Building Integrated Photovoltaics
The Solar Ark outside one of Sanyo’s Japanese factories has over 5,000 PV panels generating 530,000kWh annually, which is the energy equivalent to 128,610 litres of petroleum, and representing a CO2 reduction of 95 tons/year. [Courtesy Sanyo Canada Inc.]
by Josef Ayoub .Decentralized, renewable and environmentally-friendly sources of energy will play a key role in reducing our dependence on fossil fuels. Of the emerging green energy technologies, Building Integrated Photovoltaics [BIPV] is one that is approaching commercial viability in Canada.
What is BIPV?
Photovoltaic technology, which converts sunlight into direct current electricity, was developed for NASA 50 years ago. Photovoltaic arrays first appeared in terrestrial 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 silicon which is more efficient and more costly, but which is rigid and can only be incorporated into flat sheet materials; and amorphous silicon, which is less efficient and less costly, but which can be incorporated into formed or flexible components.
Under ideal service conditions BIPV represents one of the most efficient technologies in terms of energy payback, in part because it displaces some of the conventional building material. 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.
Design Considerations
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 have rarely been 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 is 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 may potentially be in conflict with other elements of that strategy, such as the planting of trees to provide summer shade to building facades. Building-Integrated-Photovoltaic arrays embedded in glass can of course be used as shading devices themselves, replacing fritted glass in exterior louvre vertical glazing systems and skylights. 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 modules [panels of individual cells strung together] generate DC electricity and, if grid connected, 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 modules themselves are essentially maintenance free.
PV 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 either to emphasize or to suppress the expression of the 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. Building-Integrated-Photovoltaics 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 35-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. Over 90% of PV installed to date is in remote locations such as fishing camps, lighthouses or summer cottages, away from grid distributed electrical supply.
There remain some technical and non-technical impediments that discourage grid connected PV systems. National Resources Canada’s [NRCan] CANMET Energy Technology Centre in Varennes, QC 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.
NRCan 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.
NRCan’s recent focus has been on grid-connected BIPV. In addition to the Government of Canada Building in Yellowknife [see Case Study] it has completed other innovative projects: a-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 facade on Goodwin Hall at Queen’s University in Kingston, Ontario, designed by Solar Design Associates [US] and supplied by ATS/Photowatt.
It is hoped that these projects will demonstrate the viability of BIPV technology in a variety of applications and lead to an increased demand for green energy alternatives, and the removal of technical and legislative barriers to grid-connection. Financial incentives will undoubtedly be needed to encourage owners or utilities to pursue green alternatives to traditional forms of energy generation, and to bring these choices to the marketplace.
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Emerging BIPV Technology
Although probably three to five years from widespread commercial application, and with less than 1% of the world PV market in 2006, a new super-thin-film PV technology developed by Helio Volt of Austin TX, known as CIGS [Copper Indium Gallium Selenide] is nonetheless causing excitement in the green power sector.
While there remain some technical hurdles to be overcome in the application of CIGS at the scale of the fully integrated modular building component, test results on the individual solar cells promise greater efficiency, lower fabrication costs, and more design flexibility in geometry, base material and colour. Over the next several years, the refinement of CIGS will undoubtedly improve the cost competitiveness of BIPV, resulting in more widespread application and even mainstreaming of the technology.
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Case Study: Government Building, Yellowknife
by Vivian Manasc
.The four-storey, 7,200 sq.m Government of Canada building in Yellowknife NWT, opened in the fall of 2005, houses 200 public service employees, and is the first project “north of 60” to seek LEED Gold Certification [in progress].
Energy modelling was used from the start of the integrated design process, to optimize daylight, as well as energy performance. A south-facing atrium has given Yellowknife a unique public amenity, while creating a sun-trap for the benefit of those working in the building.
The south facade had originally been conceived as a high performance curtain wall system with exterior aluminum shading devices, and it was not until the design development stage that the idea of BIPV first arose. Although it was recognized that these systems are not usually cost effective given current energy pricing, the annual solar profile for Yellowknife was particularly encouraging.
The new direction was confirmed when discussions with NRCan revealed that leading curtain wall manufacturer, Visionwall, had received funding from its TEAM [Technology Early Action Measures] Program to investigate the integration of PV cells into its high performance glazing systems and needed a building project on which to test the technology.
The curtain wall of the atrium now comprises a BIPV system in which photovoltaic elements are sandwiched between two layers of glass in the exterior elements of a high-performance four-part glazing system. In plan the wall forms a quarter circle with a radius of 32.5m. The 35 kW installation is the largest BIPV curtain wall system in Canada, and generates more than 5.5% of the building’s annual energy needs.
Financial and Technical Considerations
There was no additional capital budget available for the BIPV. Preliminary calculations suggested that the base budget for the building, plus the cost of the BIPV array, minus the cost of the sunshades, could be balanced by the available funding from TEAM.
The construction and installation of this wall presented a logistical challenge, with the PV glazing panels being fabricated in France, tested at BCIT in Burnaby BC, assembled into prototype frames and re-tested in Edmonton at the Alberta Research Council, prior to final shipping and installation in Yellowknife.
Architectural considerations
Architecturally it was necessary to address the need for daylight and shade, the need for views through the glazing, and the need to balance the visual monotony of the photo-voltaic array that consisted of circles on the outside, and a grid pattern on the inside. Ultimately, it was decided to alternate bands of clear glass with bands of PV glass, giving the exterior facade a layered appearance.
In-Service Observations
The BIPV is performing well so far. The array provides a satisfactory level of light and shade in the atrium. The dappled appearance of the interior is attractive, and there have been no complaints of overheating. The exterior appearance could be refined, however, and should in future be studied more carefully.
Although the present high cost of photovoltaic technology limits the market for BIPV curtain wall, this market could grow dramatically as economic conditions change. Continuing Natural Resources Canada support will ensure that the technology is market-ready.
As the market demand for this technology increases, prices will come down, rendering this and other green technologies cost-effective mainstream solutions. It is important for government to continue to support demonstration and pilot projects, to showcase the potential of this technology. Indeed, Canada has an opportunity to lead the world in the research, development and implementation of BIPV, especially in cold-climate applications.
Credits
- Architect: Manasc Isaacs Architects, Edmonton
- Energy Engineer: G.F. Shymko & Associates Inc., Calgary
- Electrical Consultant: Crossey Engineering, Toronto