Have these. Now what can I do with them?

K4KMG · July 2014

Hello. Solar newbie. I was given the following with the understanding I would use them. He went crazy trying to figure it out, and after reading for many weeks, I can certainly see why!

I know loads should be considered first, but it just didn't work out that way. I just want to see what I can get out of what I have.

4x220w panels (I'm assuming parallel configuration?)
Vmp 29.5V
Imp 7.46a
Voc 35.4V
Isc 8.36a

MPPT solar charger controller SL-40A
Rated Voltage
12/24 dc auto-detection

Rated charge current (include load current)
40Amp

Load current
15Amp

Input voltage range
15 to 40V / 30-55Vdc

Max. PV open circuit array voltage
55Vdc
Max. Current input from PV
40A
Max. Power input from PV Between 1000 to 3000 Watts.

Overload protection (DC load)

Current intention is to setup as a 24v system
Batteries I'm thinking 4xT105RE's in series. 880ah total. (I can get t105's locally for $125)

What will this system provide from battery output? (before any inverter or load is considered)
Will this setup keep the batteries charged properly assuming I keep the batteries at no less than a 60-70% charge?
I'm in Florida and average Solar Insolation for my area is 4.5-5 (low of 3 and high of 6)

Loads are unknown at this point. I just want to know what this setup will provide and if it's close to being a decent 24v setup.

Thanks
Tom

Cariboocoot · July 2014

Re: Have these. Now what can I do with them?

Welcome to the forum Tom.

Let's start with the array. Four 220 Watts gives you 880 total. With a Vmp of 29.5 you want to run them as two parallel strings of two in series for a 24 Volt system & MPPT controller. You should get about 28 Amps peak current from that, which is quite respectable.

Now about that controller. It does not sound like a good piece of equipment. The Voltage input limitation of 55 for a 24 Volt system, for example. Right away you have a no-go as the panels at 29.5 are not high enough Vmp to be used on a 24 Volt system (Voltage losses from heat and wiring could result in too low V to charge the batteries) and the controller won't take a string of 59 Vmp (not to mention Voc). The same problem occurs if you try to use it on a 12 Volt system: V max 30 there, which means these panels would go over on Voc. Obviously this controller was meant to use 'standard' panels (17.5 Vmp for 12 Volt, 35 Vmp for 24) and only in parallel. My advice: ditch the controller. Buy a MidNite Kid 30 Amp MPPT controller instead.

Batteries. There is no way 880 Watts of panel will charge 880 Amp hours @ 24 Volts. Nor is it likely you need that much. With 28 Amps output you can easily do a set of GC2's @ 220 Amp hours & 24 Volts which is a really inexpensive place to start. You could also run slightly larger batteries, up to around 300 Amp hours (but be careful as the 'tall case' L16 type could be shortchanged for charging).

What you'd get out of that is about 2.4 kW hours AC, possibly a bit more if you can manage your loads well.

BB. · July 2014

Re: Have these. Now what can I do with them?

Welcome to the forum--And join the "solar balding club"...

I am guessing this is your solar charge controller?

http://zlpower.en.made-in-china.com/product/iezJnavGVBhf/China-Mppt-Solar-Charge-Controller-12v-24v-40a-SL-40A-.html

You are running into an issue with matching solar panels to solar charge controller to battery bank.

Working backwards, a 24 volt battery bank needs ~30-32 volts to properly/quickly charge under room temperature conditions.

A typical solar charge controller (about 99% of them) needs about 35 volt minimum rated solar panel input voltage to properly charge a battery bank over standard temperature range (of solar panel+battery bank).

Then there is the solar panel itself. In the olden days, solar panels were designed to "optimally" charge a lead acid battery bank of 12/24/48 volts. A "24 volt" solar panel (or solar array) would have a Vmp-array of ~35-39 VDC minimum (Vmp= voltage maximum power).

Your panels are designed (originally) for Grid Tied solar power AC inverters, and not for "optimally" charging a battery bank. Your panels have a Vmp rating of 29.6 VDC, and in typically hot summer operation, their Vmp-hot can drop down to 24-25 VDC--Which is not good for quickly/properly charging a 24 volt battery bank (a "24 volt" lead acid battery at 24.0 volts is around 50% state of charge).

