For residential, commercial and municipal solar projects, roof-top solar often provides the lowest cost per watt of installed capacity. Roof-top solar installations are also considerably faster than ground-mounted, as no geotechnical soil investigation is required, while structural engineering is in most cases is straightforward. The speed of installation makes roof-top ideal for small-scale projects.
A combination of several factors determine the roof-top solar system sizing:
- An area of the available roof-space with good solar exposure. For example, an average residential solar PV system with 18 x 60-cell solar modules requires 30 square meters of the roof space.
- Ampere ratings of the main breaker and rating of the solar panel busbar where the solar will feed. For example, a typical for small-scale residential solar system 125Amp rated bus with 100A main breaker would allow to connect 13.5KW of AC inverter capacity.
- Transformer capacity. The combined AC capacity of all inverters cannot exceed the rated transformer capacity.
- Historical power consumption for Net-metering in SK, micro-generation systems in AB and Net-metering for systems in Fortis BC. The intent of the most net-metering programs is to allow customers to offset their historical power consumption.
- Customer budget.
As the roof orientation and roof tilt dictates the orientation of the solar array, it is important to understand how much of the roof-top solar energy is produced under the given roof constrains as a percentage of the ideal South azimuth and ideal tilt. The table below shows Edmonton, Alberta losses compared to the optimal conditions:
When budgeting for the roof-top solar systems operations and maintenance, take into account the age of the roof. Additional expenses required for dis-mounting of the solar array during roof repair or replacement may overweight the economical benefits for the roof-top solar PV installation. Also, the building economic life has to be long enough for the solar to pay-off.
Roof-top solar systems vary by the type of racking used to attach solar array to a structure.
Pitched solar systems have stand-offs screwed through the roof, typically into the rafters, or stand-offs are attached to the metal roof ribs.
Ballasted racking systems are installed on flat roofs or roofs with less than 5 degrees tilt. The racking helps to tilt modules towards the sun and concrete ballasts are used to hold the racking in place. Often, ballasted roof-top solar systems do not require roof penetrations.
Wall-mounted awning systems provide the benefit of an easy installation combined with steeper and optimal array tilts.