Simple system but I need help with it.

[Whats-n-Watts]

Why do you want 3 charge controllers? I like redundancy, but within reason. A Victron 150/60 would run 3 of those panels in series, which would let you run off-the-shelf 10awg solar extension cables from the panels to the controller.

I was thinking I needed to keep PV output based on battery voltage. Is that wrong? I keep finding conflicting data about that. So the separate controllers would keep amps/wire awg low and keep it at 18v was my thought process. Thanks for your help!

 

[Q-Dog]

An MPPT charge controller will take whatever voltage it can handle and convert it to the proper charge voltage for your batteries.
The VOC on those panels is 22.1. That gives you total VOC of 66.3 (22.1 X 3). The 150/60 can take no more than 150 VOC, so you could add 3 more of those panels in series and still be under the 150.

Yes, you could use a smaller charge controller, but I didn't have a chart in front of me to make a recommendation. I have a 150/60 so I know what it can do.

 

[Q-Dog]

So, if you run higher voltage from the panels to the charge controller, you can run smaller wire. Then you only need to run heavier wire from the controller to the batteries where the voltage is lower.

 

[Whats-n-Watts]

So, if you run higher voltage from the panels to the charge controller, you can run smaller wire. Then you only need to run heavier wire from the controller to the batteries where the voltage is lower.

I was thinking by doing that it waste solar power. Or does that only apply to certain controller set up or controller? Seems like I read that about Mttp or maybe the PWM. I've read so much it's all running together. Or maybe it was just about keeping volts the same for bank and panel. Good to know the Mttp will work. So as long as it's Mttp I'm good without losses. I will have to remember that. Any switches, breakers or other accessories needed for a set up this small?

 

[Whats-n-Watts]

Good morning Guys! I wanted to share with y'all what I decided on the shed system. If y'all remember I did some purchasing prior to learning from you all. i learned that the statement made above that just enough is never enough. The 3*300 watts of PV wasn't going to cut it. The 2 lead acid interstate batteries 12v batteries I had are not enough and the 1500 watt modified sign I already had would not be good for the appliances. When I ordered the PV and a 2,500 watt 12v pure sign I now wish I had went 24v in this application. After this one drops dead I will make that change. But for now I want y'all to know y'all got me here, hope I made ya proud that you gave me your time to help me. I listened to each of you and I think I used some if not all of your knowledge to build a good system so here goes.