So--Normally, with many MPPT charge controllers, you would put two of your Vmp~30 volt panels in series, which would give you a Vmp-array~60 volts and a Voc-cold~90-100 VDC (in sub freezing weather).

Your MPPT charge controller are not really designed to function with Vmp~30 volt panels on a 24 volt battery bank. Your input voltage range is (probably, if I have guessed correctly) around 15-55VDC ... So, you cannot put two of these panels in series for proper charging of the 24 volt battery bank.

Your choices:

1) go with a 12 volt battery bank, wire panels in parallel.
2) get "12 volt" (Vmp~17.5 to 18.9 VDC solar panels)
3) get a more expensive MPPT charge controller that has a higher input voltage range

About the "cheapest" MPPT controller that would meet your requirements:

MidNite Solar The Kid MPPT Solar Charge Controller (150 Voc max)
Rogue 30 amp 12/24/48 volt charge controller (100 Voc max)
Morningstar TriStar 30 amp MPPT Solar Charge Controller (150 Voc max)

You are looking at ~$300-$350 minimum for these controllers.

Note that Vmp~30 volts are about 1/2 the $$$/Watt pricing vs Vmp~17.5 volt panels.

You should do several paper designs with a mix/match of solutions and see what works best for you.

-Bill

K4KMG · July 2014

Re: Have these. Now what can I do with them?

Thanks for the fast responses guys. Most appreciated.

Is the 2.4 kwh per day, and at what soc? Is that full depletion? I'd need to cut that in half?

So, I don't have a problem getting a different cc. The one I have is new and I'll just sell it for what he paid for it. Assuming I set it up like Cariboocoot suggests, what size inverter?

I don't have an issue with purchasing 'good' batteries, and have every intention of maintaining them properly, but for the sake of argument, what's a decent brand gc2?

By the way, I do have generator power available.

Power would only be drawn from the solar system on weekends.

What about upgrading the system in the future? More panels? More batteries? Both?

I can build a house or tear down a Harley and put it back together but this solar stuff makes my head spin!

Thanks again

Cariboocoot · July 2014

Re: Have these. Now what can I do with them?

K4KMG wrote: »

Thanks for the fast responses guys. Most appreciated.

Is the 2.4 kwh per day, and at what soc? Is that full depletion? I'd need to cut that in half?

2.4 kW hours per day with 50% DOD. How much you can draw 'directly' from the panels (loads used during the time when there's still sun but the batteries are full) may improve that.

So, I don't have a problem getting a different cc. The one I have is new and I'll just sell it for what he paid for it. Assuming I set it up like Cariboocoot suggests, what size inverter?

Inverter size is mainly dependent on the maximum load. If you need 1200 Watts total at some time during the day the inverter needs to be able to supply at least that much. Watch out for the inverter's own consumption as well: not all of them are the same, even though the output rating may be.

I don't have an issue with purchasing 'good' batteries, and have every intention of maintaining them properly, but for the sake of argument, what's a decent brand gc2?

Almost any of them in fact. People even get good service for the money out of 'warehouse' brands. At the onset it's easy to wreck any battery, but you cry less if they didn't cost much to begin with. I have had the best luck with East Penn/Deka/US Battery (three brands, same batteries).

By the way, I do have generator power available.

Power would only be drawn from the solar system on weekends.

What about upgrading the system in the future? More panels? More batteries? Both?

I can build a house or tear down a Harley and put it back together but this solar stuff makes my head spin!

Thanks again

Upgrading is something not easily done. And you only need to do it if the power demand is larger than anticipated or else grows. Usually they grow. If you add more battery than your PV can recharge you either have to add more PV or run the generator more. If the loads can be used in daytime you can sometimes up the PV without adding more battery.

K4KMG · July 2014

Re: Have these. Now what can I do with them?

Thanks. I've read somewhere that an oversize inverter is not a good idea. I have access to a 3000/5000 pure sine wave. Too much?

Cariboocoot · July 2014

Re: Have these. Now what can I do with them?

K4KMG wrote: »

Thanks. I've read somewhere that an oversize inverter is not a good idea. I have access to a 3000/5000 pure sine wave. Too much?

