Took the Solar Plunge

stephenw10

A friend of mine lives off grid on a boat and over a few years we spent some time experimenting with various batteries, solar panels, wind generators etc. A lot of what we learned about solar and wind energy doesn't really apply if you're not in the UK so I'll not talk about that. Two things though:

1. By far the best way to know what your batteries are doing is to use a proper battery monitor that counts Ah in and out and accounts for charge losses, temperature etc. They are much cheaper than they used to be and tell you WAY more than off-load voltage.

2. It is pointless, and in fact worse, to have more battery capacity than you can comfortably charge.
This is really important. We started off with a set off used fork lift batteries with a combined capacity of ~2000Ah at 12V. Unfortunately there was not a chance of ever putting in a equalising charge at that capacity with the panels we had. Consequently the cells in the battery became progressively more and more unequally charged until some start sulphating and eventually die. This produces an interesting cascade of failing batteries which is not fun and expensive!

It seems surprisingly hard to find out but it seems your batteries are 125Ah each yes? So you have a 500Ah battery bank but with a 100W panel a maximum charge rate of ~8A. I think you could run into the same issue. ;)

Phil is the man to ask about this as he's out in Nepal where many of the installations he has are solar/battery powered. Though Kejianshi also has experience here.

Steve

kejianshi

I didn't even look those batteries up - They came from walmart which is pretty much all I needed to know…

http://upsinverterinfo.com/exide-inva-tubular-battery-models-available-in-market.html

These also work well if you need something you can easily order from napa or auto zone:

http://www.carid.com/optima/optima-bluetop-marine-battery-4309821.html

http://www.marine.hr/webshop/eng/products/battery-exide-dual-agm-50ah-orbital-deep-cycle-18.html

But having an actual solar battery is even better:

http://www.wholesalesolar.com/products.folder/battery-folder/rolls-s550.html

Any of the batteries listed above and especially the last one will allow serious daily cycling for years.

Or... You can buy a new bank of batteries from walmart every 6 months.

Thanks All for Reply's

So i found this supercheap battery gauge that might work for a small battery bank. S30 dollars ebay. Over 10A load needs shunt.

http://www.servovision.com/Battery fuel gauge battery monitor/Battery Fuel Gauge SVEB1 for 12V-72V.html

pdf shows you can set the AMP/HR rate of the batteries.

My batteries:
Yes 125ah@20hr each i assume. They are big so AH size doesn't surprise me. I had an 27DC in prior test was 100ah.
So 4x=500ah at 12V

Obviously these are walmart batteries and for boats but lead is lead and they got it. If they last 2 years i will be happy.
I tried going to the local industrial fleet battery dealer(Intestate) and they were clueless. It really blew me away they had no idea what a T105 was and they sell Trojans. I just went the cheap route for learning.

What about distance. My panels are going to be 70ft. from my batteries. Is this terrible. Where should i put the charge controller, dead in the middle or closer to the solar panels in my cable run? The MC4 cables are 10gauge and seem healthy for 5A from panel max. I see a pigtail for mc4 to branch or Y i suppose for a second panel.. The controller is junky but OK for starter. Can do 12V or 24V.
Obviously I would like a forklift battery, or RollsSurrette but my yard is shady and I doubt this will go far…Another hobby.

stephenw10

That's the sort of meter I'm talking about. I can't see a price there.
The charge controller needs to be as close to the batteries as possible unless it has seperate measurement wires to take cable loss into account.
Are those cable size figures in AWG?

Steve

Yes sorry 10AWG maybe a 20 foot lead. May get the y-splitter since MC4 is standard. I do see different gauges MC4 like 12AWG but on ebay some are hard to tell.

Here is the meter no housing
http://www.ebay.com/itm/111296152208

I think this in the description is quite amusing:

Percentage of capacity and totem pole

Here is the bigger step up circuit i bought for 12V to 48:

http://www.ebay.com/itm/161297901843

Terminal Blocks on ebay=2 dollars
Terminal Blocks at Northern Hardware=12 dollars

kejianshi: I really appreciate your reply. I posted late about distance. So 70ft. Would see extreme loss that is what i needed to (not)hear. I could mount the batteries on my temp lawn cart to make it heavier but winters are tuff -if i am reading that battery chart correctly. Like 40 percent off the top on really cold nights. So my shed was an alternative but at a distance.

