Thread: Solar Green Steam Questions.

depends on how long the run is from the panel to the box...

with 6mm carrying it both ways you should be good for 15a with minimal loss, the trick is to mount the regulator as close to the batteries as is practicable. the panels might be pumping out 17v which the regulator pulls down to 12... (rough numbers)

why take the loss on the 12V side when you can take it from 17
V and not work the regulator as hard? (not how it actually works but near enough for laymans terms)


All of the panels I've had to work with dont have the regualtor glued onto the panel its in a box with a screw down lid.

you might find that all thats in the box on the panel (if its small enough) is a blocking diode, to check for this expose the panel to full sunlight and check the output, if its over 15v without a load on it its not regualted just fitted with a blocking diode (note that some of the newer ones require a load or initial voltage on the wires to get the panel to start but once started will pump out to their maximum voltage)

The regulator stuck to the back of my folding 120W panel is an MPPT controller. I fitted a heavy duty lead from it rather than move it.

Moving the solar regulator from the back of the panel(s) to near the battery is a real good move. What's the point of regulating the panel output voltage to battery charge voltage and then running a long length of cable so that this voltage can be decreased before it gets to the battery ? By putting the regulator at the battery this problem is overcome. It doesn't really matter if the voltage varies in the cable from the panel to the reg (apart from power loss) as the battery/solar setup will be more efficient and the battery will charge correctly. But I guess you know this because this is what you're doing.

Your typical 12 volt panel will work most efficiently at around 18 volts so that power loss from the panel to the reg will be significantly less in the cable than it was previously when run at 12 volts (nominal) from the reg at the panel to the remotely located battery. The reason you will be upgrading cable size is to decrease power loss between the panel and the reg but it may be able to achieve the same result without using larger more expensive and bulky cable.

A typical portable solar array consists of 2 panels wired in parallel to a cheap and nasty non MPPT reg siliconed to the back of one of the panels and a couple of metres of lightweight cable with alligator clips. It may be accompanied with a poor quality Chinese/English instruction sheet/booklet. A wide bladed paint scraper is the best to lift the reg off.

A typical 12 volt solar panel has a Voc of around 22 volts and you've got 2 of them, so wired in series (not parallel) you get a Voc of 44 volts. If your solar reg is capable of handling this voltage you can run a 24 volt (nominal) solar panel set up into your solar reg and use it to charge a 12 volt house battery. The efficiency gains here are huge. Without going into the maths and technicalities you can transfer the same power to the regulator from the panel using the same cable but with 1/4 of the cable power loss you would have with a 12 volt set up. Or put another way for the same power loss as with a 12 volt set up you can use cable 1/4 of the diameter as before.

Deano

Originally Posted by Blknight.aus

.................................................. ....you might find that all thats in the box on the panel (if its small enough) is a blocking diode, to check for this expose the panel to full sunlight and check the output, if its over 15v without a load on it its not regualted just fitted with a blocking diode (note that some of the newer ones require a load or initial voltage on the wires to get the panel to start but once started will pump out to their maximum voltage)

A couple of points to note here, you will need 3 diodes in the setup I described earlier. One diode 'reverse biased' connected across each panel and one diode 'forward biased' in series with the panels. That is the cathode of the diode (white bar symbol) connected across the panel connected to the +ve of the panel and anode of the diode connected to the -ve of the panel. As there's 2 panels you need two diodes for this. You wire the panels in series, just like batterys, -ve of one panel to +ve of the other panel. A third (protection) diode is needed to protect the panels from inadvertent reverse connection and can be connected with its anode (the diode end without the bar symbol) towards the +ve of the panel array with its cathode end (bar symbol) to the +ve solar reg input.
This series connected diode will result in slightly decreased efficiency of the panel array (as 1/2 volt is dropped across the diode) and can be dispensed with if you reckon you will never,ever connect the panels backwards to the controller. This can result in the instant letting out of smoke from the panel along with tears and emptying of wallet. Some controllers have this diode built in and compensate for the 1/2 volt loss but I reckon the slight efficiency loss (with an external protection diode) is well worth it for peace of mind.

