12v VS 24v panels

[BradKW]

As seems to be the normal case for me, I had read a bunch of stuff and decided that 12v panels were the obvious choice. Still on the fence about poly vs mono, but going 12v seemed like a blessedly simple choice that I could scratch of the decision list.

But something caught my eye today and I've now realized there's at least 2 builds I've been studying that use 24v panels, and they appear to be done by people who pretty much have their electronics dialed in.

I understand that going 24v would require a MMPT controller...but does it take different batteries too? Anyone here using 24v that can explain why they made that choice?  Thanks  

 

[Reducto]

The only reason I know of to go with 12v is to save money on the controller. Higher voltage panels can be found cheaper though, which negates some of the price difference. The one I got was a cosmetic second. It was designed for use in a large array but the coloring was off so it was rejected, but it still puts out rated power and is still like new 3 years later. I was going to get an MPPT controller anyway because I wanted to get the most out of whatever panel I got.

It connects to the same 12v golf cart batteries I would be using with a different panel.

 

[Sabatical]

I'm sure folks with more knowledge will chime in here but no replys yet so i'll throw my 2 cents in. With an mppt controller you can use any voltage panels you like and feed a 12 or 24v battery bank.
I believe that by using a 24v battery bank line loss is less of an issue. But then how do you adapt to 12v appliances?

 

[jimindenver]

It only becomes a choice if either fits on the roof. Other than that PWM controllers can be less expensive and 24v panels are less than 12v. In the end the cost of two systems can be rather close together.

24v panels take up less foot print and require fewer mounts and connections. 12v panels can be run in series and then run into a MPPT controller OR PWM. This is important because you may have a odd number of panels and not be able to run the in series.

I have only done 24v panels but I have tested four different ones. The monos are advertised to be more efficient and t one time my 220w mono was noticeable smaller than my 230w poly. Poly tech has advanced and my 250w polys use the same sized frame as my 245w monos did. The difference was a inch inside the frame so both took the same foot print.

What I did notice is Monos are great for grid tied where if the sun goes behind a cloud it doesn't matter because the grid is going to back you up. Off grid they drop from full power to a fraction as soon as the sun is hidden at all. For my 245w monos that drop was from 17a to 2.38a with the lightest cloud cover.

All of my polys have dropped depending on just how thick the clouds are and still produce in pea soup where you can't even tell where the sun is. My 230w poly will produce 4 to 5a when the Monos are asleep. The big system can cover the rigs needs when it is overcast, just not the high powered loads.

Can your panels require special batteries? No but your batteries may require a certain controller that can be adjusted to work with them. That is true in MPPT and PWM.

I went 24v panels because I went on craigslist and found two for $50 each. The least expensive controller to run them at the time was over three times that so they sat in the garage until I found the Eco-worthy controllers for $100 or less if you won a auction. 24v panels are produced in higher numbers and their prices make them really attractive like a 435w for $375 dollars. Four or five 100w 12v panels will cost you considerably more than that.

Again the beginning is what fits on the roof.

 

[BradKW]

So what I'm finding confusing (one thing anyway) is what would be the practical difference between a 250w 24v panel, and a 250w 12v panel? If you're charging a 12v batter bank, wouldn't end result be identical since both panels can meet the battery requirement of ~15v ?

 

[jimindenver]

Have you seen any 250w 12v panels? I remember seeing some 300w 12v panels but they were old.

The question you are asking is the difference between PWM and MPPT. MPPT will give you an advantage early on when the batteries voltage is low and limiting the systems output on PWM. It does this by taking the excess voltage from the panel and creating extra amps with it. Those amps are wasted in a PWM system. This applies to 12v panels in parallel or series. The voltage of a 12v panel is higher than you charge at and while the advantage is small, it is better than wasted. In my panels the amps listed in 8a and they put out 18a with MPPT converting lots of excess voltage.

Realistically if you have more solar than you nedd, it doesn't really matter which way you go.


