diy solar

diy solar

Newbie looking for solid upgrade advice.

Davidzak

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Joined
Sep 15, 2021
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Hi all, I'm fairly new to solar setups and learning more every day. I bought my first setup listed below. I'm on a fairly tight budget and would like to upgrade to get at least another 500 Wh per day or so to meet our needs. This is our SHTF back up system. No particular Watt requirements are required. Just looking to get the most out of the $200 we have for upgrades.

30 amp @ 12V cheap pwm controller
2 Mighty max 100 Ah gel batteries
300 W constant watt msw 12V inverter
2000 W constant watt msw 12V inverter
Cheap Watts meter only 14 awg wire
The rest of the wiring is at least 12 if not 10 awg.
Two mightymax Poly 160 W 12V panels
20 ft of 10 Awg power cables with connections.
The panels 320 Watts worth are mounted on the roof at approximately a 35 degree angle facing south with room underneath to breath. These panels get sun most of the day.

So I got the chance to test out what it can do on a beautiful day in NC. Testing was done with a constant load on the inverter to keep the controller working hard. Results listed below.
The temperature was at 91 Deg for a good part of the afternoon. Lots of sun, almost no clouds.

1128 Wh produced 93.2 Ah produced
12.1 Vm. 233 Wp. 18.1 Ap

Watt meter is placed between the controller to the Battery.

These numbers seem slightly below what I expected but it was still pretty satisfying. Should I have expected to see better production out of my system? Or was it par for the course for what it is?

I'd like to add another 160 Watt panel to start with thinking it would be my biggest bang for the buck. Or not?

I have another identical 30 amp controller that I would like to use in this setup with the battery bank. I plan on buying a couple more for back up.
My weak little 14 awg Watt meter couldn't handle any more then the max 18 amps peak now. I doubt the controller would handle anymore either.
So I'm thinking of duplicating the 30A controller setup with watt meter in the same box and bank for dirt cheap. I hear running two controllers on the same bank is fine.
I could eventually add another 160 W panel and 100 ah battery for an upgrade to 640 Watts of panels and 300 Ah battery bank.
So my upgrade cost would initially run me about $200 adding another panel, controller, watt meter and power cables.
I'm aware that a Mppt controller and pure sine wave inverter would benefit this system greatly but feel my money would be best spent on another panel or two. Most of the items I will be powering will be VDC to prevent loss from converting to AC power.

These are my thoughts for my Best bang for the buck. I'd be interested to hear your thoughts. Any input you have is appreciated. Thanks for listening.
 

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I think I would probably upgrade the controller to MPPT. You will probably get better output even without adding another panel.

Hard to argue with results though, so if you are happy with what you have and can duplicate it for the cost you are looking to spend, seems like a no brainer. Nice thing about a second setup is that you could arrange the panels to face another direction to extend your solar day. Maybe a little less power hourly, but more total power over a longer period of time.
 
I think I would probably upgrade the controller to MPPT. You will probably get better output even without adding another panel.

Hard to argue with results though, so if you are happy with what you have and can duplicate it for the cost you are looking to spend, seems like a no brainer. Nice thing about a second setup is that you could arrange the panels to face another direction to extend your solar day. Maybe a little less power hourly, but more total power over a longer period of time.
Thanks for the reply. Do you think a mppt controller would benefit me more than another 160-180 watt panel? I figured to get maybe 15% more efficiency at best out of a mppt. An extra panel would give me 33% more power. Especially if I make it mobile one. Do you feel my numbers are way off base for what it is? Thanks again for your input
 
Panel now, MPPT later. Rough calculations: You're maxing out at about 70% of your panel capability now with the PWM. I agree that you'll get maybe another 15% with the MPPT. So Another panel will get you about 110W more while an MPPT will get you maybe 50W more.
 
2x 9.49A Isc panels, 20A PWM SCC
That's maxed out, with two panels of same orientation.

If you tilted one East and the other West, for a 90 degree or acute 60 degree angle between them, that would reduce peak current to about 14A or 10A respectively.
One more panel facing due South with a winter tilt could then be added.
For more summer production, the two panels with 60 degree angle between them plus one having same 35 degree slope but due South might work, but you risk over-current killing the SCC. (direct sun on panels plus reflected light from nearby clouds, assumed to reach 125% of Isc). Once it shorts, battery over-charges.

A quality MPPT would be more forgiving of over-paneling.
 
2x 9.49A Isc panels, 20A PWM SCC
That's maxed out, with two panels of same orientation.

If you tilted one East and the other West, for a 90 degree or acute 60 degree angle between them, that would reduce peak current to about 14A or 10A respectively.
One more panel facing due South with a winter tilt could then be added.
For more summer production, the two panels with 60 degree angle between them plus one having same 35 degree slope but due South might work, but you risk over-current killing the SCC. (direct sun on panels plus reflected light from nearby clouds, assumed to reach 125% of Isc). Once it shorts, battery over-charges.

