The development of commercial grid-connected photovoltaic (PV) markets continues to be one of the hottest markets in alternative generation. From the experience gained with the PV system on Edmonton's Cold Climate Demonstration House, EPCOR developed a commercial PV project which they installed on the roof of their downtown office headquarters. The building's owners, Lehndorff Tandem Group and PV consultants Howell-Mayhew Engineering also contributed to the project.
The 13.4 kW grid-connected, building integrated PV system is the third largest in Canada, behind Ontario Hydro's 75 kW system at the Hugh McMillan Rehabilitation Centre in Toronto and CANMET's 20 kW system in Varennes, Quebec. And at twenty stories, EPCOR's PV system is the tallest building-integrated system in the world. Although height is of little significance to its electricity production, it did have (along with the downtown location) a considerable effect on design and installation costs.
EPCOR contracted with California's PowerLight Corporation to furnish the design and materials FOR the PV project.
The project goals include:
System Description
This is the first time in Canada that such a large PV system has been installed on the horizontal. Serious initial concern was expressed about the high potential for significant structural design and installation costs for a tilted system because of the wind loads and uplifts at that height. In addition, the building's owners would not permit roof penetrations nor any substantial weight additions. PowerLight's PowerGuardª roof system met all these concerns with a horizontal mounting weighing less than 20 kg-m-2 that had undergone extensive wind testing.
The system consists of 112 PowerGuard tiles mounted horizontally and interlocking seamlessly with walkable concrete-topped insulated Dow ROOFMATE CTª roof pavers. One was mounted on the raised penthouse of the building's roof, and one was mounted on the south west lower roof. The portion on the lower roof was split into three sections, with walkways to allow equipment-access to the roof edge for building maintenance activities such as window washing, caulking and any repair.
Only a small number of grid-connected inverters are available on the market. The array needed to be split into two 6.7 kW sub-arrays to suit the input voltage of the inverters selected for the system. The array is configured as two sub-arrays running at +218 VDC each of which feeds a 6kW AC Omnion Series 2400 inverter. The inverters feed into the building's electrical system through a breaker panel on the twentieth floor.
Unlike EPCOR's previous residential PV project, this project does not trigger any of the regulatory requirements of the Alberta Energy and Utilities Board, since it does not export its production beyond the building's property line. This is due to the array's small capacity (13.4kW peak) compared to the building load (100kW + minimum).
System Installation
Pallets containing the PV tiles were unloaded from transport trucks using a forklift and pallet jack. Work was done at night so as to minimize traffic disruptions and ensure public safety. Once unloaded, A mobile roof crane lifted the pallets from the street to the fifth floor mezzanine, where they were then lifted by a roof crane. The whole system was completed in under two days from contract to start-up, and installed in five days in late October 1996.
By connecting the array to the roof using tongue and grove joints with surrounding insulated roof pavers, no roof penetrations were necessary.
Because of the extreme potential for wind uplift, and the results of prEvious wind tunnel testing, the tiles and pavers were installed with an interconnected grid of 24 gauge galvanized-metal strapping between the rows of modules. The roof's top layer of gravel and insulation was removed, a new membrane was installed and the tiles and pavers were placed down. Installing the tiles was easy. The roof pavers were surveyed into position on the edge of the roof, then rows of PowerGuard tiles were laid down.
Performance
Though this is the tallest building-integrated PV system in the world, the height has no bearing upon its energy production or efficiency.
Downtown locations have potential restrictions to solar access by nearby buildings. In this project, the 33-story Telus tower to the south-east blocks the sun only for early portions of the spring, autumn and winter mornings. Otherwise the system has a clear view to the south and south-west. Several nearby buildings to the north and north-west are constructed of reflecting glass. Although this may at times increase the array's power production and may assist in removing snow, it is not expected to add a significant amount to its firm capacity.
The optimum angle for summer electricity production is between 20¡ and 53¡ latitude. While the horizontal mounting of the system does not lend itself to optimum electricity production in the winter, such generation was not the focus of the project's goals. For much of the winter the system is covered in snow.
Horizontal mounting allowed the designers to achieve the desired system capacity of 13.4kW over the available rooftop area. A significant drawback to tilting the modules is that row spacing needs to be increased to avoid module shading. This reduces the system capacity to a fixed area.
Figure 1 shows a WATSUN PV simulation of the system's performance for a typical meteorological year at array tilts of 0¡ and 40¡. Maximum annual electricity production would occur at 40¡. The system's annual simulated production is 13.6 MWh.
Plans are also underway to monitor the system's energy performance and the site's potential wind uplift. At this date, no monitored performance is available.
Conclusions
By strengthening their involvement in the PV industry, EPCOR Utilities has become a member of the American-based Utility Photovoltaic Group, a non-profit association of utility buyers of PV systems which have banded together to develop and implement market assurance strategies that will enable PV manufacturers to invest in the next critical round of cost reductions, while rewarding those utilities that have made the future happen through their early involvement.
EPCOR is now analyzing the Canadian market for PV to pinpoint commercial niches that the utility might serve. As a result of this project and Howell & Mayhew Engineering's Cold Climate Demonstration House project in 1995, they have been approached by some of their customers to assess PV opportunities for them. They are currently looking at six opportunities, all commercial applications of the technology.
Joel Nodelman and Tannis Tupper are with EPCOR Utilities Inc. Thomas Dinwoodie is President, PowerLight Corporation and Gordon Howell is President, Howell & Mayhew Engineering Inc. ET