Tuesday, 28 October 2014

Mounting Structures or Module Supporting Structures for Solar Panels





Overview

The module support (array mounting) structure shall hold the PV module(s).

When deciding about the optimal mounting location for solar modules the following criteria should be considered:
  1. To which extent does the place receive high radiation of sunlight?
  2. is it free of shading?
  3. is it not exposed to dust and other particles which may cover or damage the modules?
  4. will the modules be exposed to excessive heat?
  5. does the place offer protection against theft and vandalism?
  6. is it close to the battery?

Solar modules can be mounted in a fixed, flexible or tracking way.

Fixed Modules

Fixed modules (either as single module or as array of several modules) are mounted on:
Fixed mounting structures tilt the modules at a fixed angle determined by the latitude of the site, the requirements of the load(appliances which are powered by the PV power system) and the availability of sunlight. The fixed mounts should be stable, flat and well ventilated. They must withstand heavy wind and heavy rainfall.
Flexible System
Flexible system use basically the same mounting structures, but the modules are removable.
Tracking Structures
Tracking structures are more expensive and require higher maintenance efforts. The trackers orient the modules towards the Sun, thus increasing their output.

Mounting (Pole / Roof / Free-standing / Building Integrated)

Modules that are mounted on a pole are easy to install an can be easily oriented towards the Sun. They can be free-standing or installed on the side of a building. Usually, a small array of one or to modules is mounted per pole. Thus, pole mounting is suitable for small solar home systems, especially, if the roof support structure of the house is not stable enough to support a PV array.
For roof mounting the most common support structure consists of racks. It is important to leave a space of at least 10 cm between the roof and the array to allow ventilation. Otherwise, the array gets too hot and the performance of the modules decreases. The mounting structure must be fixed to the building or the under-roof beams to ensure durability and safety.
Free-standing arrays on a ground support, usually consisting of racks, are easy to install and to orient towards the Sun. It might be difficult to avoid shading and therefore, enough space is needed to install the array far from trees, buildings and other objects that might cast shadows on it. The modules are easily accessible which is beneficial for maintenance, but could also imply a higher risk of theft.
Building-integrated PV arrays consist of thin film modules. This kind of mounting structure is not common in off-grid installations.

Mounting Structure Materials

Mounting structures can be made of:
  • galvanised steel,
  • painted steel,
  • aluminium or
  • wood.
There is a vary large offer of factory-made mounting structures available on the market, but it is usually possible to produce them locally, too. It is important that mounting materials are corrosion-resistant and weather proof.

Module Support Structure

The module(s) shall be mounted either on the rooftop of the house or on a metal pole that can be fixed to the wall of the house or separately in the ground, with the module(s) at least 3 (4) meters off the ground.

Roof-mounting

Minimum clearance between the PV module(s) and the roofing material must be at least 10 cm. It is recommended that the module mounting structure be supported on top of a pole at least 50 cm long or fixed with supporting angles at four positions. The mounting structure must be anchored to the building or to the under-roof beam structure and not to the roofing material.

Wall-mounting

A metal pole must be fixed to the outer wall of a house by appropriate clamps and fixing material (screws and wall plugs in solid walls or screws in wooden beams) in at least two positions at a reasonable distance. If the pole is not higher than the top of the house, the problem of shading from house-walls or roof-parts must be taken into consideration.

Ground-mounting

A metal pole at least 2“ (50 mm) in diameter must be used with the modules attached at the top of the pole. The pole must be anchored in concrete at least one meter deep in the ground.
The pole and mounting structure shall be sufficiently rigid to prevent twisting in the wind or if large birds alight on the array. The support structure shall be able to withstand winds up to 120 km/h (150 km/h in windy areas).
All metal parts shall be made of non-corroding materials (aluminium, stainless steel) or adequately protected against corrosion by galvanisation (layer approx. 30mm). The support structure should be able to withstand at least 10 years of outdoor exposure without appreciable corrosion or fatigue.

Optional

The structure shall incorporate galvanised steel or stainless steel hardware (bolts, nuts, washers, etc.) for all external connections. These include the modules-to-structure, structure-to-pole and pole-to-building attachments. Particular attention shall be given to protection against galvanic corrosion if different metals are in contact. Different kinds of metal have to be kept separate. Under corrosive environmental conditions (high humidity, high salt content), only stainless steel hardware is allowed.
Optional: The use of rivets or tamper-proof (non-removable) screws for theft protection is recommended.
No objects (trees, buildings, etc.) shall shade any part of the PV modules at any time of the year between 90 minutes after sunrise and 90 minutes before sunset. It should be noted that shading of even a small part of a module or array could cause a considerable reduction in power output. In situations where partial shading is unavoidable, this must be compensated in the system sizing calculations.
The PV modules shall be mounted in a position which allows safe, controlled access for inspection and cleaning. However, security from possible theft and damage may also be important considerations. Where necessary, suitable measures shall be taken to reduce the risk of theft or damage (e.g. from flying stones). It should be possible, however, to remove modules for service, using appropriate tools.
The module(s) shall be installed facing towards the equator (south in the northern hemisphere and north in the southern hemisphere).
The tilt angle should be selected by computer simulation to optimise the energy collection during the month with the lowest mean daily irradiation. To guarantee a self cleaning effect of the modules by rainwater, the modules shall not be installed at a flatter angle than a minimum tilt angle of 15°.
Optional: If computerised calculation is not available, as a general rule (in areas up to a latitude of 40° around the equator), a tilt angle to the horizontal plane equal to the latitude +10° can be assumed as a good approximation.
Optional: Where necessary, deviations ±5° from the orientation to the equator shall be acceptable, unless otherwise specified. Where necessary, deviations of ±5° from the optimum tilt angle shall be acceptable.
Optional: Facilities for users to adjust the tilt angle in different seasons or to perform a manual tracking throughout the course of the day shall be acceptable, provided the users are well informed and wish to do so. In this case, the strength of mounting (e.g. resistance to wind-loading) shall remain sufficient.
Optional: Passive tracking systems for the PV generator shall be acceptable, if the additional gain of energy justifies the additional cost, provided that the tracking system can withstand wind-loading requirements and is of proven reliability. As the advantage of a tracking system is only valid during direct sunshine periods, the energy gained by the tracker can only be considered for system calculations if detailed irradiation statistics, including measurement of direct and diffuse insolation, are available for the site. Active trackers (requiring electrical power) are not allowed.

References

https://energypedia.info/wiki/Solar_Module_Mounting