48 Volt Solar Panel System

[WaltL]

Hello everyone

First let me say that these boards are the greatest and you guys seem to really know what you're talking about. I'm new to this solar thing but have found that if I want to have electricity where I am planning on building (several miles from electric lines) then I must learn solar/wind.

Anyway I have started with 15 50 watt 48 volt solar panels I bought for about $100 each including shipping. I do have these questions about the panels... They are sold as 48 volt but say 78 volt on the labels and in sunlight they register about 95 volts?? Is that correct??

I was planning on placing the panels on the roof of a cabin I have where the house will be someday. I have chosen the roof because the cabin is not occupied all the time and I feel this would minimize vandalism or theft. I was planning on wiring the panels in parallell (48 volt).

I was planning on buying 4 12 volt deep cycle batteries at WalMart for about $60 each which I believe I would hook in series.

Items I still need (I think) would be perhaps: 1) Lightning arrestor hooked to the frames of the panels? 2) 48 volt charge controller between the panels and the batteries? 3) Some kind of fuses between the batteries and the service lines.

Should I get a 48 volt inverter (rather expensive) or could I use 4 12 volt inverters on each battery?? Also, I do use 12 volts for some applications in the cabin now. Can I tap off one of the 12 volt batteries even though the 4 are hooked in series.

Also what organization regulates and controls solar panel installation and where would I find their specs??

How's that for some stupid questions??

Thanks for your time and experitise

Walt

[srnoth]

Hey Walt,

Pretty slick setup you are planning there with all that solar stuff. I personally haven't really played with solar yet, but I do know a bit about the batteries:

If you hook the four batteries in series like you said, and measure the voltage on one of the batteries, you will get ~12V, and so, theoretically, you could have four different 12v circuits, each running either a 12v inverter or some 12v light or something like that. There are real life problems with this though. For example, you will never be running exactly the same load on all four 12v circuits, and this will lead to imbalances in the charging of the batteries, possibly ruining one. Another possible problem with this, is that the total amperage will be spread out over the four batteries, so you will never be able to take full advantage of your system with one large load. This means that if say your solar panels are 1kw total power (just an arbitrary figure, i didn't work out the numbers you called in you post), you will not be able to run a 1kw load at any extended time period using the 12v system. So this brings me to my concluding point:

It would seem that you have already spent a lot of money on the panels, and I would therefore assume that you are looking to build/install a good quality, long-lasting, properly setup system. If this is the case, it would make a lot more sense to properly complete the system with a 48v inverter. That way, if you by a good one, your system should last for years, and you would never have to worry about load balancing, or which inverter you were on etc, and you would be able to operate high power equipment (power tools, fridge, etc), and therefore use your solar panels to their full potential.

Why make your high-quality solar panels suffer the shame of being mated with a half-way, knock-together, make-shift 12v setup?

DISCLAIMER:

I do not guaranty that what I have posted is 100% accurate.

I also do not mean to offend anyone. If you disagree with what I have said, please say so nicely.

Lots of Love,

Peace and Unity,

Stephen.

P.S. Only four batteries sounds a bit limited. I guess you could see how they work and get more as your need increases. They certainly won't last you a week's use without proper sunlight. Maybe consider wind as well, or the simple thing to do would be to get a lawnmower style engine and attach four automotive alternators to it, connect each to a separate battery, and charge away in the days of no sunlight!!

[richhagen]

I am not an "expert", but I have an interest in the subject.  My humble attempt at answering the questions which you pose is below.

It sounds like you purchased some of the thin film panels such as Solarex MST-50MV Millennia Series 50 watt-48 volt PV module.  If this is so, the panel is designed for 48V battery charging, the panel however produces a maximum number of watts at 72 volts.  With no load on the panel, it produces an open circuit voltage that you measured at 95volts which would be about right. My attempt at an explanation of these different voltages is here:

http://www.fieldlines.com/comments/2004/9/29/17922/4377/5#5

I have a small 200W 48 volt system






I draw the power out 48 volts so as to avoid discharging the 12 volt strings to different levels.  Some recent discussion of the topic of unevenly charging and discharging battery banks is located here:

http://www.fieldlines.com/story/2004/10/13/121519/52

Basically, I would splurge for the 48volt inverter.

As for the batteries, this site has a nice introduction to types of batteries here:

http://www.otherpower.com/otherpower_battery.html

As for the lightning arrestor, when lighting strikes, it induces a massive current and voltage spike in nearby power leads.

In common strategies, inductance is added to the line between the leads and the charge controller, with reasonably sized grounded wires on the panel side such that a high enoungh voltage strike would break down the insulating material between them and conduct the majority of the energy to a good earth ground.  Surge suppression is added on the controller side of the inductance to handle the remaining current that conducts past the inductance.  

There are various commercial producers of lightning arrestors, and I would follow their recommendations to the letter.  

I am not sure who regulates installations of panels, but since they are electrical systems, the NEC (National Electric Code) would be where I would look first.  

Hopefully some of this will help you at least a little bit, Rich Hagen

[drdongle]

we these new or used panels?

Carpe Vigor

Dr.D

[ghurd]

All good information.

The 48/78/95v is about right.

Go with the 48v inverter.

Batteries- Maybe 8 T-105 type, 6v golf cart batteries in series? (search this site for T-105 or t105) Maybe even 16.

