solar installation question.

[slowbell]

I will be installing solar panels for my RV on Monday, and was hoping to get some thoughts on the install.

The battery bank is two batteries, a group 24 and a group 27 battery, in parallel. The panels are two 110 watt panels, for 220 watts total. Is this overkill for such a small battery bank? Should I just install one 110 watt panel instead of both?

I'm leaning towards installing both, just because they will be mounted flat on the rooftop, ie...not angled towards the sun as most solar installs are. I'm going to lose some output from the panels because of that.

[gunDriller]

I will be installing solar panels for my RV on Monday, and was hoping to get some thoughts on the install.

The battery bank is two batteries, a group 24 and a group 27 battery, in parallel. The panels are two 110 watt panels, for 220 watts total. Is this overkill for such a small battery bank? Should I just install one 110 watt panel instead of both?

I'm leaning towards installing both, just because they will be mounted flat on the rooftop, ie...not angled towards the sun as most solar installs are. I'm going to lose some output from the panels because of that.


sounds like a sweet set-up.

since you have the capacity in terms of solar panels - what happens when it gets cloudy and the panels are putting out less ?

i would install them physically, but also connectorize them to facilitate re-configuring them.

i got about 800 watts of solar panels a few weeks ago, couldn't resist, got some of them for $1 a watt, got some others for 10 cents a watt - they had broken glass, but the supplier gave me non-functional panels with intact glass so i just have to do some fixing.

what i ended up doing is setting them up initially with computer power supply connectors, the 1x red, 2x black, 1x yellow connector. i tie the red & yellow together so +12 (or +17, the approx. panel voltage) gets 2 wires, as does ground. not big wires.

anyway, having those connectors makes it easy to swap them around. my first set-up was - an air-conditioned cubby-hole for the chickens, using a cooler designed to run off of car batteries.


about your set-up, i am thinking -
* have them in parallel when the sun is shining.
* have them in series when it's cloudy.

2 panels might seem like overdose for charging 2 hefty batteries. maybe it is. but keeping your charging power intact when it's partly cloudy - that sounds good.


what kind of inverter are you using ?

i am working on one of these flip-flop inverters. nice & simple, square wave output. might need some noise protection or a 60 Hz filter before i hook sensitive electronics up to it.

i guess that's the advantage of a sine-wave inverter but ... only when the price is right :)

[Dogman]

What is the voltage output of one of your panels, is it enough to charge your battery? In series you will double your voltage and keep the same watt output of one panel. In parallel you will double your watt output but keep the voltage of a single panel.

Does your controller have a switch to allow flicking a switch for series or parallel input? Here are some links.

This one shows using relays to do the switching.

http://electronics.stackexchange.com/questions/20763/solar-panels-series-parallel-switching-circuit

Or you can use a double throw double pole mechanical switch.

http://www.guitarnuts.com/wiring/humserparpp.gif

[slowbell]

What is the voltage output of one of your panels, is it enough to charge your battery? In series you will double your voltage and keep the same watt output of one panel. In parallel you will double your watt output but keep the voltage of a single panel.

The voltage, if I remember, was around 17 volts max output per panel. This to me seems high, but the charge controller will regulate it. Since these panels will be permanently mounted, I think I'd rather keep it simple and in parallel for a 12 volt system. Also, I need to put a ladder to the RV to get up there, so this should also deter theft.

I think I'll install both panels and see how it works. If they always keep the batteries topped off, I should be 100% off the grid with this vehicle. I can always add another battery if I need to. Gundriller, I don't have an inverter except a small 400w one you plug into the cigarette lighter.

[slowbell]

Got the two panels installed and wired on the roof of the RV today. Long day, just need to do the wiring down below to finish the job. It helps having a brother who's an electrician. :) The install on the roof looks very professional, and should last quite some time.

We tested the output and got a full 20 volts from the panels. Now I just need to wire up the controller to the batteries, and this rig..should be off the grid. Exciting day.

