The diodes will give you some protection so that you don't lose everything but it is still better to parallel them if you can. On my arrays I have two panels paralleled, then I series groups of them together. I have seen just a small amount of shade on one panel virtually knock out the output for that particular pair in the array. The shaded panel really drags its partner down. I mean like 10% shade cause a 70% loss in some circumstances.
The diodes protect the output of the individual panel so the whole thing isn't killed by a little shade but the current of the two panels will be limited by the shaded one and if the shade happens to cross more than one circuit on the individual panel, the pair can really take a hit.
Paralleling is better whenever you can unless there is no shade issue and you want to save on wire size.
On Monday, January 27, 2014 9:07 PM, James Sizemore <james@deny.org> wrote:
The shading issues is not a concern between parallel/series panels setups. Almost all solar panels have at least one bypass diode. The manual for you MPPT will have a voltage range it works best at. However you configure your panels to reach that voltage range is your best option. Most vendors have a string calculator. Use it to find the best combination. Your vendors is below:
Most vendors have a sizing calculator on there web site.
Steve,I don't know anything about your particular charge controller but most of the MPPT controller I've seen will take much higher voltages and step them down for a 12V bank. My Outback will accept 90V and charge a 12V bank if you want to set it up that way. Paralleling the two panels to feed your controller 24V would definitely be the way to go to avoid the partial shading issue. The advantage to series them and feeding it 48V would be to use a smaller wire but a 240W panel at 24V is only going to give you about 10 amps so the two of them together will only require about 12 guage wire, although 10 would probably be better.I'd buy a panel that was made in the USA, you'll pay a few cents more per Watt but I don't think you can go wrong that way. Some of the Chinese stuff is fine, a lot of it not so much. The trick is in the solder connections, a lot of things are done by hand in China and all the stuff from the USA is done by robots and they generally provide more consistent quality control.Carter
On Monday, January 27, 2014 12:33 PM, Steve Dolan <sdolan@scannersllc.com> wrote:
I'm getting ready (therefore just know trying to learn) to install solar panels on my cat for the house bank. They just don't have anything out there for 144V (Propulsion pack) systems as far as controllers go. So I have decided that rather then charge my Propulsion pack I'm going to charge just the House bank made up of 3 12V AGM batts. All charging of the House Bank is through the Propulsion bank down to a 144V to 12V charger. I have a few questions on solar systems.I'm looking at 2 Mono 240W panels with a TriStar MPPT 45 controller.It seems that I should go parallel with 2 panels in case one panel is partially shaded.When wiring in parallel will the individual panels both go to a junction box at the panels then I can run a single heavy wire (probably 4/6 gauge) back to the controller?I like the TriStar because I can get a remote display. Any comments on the controller?My panels will be mounted on the davits so I can tilt them.I'm guessing that the panels should be 24V ea. Is there any advantage to going with the higher voltage rather than going 12V ea.?Any suggestions on the manufacture of the panels or who to stay away from?The loads on the house bank are about 18A so by eliminating this draw down from the Propulsion bank I'm hoping to extend the travel time on batteries alone and decrease the genset run time.Thanks guys for any input. I would like to get this right the first time, 8o)Steve in Solomons MD
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