6 used 260 Watt 30.6v 8.5A panels and a large imagination beginning to get me in trouble

[Jeff From NJ]

I purchased the six used panels knowing they would most likely produce 80% of their rated capacity or so and I was fine with that since I paid $60/panel. I purchased two new Renology Rover 40 Amp MPPT controllers with the plan to connect 3 panels in series and run them to a Renology, then connect the other three panels the same way, and then taking the output from both controllers to a battery or two.

I've since learned that I should add fuses after the controllers and been told that I should be using 100 Amp LiFE PO batteries to hold the power. I've priced them out here in the states and learned that the panels are forcing me to buy expensive batteries where this project began as a tow dipping exercise since I got cheap panels. I've looked at importing from China and believe I can get two 100 Amp LiFEPO batteries delivered for about half what they appear to sell for in the states, I know the risks of buying from China, but since this began as a fun project to see what solar could do, I can't justify paying $600/battery and believe my choices are to buy Chinese direct or use a deep cycle marine battery instead.

I would be using this initially for back up power in case of power outage, not planning on mounting on the roof, but rather on some support structure ground based, but once I built the system, would consider connecting it to my residential system if the panels throw off enough power to justify the expense and hassle. Living in NJ, I am not getting the best sun, especially in the winter, so perhaps I need some scaling back.

Any thoughts on the best configuration to accomplish this goal based on the starting point of what I have, 6 panels and 2 controllers.

Thanks

 

[DThames]

You can use whatever batteries you like. Whoever is telling you to do something you don't want to do (unless with very specific details that you can understand), you should be looking somewhere else for advice.

What type and size of battery were you planning for? A 12v 7amp hour, I would say 40 amps might be overkill. If your planned battery can take 40amp charging current, you should be good. I would not buy lead acid but if you want to, it is your money.

You might consider only using 2 panels for now if your battery isn't large enough to handle 40 amps. Or even one panel.

 

[DThames]

Also, look at Will's low end 12v LiFePo4 review videos on Youtube. Amazon supplied 100ah are down to $400.

 

[Jeff From NJ]

I really was hoping to use all the panels, I have them so why not? I assume from your comments that the panels are going to generate more power than one battery can handle, but the actual battery has not been chosen, that is where I am frozen.

I know each type of battery has a different ability, and higher price for the longest lasting/most cycles. So, I am trying to figure out the total number of batteries I would need for the 6 panels at the lowest price point, that makes long term sense. No point in buying a few $100 batteries if I will be upset and replacing them in 3 months.

​

 

[DThames]

I really was hoping to use all the panels, I have them so why not? I assume from your comments that the panels are going to generate more power than one battery can handle, but the actual battery has not been chosen, that is where I am frozen.

I know each type of battery has a different ability, and higher price for the longest lasting/most cycles. So, I am trying to figure out the total number of batteries I would need for the 6 panels at the lowest price point, that makes long term sense. No point in buying a few $100 batteries if I will be upset and replacing them in 3 months.

​

If you have not purchased an inverter, consider going to 24v or 48v.

If you have more time than money (for this project) you might consider building your own batteries. Buy cells or a kit and assembly yourself. Watch Will's beginner videos about battery building. Here is one of them.

 

[MichaelK]

A cheap toe-dipping strategy would be CostCo golf-cart batteries. They are priced around 99$ each in my area. Even if you only get to use half the capacity, at 24V that would be 210Ah X 24V X 50% = 2520Wh, or 2.52 kWh of power for about 400$. That's enough to keep the lights on and the refrigerator running for the night.

How big are the panels you are talking about? Assuming the GC batteries are 210Ah, and you want to charge at 1/8th of C, the math works out to be...
(210Ah/8) X 25Vcharging X 1.175 fudgefactor = 772W of panels. That would be three 250W grid-ties.

With the Rover controllers you bought, most likely you can not use all six, even at 24V? The Rover has a voltage limit of 100V, and assuming you bought grid-tie panels, they will have a Voc of around 40V at freezing, and I know New Jersey goes down to freezing. So, you can not wire three panels in series unless they are only 12V panels.