3*300 watt pv wired in series to a 100a/100v scc with all 3 panels individually inline fused with diode at 30 amps since the ISC totals 18.1A I figured there needed to be more wiggle room than just 2 amps to utilize a 20A. If that's too much please. I planned one for each panel.
I had planned to use three 30A scc for each panel to keep amps down and avoid series wiring. I just don't like the idea of on panel fails they all stop producing but oh well it is what it is. So I bought the 100a/100v scc to allow those 3 in series. Not enough pv for low solar days I quickly learned.
I was going to order more of the same panels but they were out of stock backordered. I really like uniformity (probably because of being in the military) but I wasn't paying 3 prices from the only vendor that had them for the sake of appearance. Nobody can see them anyways but my wife and I.
Moving along I decided on 6 more panels of 100w each because they were the best deal without buying a pallet while I plan to do later. I ordered a pallet but cancelled due to Signature Solars slack customer service. I found a much better deal after dropping them so it worked out in my favor.
So the 600 watt panels will be 2s3p and all individually fused with diode at 10A since ISC is just 6.11 and have the final positive to scc fuses to 30A as that will be 18.33A. I wanted to use one of the three 30A scc that I had purchased but 12v * 30A = 360 watts so it can't handle the 600 watts. So I ordered another 100/100v to be done with it and still keep it at 2 SCC's rather than 3. Lesson learned there about why 24v is better than 12v in a system this size. The damn SCC limits on array watts. No problem I now have three 30 amp MTTP to experiment with I and I love doing that lol
Moving on the battery selected is 12v300ah as the highest my whrs I recorded was 2,310wh. I never had an overnight reading higher than 620wh though. I figured 300ah would give me more than enough buffer to allow for the total of 13.2w inverter idle draw.
Pv cable is at 12awg , batter to inverter is going to be 2 awg and 8 awg from SCC to battery since I already had about 15 feet of it. I allowed for a 30A double pole dc breaker between the battery and the SCC. The inverter is already fused so I'm good there I hope. I ordered a 250A 600v battery disconnect to install between the battery and inverter. I don't think I am leaving anything out except maybe a rapid shut off at the array and I just haven't picked one yet. I plan to install a grounding rod at the pv array as well as one for the inverter. I am leaving the building on grid power but will hardwire the inverter to a secondary sub panel and run outlets from it to the appliances from there. Should I have a failure just unplug from my systems outlets back to a grid power outlet 2 inches away. Oh I have plenty of 4 awg barge grounding copper for the grounding rods already.
Too much PV for a 2400whr demand I know. Low sun is a term I have learned is my enemy and I must defeat this asshole!
If my calculations are right that will be a next to zero problem. As I said before the array even now in winter will be in full sun all day with zero shade issues unless a blimp hovers lol!
1500w * 25% * 4hrs (peak low solar day) = 1500w approximately produced.
With no other loads is it safe to assume potentially this?
1500w * 25% * 6hrs (low solar day) = 2250w possibly produced?
The sun hits the panels spot from about 8 am in until 4 then some shading begins until sunset. Same for the east. Some shading from sunrise until 8 am.
Now my cold storage commands 2400wh and on a good winter day I should get 1500 * 80% * 4hrs = 4800whr? I know there are other losses but close enough to say the rest of the 4 hours they are in the sun will more than compensate I would think to just go with the 4800 value on a good winter day. Insanity right?
You can't send a soldier into combat with a BB gun and you can't cheat solar!
I wanted to make certain that within reasonable doubt my system functions off grid without worries about my new enemies! Cloud cover ?
Now for the kicker. None of that excess is wasted money as I plan to heat water in a buffer tank from the LVD power when it's available.
If this won't cut I the only thing I know to do is feed this heffer another 900w of PV. I should be able to charge my battery in 2 hours with a 60 watt bulb in that case ?
All jokes aside what do y'all think? A good system for the job? I hope so because have already ordered the rest of my components.
I want to thank y'all for putting up with my hard head and over thinking to help me. I could have done it (eventually) but you guys saved me from lots of stress and frustration which is priceless as I value peace. I can't wait to hear what my teacher's think! Have a great day and stay warm! It's been 27 degrees here the last 2 mornings burr

 

[MisterSandals]

3*300 watt pv wired in series to a 100a/100v scc with all 3 panels individually inline fused with diode at 30 amps since the ISC totals 18.1A

These don't need to be fused, only 3 or more in parallel need fusing. What are the diodes for?

And panels in series do not sum the amps as your math suggests.

300W / 6A (?) = 50V
If this is the case then your 3 panels in series will smoke your 100V SCC immediately.

I didn't read any further.

 

[Whats-n-Watts]

These don't need to be fused, only 3 or more in parallel need fusing. What are the diodes for?

And panels in series do not sum the amps as your math suggests.

300W / 6A (?) = 50V
If this is the case then your 3 panels in series will smoke your 100V SCC immediately.

I didn't read any further.

And here I thought I was on the right track. Are these calculations wrong? Keep in mind there are two SCC's of 100A/100v

 

[MisterSandals]

And here I thought I was on the right track. Are these calculations wrong? Keep in mind there are two SCC's of 100A/100v

Ok, the 300W panels in series to your SCC look good. No fusing necessary.

 

[MisterSandals]

Your 6x 100W panels should be configured 3S2P so you don't need as many Y connectors or any fuses.

 

[Whats-n-Watts]

Your 6x 100W panels should be configured 3S2P so you don't need as many Y connectors or any fuses.

Thanks for pointing that out. I didn't draw it to final plan but that was the plan. I have a dissociative disorder and it sometimes gets in the way. The way you suggest was the way one of my alters drew it last night. He's smarter than I am.
Thanks for the help. So all else looks to be okay?

 

[MisterSandals]

Its a big wall of text and odd abbreviations for everything. Let me venture back in.

Moving on the battery selected is 12v300ah as the highest my whrs I recorded was 2,310wh.

