diy solar

diy solar

New to forum - a few questions

MrZZeroG

New Member
Joined
Jun 3, 2021
Messages
5
Hello

long time follower of Will and he’s been an incredible help to us. We have a YouTube channel (abandon shed to tiny house - /DannerCronise). It’s a project that my son and I can work on together so he can learn about construction, etc. He’s a senior in Computer Engineering, so we are planning some fun DIY controls.

we have the rich solar 40a MPPT and two SOK 12VDC/100A and 2 12VDC 100s “deep cycle” (yes we know) lead acid. There are 4 100W rich solar monocrystalline panels in series and at present we are using parallel (12VDC). input cion the controller is limited 100v/50A and panels are 22.8V/5.38A

I know we are fine with the first 4 panels in series. Can we add 4 more in series and stay at 12VDC or do we need to move to 24VDC when we add 4x more panels? I don’t quite understand the input to output rules, but realize it’s controller specific.

Once we get a feel for this we will transfer all or part of this to our GMC motorhome and probably build a system for rhe house. This gives us power now and we can learn with it.

thanks again!

Ray
 

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You can stay at 12 volts with the additional panels as long as the controller has the proper rating. Otherwise you need a second controller. I suggest going to 24 volts as you expect to get in the 170 to 200+ amp zone (12v) at some place in the circuitry such as 3000 watt inverter. 24 volt battery will cut all amps in half for more practical wiring.
 
You can stay at 12 volts with the additional panels as long as the controller has the proper rating. Otherwise you need a second controller. I suggest going to 24 volts as you expect to get in the 170 to 200+ amp zone (12v) at some place in the circuitry such as 3000 watt inverter. 24 volt battery will cut all amps in half for more practical wiring.
Thank you. So if I put the second four panels in parallel with first four (each four in series) then I’m under the input voltage and current.

we do plan to move to a 24vdc or larger inverter system, but want to get some experience at this level (usage, charge, etc..) to help in designing the RV systems.
 
Here is what's happening inside the controller. As the 400W of power is coming in, the <5.38A is arriving inside the controller at 18.6V X 4 panels = 74.4V. The controller than transforms the raw high voltage solar down to the battery charging voltage of ~13.0V. Let's assume there's always some loss, and I usually use a fudgefactor of 85%. So, what comes out of the controller to feed the batteries, is (400W/13V charging) X 0.85 fudgefactor = 26.2A.

So, the 40A controller could handle 26.2A with no problems. Double that and you now have 26.2A x 2 strings = 52.4A. So, on paper, the amperage is too high for both a 40A and 50A controller (you mention both).

Getting back to the batteries, lead-acid batteries are happiest when being charged at around 1/8C. Since you have two 100Ah batteries in parallel, that works out to be 100Ah X 2 batteries X 1/8C = 25A. So, the 400W you have right now is just right for your size of battery. If you double your array wattage, you really need to double your battery capacity.

Personally, I definately would advise you to move up to 24V, but with 800W you'd still need more batteries. How old are the set of two you have now? Keep in mind that in general, it is never good to mix new batteries with old. The old pair will drag down the new pair to it's level in a short amount of time.

With 800W you'd need a 24V battery sized at 800W/25V charging X 0.85FF X 8X = 218Ah. I would trade in your two 100Ah 12V batteries and get four 6V 210A golf-cart batteries. Then you'll have a single string of 24V batteries at the correct capacity. The panels will be putting out 800W/25V X 0.85FF = 27A, which you current controller should handle just fine.
 
Here is what's happening inside the controller. As the 400W of power is coming in, the <5.38A is arriving inside the controller at 18.6V X 4 panels = 74.4V. The controller than transforms the raw high voltage solar down to the battery charging voltage of ~13.0V. Let's assume there's always some loss, and I usually use a fudgefactor of 85%. So, what comes out of the controller to feed the batteries, is (400W/13V charging) X 0.85 fudgefactor = 26.2A.

So, the 40A controller could handle 26.2A with no problems. Double that and you now have 26.2A x 2 strings = 52.4A. So, on paper, the amperage is too high for both a 40A and 50A controller (you mention both).

Getting back to the batteries, lead-acid batteries are happiest when being charged at around 1/8C. Since you have two 100Ah batteries in parallel, that works out to be 100Ah X 2 batteries X 1/8C = 25A. So, the 400W you have right now is just right for your size of battery. If you double your array wattage, you really need to double your battery capacity.

Personally, I definately would advise you to move up to 24V, but with 800W you'd still need more batteries. How old are the set of two you have now? Keep in mind that in general, it is never good to mix new batteries with old. The old pair will drag down the new pair to it's level in a short amount of time.

