Two "free" solar panels

[Cajun Bill]

Long story short, I am now in possession of two LG solar panels through a swap with someone else for something else. They appear to be nice panels, LG 280S1C-B3, and have never been used before. I would like to rig up a small solar system to run small appliances in my shop. Because I had previously rigged up my RV to run on DC power, I already have 4-6V golf cart batts, an inverter, a Tri-metric power monitor and now I have the panels. I am in the process of studying what else I need to make this system work. From what I can see, besides the wiring and some type of frame for the panels, all I need is a controller. Would someone please recommend what size/type of controller I need to make this system functional? Also, a reference to a "solar panel 101" website would be helpful.

[SunEagle]

Hello Cajun Bill and welcome to Solar Panel Talk

There is a lot of good advice and direction in the Off Grid section of this forum.

As for providing you any advice on a charge controller, I would say to get a real MPPT type and do not go for a cheap one.

The only way to properly size the CC would be to know more about those batteries and the spec on the LG panels.

[Sunking]

OK you have 560 watts of solar panels. Which means you can run either 12 or 24 volt battery. If you run 12 volt battery will need a minimum 40 amp MPPT Controller like a Morningstar TS45. If you run a 24 volt battery, you should run 24 volts with your 4 6-volt batteries,, a 20 amp MPPT Controller like a Morningstar Sun Saver.

As for a Solar 101 try these:

Off Grid Design
Battery Tutorial

[Cajun Bill]

Thanks for the initial responses. I see I'll need to do some homework before I post again. Just an FYI, the panels are 280W each. When I get my camper back from my son, I'll get the info on the batts and post at that time. My goal would be to see if I can run my chest type freezer along with a small fridge 24/7 just for the heck of it. I know I'll have to make sure that the system is sized correctly cuz I don't want to lose my precious venison and fish. Sounds like a fun project and thanks for helping to hold my hands on this. I'll be back.

[sensij]

Those a grid-tie panels, aka 20 V panels. They aren't appropriate for use with a PWM charge controller, so you are limited to MPPT, which is probably better for you anyway.

[SunEagle]

Thanks for the initial responses. I see I'll need to do some homework before I post again. Just an FYI, the panels are 280W each. When I get my camper back from my son, I'll get the info on the batts and post at that time. My goal would be to see if I can run my chest type freezer along with a small fridge 24/7 just for the heck of it. I know I'll have to make sure that the system is sized correctly cuz I don't want to lose my precious venison and fish. Sounds like a fun project and thanks for helping to hold my hands on this. I'll be back.

As Sunking and Sensij state your best bet is a MPPT type charge controller. You should be able to get ~ 45amps out of the 2 x 280watt panels charging a 12volt battery. The battery system should have a rating somewhere between 360 and 540Ah.

A typical 6v battery for an RV is rated about 230AH so 4 of them wired for a 12volt system would get you about 460Ah which is just fine with 45amps of charging.

The problem you might have is that a 460Ah battery system can safely provide about 1380watt hours daily which is about a 25% discharge of a 460Ah 12v battery system. Hopefully your freezer and fridge do not use more than that amount or you will hurt the life of the batteries.

[Cajun Bill]

Here are the specs on the label on one of the panels: Pmax-280W, Vmpp-31.9V, IMpp-8.78A, Voc-38.80V, Isc-9.33A, Max SYS Volt-1,000V(IEC) 800V(UL), Max series fuse 15A. Besides the 280W, what other specs listed are important? Just wondering

[Cajun Bill]

As Sunking and Sensij state your best bet is a MPPT type charge controller. You should be able to get ~ 45amps out of the 2 x 280watt panels charging a 12volt battery. The battery system should have a rating somewhere between 360 and 540Ah.

A typical 6v battery for an RV is rated about 230AH so 4 of them wired for a 12volt system would get you about 460Ah which is just fine with 45amps of charging.

The problem you might have is that a 460Ah battery system can safely provide about 1380watt hours daily which is about a 25% discharge of a 460Ah 12v battery system. Hopefully your freezer and fridge do not use more than that amount or you will hurt the life of the batteries.

If not, maybe I'll just run one or the other. It's just that with the components I have, except for the controller, there will not be an expenditure for me so it seems to be a no brainer to do this, even if I do it just for the experience of the project.

