Roof Mounts
Perhaps the simplest mounting system is to attach the panels to a solar-south facing roof. Solar south differs from magnetic south as a result of a phenomenon known as magnetic declination.
If you live in Florida, for example, there is no change between magnetic and solar south. If you live in Albert, the error in the compass-magnetic versus solar south reading is so large that it will affect your system’s energy production if you use fixed-mount PV arrays.
Another problem with fixed-mount solar module panels array is their inability to change their angel of view throughout the seasons. The winter sun barely scrapes across the horizon in most of the northern United States and Canada. During the summer, the change in the earth’s angle places the sun almost directly overhead. If your roof mount or other fixed mount cannot be adjusted for summer-to-winter sun angles, a good rule of thumb is to set the array at an angle from the ground equal to your latitude. Mounting racks, which have a summer/winter angle adjustment, should be lowered by fifteen degrees for summer. Likewise, raise the angle towards the vertical by fifteen degrees for winter.
Ground Mounts
If the thought of climbing into your roof to wipe snow off the PV array has you going woozy, then ground or pole mounting is for you, a simple and inexpensive method of mounting the panels.
Select galvanized steel or aluminum to limit corrosion. When designing your mounting system, make sure to include a hinge assembly to allow for seasonal adjustment. It is possible to make a ground mount using preserved wood or cedar, but keep in mind that the panels will almost certainly outlast the wood.
A word of caution regarding ground mounting: PV modules are expensive and may have a tendency to walk away. Ensure that you have security bolts (or a good guard dog) to prevent theft. If possible, place the mounting legs in concrete footings to make sure that everything stays in its place. Snow is another problem. If you live in an area where “sweeping” the array requires a snow blower rather than a broom, then ground mounting is not for you. Be careful to ensure that lawnmowers and playing children will not send rocks or other debris flying at the modules. Although it is very likely that no damage will result, there is no sense tempting fate.
Tracking mounts
Solar module panel or PV arrays comprising up to twenty panels are mounted on the tracker, forming a billboard-sized unit. (A sixteen-module array measures 16’ x 8’ or 4.9 m x 2.4 m.) The tracker is designed to move to an easterly location when it gets dark. At first light it follows the sun on its westerly track across the sky. At day’s end, the unit returns to the easterly heading to repeat the process. Electronically controlled trackers can be fitted with a manual seasonal-adjustment device or with an automatic version.
Passively controlled trackers are also available. The Track Rack manufactured by Zomeworks (www. zomeworks.com) uses heat from the sun to operate a tracking mechanism. Although this mechanism is simpler than those used in active tracking units, The Track rack model will go to sleep facing west and may require an hour or two of valuable sunlight before it will start tracking correctly on cold days.
Should you use a tracker? The debate rages on, but the following are considerations that may affect your decision:
- Trackers increase summer PV production by up to 50%. Winter production is improved only 10-20% due to the lower, smaller arc of the sun. If your energy consumption is higher in summer than in winter, perhaps due to the operation of a spa, swimming pool, or air conditioner, then tracking will be a benefit.
- The further north you are the less sense it makes to track in the wintertime. This is especially true along the United States/Canada border are.
- If your site has a limited window of sunlight-less than six hours-then tracking will not greatly improve system performance.
- Trackers are not cheap. The cost of the tracker may be used to purchase a fixed rack and more PV panels, which might offset the loss in non-tracking production.
- Trackers add a degree of complexity to the system. The bits and pieces are just one more thing to have to maintain.
Regardless of which type of PV mounting system you decided to use, keep in mind that they take up a fair bit of area and make wonderful kites or sails in high winds. Ensure that proper mounting and foundation work has been undertaken in compliance with the manufacturer’s installation instruction. If you want to harness the wind, don’t use your PV panels.
References: The Renewable Energy Handbook, by William H. Kemp.
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