[hoarder]

The battery bank is two batteries, a group 24 and a group 27 battery, in parallel. Paralell or series, batteries should always be matched. Otherwise they will not charge evenly. I would recommend getting 2 golf cart batteries like Trojan T-105. They're deep cycle batteries.

http://www.altestore.com/store/Deep-Cycle-Batteries/Batteries-Flooded-Lead-Acid/Trojan-T-105-6V-225AH-20HR-Flooded-Lead-Acid-Battery/p1771/

[slowbell]

Paralell or series, batteries should always be matched. Otherwise they will not charge evenly. I would recommend getting 2 golf cart batteries like Trojan T-105. They're deep cycle batteries.

http://www.altestore.com/store/Deep-Cycle-Batteries/Batteries-Flooded-Lead-Acid/Trojan-T-105-6V-225AH-20HR-Flooded-Lead-Acid-Battery/p1771/

Those golf cart batteries are definitely the way to go. If I find I need more battery power, I may upgrade to those and put them in series later.

These two batteries are in parallel. They are slightly different sizes, but the way it was explained to me, in parallel, you are basically making one battery out of two. So, they can be different sizes being they are the same volt. In series, you definitely want same size batteries.

Well, I have to share my excitement, after two long days....the solar is installed, and a complete success. This little RV is off the grid!! I'm very very happy with the install, it's about as professional as you can get. The guy helping me is an electrician.

The charge controller is cool, tells me the exact voltage of the batteries. In the sun, it's a constant 13.7 volts. I'll be able to quickly and effectively monitor my batteries, and if they get too low, turn some things off. I have a feeling though, that I'll be more than able to keep these batteries charged with the two 120 watt panels. So, the RV is parked with the fridge on, stocked full of food (and beer).

Anyway, cheers folks! What a great feeling it is, to produce your own electricity!

[hoarder]

These two batteries are in parallel. They are slightly different sizes, but the way it was explained to me, in parallel, you are basically making one battery out of two. So, they can be different sizes being they are the same volt. In series, you definitely want same size batteries. It would help if they were both brand new because if one is weaker, the pair will not charge correctly. They might work OK for a year or less.

[slowbell]

It would help if they were both brand new because if one is weaker, the pair will not charge correctly. They might work OK for a year or less.

They have to charge correctly. They are now one battery. In parallel, you don't have multiple batteries anymore, they are linked together to create one battery. The whole system is 12 volts. The batteries are new, I hope to get more than a year out of them. If not, they are under warranty for 2 years.

[zap]

They have to charge correctly. They are now one battery. In parallel, you don't have multiple batteries anymore, they are linked together to create one battery. The whole system is 12 volts. The batteries are new, I hope to get more than a year out of them. If not, they are under warranty for 2 years.

Don't forget to check the water in em.

[Dogman]

Don't forget to check the water in em. Also get a jug or two of distilled water and use that as your battery water, DO NOT use tap water! As zap said, make checking them part of your weekly schedule.

[slowbell]

Also get a jug or two of distilled water and use that as your battery water, DO NOT use tap water! As zap said, make checking them part of your weekly schedule.

Yeah, thanks zap and dogman for the reminder. I need to be diligent about this. At work, I never start anything without checking the oil and water levels. I've got to get into a habit of weekly checking the water levels of the batteries in this rig. I'll get some distilled water as well.

I have a question, what happens to the power the solar panels put out that isn't being used?

What I mean is, at high noon, these 240 watt panels should put out 20 amps. I checked, and the batteries were charged, and floating at 13.7 volts, and the controller was floating the battery at around 1 amp, since the batteries are charged. Where does that excess power go? The controller will charge the batteries up, but to avoid overcharging them, that excess solar output must go somewhere, right? Or maybe I'm over thinking this....

Thanks, folks.

