggest planned load is a 900W microwave for a few minutes run so this should not present any problem for such a battery bank in my humble opinion.

To be continued...

I'll wait till you read this post to see what are your thoughts on this before proceeding to the SCC/solar panel part.

Best,
D.
 
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@Daxo Thank you! for the write up!

As stated, the primary driver is the cpap (12V) (I see using this system as power outage backup at home also)
Another desire - portability - so this system remain this size
Therefore, I agree with your 12 volt vision for this system
If larger, or grow larger, then 24 volts makes sense
Failure of one battery leaves me with a functional 1/2 size 12 volt 100Ah system still powering my cpap

In my reading (IMR) I thought the MRBF fuses would work. I purchased a 125A fuse/battery post mount holder and will purchase a second

IMR, keeping cable lengths the same approach you discuss was important

I’ve not yet ordered cables, so as to need to purchase most of them only once ?

I understand the 24V/half the Amps/smaller cables, but the primary 12V dc-dc use/limited size swings me to the 12V version

I’ve seen discussions of sizing inverters for 12V systems at 1000-1500W. I figured my largest load, a 900W microwave 2-3 minutes, 20% efficiency loss is 1080W which is 90% of a 1200W inverter.

Uses beyond my cpap (LED lights, cell charging, limited microwave use) will all be used based upon real-time monitoring. If it’s poor solar conditions, or I only have 400W of pv, I don’t need the luxuries, or I limit their use. My pickup has a quick charge pad for my cell phone and I own flashlights etc.

I look forward to your further thoughts and info.
Thank you,
Mark
 
@Camp20144

After defining an appropriate system voltage for your power needs, a 12V nominal, we can proceed forward.


Solar panel selection part;

Since now we know that we are going to utilize the 12V side of the SCC, we know exactly what are we looking for from a solar panel. The Rich Solar 200W '24V' variant.


Rich Solar 200W '24V'
Type: Monocrystalline 24 volt
Operating Voltage (Vmp): 37.6V
Open Circuit Voltage (Voc): 45.4V
Short Circuit Current (Isc): 5.83A


The fact that the 200W panel Isc is 5.83A Array voltage means a parallel panel configuration.

Remember, I said redundancy wherever possible :)

The SCC part.

In your design requirements, you've said that sometimes you'll use only 400W or solar and at other times 800W of solar so it's best to take the maximum solar power and work from there.

While the 100/50 SCC could accommodate this nicely, it would be working near its maximum, and keeping things cooler usually means it will last longer. Also, it might be necessary to back off the charging to 47A, which in turn means a certain loss of solar production.

Plus, if a single SCC stops working your system is done as far as solar production to charge your batteries goes. The range of inconveniences this could entail can vary.

Certainly, having redundancy here as well would further bulletproof your system and open up another set of options going forward.


For an additional 100$ for 2x100/30, you would further bulletproof your system where if one of the SCC fails for whatever reason, your system will keep going at reduced solar production capacity.

Personally, I'd go with 2x Victron 100/30 SCCs any day.

Though, 100/50 would suffice if cost is a factor. Just that it would require additional investments in fuses and perhaps, cable wire size and finding out if you need to limit the SCC charging current to keep the SCC temperature down at peak production.


Hope it helps a bit.

Best, D.
 
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@Daxo Thank you much! Most helpful! My first read through you have answered things I’ve wondered about and created some questions. I’ll think through this info and reply back.
Thank you again,
Mark
 
I’ve added questions, comments in blue print to your discussions. I hope they come through. I welcome your further comments. Unfortunately it appears you have to “expand” sections to see my questions/comments on your discussions. I didn’t realize this when I did this.
After defining an appropriate system voltage for your power needs, a 12V nominal, we can proceed forward.
Agreed
Solar panel selection part;

Since now we know that we are going to utilize the 12V side of the SCC, we know exactly what are we looking for from a solar panel. The Rich Solar 200W '24V' variant has a favorable voltage ratio of 2.6:1(Vmp/charging V).
I would like to understand this ratio better. Is there some reading you are able to suggest? Or, explanation of this ratio? I was unable to obtain search results from the forum (bad queries?). I venture a guess that it is easier to obtain charging voltage from non-optimal solar conditions?
This tells me that as far as the Solar array voltage goes, we are set and good to go.


