Summary: Among the many educational opportunities at the AIA 2007 National Convention and Design Exposition will be free continuing education presentations on the Expo2007 show floor. As a sample, AIArchitect offers a discussion of a roof-system-integrated, self-adhering photovoltaic membrane manufacturer that provides design guidance for building-integrated solar-power systems.

Photovoltaic systems are in demand, note United Solar Ovonic engineers Doris Harber-Hollins and Terence Parker. “Architects come to a manufacturer when they have clients who are looking to do solar with their roofing solution. They look for help identifying what kind of roofing material they can use and what system configuration they need. The manufacturer teaches them how to design the system, get it installed, and integrate their roofing solution with the material” says Harber-Hollins.

PV begins in design
The architect’sinitial considerations are budget, roof size, and the percentage of the building’s predicted energy load the client wants the array to provide, Parker says of the product-integration service the company has been offering for a decade.

System components, he explains, include a direct-current (DC) disconnect for the solar panels; an inverter, to convert DC to alternating current (AC); and AC disconnects between the inverter and the connection to the building’s AC service panel.

“One of the great things about PV systems is that after the system is turned on, the inverters will work automatically,” he says. “The solar panels don’t have any moving parts. They are either in the sun or not in the sun. Unlike other power-generating systems, you don’t need someone to watch the solar system. If something malfunctions, it just shuts down.

“Roofers put on the specified underlayment, and electricians make the connections. The integrated system has to perform as a roof first, and as a solar generator second. So we encourage the roofer to get involved to leverage their installation labor for the installation of the solar modules.”

They also look to integration of the PV modules into the roof as a cost-saving measure. “If you look at the cost of a PV system, on average the modules account for 55 percent; the inverter is maybe 7 percent; the balance of system components, such as wires, fasteners, and conduit, is 7 percent; indirect cost such as engineering, staging, and freight are 6 percent; and the labor is 25 percent. Indirect costs are fairly stable, so manufacturers work on the installed cost of PV systems through product innovation and connecting solar-panel installation with installation of the roof. Moreover, as the substrate or structure of the PV system, the roofing system might be included in the PV rebate calculation.”

Paying for PV with a PPA
The most complicated part of installing a PV array for the client comes in financing the system, Parker says. “Metal or membrane roofing alone might be $4 to $12 per square foot, installed. The same roofing integrated with a solar energy system might be between $15 and $40 per square foot, installed. So, because of the high capital cost, there is usually some sort of financing arrangement.”

One is a power purchasing agreement (PPA) where a financier owns the system and sells power to the building owner at a set rate as an operating expense. The contract may be fixed for the 20-year warranted life of the system, and, after 5 or 6 years, the financier may provide an option to turn the system over to the building owner. In the cost/benefit analysis, the attributes are not just the power, Parker notes. There may also be carbon dioxide and property depreciation tax credits to consider.

Another element is how a state regulates selling power to the utility. Most states offer net-metering: the owner receives the retail value of the kW hours put onto the grid, as opposed to some avoided-cost value that the utility company sets. In all 50 states, though, Parker says, owners are allowed to connect a solar-energy system to the grid, usually with an interconnection agreement with the utility.

Many solar-panel manufacturers are also well-suited to provide battery-based PV-power systems as well as on-grid systems, Parker says, though batteries require maintenance; add significant cost in installation, housing, and security; and present a higher threat of electrocution. Parker estimates that 80 percent of PV systems are on-grid and that those systems are at least 20 percent cheaper than battery-backup systems. “And there is zero maintenance with properly operating on-grid systems.”