I was actually thinking of using a lawn/custom pvc cart to temp mount the panels to determine best location for a pole mount. Probably 2 panels. I am fabbing up a mount as they want premium money for steel parts and i am a stainless guy.

y251.JPG_thumb

kejianshi

For small installs that get exposed to weather, I like these:

Morningstar SunSaver SS-6L-12V 6A, 12V Solar Charge Controller w/LVD (Gen3)

http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/PWM-Type-Solar-Charge-Controllers/Morningstar-Charge-Controllers-PWM/Morningstar-SunSaver-SS-6L-12V-6A-12V-Solar-Charge-Controller-wLVD-Gen3/p10505/?gclid=CjwKEAiA28ilBRCy5cXrgtfTxTISJABgX7E2zdDyBmMo1jzDc8vzdV3W4F10X3vqDQ35DZFX20kNqhoCFfzw_wcB

Its a pulse width modulated charge controller. I also has a built in conditioning circuit. It won't raise the voltage above 14.2 volts or so.
I'm not sure what type of controller you are using but if it goes through the same sort of charge cycle as most of them and includes a desulfication (sp) phase, it will make a mess of your AGM battery in short order. Its better to use a rapid RF pulse for that. I've had great luck with these.

The morningstar MPPT controllers are also great.

As for you distance problem, its best to collocate the batteries and panels (or close as possible). How cold will it be getting? Or how hot?

Also, lead isn't lead… Quick talk about differences.
First lead purity - The solar type are super pure lead and the batteries are designed with low internal resistance so thay can accept charge at a very high rate, discharge at a high rate.
Lead plate composition - Solar batteries plates are smooth and can endure very very deep discharge often. Starting batteries are not smooth. They have spongy like surface and are really only meant to be discharged 5% or so. Most deep cycle batteries you get at a place like walmart are not very smooth plates and won't take many discharges especially beyond 50%

Lastly, plate thickness. True quality deep cycle batteries have very super thick hard plates. This keeps the material from shedding away from the plates during deep cycling. So the difference here is the quality batteries can endure greater than 50% discharges for years and years (thousands of discharges) while a average department store deep cycle battery might endure 50 or 60 deep discharges at most. So later do keep that in mind.

With the batteries you have, I'd recommend not testing them too much. I'd try to keep the cycling light. Say 20% or less which might be easy enough since you have a pretty large bank.

I have not tested LIFEPO4 much but the thing I like about those is the cycle life and that they can be cycled to nearly 100% without killing them.
The thing I don't like about them is the charge control and discharge control mechanisms that you need with the battery. It limits how many AMPS I can pull off the battery safely and the rate I can charge at.

As for the batteries and COLD weather, this is much easier problem that very hot weather.
When you are charging batteries, they heat a bit, so if you put an insulation jacket on the batteries they should be fine. This is especially true for AGM. They do well in cold weather when insulated. If you throw up 3 more solar panels, you will have enough for your batteries.

I charge at 10 amps but My batteries can take as much as 50amps per each 50AH battery. Exide batteries can really take a beating. In some cases I have 4x as much solar panel as you charging 1/8 the battery. I do prefer to have a very large battery bank when possible though because it prevents you from having to deeply discharge the cells.

What about the backside's of the panel?? I work on boats and that open back just don't cut it. Was thinking of enclosing it with some sheetmetal to help reduce the "Sail effect" That 1.5" Lip is unsat design in my opinion. The cheap panels i got really need angle re-enforcements in corners for me to feel confident about them withstanding 100mph winds..Flimsy lightweight aluminum it seems. I may do some bracing as well where the pole mount meets the back.
Is tracking worth it??

kejianshi

No tracking. I wouldn't even say "tracking" and "100 MPH wind" in the same sentence.

I'd say mount the panels either flush with some other sturdy rigid surface or box them in so that wind cant get under them to create lift.

Where EXACTLY are you mounting the panels and why EXACTLY can't the batteries be mounted very close to them?