[sensij]

Here are the specs on the label on one of the panels: Pmax-280W, Vmpp-31.9V, IMpp-8.78A, Voc-38.80V, Isc-9.33A, Max SYS Volt-1,000V(IEC) 800V(UL), Max series fuse 15A. Besides the 280W, what other specs listed are important? Just wondering

Voc - Must be corrected for temperature, and compared to the maximum allowed voltage for your charge controller (or grid-tie inverter). Panels in series
Vmp - Used when selecting conductor size and calculating transmission losses.
Imp - Used when selecting conductor size, and calculating transmission losses.
Isc - Used when selecting conductor size, to make sure conductors are rated for the maximum possible current.
Max system Voltage - 600 V is max for US residential, so this panel complies with anything you'd want to do.
Series fuse - If you have three or more strings of panels in parallel, each string needs to be fused individually at this value.

[Mike90250]

"free panels" are just the beginning of an expensive journey ! Batteries, wires, charge controllers, fuses, enclosures and mounting gear for the free panels will all cost you! Just a warning.

Free Sheep:
Someone gave my wife and I, 3 free sheep. Then the pregnant one had twins, and we have 5 sheep. Then we had to call the vet to get them all shots and stuff, that cost some $$$ then it was summer and we had to buy feed $$ every month. We bought fencing and dug holes for it, to get them more pasture. Then we had to buy a freezer to put 2 of the sheep in, after calling the mobile slaughter house and having 2 taken to the butcher. The 80# of chops and legs have cost up upwards of $150 per pound. We are not accepting any more free sheep. Then i had to install more solar array to handle the unplanned load of a freezer.

[SunEagle]

Here are the specs on the label on one of the panels: Pmax-280W, Vmpp-31.9V, IMpp-8.78A, Voc-38.80V, Isc-9.33A, Max SYS Volt-1,000V(IEC) 800V(UL), Max series fuse 15A. Besides the 280W, what other specs listed are important? Just wondering

That is good data on the panels. Sometimes just given a model number may not provide the specifics of solar equipment since they keep changing.

To get the most out of those panels a 45Amp MPPT charge controller is the best investment.

[Sunking]

CB the panels are just fine. Being a Grid Tied Panel just means you need a MPPT Controller to use them. If you used them with a PWM controller on a 12 volt system changes them from 560 watts into 120 watts. You do not want to do that. With the right MPPT Controller you can wire the panels in series, (less,, smaller wire, and least expensive). A great candidate for you is MS TS 45.

As for battery 560 watts of panels can support a battery as small as small as 350 AH up to 540 AH. 12 volts @ 450 AH is a perfect fit. Something like a pair of Trojan L16P a 6 volt 420 AH battery would be a perfect fit for 560 watts of panels and a 45 amp MPPT controller.

What we do not know is if it will work for your application, we just know all the parts are matched up. The batteries are capable of providing you up to 2 to 2.5 Kwh per day if the panels can generate that much power under the circumstances. With an RV Solar Panels cannot be installed to optimize power generation. You cannot orient them correctly solar south with the proper tilt angle for the season and location.

Having said all that, a lot of problems and short comings can be overcome via Electronic Battery Isolator to use the RV alternator as the main source of power and charging. It will also allow the RV alternator to charge the House battery when the engine is running. The alternator can generate more power in 30 minutes than panels can do in a couple of days. So as you can see, you will want an Isolator to CYA. Something like this one.

You are on the right track now. Do some homework and come back with your questions.

[Cajun Bill]

Thanks for the encouragement Sunking. Just a clarification, this will be connected in my shop, not my RV. The batts, power monitor and inverter will be taken out of my fifth wheel as I am planning on selling it soon anyway and downsizing, The panels are not RV panels, they were intended for a residential installation. Additionally, I have four 6V GC batts, not two so that should be even better I'm sure.

I should have more info soon to post regarding the expected load and also the AH of the batts themselves. Everyone recommends a MPPT controller so I'm sure that's what I will end up with. This forum has been very helpful so far and I am looking forward to making my little project work.

[Cajun Bill]

Just took a look on Amazon on the recommended controller, i.e. a MS TS 45 MMPT. Pricey little booger! I accept the advice already given that I need an MMPT controller, but was just wondering if a more economical controller might be available? Especially given the fact that this is kind of an experimental project. (looks like Mike's prediction is coming true regarding the "free sheep")

[littleharbor]

Go with a 24 volt system and a quality 30 amp MPPT controller. Midnight Solar Kid is about $300.00. I don't see any info on your existing inverter but if it is a 12 volt modified sine wave type you aren't giving up any substantial dollar value there.