Electricity From Your Roof - Lessons Learned From Canadian PV Installations

Real Estate — January 11, 2013

OTTAWA, ONTARIO--(Marketwire - Jan. 11, 2013) - 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 and 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 to the homeowners who install them.

Lessons learned

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 security 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. If they say that you are going to produce 3,000 kilowatt hours (kWh) every year, this will be very close to what you will get in any given year from a properly designed and installed system though weather fluctuations will impact performance from one year to the next. A good initial estimate will help you to figure out how much you might earn from a PV system over time.

Another lesson learned about 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. It is comforting to know, given the relatively large investment you have to make to get a PV system installed on your home, it should have steady and predictable performance for many years to come.

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. When such conditions exist, PV modules that have their own integrated inverters (rather than one central inverter) can be a better choice as if one PV module is shaded, the other unshaded modules will continue to produce electricity. Another benefit of integrated inverters is that your electricity output will be relatively higher. While south facing roofs are best, you can still install PV systems on roofs that face east or west. The electricity output will be lower but sometimes the decrease is only 10-20 per cent and the revenues may still justify the capital costs. The slope of the roof will also affect output, with flatter roofs working best in summer and steeper roofs in winter.

Experience is also showing that snow and ice don't just make it more difficult to get to work in the morning - they also impact on the electricity generating capacity of PV systems. Originally it was thought that snow would slide off the slippery glass surfaces of the PV modules, but experience is showing that this doesn't always happen. Canadian houses can have periods of winter, up to months in a row, where snow coverage can reduce PV electricity output to near zero. Wet snow followed by a freeze is particularly troublesome as the frozen snow sticks hard to the PV modules.

Fortunately, snow accumulation usually does not result in a big decrease from the predicted overall annual PV output estimates. Mid-winter PV output is already low because of short days, low sun angles, and frequently overcast conditions and the snow effects happen when the potential PV output is lowest anyway and this reduces the impact. If you were off-grid and dependent totally on PV output for your electrical needs, preventing snow coverage would be much more important.

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 depending 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. Whether or not investing in a PV system makes financial sense will depend on what your local utility offers for the electricity it produce,s so find out before you invest. For some, knowing they are generating clean energy is enough to make the investment worthwhile.

So if you are thinking about installing a PV system, having a simple, unshaded, south-facing, sloped roof on your house is a good start. If the province, municipality or utility where you live offers financial incentives for residential PV systems, this can make the purchase even more attractive. Regardless of why you choose to install PV, recent evidence suggests that these systems are predictable, reliable, and durable. Photovoltaics in Canada have come of age.

For more information on photovoltaics and other sustainable technologies and practices and innovative housing projects, visit Canada Mortgage and Housing Corporation's website, www.cmhc.ca.

For over 65 years, Canada Mortgage and Housing Corporation (CMHC) has been Canada's national housing agency, and a source of objective, reliable housing information.

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