I've built south facing solar generators that are mounted on a wooden "wedge" of about 26 degrees sitting directly on the ground with the batteries under the panel and the whole box anchored for exactly same reasons - To keep the wind from carrying it away, to keep all components close and make cleaning snow off the panels easy.

Generally there is no advantage in raising the panels other than to keep clear of shadows if they exist or to avoid flooding damage.

Elaborating on the length of wire run. The high voltage AC side can be long. 70 feet is ok. Only the low volt DC wiring must be kept short.

Yea anything is possible but you are correct. Stabilizing that weight would need a mighty positioner at 100mph. Truthfully i thought about a ground hugger but i dunno if i like it. I may mount more equipment on the pole. And yes i could build the battery boxes right onboard for stability. I liked the variable angle is why i chose the pole mount. I am not married to it. I was planning on mounting some other gear onboard like a weather station(weewx) and antennas.

kejianshi

Weather stations can still be mounted on poles even if the solar, battery and inverter are on the ground.

People mount solar panels in the air all the time and get away with it, but 100mph wind…. Sounds like recipe for disaster.

So, I'm a tiny bit confused. Is this going to be on a boat or a yard?

Smallish Yard just a home project…
I appreciate your system sizing advice. So you saying roughly one 12V-125ah battery per -100W/5A max@17V/12V panel? or 4 panels for 500ah of battery? All roughly.
I don't plan on inverters. Just DC loads... I seriously eyeballed the 200W class panels by the big names. I just want to experiment for now.
I may just use an old lawnmower deck for temp mounting of batteries and panel.
And i just pulled the 100mph figure out of the air. My point was i want something sturdy and not blowing away at 70mph gust.
Thanks for the great advice.

chpalmer

My cousin did a tracking unit that only utilizes freon gas and properly placed "exposure tubes" and air shocks from a vehicle. Got it from "Popular Mechanics" magazine from the 70's He uses it to this day and for the last 25 years.

It supplies 30 amps in the top of the day and supplied their family of 4 off grid all this time till the kids moved out.

Luckily he messed up the gas and the panel makes it way back to the east overnight and is waiting for the sun first thing. Id love to find that article.

He is on top of the hill and the wind has never been an issue. I suppose he got lucky.

Deka makes terrific solar batteries as well.

kejianshi

You have to measure the current coming off your panels to know what you are getting.

A 100w panel in full sun at the equator will probably get you 100w or 8 hours or so.

In some northern place, it may only put out 30 or 50 watts and may not get many hours of sun.

So, you have to figure, up north you will need 2x the panel (at least) as panel advertising my lead you to believe.

You only get a few hours of sunlight - So, lets say for instance its 4 hours average for your place.

So you discharge 24/7 but only charge for 4. so your charge rate needs to be 6x higher than your average load.

Not only that you vane to compensate for load. A great lead acid battery only stores about 60% of what you put into it. 40% may be lost.

So you have to take your original calculation of 6x the load and multiply by x 2.

So, if you average load was 10w you would need about 120w input during your 4 hours of sun to keep things working well.

So yeah - More panels.

kejianshi

Deka - I've heard good things but have never used them. No experience with those.

Good thing is I'm pretty sure what you have, if you add abit more solar panel, will easily run a small 10w pfsense (-:

(The above comment is a blatant attempt to prevent deletion of thread due to irrelevance to pfsense boards)

Thanks for every-ones advice. I'm sure the Renogy panel i got probably only work half their rated capacity, I saw Amazon writeups stating their inefficiency. For $150 for the kit it was worth it for me just to learn with.

stephenw10

When we looked into sun tracking most advice (and our own conclusions) was that it's cheaper and far more reliable to just add panels. My friend adjusts the angle of his panels a few times a year manually. Never tried a maximum power point controller, kept meaning to bulid one.

This is general discussion:

Feel free to talk about anything and everything in this board.

:)

Steve

kejianshi

I need to build another big one soon. I'm thinking that in the Philippines I can totally disconnect from the grid if I want - At 25 cent per kw/hour it should be nearly three times as economical as in the USA.

Would you build an array with a "Branded panel", Hoping in 20 years they will still be around to honor warranty? Or would you go generic.. Like you said earlier Poly looks to getting better.