Rich Solar 200W '24V'
Type: Monocrystalline 24 volt
Operating Voltage (Vmp): 37.6V
Open Circuit Voltage (Voc): 45.4V
Short Circuit Current (Isc): 5.83A


The fact that the 200W panel Isc is 5.83A and we are set with the Array voltage (from above ratio discussion?) means only one thing, a parallel panel configuration where every single panel will produce independently of the other in case of shading in any given part of the day is the preferable design direction. (Panels acting independently is an effect of parallel config. that is useful as another “redundancy” that is afforded due to the Array voltage value?)

The Voc-cold temperature-related concern is gone. When connecting two solar panels in parallel, the current doubles while the voltage remains the same. (I think these statements are rooted in - Record coldest is -25F so the correction factor from the correction factor chart is 1.23 which is (1.23)(45.4V)=55,84V?) 55V is well below SCC voltage ratings)

This is as good as it gets because these 200W panels are not half-cut panels, but the sets of two panels(400W total) will now work as one and the Array Isc is low enough to be able to use cheaper size 10AWG PV cables for connecting it to the SCC. (I’m not sure I understand “but the sets of two panels(400W total) will now work as one”. The “work as one” part of your statement. I follow the lower Amperage flowing gives the smaller wire cross-section equates to lower cost. Savings where it makes sense.

Remember, I said redundancy wherever possible :)
(Agreed, redundancy whenever possible)

In addition, IMO in a well-designed small solar system, you should not be dealing with additional parts such as panel fuses. Unnecessary cost and above all, higher part count or in other words points of failure. This will be further addressed in the SCC selection part.
(Agreed, fewer parts equals less complexity and lower cost where it can be accomplished when safety is not compromised)

The SCC selection part.

In your design requirements, you've said that sometimes you'll use only 400W or solar and at other times 800W of solar so it's best to take the maximum solar power and work from there. (Yes, I believe this is important as I envision the different uses of this system)

800W(STC) of rated solar power
800W*0,85(85% of STC) = 680W of actual solar power at peak in near-perfect conditions (derived from the fact that one can never meet optimum charging conditions - tracking sun, panel angle, never at STC etc)
680W/12V(charging V) = 56,6A charging
680W/14V(charging V) = 48,5A charging

52,55A charging average at peak.

While the 100/50 SCC could accommodate this nicely, it would be working near its maximum, and keeping things cooler usually means it will last longer. Also, it might be necessary to back off the charging to 47A, which in turn means a certain loss of solar production. (Agreed, Not pushing equipment to the top end of its rated values)

Plus, if a single SCC stops working your system is done as far as solar production to charge your batteries goes. The range of inconveniences this could entail can vary.
(Agreed, Redundancy)
Certainly, having redundancy here as well would further bulletproof your system and open up another set of options going forward.


100/50 SCC cost: 300$ ish
2x100/30 SCC cost: 400$ ish

100/30@12V=440W solar
680W(85% STC rating)/2 sets = 340W solar per set
340W/12V= 28,3A
340W/14V
= 24,28A

Charging average = 26,29A
or 87.6% of rated SCC power /a lot better than working at 100% in the 100/50 case, in my humble opinion.(Agreed)

For an additional 100$ for 2x100/30, you would further bulletproof your system where if one of the SCC fails for whatever reason, your system will keep going at reduced solar production capacity. (Agreed, not pushing SCC’s to limit lessens chance of failure, but failure’s can still happen - again redundancy)
Plus, you now don't have to deal with any fuses as you would if you would use 4 panels in parallel with the 100/50. (Fewer parts, smaller replacement parts to keep on hand)

Personally, I'd go with 2x Victron 100/30 SCCs any day. (Agreed. This was a question I was trying to read on. One vs two SCCs - which version made more operational sense.)

