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nimblemotors · 13-05-2013, 19:36

The ideal is to have all cells in parallel, then each cell can contribute as much as it can given what sunlight it gets. For this to work, they must all have the same voltage, otherwise a lower voltage output won't contribute its current.
A dc-dc converter must be used. STmicro has a chip designed to do this, the SPV1040, using MPPT control on cells and outputs fixed voltage so they can all be combined.
It adds a lot of cost relative to cells, but when shading or sun angle is varied I think it is worth the expense. The target market is small portable panels where maximizing output is critical. I'm working on building panels using the chip for my boat.
A larger-grained version is to use multiple 12v panels with a MPPT controller for each one. This also increases the cost a lot vs bare panels. e.g 4x $200 150w panels needs 4x $200 MPPT controllers. I'm not even sure the controllers available can be combined like that.

hamradiosailor · 16-05-2013, 05:29

To be fair, and probably to keep the controversy going, there is experimental work reported that shows that the series panel configuration is actually better than parallel in many instances. RV.Net Open Roads Forum: Tech Issues: Parallel or Series Solar?
This complements work based on theory that show the same result.
http://www.cruisersforum.com/forums/...lel-68096.html

The bypass diodes, if present and operating in a series panel configuration, provide an alternate current path if a shaded panel becomes highly resistive.
There may be a gray area, so to speak, where you could adjust the shading of one panel, wired in series with other panels, to just be enough to not allow the bypass diode to be forward biased. This could make it look as thought the series configuration was inferior when selectively shaded. However, this is only a hunch since I have not tried this, or really thought about it very deeply. Certainly everyone would agree that a series configuration allows the use of smaller diameter wire, and I believe that most would agree that with the series configuration, a MPPT controller is desirable.

In reality solar panels are most typically groups of parallel solar cells which are then connected in series with internal by-pass diodes. It is common to have three groups of parallel cells wired then in series. So, in shading tests of parallel versus series wiring of panels, it becomes quite complicated because of the already parallel-series combination in each panel. There are a lot of variables, and wrong conclusions can be reached if these are not all taken into account.

Utahsailor · 18-05-2013, 07:27

Utahsailor: Just arrived in Chesapeake VA after a very nice drive from Salt Lake City across the SW (hiking in Moab, cowboy music in Durango, great food in Santa Fe, great food in Oxford, MS to see Faulkner's environs, ribs in Memphis, walking down Beale St, country music in Nashville, hiking in Asheville, sitting in an F15 in Goldsboro (cousin flies them)) and finally here to a disheveled boat. What a great trip.

Anyway, hard bimini is near complete. After the many discussions regarding serial vs parallel and other issues, I've had a 12" square panel fabricated near the center of the bimini (underside) and arranged the panels so their outputs are near this box. By having a buss bar for each panel, I can easily try different combinations. The starter layout will have the two port and two starboard in series (as suggested by s/v Jedi), each lead to a Morningstar MPPT- 45. There will be a disconnect switch in the box for each series unit and a distribution buss for 12V, for 4 LED lights. It will be easy to measure currents and voltages here as well as easy to rearrange the panels in any configuration.

I'm learning how to set up a blog and will take enough pictures to illustrate the setup and lessons learned, as a couple of contributors have requested.

CAELESTIS · 07-07-2013, 07:35

I would like to hear from those users that have split backstays, and the resulting shading, about power output. I see no way to avoid some shading. The backstay is -22 rod and not that thick. Series or parallel with this shading problem?

I am looking at 2 240w Sanyo panels with an Outback 60 controller (plug and play with my Outback inverter).

hamradiosailor · 07-07-2013, 09:36

The install of the 4 Sanyo 240 watt panels with two Tri Star 45 converters is complete. Each converter connected to two panels in series. One set of panels stopped working yesterday, but I think that it was just a connector that needed attention. It works today, after fiddling a bit with the connectors. The reason for choosing two Tri Star 45's over one Outback 80 was redundancy.

I am very satisfied so far. We have 800 Ah house batteries and I haven't run the generator in a month, although it is summer in the Bahamas. We did not even use shore power at the marina in Florida before leaving, except for A/C. I probably could get by with less solar power as the typical amperage called for to charge each day is about 40 amps maximum, (20 per controler). I don't know if this is operating properly yet, but it seems to fully charge each day. (I am still wondering why it only charges using 450 watts, 225 per controller, when it could charge at twice that rate in full sunshine.) I am looking forward to seeing how the panels perform when we have many cloudy/stormy days in a row. I may just turn off the solar panels for a day or two just to see what the charging rates are when the batteries get down to <25%. After living on an O'Day 35 for 2 years, struggling to keep the 200 Ah house battery charged, with some solar, wind, and mostly just running the engine, pure solar seems like the way to go. So much less noise and trouble. The physical installation was done by Certified Marine Electric in Stuart Florida, although I told him the panels and controllers that I wanted. I also specified how I wanted the panels mounted so that they were in line with the SS horizontal pipe. Certified ME subcontracted the metal work with a local welder that ended up being more expensive than we originally thought. The final assembly still required us to provide some more support to the Bimini, with diagonal 1" SS pipe pieces, but overall I was happy with the way the panels were mounted.

nimblemotors · 07-07-2013, 10:29

Quote:

Originally Posted by hamradiosailor

The install of the 4 Sanyo 240 watt panels with two Tri Star 45 converters is complete..

Excellent, any pics?

cfarrar · 07-07-2013, 10:53

Quote:

I would like to hear from those users that have split backstays

We have split backstays and three panels in parallel on the bimini. The shadow cast by the backstay wire doesn't make a noticeable difference in output. As you'd expect, the mast's shadow does reduce output.