Solarex MSX120(R) Panel.

If you've done this before, don't laugh at this writeup. There are classes for installers in which they learn step by step how to do this assembly process! I haven't taken any of the classes, but after assembling and mounting 34 panels on the roof, I feel privileged to give a description of this process. I am still learning all the time, but the methods I use are working for me and there are no noticeable differences between my setup and that in professional installations I have looked at.

I'll try to add pictures to this as soon as possible. Please don't hold your breath, though.

The panels come taped or banded in a flimsy cardboard box with 2" cardboard stiffeners on the corners and one extra sheet of cardboard on the back, inside the box. There is also a one or more page instruction booklet included within the box. Cut off the tape or banding material, take out the PV panel and set the packaging material aside.

Since I am mounting the panels in stiff mounts and dragging them up on the roof already assembled, I mount two panels on the pre-manufactured aluminum angle rails at this step in the assembly process.

The manufactured mounts I get at Atlantic Solar, so the MSX120(R) panels can be bolted with the included stainless steel hardware to the rails using the preexisting holes in the back of the frames. This way no holes need to be drilled in the panels. There are a number of other mounting methods which were designed by the Solarex engineers and are demonstrated in mounting structures on the grounds of the Solarex facility in Frederick, Maryland. I went on a tour of this facility a few years ago with the Potomac Region Solar Energy Association, though I have not been through any of the classes.

There are also other standard mounting techniques which might be used. With panels of this size one must be careful to make sure they do not flex in 120mph winds or the tempered glass in the front WILL shatter. Mounting the panels, raised a few inches up to keep them cool, directly to the roof, is the cheapest and perhaps the simplest method of mounting. This does not permit tilting the panels according to season, though. It also relies on the stiffness of the panel frames, so one must be very careful in the process to keep from flexing the panels too much.

Solarex engineers also designed a mounting technique where the panels are attached to angle frames with double sided tape. My feeling on this is that one might have to remove the panels for whatever reason, and this might make that a pretty difficult process. The tape could always be cut with a very sharp knife, but one would have to do it very slowly and carefully. Not something I would want to try.

There are integral frames for mounting MSX120(R) laminates as an integral part of the roof. With the "panel of the month" technique, this integral mounting is not really feasible unless one lives way out in the country and has no neighbors to complain about the tarp over the roof for a few years. A problem with the integral mounted panels is that the structure must be designed to expand and contract within the design limitations of the panels and the structure itself. For this reason, I suppose, the laminates may be only available to architects and engineers at this time.

With the mounts I am using, I bolt the two panels securely to the frame rails before I go on. This makes for a solid assembly that I feel comfortable dragging up a ladder onto the roof. (It's heavy, though, so take your time moving it.) I recently learned that a half inch air space between all adjoining panel sides is desireable to allow free expansion and contraction of the panel as a unit. I may have to re-drill some mounting holes to allow this extra space between the panels.

There are two junction boxes on the back of each panel. The covers and a packet of extra connecting hardware are taped to the back of the panel. This extra hardware can really come in handy if one is connecting up on the roof and drops something. Really first class!

There are a number of ways these panels could be wired. Internally they are actually four six volt panels. Each junction box is factory wired for 12 volts, with a jumping block, so one can parallel the two boxes to get 12 volts out or series them to get 24 volts out or series the four boxes on two panels on a mount to get 48 volts out.

I'm going to try to make up diagrams here to show some of the possible wiring configurations. It is unfortunate that Solarex does not include these in an easy-to-follow format in the manual that comes with the panels or on its web site. Not very user-friendly. Blocking diodes are recommended for greater than 12 volts, if I'm not mistaken. Solarex avoids putting these in by wiring the panels for 12 volts. Many panel manufacturers factory wire blocking diodes into their panels. Solarex also recommends shunt diodes between arrays. The diodes will help prevent large currents from going in reverse across a shaded solar cell and damaging it.

Anyone who is using multiple 120 watt panels will often be running the system at more than 12 volts to use lower gauge wire. I'll draw the blocking diodes in the higher voltage configurations. Remember to get the polarity right on the diodes. If one mounts them with the polarity markings facing out, the wiring can be easily double-checked by looking in the boxes. If the structures are assembled on the ground, one can shine a light on them or put them in the sun and put a meter on to measure the voltage and short circuit current through them. Solarex, I have heard, considers short circuiting the panels as abuse, so perhaps it would be better to place a load such as a motor on the panel and measure the current through it, instead. Please feel free to email me if any of this is not clear. My email address is: pv_power@yahoo.com

Atlantic Solar sells the diodes I used in my panels, as well as the wire, connectors, etc. The quality of their components is better than you would find at Radio Shack and the home in the box home supply places like Home Depot or Lowes and such. Contact information for Atlantic Solar is at the bottom of their home page: Atlantic Solar.

Atlantic Solar's diagram showing the wiring with shunt diodes is located at the following link: Panel wiring.

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