It is only not a good idea if it results in A). too much self-consumption (tare loss) or

. too much expenditure of money.

Edit to add: more Watts does not necessarily mean a better inverter either. There are quite a few "high power" inverters which are absolutely junk. And don't put too much credence in their surge ratings unless they want to give you a time for that rating (as in 2X output rating for 15 seconds).

vtmaps · July 2014

Re: Have these. Now what can I do with them?

K4KMG wrote: »

Current intention is to setup as a 24v system
Batteries I'm thinking 4xT105RE's in series. 880ah total. (I can get t105's locally for $125)

Four t105re in series is 24 volts, but is NOT 880 ah.

Cariboocoot wrote: »

Batteries. There is no way 880 Watts of panel will charge 880 Amp hours @ 24 Volts.

And there is no way he will have 880 ah with four of those batteries.

Cariboocoot wrote: »

With 28 Amps output you can easily do a set of GC2's @ 220 Amp hours & 24 Volts which is a really inexpensive place to start.

And that set of GC2's at 24 volts would be four batteries in series.

--vtMaps

K4KMG · July 2014

Re: Have these. Now what can I do with them?

vtmaps wrote: »

Four t105re in series is 24 volts, but is NOT 880 ah.

And there is no way he will have 880 ah with four of those batteries.

And that set of GC2's at 24 volts would be four batteries in series.

--vtMaps

You're correct. I screwed up in the original post. 220ah. So, back to the original question.....

Maybe we should simplify. (if that's possible!)

I have these 4 panels. Best way to maximize there potential?

4x220w panels
Vmp 29.5V
Imp 7.46a
Voc 35.4V
Isc 8.36a

PNjunction · July 2014

Re: Have these. Now what can I do with them?

You could run your amateur radio station from them for a start!

If you do HF, running from batteries means that you don't have a direct connection to the structure's own wiring, where common-mode current can drastically alter the radiation pattern from your antenna. In some case, you may find that common-mode was doing most of the work, and not the antenna itself.! Of course run a safety ground, and I'd still recommend choking that, but now you are free from the residential wiring. Still, safety ground!

Run DC whenever you can, which much amateur gear operates on already, although in your case dc-dc converters may make more sense than running an inverter. That inverter may be too noisy from an HF standpoint to begin with, so look for HF friendly inverters, or backup ac chargers like Samlex, Iota and the like.

You'll get plenty of hand-on experience by properly maintaining those batteries, which will help guide you in your selection should you wish to design your own system. And since the whole system is already free, why not!?

We have no idea what you are using, so get your power-budget in line first. Grab the fluke and start measuring currents over your intended time period. Use a P3-International Kill-A-Watt meter to get a handle on wattage over time to simplify the AC wattage needs. Now you'll be able to make a much more accurate prediction of the feasability of using your system with the present hardware.

K4KMG · July 2014

Re: Have these. Now what can I do with them?

PNjunction: Power Line Noise has been so bad, and I've been fighting with the power company for years to no avail...... Whole other story.

I don't know why this solar stuff is so difficult. Regardless of 'loads', these 4 panels should produce a certain amount of power. (depending on sun conditions) Assume for a minute that I don't care about the loads. I have what I have. What can I do with it? I don't mind getting a different cc if needed.

4 panels. Series or Parallel?
12v or 24v system?
How many batteries? 6v or 12v?
CC?
Inverter?

I'm not trying to be difficult. I realize that for most people, figuring out your loads is the first step. My situation is different. I just want to maximize the panels I have and whatever I get out of them, I'm happy with.

I just want to know the best setup for these 4 panels.

Thanks again. This a great forum and I've gotten more and faster responses than any other forum I've been on. (regardless of content)

Cariboocoot · July 2014

Re: Have these. Now what can I do with them?

Do not go with a 12 Volt system unless there is a specific need for 12 VDC that you can't get around. A 24 Volt system offers a noticeable improvement in performance for a small amount of money.

Change the controller. That one is too limited to be of much use. Put the panels in two parallel strings of two in series on a good MPPT controller and it will all work fine.

