Growing my PV system

[mh46107]

I currently have a small Renogy 400w 12v solar system that my wife bought for me off amazon and that I use to power a second garage that I built on my property. Until now I've just been using the space as a workshop and the most things I ever power on it simultaneously are a few lights, tool battery chargers, a radio and a pair of fans. Now, i'll be turning that space into more of a man cave / hangout area. I'll need to grow the space to accommodate a TV, some speakers, a few more lights, same fans, and a small refrigerator. Here is what i currently have:

Renogy 400w 12v system: with MPPT


4 x 6v 370AH AGM batteries set up as a 12v 740AH (overkill for before, but I knew this day would come)

1 x 12v 2000w (4000wP) PSW Inverter

http://www.amazon.com/dp/B00BSZUHRC/ref=twister_B00VU4Z1KE?_encoding=UTF8&psc=1

So, due to physical space limitations, the max I can do is either a set up of 2000w of 24v panels, or 2400w of 12v panels. I have since learned that it'll take several charge controllers to manage the latter, which I am fine with, but i don't know how feasible it is to have a 2400w 12v system.

I was thinking of doubling the batteries to 24v 740AH and getting the 24v Panels, but then i'd need a new inverter as well, which still really isnt a big deal. I also am a little fuzzy on the benefits of the 24v system over the 12v system, other than voltdrop, since I dont have any high draw items. I understand the lower amps and all that. Anyway, if anyone has had similar experience with this, or can give advice before I trial and error my way to a solution, that would be great. thank you all for your time!

[solar pete]

Howdy mh46107 and welcome to Solar Panel Talk. As with any off-grid system you first have to determine what your daily usage is, start by reading up in the off-grid section of the forum. If you dont know the kwh (kilowat hr number) you cant design a system. If your going to use this man cave on a daily basis I would be thinking of 24v or 48v but that really depends on what our daily requirements are. If your going 24v or 48v go with standard grid tie panels.

[SunEagle]

The first issue I see is that you do not have enough panel wattage right now to properly charge that 740Ah 12v battery system. You should have around 10% of that system or 74amps.

With 400 watts at 12 volt MPPT you only get around 33.3 amps or ~ 4.5%. Also that CC you show is a PWM type not MPPT which will only get you about 23 amps even if those panels are all wired in parallel.

[mh46107]

Thank you both for your responses. I used Trojan Battery and it recommends that I have a battery capacity equal to what I have now if I also need 1 day of autonomy. The only thing that will run 24/7 is the refrigerator which uses 1100Wh per day. The man cave will be used maybe once per week at its maximum draw of 2900wh in a day, and maybe 2-3 times a week without the TV or Surround system for a total draw of around 1500wh per day.

The Renogy system that I have comes in two options, PWM and MPPT, i have the MPPT, and I didn't know that about charging and needing 10% amps, very interesting, my batteries haven't had any issues, but currently the garage is seldom used.

Doing some research, I do think it would behoove me to run a 24v System over the 12v System. It'll be a little more expensive, but, please correct me if i'm wrong, 8x 250w 24v(2000w @ 24v) panels will provide more power than 16x 150w 12v(2400w @ 12v) panels will.

[SunEagle]

Thank you both for your responses. I used Trojan Battery and it recommends that I have a battery capacity equal to what I have now if I also need 1 day of autonomy. The only thing that will run 24/7 is the refrigerator which uses 1100Wh per day. The man cave will be used maybe once per week at its maximum draw of 2900wh in a day, and maybe 2-3 times a week without the TV or Surround system for a total draw of around 1500wh per day.

The Renogy system that I have comes in two options, PWM and MPPT, i have the MPPT, and I didn't know that about charging and needing 10% amps, very interesting, my batteries haven't had any issues, but currently the garage is seldom used.

Doing some research, I do think it would behoove me to run a 24v System over the 12v System. It'll be a little more expensive, but, please correct me if i'm wrong, 8x 250w 24v(2000w @ 24v) panels will provide more power than 16x 150w 12v(2400w @ 12v) panels will.

Not really. 2400 watts is the same using 8 x 250w panels or 16 x 150watt panels. A 24volt battery system allows you to use smaller wire and fuses.

What makes a difference is the type of CC you use and what the max DC input voltage is allowed. Knowing that max DC input rating will determine how your panels are wired to in. Most PWM CC have a much lower DC input rating which requires you to wire the panels in parallel. That means including fuse protection for each parallel string above 2 per the electric code.

