Taking in the Sun
March 1, 2007
By Virgina Heffernan
Solar power has been providing electricity and heat to Canadian buildings in a limited way for decades. But the technology has been receiving greater attention as its costs fall and the pressure to re...
Solar power has been providing electricity and heat to Canadian buildings in a limited way for decades. But the technology has been receiving greater attention as its costs fall and the pressure to reduce greenhouse gases intensifies.
Buildings in the residential and commercial-institutional sectors account for about 30% of Canada’s final energy consumption and 29% of the country’s greenhouse gas emissions, according to Natural Resources Canada. Commercial and institutional buildings are the biggest consumers, with demand growing at a rate approximately twice that of the residential sector.
Solar power can service commercial buildings in three main ways: by heating air, by heating water and by generating electricity. Whereas the associated capital costs were once considered prohibitive except for applications in the most remote sites, interest has been growing in grid-connected applications as costs go down. The cost of photovoltaic (PV) modules, for instance, has declined by more than 63% since 1999, according to the Canmet Energy Technology Centre of Natural Resources Canada.
The zero energy dream: Canada tries to catch up
In the U.S., the Department of Energy’s goal is to create the technology for marketable, commercial buildings that use zero net energy from the grid by 2025. Programs such as the Solar America Initiative suggest Washington believes solar power will play a significant role in achieving this goal. California has gone even further, providing US $2.9 billion to fund new solar systems over the next decade
Canada lags behind, ranking 14th out of 20 reporting countries in photovoltaic applications and 17th out of 22 reporting countries for use of solar thermal technology for water and air heating, according to the Canadian Solar Industries Association.
But although low energy costs in this country continue to hamper the development of alternative energies, solar power is beginning to gain respect. The federal government recently announced it would continue a program that provides 25% of the capital costs to companies installing solar thermal technology. At the local level, the Green Municipal Fund has announced a $250,000 grant towards the installation of the largest solar photovoltaic system in Canada — a 100-kW photovoltaic system on the rooftop of the Horse Palace of Toronto’s Exhibition Place. Also near Toronto’s waterfront, Arise Technologies is designing Canada’s largest solar research facility at the Portlands Energy Centre. The 500-1,000 kW plant will incorporate technology developed by Arise and the University of Toronto. The researchers’ task will be to find ways to increase the use of PV systems on a commercial and utility scale.
Meanwhile, the National Sciences and Engineering Research Council is funding the Solar Buildings Research Network, a group of 24 researchers from 10 universities. The researchers are charged with developing solar-optimized homes and commercial buildings. Their approach is to integrate different thermal and electrical technologies to create combined energy efficiencies of about 80%.
Facades as solar power plants
The goal of these initiatives is to develop practical and cost-effective solar power systems that can be integrated into building design. The challenge for engineers and architects will be to work together to incorporate these systems into buildings.
“Buildings of the future will have high quality dynamic facades that will automatically adjust their properties to optimize their energy performance and indoor environment while allowing occupant intervention as well,” says Professor Andreas Athientis, P.Eng. of Concordia University, scientific director of the Solar Buildings Research Network. “Architects are typically responsible for the building envelope, but a dynamic envelope becomes an energy system and they need to work closely with a knowledgeable engineer.”
Athienitis says daylighting — using glazing and reflective surfaces so that natural sunlight provides illumination inside the building — is the most common solar energy source in Canadian buildings. But because it is not always integrated with the electrical and thermal design, daylighting it not as effective at reducing energy consumption as it could be.
The network’s goal is to develop facades and roofing materials with photovoltaics that can (a) generate electricity, (b) control the transmission of daylight with advanced glazings and shading systems, and (c) possibly also pre-heat fresh air. The ultimate dream is a building that approaches a “zero energy” target (i.e. it consumes no energy from the grid), while being cost-effective.
Advanced glazings, Athienitis explains, could be glazings with electrochromic coatings or transparent insulation. They might incorporate blinds with specific directional characteristics. A small PV panel that also acts as an overhang could power a motor for the blind. Existing curtain wall structures can be readily adapted to fit the glazings and incorporate these systems, he suggests. No extra support is needed, but inlets and outlets have to be designed for airflow.
By integrating solar technology into building roofs and facades, the static building envelope becomes a dynamic solar energy conversion device and an integral part of the building’s heating-cooling system, says Athienitis. The investment in the advanced solar facades means the engineers can reduce the size of the HVAC and lighting systems, giving substantial savings. A lot of work that the solar research network is doing is on how to integrate and link new solar technologies into more conventional HVAC and automated controls.