So, if your panels are grid-ties then you would be limited to two strings of two. If the panels happen to be 72-cell panels though, and their Vmp is around 37-38Vmp, then maybe you can wire them 1S3P and 1S3P and still charge a 24V system.

Get us the details on what panels you have, and we can refine these recommendations.

 

[Browneye]

Best to determine what you want to do with the stored battery energy and how much you need. That will determine your batteries/capacity, etc.
Santan panels??

I've been using a pair of costco golf-cart 6V's in the RV for the past 15 years - they work great and are cheap. This forum convinced me to build a 230A lifepo pack to replace them.

Building some kind of power generator for blackouts is a good plan. You just have to decide what your priorities are, and for how long you need them to run your stuff. I would think some electronics charging is a start, some lighting, then maybe a fridge or freezer, etc. I keep rolling these ideas around in my head. I don't want to get too carried away - the RV sits next to the house and serves as a backup power supply, and we plan to move within a couple of years anyway.

Something mobile might be the hot ticket - like a cart or something you can wheel out, connect to your panels, and put into duty.

 

[sunshine]

Best just to use some junk auto batteries until you have more experience.
Not all old batteries fail the same way. The ones that will start a car when its warmer but not when cold are best.
This eliminates those with failed cells or no resistance across the cells.

 

[rmaddy]

3 260W panels is 780W. At 80% that's 624W. At 12V that's a charge current of 52A. With a 40A charge controller you are losing some potential. You also need to worry about the voltage. What is the max input voltage of the charge controller? And is the 30.6V you mentioned the Voc or the Vmp? The Voc is what matters with regard to the max input voltage. And Voc goes up in the cold. If the 30.6V is the Voc then 3 in series is almost 92V at 77ºF. You can easily get over 100ºF in the colder temperatures. Never exceed the max input voltage.

Ignoring all of that for the moment, if you have two 40A charge controllers you need a battery that can handle 80A of charge current. So whatever you get, make sure it can handle that. Putting batteries in parallel is an easy way to increase the supported charge current.

 

[MichaelK]

Oh, I only saw the voltage of the panels in the title now, sorry about that! Then what I said in post #6 is correct for your situation, you can NOT wire three panels in series. If their Vmp is 30.6, then their Voc will be 37-38V. That means below freezing they will go above 40Voc. Even at room temperature, 3 in series would be ~112Voc, which would fry that controller. Use this panel string tool to determine what your voltages will be with your lowest winter lows. https://www.midnitesolar.com/sizingTool/index.php

You have three choices at this point (that's two degrees of freedom). Either utilize only four of your panels, wired to two controllers; buy a third Rover; or third, forget about using the Rover's and buy a higher capacity controller like Epever's 6415AN. That can handle 60A and 150V.

Using 4 panels wired 2S2P into two controllers, you'd be charging your battery at about....
{(260W X 4 panels)/25V charging ] X 85% fudgefactor = 35.6A. Divided between two controllers that would only be <18A. You could actually get two more panels for a total of 8 and wire them 2S4P between the two controllers. But, with 71 amps of charging current, you'd need a bigger battery than a single string of golf-carts.

 

[Browneye]

6 X 260w panels is actually quite a lot for an off-grid small setup. As an example, I have 2 X 215W on the roof of my RV, wired in series, they are lower voltage (about 20) and rated for right about 10A each. They feed a Epever Tracer Xtra 3215N which is rated for up to 100V and 30A of charging. It's easy to get them to kick out 20A, just flat on the roof.

So yeah, you could get quite a lot of energy out of them, so you want to consider what you want to do with all that. It's not really a large enough array for a grid-tie type system, but could put out a helluva lot of juice for a simple battery setup.

Unless they're really old, they should not have degraded output much - you should still get pretty close to whatever the sticker on the back says.

