Electricity from Your Roof

Canadians are used to seeing photovoltaics (PV) – devices that create electricity from sunlight – embedded in calculators, garden accent lighting and other electronic devices. More recently, we have also become more familiar with the sight of the flat, black panels of PV systems mounted on the roofs of houses everywhere. As more systems get installed, we are learning more and more about how well they work in our extreme Canadian climate and the relative costs and benefits.

Most residential PV systems are installed on houses connected to the electricity grid that spans each province or territory. The “grid-intertie” allows homeowners to both receive electricity from the grid as needed and deliver the electricity produced from their PV systems back to the grid. Another finding about PV systems is that most of them do not store electricity in batteries – a feature that would allow the PV/battery system to provide power to the home in the event of a power failure. However, this also results in a more complex and costly system that most homeowners avoid despite the se- curity a backup power system can provide.

Another key finding is that the methods available for contractors to use to estimate how much electricity your PV system will generate have been quite accurate. One of the benefits of PV systems is that they work reliably. There are no moving parts to set up and look after and to fail. The components that make up the system are also all relatively well-proven technologies. The electricity output has been found to stay quite steady for years but may taper off over decades. Inverters are the devices that convert the direct-current (DC) electricity generated by PV systems to the alternating current (AC) electricity used in our homes and electricity grid. There have been a few reports of inverter failure, sometimes due to lightning strikes, but overall inverters have been performing well.

Performance data on PV systems monitored to date reinforces the idea that simple, south-facing, sloped roofs are the best locations for PV installations. Roofs that have complicated shapes, chimneys and overhanging trees that may shadow all or some of the PV modules will reduce electricity production and makes it more difficult to predict the output accurately.

We’ve also seen that the installed cost of a PV system has dropped at least 30 per cent in the last several years, making them more affordable. Estimates for grid-tie solar PV systems (without battery backup) range from $3,000 to $5,000 per kilowatt depend- ing on the local market prices, roof type and complexity, efficiency of the solar panels selected and overall size of the system. Larger systems will cost less per kilowatt than smaller systems.

For more information on photovoltaics and other sustainable technologies and practices and innovative housing projects, visit www.cmhc.ca or call Jérémie LeBlanc, CMHC’s Consultant in Research and Information Transfer, at 902-426-4715.




Canada Mortgage and Housing Corporation (CMHC) is Canada’s national housing agency. Established as a government-owned corporation in 1946 to address Canada’s post-war housing shortage,

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