12.8V x 300Ah = 3840Wh

What watt hours are you talking about recording? The number produced in a day from solar?
If so then your daily solar (with no loads) should charge about 50% of your battery.
(2310Wh/ 3840Wh) = 60% if operating at 100% efficiency

batter to inverter is going to be 2 awg and 8 awg from SCC to battery since I already had about 15 feet of it.

The wire size depends on the volts, amps and distance. I cannot find how big your new inverter is going to be.
8Awg is small for a 100A SCC to battery.
900W solar / 14V charging = 64A so 8AWG wire not big enough. If you have enough, double it up.

1500w * 25% * 4hrs (peak low solar day) = 1500w approximately produced.
With no other loads is it safe to assume potentially this?
1500w * 25% * 6hrs (low solar day) = 2250w possibly produced?

How are you figuring 10 hours of solar?

Its more like 3.5h in December
1500W x 3.5h = 5250Wh

Solar Irradiance Calculator

www.solarelectricityhandbook.com

 

[Whats-n-Watts]

Its a big wall of text and odd abbreviations for everything. Let me venture back in.

12.8V x 300Ah = 3840Wh

What watt hours are you talking about recording? The number produced in a day from solar?
If so then your daily solar (with no loads) should charge about 50% of your battery.
(2310Wh/ 3840Wh) = 60% if operating at 100% efficiency

The wire size depends on the volts, amps and distance. I cannot find how big your new inverter is going to be.
8Awg is small for a 100A SCC to battery.
900W solar / 14V charging = 64A so 8AWG wire not big enough. If you have enough, double it up.


View attachment 184394


How are you figuring 10 hours of solar?

Its more like 3.5h in December
1500W x 3.5h = 5250Wh

Solar Irradiance Calculator

www.solarelectricityhandbook.com

View attachment 184397

Power audit revealed 2,310wh max for weeks. It was over the course of 24 hours. 1 mini fridge, one small chest freezer and another medium upright freezer. All soft start brand new appliances.
Correct me if I am wrong but shouldn't a 1500w array produce excess?
As in:
1500 * 80% = 1200 * 4hrs peak = 4,800 watts

 

[MisterSandals]

4,800 watts

4800Wh

If you're assuming 80% efficiency and 4 quality hours (total) of sun, then your numbers look right.

Are you seeing the watts on your charge controllers? Are you seeing 80% of 900W array and 80% of 600W array? For roughly 4 hours (maybe really over a 6 hour period with low production in first and last hours)?

Do you have overcast skies or any shading issues? Based on your audit and equipment specs, you should have more power than you are seeing and using.

 

[Whats-n-Watts]

4800Wh

If you're assuming 80% efficiency and 4 quality hours (total) of sun, then your numbers look right.

Are you seeing the watts on your charge controllers? Are you seeing 80% of 900W array and 80% of 600W array? For roughly 4 hours (maybe really over a 6 hour period with low production in first and last hours)?

Do you have overcast skies or any shading issues? Based on your audit and equipment specs, you should have more power than you are seeing and using.

As I said in the thread 100% sun with zero shading from 8 am to 4 pm ground mounted facing south by compass when installed. Here ideal in winter is 47 degrees, spring and fall 27 degrees and summer at 22 degrees per my physical address. The system has yet to be installed as also mentioned above I
have only some of the components and have ordered the rest. The rule of thumb I was taught was get daily use and do the math. That seems to be the standard. The overnight measurement was never over 610whrs. So I hardly see even on a mostly cloudy day, a system capable of producing 4800 watts on a good will struggle to keeping the battery charged. With all 3 running at once it only totals 202 watt on the meters combined. I guess I shall see.

 

[Whats-n-Watts]

Its a big wall of text and odd abbreviations for everything. Let me venture back in.

12.8V x 300Ah = 3840Wh

What watt hours are you talking about recording? The number produced in a day from solar?
If so then your daily solar (with no loads) should charge about 50% of your battery.
(2310Wh/ 3840Wh) = 60% if operating at 100% efficiency

The wire size depends on the volts, amps and distance. I cannot find how big your new inverter is going to be.
8Awg is small for a 100A SCC to battery.
900W solar / 14V charging = 64A so 8AWG wire not big enough. If you have enough, double it up.


