A rooftop solar PV installation comprises of PV panels assembled in arrays, mounting frames to support the panels and secure them to the roof, wiring, inverters, and other components depending on the type of installation. The roof site must be able to accommodate all of these components, which requires examining the following aspects:
Accessibility: The roof must be accessible to carry out installation and maintenance. It must be possible to lift the solar system components onto the roof and for personnel to physically access the site to install and maintain the system.
Roof configuration: A roof plan can help quantify the roof area available for the PV power plant. The plan should indicate the location (including longitude and latitude), height, and slope of the roof itself, as well as any additional structures present on the roof. Identify any possible conflicts in usage of the roof, such as a helipad or communication antennae, and contact relevant bodies to ascertain if any special permission is required to use and/or alter usage of the roof space.
Roof materials and structure: For existing buildings, first find out when the roof would need replacement. If a roof is nearing the end of its life span, it is more cost-effective to install the rooftop PV system once the new roof is in place. It is also easier to integrate a system into the design of a new roof.
Next, engage a structural engineer to determine if the roof can be penetrated to secure the mounting frames. Often, flat roofs have a membrane that will lose its waterproofing properties if penetrated—in this case, the system may require a ballasted mounting system (with concrete weights).
The engineer should also be able to determine if the roof can bear the additional weight of a PV system. As a general rule of thumb, a crystalline PV system will place about 15–20 kilograms per square meter (kg/m2 ) (3–4 pounds per square foot) of dead load on the roof (California Energy Commission 2001), but this varies depending on the panels and mounting system used, the spacing between panels, and the wind load.
Generally, a flat, concrete terrace roof will normally have the strength to accommodate the additional weight of the panels and supporting structures. Inclined roofs of storage sheds and residential buildings may be made of metal sheet, tiles, or similar materials, in which case it would be necessary to examine whether the trusses can support additional weight.
In the event that the roof is unable to support the load of a crystalline PV system, lighter thin-film modules could be an option.
Finally, if the roofing installation and manufacturing warranties are still valid, determine if installation of a rooftop solar system could void the warranty.
Shading: Nearby buildings or trees can shade a roof during certain periods of the day, which will lower the power output of the solar PV system. Although shading changes throughout a year, observing the roof at various times during a day gives a fair idea of the typical number of sunlight hours.
Aesthetics: Check that the solar PV modules would not negatively affect the aesthetics of the building. From street level, solar modules will be more visible on a sloped roof than on a flat roof. If they will be seen, find out if there are any local building restrictions preventing a visible rooftop solar PV installation. With growing support for the use of renewable energy, guidelines are being modified, where necessary, to allow rooftop solar installations.
Roof leasing: If planning to lease the roof space to the owner of the rooftop PV system, consult a legal advisor who would be able to confirm whether that type of arrangement is permissible.
Electrical load: Obtain the current and expected electrical load of the building or facility. Should the load be comparable to or less than the electricity generated through solar PV, plan a smaller system or plan to use the excess energy—either store the energy in batteries, send it to another building within the facility, or feed it into the grid.
These aspects can easily be incorporated into the design of a new building. However, the investigation will take more effort for solar installations on a preexisting roof.
Source: Asian Development Bank’s Handbook