September 1, 2003
by Jim Taggart
Now that Canada has ratified the Kyoto Accord, this country’s commitment to dealing with global climate change has become, implicitly at least, the cornerstone of a national energy policy. At the same time, as fossil fuel reserves decline, the autonomy and security of energy supplies is a growing concern for all nations. Decentralized, renewable and environmentally friendly sources of energy will play a key role in addressing these issues on a national and international scale. Of the emerging green energy technologies, Building Integrated Photovoltaics (BIPV) is the closest to achieving commercial viability in Canada.
What are BIPV?
Photovoltaic technology, which converts sunlight into electricity, was developed for NASA 50 years ago. Photovoltaic arrays first appeared in architecture in the 1970s, mounted conspicuously on the roofs of first generation solar houses. BIPV is the next significant step in the evolutionary chain, and the acronym covers arrays that are embedded in a variety of building envelope components.
The photovoltaic cells themselves are of two basic types: multi-crystalline which are more efficient and more costly, but which are rigid and can only be incorporated into flat sheet materials; and amorphous, which are less efficient and less costly, but which can be incorporated into formed or flexible components.
Under ideal service conditions BIPV represent one of the most efficient technologies in terms of energy payback. It takes on average only three to five years for a PV array to generate an amount of energy equivalent to that used in its manufacture. Most BIPV products come with a 25-year power generation warranty, although some PV arrays installed in the 1950s are still in operation. With a potential service life in excess of 50 years, BIPV offers the prospect of almost half a century of zero-impact energy.
BIPV in Europe and Japan
BIPV already has a strong market presence in Europe, particularly in Germany and Holland, encouraged by conventional energy prices several times higher than those in North America, and by substantial ‘green energy’ subsidies. Large installations of BIPV arrays, some capable of generating more than 1 gigawatt of electricity per annum, have been completed in market and non-market housing projects, and in commercial and institutional developments.
Green electricity is not subject to the European Union’s energy tax, and may also be sold to the electric utility at times when the power being generated is surplus to requirements. This latter benefit is possible because almost all European BIPV installations are designed to specifications that enable them to be connected to the national electricity grid.
In Japan there is a similar situation of high conventional energy prices and a comprehensive system of subsidies. Initially, to provide impetus to the market, subsidies for residential installations were 50% of the initial capital cost. As manufacturing capacity, commercial competition and consumer awareness increased, the subsidy was reduced to 10%. Currently, there are more than 120,000 residential BIPV installations throughout Japan.
Even with high electricity prices and the available subsidies, the capital and life cycle cost of BIPV in Europe is still higher than that of conventional energy. However, concern for the environment is such that a significant proportion of European consumers have been willing to pay this premium to ensure they are getting green energy. This concern is also evident in the corporate sector where many companies have installed photovoltaic arrays so as to present a green image to the public.
The range of BIPV products now available in Europe is considerable. Arrays embedded in components designed to look like and interlock with traditional profiled clay or concrete roof tiles have been used in new and heritage projects. A roll roofing product that contains integral flexible PV arrays has been used for roofing warehouses and large commercial buildings. BIPV components can be integrated into a variety of curtain wall systems, replacing either glass or cladding elements. In other architectural glass applications, BIPV can be used to replace fritted or other special glasses.
Prominent recent projects include Bill Dunster’s BedZed housing development in Hackbridge, England, in which the photovoltaic arrays in the sunspace glazing system provide power to recharge the fleet of electric cars owned by residents.
According to Dr. Ingo B. Hagemann, a leading expert in the field, photovoltaics in Germany have been incorporated into many high-profile projects. Among them are the new federal buildings in Berlin, including the Reichstag and the Chancellor’s Residence. The latter features a roof-mounted PV array generating up to 163kW/hour of green electricity.
In the Netherlands, Tjerk Reinjenga of Bear Architecten has incorporated PV arrays into a number of social housing projects across the country in which the electric utility owns and maintains the BIPV array on the roof, but the tenants benefit directly from reduced energy costs, and the sale of surplus energy back to the utility.
Photovoltaics operate at maximum efficiency when incident sunlight is perpendicular to the array, and when the cells themselves can be kept cool. While output is reduced at lower sun angles, tracking systems that enable the array to follow the sun’s path are rarely cost-effective. Given seasonal variations in sun angle and daylight hours, the optimal angle for a PV array varies with latitude and locale. In practice, most BIPV are installed on south and southwest facing vertical walls, and on flat or sloping roofs.
