The idea of residential solar arrays has been around since solar cell panels were first being developed; it gave an answer to the question of eliminating your energy needs. With advancements in technology, we are now able to supply to the consumer efficient and low-maintenance panels at a fraction of the cost they were ten or twenty years ago. On the larger scale, it can be understood that an energy revolution may be on the way as solar energy becomes more and more affordable.
The average cost of a panel averages at about $2.80/installed Watt, leading to an average cost for a total system of $10,000 to $20,000. Money, while still a deciding factor in many system sizes, is not the true limiter in solar designs. When we talk limits in solar design, we speak to the physical limitations of your house; your roof size and design, as well as the legislated limits of power production.
Legislated Limits
In designing a system for residential installations, the first we discuss with our prospective clients is the legislated limits laid out in Alberta's Micro-generation Act. Brought into law as of January 2009, the Micro-generation Act identifies how much power a residential property can produce via renewable energy sources like solar. The Act allows a residential owner to install a system that generates energy to fulfill one hundred percent of their needs along with an additional ten percent of those needs.
In terms of numbers, this means that a residential property that consumes an average of 7000 kW annually can produce up to 7 700 kW from any installed solar array. If said property produces beyond that additional 10% annually, it is seen as a power generating station and, as such, must abide by provincial legislation under those applicable laws.
Roof Size and Design
With each design, how we layout the panels is based upon the footprint of your roof. With panels only being laid horizontally or vertically, how your roof is laid out determines how many panels can be accommodated.
The major stopping point for solar layouts lie in four key areas; roof peaks, roof valleys, ventilation and roof footprint.
Roof Peaks and Roof Valleys
Solar panels are made of rigid materials and do not lie directly on roof shingles; typically there is a 1” to 2” clearance between the panel bottom and the roof. This allows for wiring and racking sitting comfortably. With this in mind, it is easy to understand why one panel cannot meet another panel at a roof peak or valley; they cannot successfully connect and arch over the roof peak or valley. Unlike shingles, solar panels cannot bend at a roof peak and the racking which holds the panels down cannot safely be anchored at a roof peak either. The same rule applies where a roof valley is concerned. For these reasons, when we design arrays, we often have panels that border the valleys and peaks of your roof, but never overlap.
Ventilation
Ventilation is another factor that determines the placement and, ultimately, the amount of panels that can be placed on your roof. Typically, with our panels have at least 1” clearance from the roof, we can build directly overtop small PVC vents for airflow. Major ventilation shafts such as chimneys, skylights, and roof turbine vents are not able to built over and quite costly to move. Due to this, our designs typically build around such obstructions in an effort to keep the project cost down. In very rare cases minor vents such as the turbines are moved in an effort to maximize solar output. However, it is a general rule of thumb that we leave large ventilations in place.
Roof Footprint
The final piece in solar design is the actual footprint of an individual residence. Due to high populations and zoning restrictions in most municipal areas, residential arrays are limited to roof anchored systems only. As the roof is the main anchor support for the array, it is understandable that no solar panel may extend beyond the footprint of the roof.