So, what fits on your roof? What's available to you and what can you afford?

 

[akrvbob]

Solar panels designed for houses are almost always high voltage because they use long wire runs and very high wattage.

I don't know actual numbers, but my guess is that for every 12 volt panel sold their are tens of thousands of high voltage panels sold. If you want to save money, buy a high voltage panel.

MPPT WILL GIVE YOU 25-40 % more amps into your battery. You want it to actually use all the wattage you bought because PWM flushes a bunch of it down the toilet.

 

[highdesertranger]

actually I have never seen a 12v panel. what you all are calling a 12v panel has output between 16-22v. if a panel were actually 12v you wouldn't need a controller and it wouldn't charge your battery. an old prospector I knew had a solar system someone set up for him, it was a bunch of panels charging 6v GC batts, running his light and TV in his cabin. when his batts got old and he needed new ones he couldn't afford the 6v GC batts so I told him to just put a couple of old car batteries in there until he got the money for the GC batts. oh no he said you can't do that those are 6v batteries and 6v solar panels they could never work with 12v batteries. just saying. highdesertranger

 

[Reverse Engineer]

Why not just convert the voltage output of the panel to whatever the voltage is of the batt you want to charge?

I picked up a couple of DC-DC Variable Transformers which will take current up to 10 A and convert anywhere between 8V-80 V.  A 120W 12V panel puts out MAX 10 A, but you need just about perfect conditions for that output.

So if I need 18V for my laptop or my power tools, I just tweak the transformer to bring 12V up to 18V.  I could go the other way round with it and tweak 24 down to 18.

There is heat loss in this process, especially at high throughput.  I tried using this with the Ewz to run straight off a 12V batt instead of wiring in series, but the transformer simply gets too hot after just a mile or so with open throttle.  Most applications don't need that much throughput though, and only a really BIG Solar PV Array is going to pump out that much power.  I work with all small panels, 30W and under, so it is no issue for me on the charging end.

 

[blars]

A MPPT controller is a DC-DC converter designed to optimize getting the most power from the panel to the battery without damaging the battery.

 

[Canine]

Jimin Denver.18 amps out of a panel rated for 8 amps?Boy howdy these mppt controllers can even defy the laws of physics.Please don't pile the bs quite so high.

 

[Reverse Engineer]

A MPPT controller is a DC-DC converter designed to optimize getting the most power from the panel to the battery without damaging the battery.

How much do they cost and what kind of throughput will they handle?  Can you use one to convert your 12V power storage system to 18V to run your laptop or portable power tools?

 

[Optimistic Paranoid]

 Can you use one to convert your 12V power storage system to 18V to run your laptop or portable power tools?

No.  They are a dedicated design.  See:

http://www.solar-electric.com/mppt-solar-charge-controllers.html/

Regards
John

 

[B and C]

Can you use one to convert your 12V power storage system to 18V to run your laptop or portable power tools?

I have an HP laptop and a HP desktop that run off 19.2VDC IIRC.  I bought a ciggy plug adapter to run them off of.  It will charge the laptop while I use it, no fancy conversions needed.  

No idea on the power tools, that will be someone else.

 

[Reverse Engineer]

I have an HP laptop and a HP desktop that run off 19.2VDC IIRC.  I bought a ciggy plug adapter to run them off of.  It will charge the laptop while I use it, no fancy conversions needed.  

No idea on the power tools, that will be someone else.

Oh, I have a cig lighter DC-DC adapter that works anywhere from 12V to 24V, plus also does 5V for USB devices.  However, it works in the milliamp range, it can't handle throughput for power tools.  It's good up to the Laptop range of power consumption but not much past that.  For this you need a fairly robust transformer, and it has to be built to dissipate heat, because there is resistance in there and you get power loss through heat dissipation from this.