As part of an overall energy strategy for a building, the installation of BIPV can potentially conflict with other elements of that strategy, such as the planting of trees to provide summer shade to building faades. Photovoltaic arrays embedded in glass can of course be used as shading devices, replacing fritted glass in exterior louvers, vertical glazing systems, and skylights. Care should be taken to avoid shading the arrays. Usually, cells are connected in series, and even a slender shadow cast across the array can interrupt the flow of electricity and greatly reduce the output of the system.
Photovoltaic cells generate DC electricity and, if connected to the grid, must be fitted either individually or collectively with AC inverters. In large installations attention must be paid to cable management to ensure a neat finished appearance, taking care to allow for future maintenance access. The PV cells themselves are essentially maintenance-free.
Initially, PV cells came only in blue, which was the colour that resulted in maximum performance. Now, cells can be produced in almost any colour, and embedded in sheet materials screen printed (at a premium) to match. This gives the designer the freedom to either emphasize or suppress the expression of the BIPV arrays. Partly because it is cheaper, and partly because of the clients’ desire to be “seen to be green”, most contemporary installations emphasize the presence of BIPV arrays.
One of the aspects of green architecture that produces both economic and environmental benefits is the development of multifunctional building components and systems. BIPV falls into this category, contributing to the creation of a building envelope that is also part of the power generation system. When the cost of the building envelope component replaced by a BIPV is taken into consideration, cost comparisons become much more favourable.
BIPV in Canada
Despite a 30-year history in the use of photovoltaic technology, on an annual basis Canada installs fewer megawatts per capita of BIPV than any other G-8 country. For the most part, the technology has been employed in remote locations such as fishing camps lighthouses or summer cottages. In brief, buildings that are away from a grid-distributed electrical supply. The situation is changing however. For example, in British Columbia, the research and testing program at the BC Institute of Technology
has laid the foundation for the emergence of off-grid PV technology as an urban phenomenon in projects such as Busby + Associates’ Telus Building in downtown Vancouver, where stand-alone PV arrays power fans that assist in the ventilation of the building’s double skin exterior wall system.
Currently, there are technical and non-technical impediments that discourage grid connected PV systems in Canada. As a result, only 2% of our PV capacity is nominally grid-connected. The federal government’s CANMET Energy Technology Centre in Varennes, Quebec is working to address these issues which include: regional power authority standards, building code compliance, and the lack of a local PV industry and infrastructure. CANMET is involved nationally and internationally in a variety of related initiatives designed to increase consumer awareness and stimulate the Canadian PV industry. It has worked in partnership with Canadian companies to develop a variety of new products including a PV curtain wall system, and new technologies such as a silicon based spherical PV cell that combines the efficiency of multi-crystalline PVs with the flexibility of amorphous systems.
CANMET’s current focus is on grid-connected BIPV, and it has two innovative projects under construction: a 10-15 unit housing project in Kitchener/Waterloo, developed in partnership with Cook Homes, that includes a grid-connected BIPV roof tile system, designed by Arise Solar Technologies Inc., and a 20kW/h PV faade on Goodwin Hall at Queen’s University in Kingston, Ontario, designed in consultation with the leading US architect in this field, Steve Strong of Solar Design Associates.
It is hoped that these projects will be the catalysts in a chain reaction that will see increased public and professional awareness translate into a widespread demand for green energy alternatives, and the removal of technical and legislative barriers to grid-connection. Financial incentives will undoubtedly be needed to encourage utilities to pursue green alternatives to traditional forms of energy generation, and to bring these choices to the marketplace.
Ultimately the success of BIPV, and other green energy alternatives, will hinge on our ability as a society to transform our narrow fixation with initial price into a broader concern with environmental cost and long-term value.
Jim Taggart is a contributing editor at Canadian Architect. The information gathered for this article was obtained at the University of British Columbia Workshop on Building Integrated Photovoltaics, which took place in June, 2003. Workshop presenters included Dr. Ray Cole, University of British Columbia, Eric Smiley, British Columbia Institute of Technology, Josef Ayoub, CANMET, Tjerk Reijenga , Bear Architecten, Netherlands, Dr. Ingo B. Hagemann, Germany, and Steve Strong, Solar Design Associates, USA. For more information, visit www.architekturburo-hagemann.com, www.task7.org and www.pvportal.com
A close view of the PV array at the top of the building
PV arrays power fans that assist in the ventilation of the building’s double skin exterior wall system.