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Solar

How to Mount and Wire PV Modules

by Richard Perez

his article explains how to make your own PV mounting rack, how to install it, and how to wire Tup the whole works. This is in response to many reader requests for this info. So, all you PV panels languishing under beds, relaxing in closets, and vacationing in garages: Listen Up, here's your chance to get your people to put you in the Sunshine to do your thing.

Face It SOUTH

The critical consideration in mounting PV modules is the yearly path of the Sun. The PV modules must receive maximum sunlight. Consider shading from trees and buildings. The decision of where to mount should be made only after careful consideration of all your options.

are so simple that I'm sure many others are using just about the same technique.

The Rack Materials

The rack is constructed out of slotted, galvanized, steel angle stock. This stock is available at most hardware stores. Our local store sells National Slotted Steel Angle (stock #180-109) for about $7.00 each retail. This stuff is 6 feet long, with two perpendicular sides each 1.5 inches wide. The stock is about 1/8 inch thick, with a heavy galvanized coating. Its entire length is covered with holes and slots that will accept 5/16

The PV modules, in most nontracking situations, should face

South. The closer the plane of the rack is to facing true

South, the better overall performance the PVs will deliver.

Only consider mounting surfaces that are within 15° of facing

true South (within 10° is much better). Any surface further off inch bolts. We have had no problems with corrosion or

will require more complex, asymmetrical mounting racks. If you don't have a roof or wall that is suitable consider ground mounting. Since PVs produce low voltage DC current, keep the wire lengths to the battery as short as practical. See the Basic Electricity article in this issue dealing with wire sizing in low voltage DC systems for specifics.

Where you are going to put your PVs determines the type of rack you need. Roof mounting (on either pitched or flat roofs), wall mounting, and ground mounting are all possibilities. So consider the variables and pick the best for your situation. These racks can be used in all three types of mountings.

So Which Way is South?

Determine South with a good compass and someone who knows how to use it. Be sure to allow for the difference between magnetic North and true North. This difference is called magnetic declination. In California for example magnetic North is some 19° East of true North. If you don't know your magnetic declination, then go to the library and look it up.

Mounting Racks-- your PVs hold on the World

The obvious purpose of the rack is to attach the panels to a fixed surface. At first glance this seems simple enough, but consider wind, snow, falling ice and temperature variations, not to mention possible leaks in the roof!

We are going to talk about a simple to build rack that can hold up to four panels. This rack uses inexpensive hardware store parts. It mounts on roofs, walls, or on the ground with the appropriate foundation. In all mounts, the rack is adjustable for panel elevation, and allows seasonal optimization of the racks tilt. This rack approach was developed by Electron Connection Ltd. for its customers. Its design and application

electrolysis with this galvanized stock after three years in the weather. We haven't yet tried this material on a seacoast, and would welcome feedback from anyone who has. To the left is a drawing of a typical length of this steel angle.

You can shop around locally, and may encounter different sizes and lengths. Six foot lengths are long enough to mount 4 of just about any type of module. We use this angle on Kyocera, Arco and Solec panels without having to drill any holes in either the angle or the PV modules. Working with this stock is like playing with a giant erector set. The only tools you really need are wrenches, a hacksaw (to cut the angle), and a drill for making holes in the surface holding the rack.

The amount of steel angle stock you need depends on the size & number of panels you wish to mount, the mounting location, and your particular environment. Let's consider the rack shown in the photoon the next page as an example. This rack holds four 48 Watt Kyocera PV modules and is bolted to the almost horizontal metal roof of a mobile home. Each PV module is 17.4 inches wide and 38.6 inches long. The mounting holes on the bottoms of the PV modules match the hole cadence in the slotted angle. This particular rack used 9 of the 6 foot lengths of the steel angle. Four lengths comprise the framework for the modules. Three lengths make up the legs and bracing, while two more lengths are used as skids on the roof. Strictly speaking, the skids are not essential, but do add rigidity and relieve stress on the mounting points on the sheet metal roof. We don't want any leaks.

A rack could be built with the about half the materials. The top and bottom pieces of the rack holding the panels, the brace on the legs, and the skids could all be deleted. If this were done then the rack would be roughly equivalent to most commercial models. In our opinion, PV modules should be mounted as securely as possible. Many commercial racks use the PV modules' frames as a structural members in the whole module/rack assembly. This rack does not do this. Many

Home Power 2 January 1988 11

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