Get picture of that and post it, tell us what you want to power up with your setup. With a big enough inverter you could run a refrigerator or freezer off the batteries and the panels would keep them charged up. Nice little backup system. Consider setting it up as a 48V system, less losses, more efficiency.

Here's a 48V 2000W-120 inverter for $275: https://www.ebay.com/itm/1150973602...oc:2&msclkid=c988ad77f30f121244e3ccdd265f743b

 

[Jeff From NJ]

Sorry for not seeing everyone's responses, been away enjoying the holidays.

As an update, I bought two 12v 100Ah LiFePO4 Deep cycle batteries for use in the system, now I need to buy an inverter and figure out how to wire up the batteries. Should I be running the two batteries in series, getting 24V, or leave them separate and 12V? This answer will direct me to the correct inverter.

Thanks

 

[Jeff From NJ]

Oh, I only saw the voltage of the panels in the title now, sorry about that! Then what I said in post #6 is correct for your situation, you can NOT wire three panels in series. If their Vmp is 30.6, then their Voc will be 37-38V. That means below freezing they will go above 40Voc. Even at room temperature, 3 in series would be ~112Voc, which would fry that controller. Use this panel string tool to determine what your voltages will be with your lowest winter lows. https://www.midnitesolar.com/sizingTool/index.php

You have three choices at this point (that's two degrees of freedom). Either utilize only four of your panels, wired to two controllers; buy a third Rover; or third, forget about using the Rover's and buy a higher capacity controller like Epever's 6415AN. That can handle 60A and 150V.

Using 4 panels wired 2S2P into two controllers, you'd be charging your battery at about....
{(260W X 4 panels)/25V charging ] X 85% fudgefactor = 35.6A. Divided between two controllers that would only be <18A. You could actually get two more panels for a total of 8 and wire them 2S4P between the two controllers. But, with 71 amps of charging current, you'd need a bigger battery than a single string of golf-carts.

I can return the Rovers and buy the Epever's 6415AN, I have no allegiance to Renology. Can that one controller handle all 6 panels though? I just bought two - 12v 100Ah LiFePO4 Deep cycle batteries as well.

I assume if I did that, I would then buy a 24v inverter as well.

 

[Bud Martin]

Dose the battery spec show that they can be connected in series?

 

[Jeff From NJ]

Yes. Zooms says up to 4 in series (48v 100 Ah) or 4 in parallel (12v 400 Ah). I bought 2 of these.

 

[rmaddy]

I can return the Rovers and buy the Epever's 6415AN, I have no allegiance to Renology. Can that one controller handle all 6 panels though?

Post the full specs of your panels (W, Voc, Vmp, Imp, Isc) and the charge controller (max PV input voltage, max charge current).

 

[Jeff From NJ]

Post the full specs of your panels (W, Voc, Vmp, Imp, Isc) and the charge controller (max PV input voltage, max charge current).

 

[Jeff From NJ]

The charge controller may be changed based on advice given by @MichaelK to an Epever's 6415AN. Currently I have 2 Renology 40 amp Rovers - 12V/24V DC Input MPP

 

[Jeff From NJ]

Here is the Epever specs:

Tracer6415AN MPPT charge controller automatically identifying 12/24/36/48VDC system voltage.Rated charging/discharging current 60A. Maximum PV input power 750W/12V 1500W/24V 2250W/36V 3000W/48V. Maximum PV open circuit voltage 150V. Common negative ground design.

 

[rmaddy]

6 260W panels is 1560W. At 24V that's 65A. So you are slightly over paneled and that's OK. With your battery more like 26.5V you will be under 60A. Plus you will rarely get the full 1560W.

Now for the voltage. The panel has a Voc of 38.2V. You certainly can't put them in 6S. At 3S2P you are at 114.6V. Even at -40º you will be under 150V. So that's a good option if you have a little to no shading issues. Or you could go with 2S3P if you have more shading issues. You will be well under the 150V max.

tl;dr - 6 of those 230W panels in 3S2P or 2S3P will work fine with one Epever 6415AN assuming your battery supports 60A of charge current.