The transformers I have are the most robust ones I could find that are variable in voltage, at a reasonable price ($18 each).  They are fairly tricky to work with, you gotta use a voltmeter with them to tweak the input/output voltages correctly for whatever your application is.  They can handle 10A throughput, but start getting too hot after maybe 15 min with that much current running constantly.  I considered running a fan for cooling to use it with the Ewz, but I really don't need to do that, I got the right batts to wire in series for 36V anyhow.  For power tools though, no issue for a drill or circular saw or reciprocating saw.

 

[SternWake]

Here is a DC to DC voltage transformer capable of passing 600 watts, but should likely have a 60MM fan mounted to it when converting voltages at those upper wattage limits:

http://www.amazon.com/DROK-Converter-Transformer-Regulator-Controller/dp/B00E8D7XYG

I have a 9.6v craftsman drill whose charger was destroyed by a MSW inverter. I hardwired the drill with 10AWG wire, it can pull 35 amps at 12.6v when braking the chuck by hand to a stop, and would overload this dc to dc transformer.

Since these are cheaper than laptop DC to DC car adapters, i would like to use one, but my Dell has a third pin on the barrell connector which must see some sort of voltage too in order for the laptop to charge the battery, so the above transformer could power the laptop, but it would not allow the battery to charge. Also I only need 90 watts, not 600 and there are 5$ dc to dc transformers which could handle this task.

 

[Reverse Engineer]

Here is a DC to DC voltage transformer capable of passing 600 watts, but should likely have a 60MM fan mounted to it when converting voltages at those upper wattage limits:

http://www.amazon.com/DROK-Converter-Transformer-Regulator-Controller/dp/B00E8D7XYG

I have a 9.6v craftsman drill whose charger was destroyed by a MSW inverter.  I hardwired the drill with 10AWG wire, it can pull 35 amps at 12.6v  when braking the chuck by hand to a stop, and would overload this dc to dc transformer.

Since these are cheaper than laptop DC to DC car adapters, i would like to use one, but my Dell has a third pin on the barrell connector which must see some sort of voltage too in order for the laptop to charge the battery, so the above transformer could power the laptop, but it would not allow the battery to charge.  Also I only need 90 watts, not 600 and there are 5$ dc to dc transformers which could handle this task.

That transformer is very similar to the ones I have.  I have never measured the throughput when running a drill with it, but the amount of time I am drilling is so short it just doesn't get that hot.  It works.  Don't try running an electric scooter with it though!  lol.  You will fry it in under a mile.

 

[SternWake]

I do not own the  600 watt transformer linked, but I do own the 150 watt version.  So far I have not come close to overloading it.  My experiments with it were merely to make 12v computer fans levitate when fed Approximately 25 volts, And to boost a wall wart transformer  from 11.9v to 14.4v to power some LEDs I was going to install in a stick and brick, but ultimately the light color and intensity was not adequate for the intended result, so i sits in my electronics bin waiting to be employed by the mad scientist.


The 600 watt version can be used on a charger's output to bring a 'fully' charged battery upto EQ voltages of 16v and try and restore lost battery capacity from chronic undercharging of flooded batteries.  Do not employ it on a battery which was not already 'fully' charged, meaning it spent 2 to 4 hours at absorption voltage first.

I am not sure how any particular  'Smart'  charger will react with one of these inbetween charger and battery though.  I imagine some will freak out and shut off.

Anyway, these voltage transforming gizmos are pretty neat, and kind of ridiculously inexpensive.  

Definitely add a 60mm fan to their heatsinks if maxing them out.

 

[akrvbob]

This is all off-topic and needs it's own thread. It's a great topic, it just doesn't belong here.

The topic of this thread is solar panel voltages and solar panel charge controllers feeding battery banks. Nothing else.
Bob

 

[Reverse Engineer]

This is all off-topic and needs it's own thread. It's a great topic, it just doesn't belong here.

The topic of this thread is solar panel voltages and solar panel charge controllers feeding battery banks. Nothing else.
Bob

So we need a new thread for Transformers?