Though, 100/50 would suffice if cost is a factor. Just that it would require additional investments in fuses and perhaps, cable wire size and finding out if you need to limit the SCC charging current to keep the SCC temperature down at peak production. (To me, the cost factor is more than the $$, it’s also related to operational factors, as here where you enumerated related factors - adjustments due to temperature, cable wire size, fusing factors etc)


Hope it helps a bit. (I consider your discussion very helpful. Thank you very much!)

Best, D.
Again, thank you very much for your valuable time assisting me with my understanding and building of my system,
Mark
 
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Frankly, the 'Ratio' I was talking about previously is just something that came to be from my humble experience with solar.


Best,
D.
 
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@Daxo Thinking about your “favorable charging ratio of 2.6:1(Vmp/charging V). Victron says that their charge controllers need battery V+5V (B+5V) to start charging. Am I looking at this correctly to think that as panel voltage jumps up with the rising sun, that it reaches B+5V quicker? How, or is, this similar to the discussion of “over paneling” a charge controller, where you get charging earlier and later in the day but the charge controller “clips” charging in the middle of the day because you exceed the output of the charge controller? (How’s that for a run-on sentence??) It appears that the ratio allows earlier and later charging without the clipping caused by over paneling?
 
As previously said, it's just something that came to be from my practical experience with solar.

Best,
D.
 
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As previously said, it's just something that came to be from my practical experience with solar.

Which I've used previously to say your '24V' panel has plenty of Vmp, enough so you don't need to connect any more panels in series for a 12V system.

In short, your panel Vmp is 2.6:1 charge V. Enough that when your 1s panel makes, say, 1Amp, you'll have 2.6A going to the battery.

There's nothing more to it really.

Best,
D
Yes, I understand that you, through your experience, have reached the conclusion that a person wants to use that ratio in array design. I wasn’t suggesting adding more panels to my array as I agree with your thoughts on array design.

I thought the system might start charging earlier, and keep charging later, than if the two voltages were closer in value, a bonus.

I think your concept makes more sense than over paneling and pushing the charge controllers harder than design limits. Even though Victron says their cc can handle 130% rated value, it seems they are working hard(er) - producing heat…

I’ll keep plugging away here.

Again, thank you very much for your thoughts, discussions and advice!

Mark
 
I've seen a lot of 12v systems that are nightmares.

What about using a system like a hybrid inverter 48v system that you could plug in if needed ether to the land or a small generator and then if you need a few 12v small draws use a DC buck from the 48v system to a smaller 12v lipo battery that can fuel usb and 12v dc stuff if you have too much efficiency loss from the 48v inverter.
 
No worries.

Was in the middle of something so I haven't had the chance to reply, that's all. :)

Got that sorted now.


Best,
D.
 
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I've seen a lot of 12v systems that are nightmares.

What about using a system like a hybrid inverter 48v system that you could plug in if needed ether to the land or a small generator and then if you need a few 12v small draws use a DC buck from the 48v system to a smaller 12v lipo battery that can fuel usb and 12v dc stuff if you have too much efficiency loss from the 48v inverter.
Hi,
Do you have a make/model you are thinking about? Kind of long winded but the following is some of my thinking.

As I started my research for a battery based system to meet my various camping (boondocking) needs, my main concern/driver is powering my cpap (12V). To me other power uses are luxuries when camping. I looked at the AIO units (12V) but they were expensive and not much power which meant more expense to expand. I also liked the idea of building my own system - more power/flexibility for my $$.

Then it was suggested I looked at a 24 Volt system, but that meant the need to go from 24V to 12V to run my cpap and associated losses. My cpap is the main reason I’m on this path, and in many excursions may be my only power requirement. So it didn’t make sense to me to deal with voltage changes.

The other thing I found while looking at the 12V/24V situation is that my system is right in the “in between” zone. On the large size for a 12V system and on the small side for a 24V system.

If I need/desire a larger system I would keep this system intact (I envision I will always have a need for this system) and start a larger system from scratch.

I have the 2 12V 100Ah LiFePO4 Battleborn batteries I plan to use in my system. I had to buy the “6V” GC2 form/size batteries so they would fit in my slide-in pickup camper battery box due to dimensional issues.

