12 volt solar panels

[Kappy]

Now that I'm gonna change my panels from 24 volt to 12 volt.

Now comes the daunting taste of panel selection.

Do I go rigid like here http://www.ebay.com.au/itm/100W-12V-SOL ... SwIgNXtVPa

Or semi flexible
http://www.ebay.com.au/itm/100W-Flexibl ... Sw8gVX3pHi
or
http://www.ebay.com.au/itm/100W-12V-Fle ... SwojRYShVK

Would you care to share what brand you have and maybe your secret mounting .

I have doscovered some bold claims mainly " Powerful Cell 25Yr output Warranty" is this realistic and what does it actually mean?

A number of panels have in their specs "MAXIMUM SYSTEM VOLTAGE 1000 VOLTS"
Can someone enlighten me?

Cheers
Kappy

[JohnM]

Hi Kappy,
"the maximum voltage 1000 v" refers to household type of installation where the panels are connected in series to form higher voltages, to drive a mppt controller or direct inversion to AC current. the advantages of the higher voltages are lower amps, resulting in lighter gauge wiring. for the actual panels many MPPT regulators accept 100 v or higher, for a 12v system. To put it simply a series of 5, 100 w 18 v maximum voltage would be capable of producing 90v at 5.5 a requiring say 5 mm sq wire (depending on the length of the run) where as the same number of panels connected in parallel, would produce a maximum of 18v and approx 28 a requiring aprox 20 mm sq for the same run length. (These figures are not correct and are only being used as an example)
I prefer the rigid type of panels mounted on aluminium angle rails, to allow air flow underneath. to help cool the panels, as well as shade the roof,
I am of the opinion that the hotter the panels the less the output, with the panels connected try hosing them down and see the immediate reaction on the controller. Granted that the semi flexible "may" get some small advantage, from the "heat sink effect", if fixed to a metal roof, but only if a heat conductive adhesive were used,

[bagmaker]

Hi Kappy,
how come the change to 12v? What is the reasoning behind the change?

[Kappy]

Hi Kappy,
how come the change to 12v? What is the reasoning behind the change?

My inverter is a modified sine wave and need to change to Pure sine wave. Also need to change my Steca controller as well.

My AGM batteries are toast so feel the need to change to Lifepo4 so thought change to 12V maybe be better.

If you can offer evidence to stay with 24v I'm all ears.

[native pepper]

24v panels are much better to use than 12v and cheaper, simply because you won't have to worry about wire size as much when connecting them, As you are getting a new controller, an MPPT makes using 24v panels a better proposition because of the higher voltage coming in.

Not being a technical bloke, could be wrong, but that's my simple understanding. I'm upgrading my bus system at the moment, just have finish of the veranda and entrance I decided to build on the spur of the moment at home. So currently on the bus is 12v panels, which are going to be changed for 24v ones, then I don't have to use bigger wiring for the long run panels. I also have to get my aluminium welding right before doing it, as its pretty new to me, having only used mig and the old stick welders. Tomorrow pick up the "D" size argon gas bottle I've bought, so no rental, then will begin building the panel frames, which will be made out of 25mm aluminium angle and if successful, will turn the panel frames into a support for automatic roll out awnings I've designed.

[T1 Terry]

We all have our preferences and mine is to use panels that are within the useable voltage range for the battery. A few reasons:
No wasted efficiency converting voltage from a higher than battery voltage down to a useable charging voltage, nothing is 100% efficient so some of the energy you collected gets wasted in the conversion process.

If all fails the solar can be connected directly to the battery and you become the solar regulator, if the battery voltages gets to high you disconnect the solar, it will get you by till you can get the problem sorted, can't do that if the panel voltage is ridiculously high.

Cabling is relatively cheap, do it right the first time and you don't have to do it again, no point in trying to save a few $$ on cable only to spend double the amount for a controller to waste some of that solar energy you collected
24v panels are not cheaper or smaller than 12v panels, only second hand roof top grid connect panels are cheaper but they are way to big to get many on the roof.

With the right combination of controller and solid state relays, the solar wiring can go directly to the battery compartment yet the regulator can be mounted some where else so you can see it, the relays are driven remotely by the regulator. This also gives you the advantage of an unlimited capacity system, you never end up needing to buy another controller because the one you have isn't big enough to handle the extra solar.

You can easily add in portable panels without the need for another controller, makes for a more efficient system and much cheaper in the long run.

These few are a bit tilted towards what I do, the solid state relay method integrates with the lithium management system so no need to change anything, just add the wiring and away it goes.

Semi flexible panels do not suit series connecting and parallel connection is not well suited to MPPT controllers, so there is nothing to be gained in the cabling and some to be lost in the controller choice, just something to keep in the back of your mind.

T1 Terry

[bagmaker]

Maybe Kappy could swap panels with Native Pepper?

[dapope]

We all have our preferences and mine is to use panels that are within the useable voltage range for the battery. A few reasons:
No wasted efficiency converting voltage from a higher than battery voltage down to a useable charging voltage, nothing is 100% efficient so some of the energy you collected gets wasted in the conversion process.

If all fails the solar can be connected directly to the battery and you become the solar regulator, if the battery voltages gets to high you disconnect the solar, it will get you by till you can get the problem sorted, can't do that if the panel voltage is ridiculously high.

Cabling is relatively cheap, do it right the first time and you don't have to do it again, no point in trying to save a few $$ on cable only to spend double the amount for a controller to waste some of that solar energy you collected
24v panels are not cheaper or smaller than 12v panels, only second hand roof top grid connect panels are cheaper but they are way to big to get many on the roof.

With the right combination of controller and solid state relays, the solar wiring can go directly to the battery compartment yet the regulator can be mounted some where else so you can see it, the relays are driven remotely by the regulator. This also gives you the advantage of an unlimited capacity system, you never end up needing to buy another controller because the one you have isn't big enough to handle the extra solar.

You can easily add in portable panels without the need for another controller, makes for a more efficient system and much cheaper in the long run.

These few are a bit tilted towards what I do, the solid state relay method integrates with the lithium management system so no need to change anything, just add the wiring and away it goes.

Semi flexible panels do not suit series connecting and parallel connection is not well suited to MPPT controllers, so there is nothing to be gained in the cabling and some to be lost in the controller choice, just something to keep in the back of your mind.

T1 Terry

So, Terry, given that we are also looking at redoing our solar, what sort of panel voltage range are we talking?

[Kappy]

Now that I'm totally confused.

Either way I need at least a new invertor, new solar controller, and BMV 700.

Assuming I change from 200ah 24v AGM to say 200ah 24 v Lifepo4 I need I think 16 x 3.2 volt cells.

Already having 3 x 200 watt 24 Volt panels I only need 2 more to give me 1000 watts of solar.

T1 terry can you PM a estimate for Lithium cells and whatever else I need to make this system work.

I figure either way I can add panel and cells as needed.

[native pepper]

Everyone has their way of doing things, think I'll stick to my simple system of a lifepo4 mppt controller, equaliser and 24v panels. I can get on ebay 250w x 24v panels cheaper than 12v.

Can't understand why a parallel connections is not suited to mppt controllers, every off grid and most RV I've seen over the last 10 years have mppt and no complaints as they work well. My own 24v panels and mppt controllers on the house do a great job and have never had a problem, because they are not over driven. I get more energy from them than the PWM controllers we used to have, But as I don't understand the technicalities, can't comment any more.

Kappy, every technological minded person I've come across has different ideas of how low voltage systems should work, seems none can agree with others. So us poor souls have to work our way through the jungle they create and find something that works for us, that is simple, easy to understand and we can fix without a degree in something.