View attachment 184394


How are you figuring 10 hours of solar?

Its more like 3.5h in December
1500W x 3.5h = 5250Wh

Solar Irradiance Calculator

www.solarelectricityhandbook.com

View attachment 184397

It was two different scenarios calculated. Not added together. Sorry I thought that was obvious since I placed "or" between them. And I don't live in Atlanta I live closer to Florida than Atlanta. I've already looked all that up. I am curious how an array of 900w that is wired for 18 amps total at the scc turns into 64 amps. The whole point in keeping amps that low is smaller wire.
You mentioned in the beginning you didn't read much of anything but you commented as if you did. Maybe that's the source of the misunderstandings. But I have yet had anyone say that the power between the scc and battery would multiply from 18a to 64a. Pretty sure it would take a 640 ah battery or battery bank to withstand that many amps without damage to the battery.

 

[MisterSandals]

I am curious how an array of 900w that is wired for 18 amps total at the scc turns into 64 amps.

Array:
900W / 18A = 50V

MPPT munges the volt to amp mix to charge your battery at 14V. In both cases, array and battery charging, volts x amps = 900W

900W / 14V = 64A

Pretty sure it would take a 640 ah battery or battery bank to withstand that many amps without damage to the battery.

Depends on the battery. This is all a part of choosing the right battery and size for your system.

 

[Larry-Cleveland]

Would using any of the "soft start" kits on the compressor help you?

 

[AmpD]

Im new too but some things you might consider.

To charge batteries the panels have to produce more than the load. The extra goes to batteries.

The sooner your panels hit charging voltage in low light the better. This might also help you choose between 12or 24V setup.

Battery charge rate and discharge rates need to allow the amperage you plan on utilizing both from panels and to inverter. This include the combined starting surge.

Usage will definitely vary depending on environmental conditions. I have a new 100w fridge that draws 10w per hour on 300+ hours of kilometer monitoring. 10whr right? It climbed up to 80whr on initial startup.

 

[Whats-n-Watts]

Array:
900W / 18A = 50V

MPPT munges the volt to amp mix to charge your battery at 14V. In both cases, array and battery charging, volts x amps = 900W

900W / 14V = 64A


Depends on the battery. This is all a part of choosing the right battery and size for your system.

Isn't the charge controller there to regulate and control the amps by the appropriate settings entered? Then those are the amps the battery receives? I understood it that the battery is the buffer or power house and between it and the inverter is where amps come into play. So what your saying is that those settings do not matter under a load and that they only applies when there is no load?

 

[Whats-n-Watts]

Would using any of the "soft start" kits on the compressor help you?

The appliances are already soft start and at this point I'm not seeing where anything needs helping. Its a low watt demand. The 3 running together only pull 210 watts and start up is under 800 watts. I will be powering them with one 12v300ah battery. After adulting for 2 months the highest wh used was 623wh in summer conditions and 200 now that its winter. A whopping 700wh max to go back into a battery being fed by 1500 watts of pv. I should be able to run it all and charge in a full day of 25% production per hour. A 600 watt array will handle it no problem on a sunny day. Where the pv will be mounted gets full sun fom 9 until 3 at the moment and about 4 hours but no more of peak sun right now. Come summer it will be barking on 9 hrs door. I guess my understanding of the current on the battery side of the controller is incorrect. I took it as it will supply the set max voltage that corresponds with pv input amps. Good to know it's not. I guess that only applies to PWM controllers? Or do the do the same thing? If I got it understood with those the array must be inline with charge voltage and amps. I have some pv wire on the way so haven't been able to wire anything yet. Also the 600 addition watts of pv just gat her this afternoon. Regular wire isn't an issue. I have a home improvement business and I have gobbs of electrical, plumbing and carpentry supplies on hand at all times. I don't mind the cable size at all just needed to understand why that large was necessary. I didn't know Mttp would multiply the amps like that. Me thinking 2 * 6.11A = 12.22 amps
3 * 22.6voc = 64.80 voc
2p3s so amps to battery would be less than 13 amps so 8awg would be over kill. I like over kill lol