A quality MPPT would be more forgiving of over-paneling.
The controller states it can handle up to 390 W max at 12V. So I'm a little confused. Maybe it is a 30 amp. I'll be adding another cheap controller to handle 2 more panels at 320 W. I figured I can use the additional panels as mobile. To start off I would number purchasing 1 panel with the ability to add another in the future.
 

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Does anyone feel that I will run in to issues with the 14awg wire on the watts meter if I keep it under 18 amps peak? Am I losing any watts with this weak link?
 
If I remove the watt meter from the system would I be able to run another 160 W panel on the same controller without any issues. Would 480 watts @ 18.2 Vmc = 26.4 amps? Is this how it works? Or would I be risking putting too much current into the controller? I don't know if I could rely on these controller specs from the manufacturer. Anyone familiar with this cheap China 30 amp controller current capabilities? Although I do like the flexibility of running dual controllers with the watt meters inline. Just weighing all my options. Possibilities of running two 180W mono panels on another controller might be better yet. The cost is just slightly more.
One other question I have. Charge rate of power bank. Would 36 amps into my two parallel wired 100 ah batteries exceed the recommeded current input. Would it be 25% of the total bank = 50 amps?
 
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If I remove the watt meter from the system would I be able to run another 160 W panel on the same controller without any issues. Would 480 watts @ 18.2 Vmc = 26.4 amps? Is this how it works? Or would I be risking putting too much current into the controller? I don't know if I could rely on these controller specs from the manufacturer. Anyone familiar with this cheap China 30 amp controller current capabilities? Although I do like the flexibility of running dual controllers with the watt meters inline. Just weighing all my options. Possibilities of running two 180W mono panels on another controller might be better yet. The cost is just slightly more.
One other question I have. Charge rate of power bank. Would 36 amps into my two parallel wired 100 ah batteries exceed the recommeded current input. Would it be 25% of the total bank = 50 amps?
I don't recommend exceeding the specs on those little PWMs.

As for the battery charging current, from what I see online the manufacturer recommends charge current to be under 30A for a single battery. With two in parallel, each or your batteries will be receiving half the charge current. So if you're pushing 36A into the bank, each would be getting 18A. That is a nice charge rate for the gels.

The simplest way to make sure you are splitting the current evenly is to wire your batteries up as shown below. Your charge sources and load devices should all connect to the positive terminal of one battery and the negative terminal of the other:

1631892627473.png
 
I don't recommend exceeding the specs on those little PWMs.

As for the battery charging current, from what I see online the manufacturer recommends charge current to be under 30A for a single battery. With two in parallel, each or your batteries will be receiving half the charge current. So if you're pushing 36A into the bank, each would be getting 18A. That is a nice charge rate for the gels.

The simplest way to make sure you are splitting the current evenly is to wire your batteries up as shown below. Your charge sources and load devices should all connect to the positive terminal of one battery and the negative terminal of the oth

Thanks for the tip. As for my 480 W at 18.1 Volts calculations. Should I assume the panels will be under the 30 amps. Or doesn't it work that way. Because voltage drops down from 18V from the panels to the controller and increases the wattage from the panels? Like 480 W at 12v would equal 40 amps which exceeds my 30 amp controller. Thanks for all the help!
 
Thanks for the tip. As for my 480 W at 18.1 Volts calculations. Should I assume the panels will be under the 30 amps. Or doesn't it work that way. Because voltage drops down from 18V from the panels to the controller and increases the wattage from the panels? Like 480 W at 12v would equal 40 amps which exceeds my 30 amp controller. Thanks for all the help!
Here's a technical article from Victron that you might find useful to further your understanding of how your panels interact with a PWM or MPPT charge controller:

 
The voltage/amperage going into the controller will be 18v and ~27a. The controller will convert that to whatever it is set to charge the batteries at (13.35v?). I wouldn't push more than two panels through that controller.
 
Looking at the other end of your system, what are you powering that will accept and run on MSW current?
Refrigerators are might finicky as are most things with motors. Fine electronics like computers sometimes gak on MSW.
I recommend testing your inverters with what you expect to power in an emergency.
 
what are you powering that will accept and run on MSW current?
That was my thought. I’d lose the modified sine inverters in a hurry for anything that isn’t a pure resistance load like a coffeemaker, soldering iron, incandescent light blob.
 
I'll be mostly using DC current I'm using alot of rechargable batteries and usb charging devices like personal fans and Led lights. Is that a bad Idea? The Wifi, Internet, coffee maker and a slow cooker seemed to run fine. I Haven't tested the mini fridge or water dispenser yet. I don't really have enough power to sustain them. Looking to generate a few more watts first. I've got my eye on PSW inverters looking to snag a deal. I figured the more items I can run off 12 v the better.
 
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Wifi internet and fridge may “run fine” but not last very long on mod sine
 
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Wifi internet and fridge may run fine but not last very long on mod sine
Understood. Would a 1000 W PSW 2000 peak do the job? I'll also be running a CB radio on DC votage. Am I wrong for running as much DC current as I could? I figured it would save on conversion to AC.
 
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