PV Mounting Systems & Tracking Devices

PV- modules are either added to existing buildings, integrated into new buildings or installed as free-standing structures in a field. Where they are free-standing, they can also be fitted on moving platforms tracking the angle of the sun.

Building applied modules

In many cases, pv-system can be retro-fitted to buildings ,either on the tilted or flat roofs

Tilted Roofs

A number of mounting systems have been developed specifically for PV- modules on tilted roofs such that no major building work has to be undertaken. The modules tend to be made from aluminium and can grip onto the roof tiles. The crucial characteristics of these systems are:

Snow Load: Weight that the structure is able to carry.

Wind Speed: Wind between the roof and the panels can create a significant force. Some mounting systems may therefore be limited to low-wind zones

only.

Roof Slope: Most mounting systems will not allow roof tilt angles higher than 60°.

Lightning Protection: It is essential that the mounting system comes with lightning protection.

Naturally, orientation of the roof is important. Ideally, facing due south at an angle of latitude - 10% - 25%.

Flat Roofs

Flat roofs provide an ideal space for solar systems, as these are often unused spaces. Moreover, flat roofs don't have the limitations of the pre-existing orientation of tilted roofs. In fact, in the U.S. alone, in excess of 100million square meters of reflective roofs are installed annually. Commercial rooftops in the U.S. alone could provide an average of 5GW! On flat roofs, flat panels are installed at a fixed tilt angle, similar to stand-alone pv- installations. However, this option may not be feasible if the panels would be too heavy or if there is too much wind, which may affect the stability of the tilted up panels. Solyndra, an American company, provided an alternative which was a thin film module in cylindrical shape. Although of lower efficiency, they were lighter and not susceptible to wind. Thin film is wrapped around cylinders. As a result, light can be collected from anyn angles, rendering tilting unnecessary. In addition, the thin film may also catch light that has been reflected off the roof itself. Due to its unique geometry, there are also no issues with wind activity. However, Solyndra filed for bankruptcy in 2011.

Building intergrated modules

Some of the major characteristics are:

Colour of the surface. Unlike crystalline photovoltaics, thin film pv does not necessarily have to be blue.

Transparency: Some thin films are transparent to the visible spectrum. This way they can be put on big window fronts of office blocks, and still

generating some electricity while not blocking the light for the offices inside.

Flexibility: Some panels come protected with glass while others are more like sheets.

Free-standing modules can be mounted such that they face the best angle. Again, wind speeds need to be taken into account. With some mounting systems, the

manufacturer advises to place the modules flat on the ground during wind storms.

Unlike on tilted roofs, stand-alone solar installations can make use of tracking platforms that can tilt the surface along one or two axis with the help of a motor.

The motor itself is connected to a device that determines the angle of the sun. Not surprisingly, tracking provides a significant energy boost. However, this comes

at a cost, as the tracking mechanics are more expensive. The energy requirement for the motors on the other hand is negligible.

To avoid these additional costs, a good compromise would be for the mounting system with only one axis (azimuth) to allow two tilt angles, one optimised for

summer, the other for winter (Seasonal Tilt). The customer can change the angle manually according to season.

Automated tracking can be passive or active. Due to thermal inertia, passive systems tend to be slow in changing from the sunset position to the sunrise position.

Active trackers either calculate the current position of the sun from first principles, or use light sensors that will point the modules to the brightest point in the sky,

not necessarily the sun - especially when it is cloudy.

Effect of Tracking Devices

Tracking will always result in a higher energy yield. The amount of the boost however is very much dependant on the location. Generally, locations with a higher proportion of direct sunlight such as Spain or Finnland will benefit more from tracking than locations with a high proportion of diffuse light such as Germany.

Ground-mounted solar systems essentially all work the same—systems anchor to the ground and hold a large number of stacked panels, often two but sometimes three or four panels high. Two rails usually support each panel, whether oriented in landscape or portrait. The anchoring to the ground is the tough part of these installations, as there are many different types of foundations.

If the soil is clear of debris, steel beams are driven into the ground and the racking system is attached to the beams. If ground conditions are not suited for smoothly driven beams, anchor systems may be used—helical piles, ground screws. These can take more time to install as they have to power through boulders and other large debris.

Ground-mounted systems don’t always have to penetrate into the earth. Capped landfills and other brownfields are ideal for solar arrays, as they are underused land areas, but their temperamental ground conditions cannot be disturbed. Arrays can be ballasted on the ground just as they are on flat roofs. Concrete blocks hold a system in place, and if ground conditions can hold the weight of a concrete truck, cast-in-place blocks may be an easier option for installers.

Ground-mount solar arrays are typically installed in mostly flat open fields, especially on utility-scale projects. Certain solar markets, like Florida, have naturally level land, which makes installs simpler, but flat terrain isn’t always an option. Solar sites in the Northeast, mountain states or hilly regions can undergo civil engineering to make level ground for mounting. Yet, grading land can alter rain runoff patterns on the site, possibly displacing native species and raising project costs.