If the batteries are undersized for your system (PV and wind), the controller will stop charging when they are full, even if there is a lot more sun left that day that could have gone into bigger batteries. Also, there is less battery to use power from if it goes a week without much sun or wind.

The big 6v batteries will hold more power, and usually last years longer.

Sam's Club has some for $48.50 ea.

Don't skimp on the batteries. You have a lot of solar power. You'll have a lot of uses. You should have something that will hold the power that is capable of being produced. 4 of the $60 batteries is awful small for a set up this size.

Good luck with the code thing. California maybe has someone who understands it, because they have to deal with it more. Most places the inspectors have never seen anything like it, and don't understand how it works.

I found out what kind of wire code calls for. Tried to buy it. Everywhere. Called the 4 biggest wire manufacturers. 2 don't make it. 1 would make it, if I ordered 10,000 feet, maybe it was 100,000 feet, but more than I can pay for. 1 had 63' in the whole country, in Texas, about $3 a foot plus shipping to Ohio.

Code will let me run 660vac, 20a, under ground or on poles, with 12-2 UF-B (.20 a foot).  Code says I can't use the same wire for 12vdc at 1 amp.  Well, I do it anyway. No choice.  Nothing solar is really subject to inspection here the way its being used.

Anything code or to be inspected, go talk to the inspector face to face. It always helps. Tell him you need to know how to do it right and he is the only person who knows (they like that).  Never irrate an inspector.

I want to know where you got those for that price too!

G-

[WaltL]

Thanks for all the advice.

The cabin (1 ½ story, 12 X 20) I'm talking about now has a small 5 watt 12 volt panel recharging 18 small 12 volt small sealed batteries which runs patio lights hung in the rooms, a small 5 inch black and white TV, a tape player/radio and fans (12 volt computer) for the solar heat panels. Believe it or not that little panel gets enough charge when we're not there to keep those batteries up enough to use every other weekend we are camping. I want to get these new panels up and running so I can add a small refrigerator and stop carrying an ice cooler.

I must have gotten these panels at a pretty good price since everyone wants to know where I got them. 14 of them were brand new still on skid in a large box which I picked up in Virginia. I believe they are the thin film panels BP850's with aluminum frame. Got them on Ebay as a single lot of 14 and final price was $1401. I thought the price looked pretty good from what I saw with other panels.

I do plan on expanding the system when I build an actual house. For now with the weekend cabin I figured that the 4 12 volt batteries should hold what I need and yes I will be wasting a lot of sun power . After the house is built I am planning on adding some wind also. And I'm watching a small stream in the back of the property to see if it stays fairly healthy all year round or is it just running fast now after all the rains??

Looks like I will plan on using a 48 volt inverter. Any suggestions on type and where to buy??

Also for the things that I will keep at 12 volt should I run one leg from a single battery or should I invest in a 48 to 12 volt converter???

I read here on the boards that welding cables do a great job for connecting batteries together and I have found a link that gives lengths and sizes of other cables and maximum lengths.

G - I see that you would recommend using 6 volt golf batteries over the WalMart 12 voledeep cycles. Since I need 8 of the 6 volts, the price will be more expensive. Do you feel dollar for dollar they would be a better buy??

Like I said these boards are great and very helpful. I really appreciate all the comments.

Thanks

Walt

[GeeWiz]

You could also consider a 48v to 24v charge controller.  

I have one of the old RV Power products charges (now blue sky) that does 48v to 12v.

They make one for 48 to 24 (http://www.blueskyenergyinc.com/pdf/SB6024Hdatasheet.pdf)and their quality products.

There is nothing wrong with a 48v inverter, it's just out of the ordinary.

48v has it's advantages, namely the size of the wire at 48v can be a smaller guage.

Make sure you don't cook your batteries.

Gw

[WaltL]

Okay, so I have a chance to buy a 48 volt charge controller (Charge-Max 1500 48 volt) with load diverting from Boston Mountain Manufacturing for $129.95 plus shipping. A description of the 12/24 volt model is on Ebay and actually sounds too good to be true for the money. Has anyone used this companies equipment??

Thanks

Walt (again)

[ghurd]

Well, I guess it depends on when you are going to build.

I wouldn't want to spend a bunch of money on something I'll have to upgrade in a year, if I could spend a little more now and have it work for years.  I'd think about it like spending $400 on batteries now saved me $240.

For every other weekend, the 4 12v batteries should be fine.  Even 4 of the smaller Group 24 deep cycles ($40?)at the same place would be fine.  You wouldn't even need to mount all the panels, just a few in a temporary setup.

For day in, day out use, at least go for the 6 volt batteries.

I think they have a longer life expectancy.

In real life, it seems they do better than the numbers say they should.

The 12v $60 batteries don't do quite as good as the numbers say they should.

Choose the refridgerator carefully. Read the amps, watts, and the yellow energy sticker. Some of the dorm size use more than some full size. The salesman is going to think you are nuts. They always do.

In the big picture the battery cost goes from $240 to $400 (only a $160 differance).

The cost of panels, mounting, wires, inverter, fuses...

$160 is a drop in the bucket for batteries that will make the setup work better, longer, hold more power, with less headaches.

48v to 12v converter. It will keep the batteries from getting 'out of kilter'. 'PowerStream' has some that are pretty decent in my experience, and cheap.  Well, cheaper than most.  The efficiency is good and they have a bunch to choose from. Used a few with no problems yet.