With 800W you'd need a 24V battery sized at 800W/25V charging X 0.85FF X 8X = 218Ah. I would trade in your two 100Ah 12V batteries and get four 6V 210A golf-cart batteries. Then you'll have a single string of 24V batteries at the correct capacity. The panels will be putting out 800W/25V X 0.85FF = 27A, which you current controller should handle just fine.
Thank you! Sorry it’s taken so long to get back. We are only using the lead acid for a short time and will spin them off to something else. Brand new (4/21 mfg) O’Reilly Super Start Marine Group 31. We have two SOK 12V/100Ah as well and this will allow us to use them side by side in similar systems to get a better intuitive feel for usage cases. I’m a scientist and my son is studying engineering so it’s fun for both of us to experiment.

I did look closer at the other “kit” systems Rich Solar offers and it follows your point exactly. They have the 800W (100w) systems using 24V and the 800w 12V uses their 200w panels (20.4V/9.8A), which stays below the 40A threshold. Now that you’ve calculated this, it’s obvious, but it’s taken a little time to navigate the variables and put them in permanent registers for immediate recall.

We are on our way to 48V in due time. I don’t need to be sold, but we are also restoring two GMC Motorhomes (76/78 Birchaven/Palm Beach) and we have plenty of places to repurpose solar parts. We also plan to do several out buildings on our property. I want a bank of parallel connected MPP Solar/Growatt/Etc… with generator back up for the final project, but it’s much better for the experience and learning for me to start with Harbor Freight and go through the process of modding the generator to autostart/tri fuel, than to buy a unit and slam it in place. Building, learning, and designing are the reasons we’re doing this together.

I have a pair of 6V in one of the GMCs, but at 12V not 24V. So I agree with you there. I’m not staying with lead acid long term. The 12V “deep cycle” were <$200 and it’s powering lights, chargers, security, etc… I can use them to jump start the tractors if necessary.

thanks again. That’s exactly the information I needed. It helps tremendously and coalesces the other facts we have gathered. And now I’m infected with the MK FF to boot! .85 it is!
 
Here is what's happening inside the controller. As the 400W of power is coming in, the <5.38A is arriving inside the controller at 18.6V X 4 panels = 74.4V. The controller than transforms the raw high voltage solar down to the battery charging voltage of ~13.0V. Let's assume there's always some loss, and I usually use a fudgefactor of 85%. So, what comes out of the controller to feed the batteries, is (400W/13V charging) X 0.85 fudgefactor = 26.2A.

So, the 40A controller could handle 26.2A with no problems. Double that and you now have 26.2A x 2 strings = 52.4A. So, on paper, the amperage is too high for both a 40A and 50A controller (you mention both).

Getting back to the batteries, lead-acid batteries are happiest when being charged at around 1/8C. Since you have two 100Ah batteries in parallel, that works out to be 100Ah X 2 batteries X 1/8C = 25A. So, the 400W you have right now is just right for your size of battery. If you double your array wattage, you really need to double your battery capacity.

Personally, I definately would advise you to move up to 24V, but with 800W you'd still need more batteries. How old are the set of two you have now? Keep in mind that in general, it is never good to mix new batteries with old. The old pair will drag down the new pair to it's level in a short amount of time.

With 800W you'd need a 24V battery sized at 800W/25V charging X 0.85FF X 8X = 218Ah. I would trade in your two 100Ah 12V batteries and get four 6V 210A golf-cart batteries. Then you'll have a single string of 24V batteries at the correct capacity. The panels will be putting out 800W/25V X 0.85FF = 27A, which you current controller should handle just fine.
Btw, my son just posted his first intro video on our system. More coming after we collect data and put some things on the oscilloscope! Thanks again for all the input on this. It really helped.


 
Welcome! I’m also relatively new to the forum but started studying off-grid solar back when there was NO on-grid solar (1988) reading Home Power magazine, an awesome resource that didn’t make it to the YouTube age. Respectfully, if you are going to make videos explaining solar to folks, please review your script ahead of time! A solar charge controller does not give anyone the option of supporting load vs. charging storage vs. “supplying the grid” - let’s leave that last one off because it is not true and also connecting to the grid is a very regulated endeavor which isn’t even the subject of your video really, I think. Unless you are going to review grid-tie inverters, disconnects, labeling, electrical inspection, building/solar permits, AC code and insurance requirements, just stick to the off-grid topic, which is already a lot. My suggestion is essentially that folks new to solar don’t need oversimplification that could waste time and money like “hey a solar charge controller lets me connect to the grid! What? It doesn’t?” I think you get my point, right? Responsibility to the community of interested souls is important IMO.
 
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