Word of caution. If you do use almost 3kWh in a day you could greatly shorten your battery system by discharging it below 60%. Even doing that once a week is bad for your batteries.

[Sunking]

You will be much happier and richer man if you bury a AC Feeder cable from your house.

[littleharbor]

Doing some research, I do think it would behoove me to run a 24v System over the 12v System. It'll be a little more expensive, but, please correct me if i'm wrong, 8x 250w 24v(2000w @ 24v) panels will provide more power than 16x 150w 12v(2400w @ 12v) panels will.

You're going to pay a lot more for the 150 watt 12 volt panels than you will for the 250 watt grid tie panels BTW, these are not 24 volt panels

[mh46107]

You will be much happier and richer man if you bury a AC Feeder cable from your house.

yes but where is the fun in that? Doesn't satisfy my need to tinker lol

To littleharbor, the 250w 24v panels that I would get are 250 each, so it would cost $2000 for those, and the 150w panels are 175 each, so that will cost me $2800, but other than a new CC i won't need anything else. I'm not overly concerned with price, if 2000w 24v is better than 2400w 12v, i'll gladly do that. This isn't out of necessity but more of a hobby

[littleharbor]

You keep referring to the 250 watt panels as 24 volt. A true 24 volt panel typically has 72 cells and a vmp of 36 and voc of 44 to 45 volts. All the 250 watt panels I have seen are 60 cell with a vmp of about 30 and a voc of about 36.

[mh46107]

Heres the 250w and 150w panels I was referring to:
24v:

http://www.renogy-store.com/250W-24V-Monocrystalline-Solar-Panel-p/rng-250d-bk.htm

12v:

http://www.renogy-store.com/150W-12V-Mono-Solar-Panel-p/rng-150d.htm

[littleharbor]

And you can buy "MPPT" controllers from china for $30.00 if you believe what the label says. A 60 cell panel wont produce enough voltage when hot to finish charging your batteries, let alone equalize them. You can use them with a real MPPT controller and series wired panels.

[mh46107]

I dont know if i'm coming across as rude or something. If so I apologize. I am open to any and all suggestions, what panel would you suggest? Also I was planning on buying an 80A Outback MPPT CC. So far as I can tell, it's a good brand

[solar pete]

I dont think you are coming across as rude, rather I dont think you really have a good understanding/terminology as yet. So are you planning on adding to the 400watt system you currently have or is this going to be a new separate set up.

If its going to be an add on to what you already have you will need to get the same panels as you have now (or panels with very similar specs) I dont think running this as a 12v set up is wise (in fact I know its not wise). I dont think you have a clue as to how much power you need on a daily basis, when you say " I'll need to grow the space to accommodate a TV, some speakers, a few more lights, same fans, and a small refrigerator" we have NO CLUE how much power in watt hours or Kilowatt hours that is, SO we cant help you. A refrigerator even a small one may draw over 1000watts when the motor kicks in, you need to check what each of the appliances draws and for how long they will be on for, this will give you your daily kWh (kilowatt hours) so 1 kettle that draws 1000watts if used for a total of 1 hour a day uses 1 kWh. Come back to us with a number and we can help you, keep reading in the off-grid section of the forum, there is a lot of good info there, cheers.

[littleharbor]

If any apology is necessary it would be from me. Just a pet peeve of mine when 60 cell panels are advertised as 24 volt. Grid tie panels have been selling in the 65 to 75 cents a watt in my area and coupled with a quality MPPT controller make for a good value.
The outback controller is a fine , if outdated. controller. Personally I prefer Midnite solar products. The Classic 150 can put out up to 96 amps and isn't much more than an Outback FM80. I'm seeing about $610.00 online, might find them lower if you dig.

[Sunking]

24v:http://www.renogy-store.com/250W-24V...ng-250d-bk.htm

These are not 24 volt battery panels, they are Grid Tied Panels. Here is how I know, there are two specifications that tell me that. The panels you linked to are 60 -cells with a Vmp of 30 volts. That panel will not charge 24 volt batteries. To charge 24 volt batteries you must have a minimum of 72 cells with a Vmp of 36 volts. It takes 36 cells with 18 volts for every 12 volts of battery. So 24 volt must be a minimum of 72 cells and 36 volts Vmp

That is not to say they cannot be used to charge 24 volt batteries because they can. You just need to use 2 or 3 of them in series with a MPPT charge controller.

FWIW 72 cell panels are also considered GT panels, because panels made for battery systems are 36 cell 18 Vmp. It just so happens by coincidence 72 cell panels will work with 24 volt batteries.