Hi Norm,
Very interesting, Mono or Poly.

I personally have a 125watt Monocrystal and am happy with its performance but any kind of shade on any part of the cells almost stops it in its tracks, for example could be outputting 6amps and I open the van roof hatch which shades some of the cells and we are down to 1 to 2amps.
On overcast days it is still not too bad could output 2.5amps instead of 7amps with full sun light.
One thing I am not happy about is I paid $1100 for a BP Mono solar cell five years ago.

I cannot comment about the Poly but I would think they are also a good cell.

I think the main issue when buying solar cells is make sure you get a good regulator not one of those cheapies.
You will probably gain more from buying an MPPT (maximum power point tracking) type regulator than whether you buy Mono or Poly solar cell.

We may have an expert that can lock in the real differences between Mono and Poly solar cells.

JR

could you post the web sites please
Thanks Andrew

Good question this one Browny and I’m following with interest. I’ve posted a similar thread concerning using both mono and poly together.

I’ll add this to this thread also as I think it follows your thread without hijacking it (I hope)

So where does photovoltaic fit in with both poly and mono?
http://www.ebay.com.au/itm/250875262715 … 1423.l2649

regards
Jdog

Hi Browny,
If you search the net there are plenty of sites about MPPT type solar cell regulators.

I will have a go and try to explain the way I see a standard regulator and a MPPT regulator, remember I am not an expert on the subject just know enough to be dangerous.

First you need to understand a solar cell when fully loaded outputs at about 17 to 18volts and the battery you are charging could be around 12 to 14volts.

As an example a 125watt solar cell delivers 7.2amps at 17.4Volts.
Power (watts) = Volts x Amps so 7.2A x 17.4V = 125 watts which is what the solar cell is rated at.

Now the confusing bit, as said Power = volts x amps and if we are charging a battery that is at 12Volts then power = 12V x 7.2A = 86 watts so you can see that a 125watt solar cell is only deliver 86watts to a battery at 12Volts if the current is 7.2amps which is all you will get from a standard regulator.
Therefore 125watt solar cell may only deliver 86watts, about 70% usually a bit more as I have chosen the worst scenario.

A normal solar cell regulator is like a high speed switch turning on and off the current flow of 7.2amps to the battery.
A MPPT (maximum power point tracking) regulator can try and mach the solar cell to the battery and adjust the current flow to a higher value.
Example if the battery was at 14volts and the solar cell at 17.4volts an MPPT regulator would try and match the volts so the amperage going to the battery would increase above 7.2amps.

When the solar cell is outputting 125watts to a battery at 14volts the MPPT regulator if perfect could deliver a current = 125W/14V = 8.9amps.

The way I see it is the MPPT type of regulator can increase the current flow to the battery to try and deliver as much of the 125watts produced by the solar cell where the normal regulator will only ever deliver the rated amperage output of the solar cell.

The normal solar cell regulators are still OK especially the better ones as they can have multiple stages of charge where as the cheapies may only charge to a set voltage then start to cut out.

Therefore an MPPT regulator is a good investment. One way of looking at it is it will I spend a bit more and buy are larger solar cell to overcome the loss from the regulator or will I spend a bit more and overcome the loss with a MPPT regulator which can be more expensive than the normal regulator. I think some of the MPPT regulators are not that expensive now but they were more expensive when I was buying my system.

Is that as clear as mud!

JR

Hi again Browny,
Tried to edit these comments to my last post but was to slow, timed out

Your system that you are proposing sounds good but not cheap, I guess I do my own work so don’t know how much labour costs are.

The Plasmatronics 20 amp looks like a good regulator and will give you plenty of data but I don’t think it is a MPPT type. One suggestion would be to upgrade to a 30amp regulator just in case you decide to add more solar later.

I have been very impressed with my AGM (absorption glass mat) batteries so would recommend them if you have not decided on a battery type.

It has been discussed before on the forum but many solar cells with aluminium angle are now glued onto the roof with Sikaflex to save having holes in the roof and create leaks.

JR