So all considered it made more sense for me to go 12V.

Now, having said all that, I never considered a 48V hybrid inverter. I’m not sure I would have a different thought process with my primary driver my cpap at 12 volts. If I move from 12V I inherit the inefficiency of changing voltages 48V>12V or 24V>12V. Or the need to carry and charge a separate 12V LFP battery. If you have a particular make/model in mind please let me know and I’d take a look at it to see what they may offer.

I received a lot of valuable insights/assistance/help from this forum along the way.
 
Hi,
Do you have a make/model you are thinking about? Kind of long winded but the following is some of my thinking.

As I started my research for a battery based system to meet my various camping (boondocking) needs, my main concern/driver is powering my cpap (12V). To me other power uses are luxuries when camping. I looked at the AIO units (12V) but they were expensive and not much power which meant more expense to expand. I also liked the idea of building my own system - more power/flexibility for my $$.

Then it was suggested I looked at a 24 Volt system, but that meant the need to go from 24V to 12V to run my cpap and associated losses. My cpap is the main reason I’m on this path, and in many excursions may be my only power requirement. So it didn’t make sense to me to deal with voltage changes.

The other thing I found while looking at the 12V/24V situation is that my system is right in the “in between” zone. On the large size for a 12V system and on the small side for a 24V system.

If I need/desire a larger system I would keep this system intact (I envision I will always have a need for this system) and start a larger system from scratch.

I have the 2 12V 100Ah LiFePO4 Battleborn batteries I plan to use in my system. I had to buy the “6V” GC2 form/size batteries so they would fit in my slide-in pickup camper battery box due to dimensional issues.

So all considered it made more sense for me to go 12V.

Now, having said all that, I never considered a 48V hybrid inverter. I’m not sure I would have a different thought process with my primary driver my cpap at 12 volts. If I move from 12V I inherit the inefficiency of changing voltages 48V>12V or 24V>12V. Or the need to carry and charge a separate 12V LFP battery. If you have a particular make/model in mind please let me know and I’d take a look at it to see what they may offer.

I received a lot of valuable insights/assistance/help from this forum along the way.
Many people on this form would do a much better job than I at picking specific units. I wanna say growwatt sounds familiar? Check with videos from ... forgot his name.

Then I search3d for solar power and up came will prowse and a video on exactly this topic



Lastly. I found it comicly humorous the size wire needed for large 12v systems.

Especially where weight and size for mobility are concerned. If low Voltage for significant power systems was good they'd run EVs on it.


Okay those last 2 paragraphs could be viewed as flame bate. Seriously haven't even read the 12v arguments. Busy work day and just wanted to gift a little perspective on this form where I have been helped so many times by so many smart people here.
 
I've seen a lot of 12v systems that are nightmares.

What about using a system like a hybrid inverter 48v system that you could plug in if needed ether to the land or a small generator and then if you need a few 12v small draws use a DC buck from the 48v system to a smaller 12v lipo battery that can fuel usb and 12v dc stuff if you have too much efficiency loss from the 48v inverter.
- 48V system for a max 1060W continuous load?
- The Array voltage required to even begin to charge the battery? Implications of it in solar configuration.
- What about the amount of space and weight the 48V storage would take for mobile applications?
- The cost for fuses?

Lastly. I found it comicly humorous the size wire needed for large 12v systems.
For a 1060W AC, he only needs 105A at a cutoff voltage of 10V. Usually, it should be around 12V low - tops, which is about 88A.

That's about 2AWG up to 1/0AWG, depending on the insulation ratings. Plus, he would most likely need maybe 5-12 feet of cable depending on how he arranges the components etc.

Especially where weight and size for mobility are concerned. If low Voltage for significant power systems was good they'd run EVs on it.
Comparing apples to oranges.

Again, his application requires a maximum of 1060W continuous load for about 4-10min, max.

It goes without saying, you are merely trying to help out, but it's important to take the time and commit to all the specifics the OP has provided and take it into consideration to be able to try and provide useful information to the OP. So that he can go from there, make as informed a decision as possible, and make an investment that will serve him well for the money spent.

Best,
D.
 
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