But optimizing building design to reduce energy consumption will require better simulation and design tools, one of the four main objectives of the Network’s program. Good building design optimizes the orientation and form of a building to achieve the best thermal and daylighting performance. The network hopes to develop a prototype design tool that integrates solar energy factors with all the building parameters at the early design stages.
Perforated plate cladding for warmth
The Canadian climate provides an opportunity to capitalize on solar air heating, whereby outside air is preheated before it is introduced and distributed through the building. A simple and efficient way to do this, according to Natural Resources Canada, is through a perforated-plate absorber.
Using the perforated-plate technology, sunlight hits dark metal cladding mounted on a wall (usually south-facing) and warms the air near the cladding’s surface. The warmed air is then drawn through thousands of perforations in the cladding into a narrow space between the cladding and the building’s wall. The air rises to an overhanging canopy, where fans and dampers draw it into the building’s ventilation system.
Another benefit of this system is that the plenum, or air gap, between the wall and the cladding also captures warm air flowing out of the wall, providing an insulation effect that is equivalent to doubling the RSI-value of the existing wall.
The SolarWall, for example, is a patented solar heating system designed in Canada that was introduced in 1994 and is now installed on buildings in Canada and around the world. The system is said to give energy savings of $20-60 per square metre of wall.
Solar collectors on a Calgary residential building
Solar collectors used to heat water include glazed flat-plate collectors and evacuated-tube collectors. The latter are more efficient in cold climates, but are less popular among architects because they cannot be incorporated into the facade as seamlessly as flat-plate collectors, says Richard Outtrim, P.Eng., a mechanical engineer for Reinbold Engineering Group in Calgary.
Take Calgary’s Gateway Southcentre, a 500-unit residential building engineered by Reinbold and designed by Poon McKenzie Architects for Resiance Corporation. The building has 148 flat plat sol
ar collectors on the roof, which are capable of heating water to 90o C on sunny summer days. The heated water is stored in a large insulated tank and delivered to each suite under city water pressure, and with a small recirculation pump. The primary function of the solar collectors is to provide hot water to the suites, but they also provide some supplementary heat to the building’s heat pump loop system (which involves 330, 230-ft. deep boreholes and vertical heat pumps in each suite). The project’s solar contractor is Swiss Solar Tech.
Using PV systems as a building material
Photovoltaic energy, the conversion of sunlight into electricity through a solar cell usually made from silicon alloys, is also gaining ground as the price drops and systems become increasingly efficient. In 1999, PV modules cost about $11 per watt. According to the Canmet Technology Centre, the costs of PV drop 15-20% for each doubling of market size, and it now costs about $4 per watt.
A recent “Evaluation of the Potential of Building Integrated Photovoltaics in Canada” by Natural Resources Canada’s Canmet Energy Technology Centre (Sophie Pelland and Yves Poissant) concluded that photovoltaics on the roof and facades of a commercial or institutional building with a ground floor area of 915 square metres had the potential of generating 78 MWh, reducing the building’s energy consumption by 15-17% and reducing greenhouse gas emissions by 16 tons per year.
“PV is limited in what it can do, but it can clad the whole side of a building within 50 feet of the load,” says Per Drewes, principal of Newmarket-based Sol Source Engineering and a former electrical system designer for Ontario Hydro.
Using PVs in this way — as part of the building material instead of just an add-on energy source — can reduce the costs of solar power considerably. Solar modules cost $100-125 per square foot, but curtains walls and quality glass windows can cost $25-50 per square foot. So by replacing conventional walls with PV modules, the cost of going solar can drop by 30-50%.
Drewes says the biggest technological breakthroughs in the PV field recently may relate to the inverters that convert DC power to AC electricity. These are usually the most expensive components of a PV system.
“Invertors have come a long way in terms of price and reliability,” says Drewes. Reliable inverters ensure that power is switched off when, for instance, lines are being repaired. As a result, utilities are more likely to allow decentralized sources of power such as PV systems to be connected to the grid.
What does Drewes, a veteran of the PV business who installed his first PV system in the remote bush in 1979, think of the dream that one day commercial buildings could be self-sustaining or “zero energy?”
“It’s a good target to shoot for, but the last 10% is almost impossible. It’s a lot better and a lot easier to reduce 10 buildings by 10% than one building by 100%.”
Virginia Heffernan is a freelance writer based in Toronto.