Just note the equipment in my signature. That runs the refrigerator, satellite Internet connection (with phone and wireless router), computers, water pump, septic pump, lights, microwave .... Get the picture? I have a few advantages with slightly improved panel performance due to elevation and being able to manage loads to maximize panel potential by running most things only during the day.

K4KMG · July 2014

Re: Have these. Now what can I do with them?

Thanks. Makes things a little easier.
Any thoughts on the Rogue MPT-3048?

Photowhit · July 2014

Re: Have these. Now what can I do with them?

I haven't heard a review of his new one, but his previous models have been popular. Marc stops in here from time to time!

ILFE · July 2014

Re: Have these. Now what can I do with them?

K4KMG wrote: »

I have these 4 panels. Best way to maximize there potential?

4x220w panels
Vmp 29.5V
Imp 7.46a
Voc 35.4V
Isc 8.36a

Series - Parallel

String 1: 2-220w panels in series
String 2: 2-220w panels in series

Both strings going into the combiner box as separate circuits.

K4KMG wrote: »

4 panels. Series or Parallel?
12v or 24v system?
How many batteries? 6v or 12v?
CC?
Inverter?

This has already been advised, above.

24 volt system
4 golf cart batteries in all, each 6vdc.
4 in a series string to make 24vdc.

Charge controller - I just received my Midnite Kid. They say it's a bullet proof MPPT controller.

Inverter? I have no idea.

Skippy · July 2014

Re: Have these. Now what can I do with them?

Surprisingly, those numbers looked familiar. . . that's because they almost match the numbers on the back of my panels... you can get small grid tie inverters and go grid intertied like I am . . . the price quote that I have here is 180 $ per panel. . . that includes the grid intertie inverter, and the "drop wires" to go into the water tight electrical box .

Just a thought.

Attachment not found.

Cariboocoot · July 2014

Re: Have these. Now what can I do with them?

Skippy wrote: »

Surprisingly, those numbers looked familiar. . . that's because they almost match the numbers on the back of my panels... you can get small grid tie inverters and go grid intertied like I am . . . the price quote that I have here is 180 $ per panel. . . that includes the grid intertie inverter, and the "drop wires" to go into the water tight electrical box .

Just a thought.

Considering we don't know the make of the panels and there's only four of them he's probably not looking to get into the permits and such required to go grid-tie. The panels may/may not be on the 'approved' list for a micro-inverter, but it is not as easy as buying four of them and just hooking them up yourself.

The complications and ramifications of grid-tie installs have been discussed at length on the forum numerous times. We warn against doing it any way other than the legal, approved method because the consequences can be severe.

ILFE · July 2014

Re: Have these. Now what can I do with them?

Cariboocoot wrote: »

We warn against doing it any way other than the legal, approved method because the consequences can be severe.

I have to be honest, I don't normally pay much attention to grid-tied discussions, because my systems are all off-grid (by necessity, not choice). But, if I may, is it the inverter that disconnects a home's solar array from the mains, when the power drops? Or, is there another piece of equipment between the inverter and the grid that shuts down the array, so as not to feed power into the grid?

Cariboocoot · July 2014

Re: Have these. Now what can I do with them?

ILFE wrote: »

I have to be honest, I don't normally pay much attention to grid-tied discussions, because my systems are all off-grid (by necessity, not choice). But, if I may, is it the inverter that disconnects a home's solar array from the mains, when the power drops? Or, is there another piece of equipment between the inverter and the grid that shuts down the array, so as not to feed power into the grid?

The grid-tie inverters have what is called anti-islanding circuitry built in which shuts them down if proper grid power is not detected.

inetdog · July 2014

Re: Have these. Now what can I do with them?

Cariboocoot wrote: »

The grid-tie inverters have what is called anti-islanding circuitry built in which shuts them down if proper grid power is not detected.

And that also means that when the grid is down, the GTI (which has no batteries) is totally incapable of supplying any power during the outage.
The only exception among batteryless inverters is the SMA TL3000-6000-US line which uses the full 3K or more of panel capacity to provide a single 1500W 120 volt output when the grid is down.

K4KMG · July 2014

Re: Have these. Now what can I do with them?

Thanks, but this is not going to be grid tied. Closest 'grid' is miles away.

Have these. Now what can I do with them?

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