[Dogman]

Yeah, thanks zap and dogman for the reminder. I need to be diligent about this. At work, I never start anything without checking the oil and water levels. I've got to get into a habit of weekly checking the water levels of the batteries in this rig. I'll get some distilled water as well.

I have a question, what happens to the power the solar panels put out that isn't being used?

What I mean is, at high noon, these 240 watt panels should put out 20 amps. I checked, and the batteries were charged, and floating at 13.7 volts, and the controller was floating the battery at around 1 amp, since the batteries are charged. Where does that excess power go? The controller will charge the batteries up, but to avoid overcharging them, that excess solar output must go somewhere, right? Or maybe I'm over thinking this....

Thanks, folks.

Good question,

I would think in a perfect world the charge controller would disconnect from the panels in a way that the solar panels see an 'open' circuit. If there is an open ckt, then nothing will happen because there will not be any current flow. And the panels would not produce anything at all, the potential, volts/amps, would be there but no current flow because the circuit is 'open'. Sort of like your battery's with no wiring attached.

Probably your charge controller handles the excess power, if that is the case, you should have nothing too worry about.

This is my best guess.

[hoarder]

Where does that excess power go? The controller will charge the batteries up, but to avoid overcharging them, that excess solar output must go somewhere, right? Or maybe I'm over thinking this....

Thanks, folks.Not to worry. Wind requires a diversion load, not solar.

[FreeEnergy]

guys, can you please explain to me the positive math of having a solar panel on the roof?

self installed, is that it?

Because IMHO installation, wiring, batteries, etc. is what kills any possible advantages.
In my area I'd have to spend $30 grand just to get something that can power what I have.

Except, of course, that you have a spare energy source.

[hoarder]

guys, can you please explain to me the positive math of having a solar panel on the roof?

self installed, is that it?

Because IMHO installation, wiring, batteries, etc. is what kills any possible advantages.
In my area I'd have to spend $30 grand just to get something that can power what I have.

Except, of course, that you have a spare energy source.The cost of installation is very high. If you live in a rural area and do the work yourself (it's not difficult), you cut out over half the cost. Then Obama rebates you a third of what you spent.

Saving really shine on new construction because you don't have to pay for the service drop, which in remote areas costs tens of thousands of dollars.

[slowbell]

FreeEnergy,

The cost is really based upon your needs. My system is small, comparatively, than most. 2 120 watt panels, a couple of batteries, a controller, and wiring/parts. Total cost was less than $1000 for everything, and 2 hard days labor installing it.

I am happy to report, that I've gone 8 days off the grid! I haven't had to plug in at all. The solar panels meet any and all of my electrical needs. Cold beer in the fridge, lights on at night, plenty of juice for my laptop. This is a complete success for me, and I could not be happier. The little RV is off the grid (good thing because my generator won't start).

I'm off for the mountains for a few days tomorrow, to enjoy some fresh air, and some fly fishing.

[zap]

guys, can you please explain to me the positive math of having a solar panel on the roof?

self installed, is that it?

Because IMHO installation, wiring, batteries, etc. is what kills any possible advantages.
In my area I'd have to spend $30 grand just to get something that can power what I have.

Except, of course, that you have a spare energy source.

In my case, we didn't have a choice ,PGE doesn't run any electric lines up this way, on this house we started with 16 panels 180 watt each, then I after a few years I added 4 more, ( 560.00 per panel ), Inverter at the time was 6000.00, But I bought a new one last year with the same specs for 4000.00, the battery bank I have now cost 8500.00 , but should last for 15 years, we read and wired everything ourselves, made the racks to hold the panels, so total cost, 25,000, but you could get away with a smaller system if you aren't a energy hog!
Mine is 3.5 KW.

What does electricity cost per month these days?

[Horn]

Solar is a great way to go, but yes the house and fixtures have to be created around it to suitable for it. IMO.

Always install the biggest solar plant you can afford. You will frind things to do with the extra power.