It is also important with a 24 volt solar panel set up to ensure that the battery is connected to the reg BEFORE the panels. This is so that the reg can sense the battery voltage (12 volt or 24 volt) and charge it at the correct voltage. Many regs today are dual 12 or 24 volt and this is how they know which application (12 volt or 24 volt) they are being used in.

Deano

Originally Posted by DeanoH

A couple of points to note here, you will need 3 diodes in the setup I described earlier. One diode 'reverse biased' connected across each panel and one diode 'forward biased' in series with the panels. That is the cathode of the diode (white bar symbol) connected across the panel connected to the +ve of the panel and anode of the diode connected to the -ve of the panel. As there's 2 panels you need two diodes for this. You wire the panels in series, just like batterys, -ve of one panel to +ve of the other panel. A third (protection) diode is needed to protect the panels from inadvertent reverse connection and can be connected with its anode (the diode end without the bar symbol) towards the +ve of the panel array with its cathode end (bar symbol) to the +ve solar reg input.
This series connected diode will result in slightly decreased efficiency of the panel array (as 1/2 volt is dropped across the diode) and can be dispensed with if you reckon you will never,ever connect the panels backwards to the controller. This can result in the instant letting out of smoke from the panel along with tears and emptying of wallet. Some controllers have this diode built in and compensate for the 1/2 volt loss but I reckon the slight efficiency loss (with an external protection diode) is well worth it for peace of mind.

It is also important with a 24 volt solar panel set up to ensure that the battery is connected to the reg BEFORE the panels. This is so that the reg can sense the battery voltage (12 volt or 24 volt) and charge it at the correct voltage. Many regs today are dual 12 or 24 volt and this is how they know which application (12 volt or 24 volt) they are being used in.

Deano

or even easier....

you tie all the panel -ve's together put a diode in the +ve side of each panel and wire them in parallel. The diode is only to prevent a panel thats not outputting from being back fed from the other panel. (as well as providing reverse polarity protection but in a permanant install thats not a problem)

The down side to series wiring panels (and this primarily relates to small systems (say 4 panels or less or less than 500w worth) is once you loose one panel you loose a a lot of your charging ability

my personal favorite method (although it gets a little pricey in the short term and required more work to setup in the first place) is to have one controller per panel and then space the panels out as much as you can as well as rigging the panels to be easily removable using quick disconnect water proof electrical fittings. Make up an extension cord to suit.

The costs are counter balanced by the following, how you weight it depends on what you want the system to do.

a, getting at least one panel at any given time in the sun
b, in the event of a single coponent failure you dont loose the whole system
c, if your staying for a prolonged period the panels that are always the least exposed can be quickly relocated to contribute more.

All that said.

as the voltage from the panels goes up the easier the panels are working and the lighter the cables you can use as well as using a lower amperage regulator (to a certain degree on the last part)

This was covered by Deano, and he was spot on.

Garry, is it a folding panel?
If it is, and your new regulator is a "proper" MPPT reg, wire the panels in series (to double the voltage) and you will half the current in the cables, which will reduce the loss hugely, or you can get away with thinner cables, or run the cables further.
If the panels are roof mounted, and identical, wire them all in series, then run the cable to the regulator.
Check the maximum input voltage on the regulator though, and make sure you don't exceed that (add up the Voc on the panels).
Most panels now have blocking diodes in the connection boxes so if wired in series, and part of that panel is covered, you just lose the voltage output of that panel, and the MPPT reg will still be able to maximise the output of the rest of the panels.

I have a proper MPPT reg (as opposed to the "MPPT" ones on the back - they are REALLY dodgy and worth nothing).

I managed to remove mine with a snap-off type knife, carefully cutting under it as it was glued on with silicon.

Could you tell us the model/brand of your regulator? and the number/model/brand of panels?


Fraser