Building integrated photovoltaic (BIPV) roofs for sustainability and energy efficiency

Objective

The objective of this project is to demonstrate and validate the building integrated photovoltaic (BIPV) roof concept by verifying whether an energy efficient roof and a solar photovoltaic system can be acquired with a roof that performs comparably to that of conventional roofing systems. This project will investigate whether a BIPV roof system is structurally sound, should not leak for 20 years under normal maintenance and repair, and can provide large-scale on-site renewable energy generation. If the system performs successfully, a Unified Facilities Guide Specification (UFGS) and Whole Building Design Guidance (WBDG) document for the installation of this technology will be developed to accelerate its adoption.

Technology Description

Crystalline silicon-based PV technology is currently the most common PV material used in medium- to large-scale systems. However, thin-film PV, which uses relatively little to no silicon, is starting to gain acceptance and has had some success in building integrated applications. Thin-film PV material currently has lower energy conversion efficiencies than crystalline silicon PV. However, the cells can be produced at lower temperatures, deposited on low-cost substrates, and can generate more energy than the energy used to produce the system when compared to crystalline silicon-based PV technology. For one form of BIPV, thin-film PV modules are factory applied to an Energy Star-rated photovoltaic control (PVC) roofing membrane material. To install these panels, the conduit for the PV system and the roof insulation layer are first concurrently installed, followed by the installation of a layer of the PVC membrane used with the previously prepared PV panels. Finally, the PV panels are connected to the conduit, then heat welded to the PVC membrane to form an integrated roofing system. This design minimizes the concerns of exposed wiring and roof penetrations associated with the installation of many rooftop PV systems.

Benefits

Facilities can become more sustainable and renewable energy systems more cost-effective if facility retrofit projects utilize an integrated approach. Replacing an old, inefficient roof system with new insulation, an Energy Star-rated roof membrane, and integrated renewable energy is an approach that can provide a positive return on investment. Low sloped reroofing costs range from $15-20 per square foot. Depending on the size of the PV system and roof, a BIPV roof can cost up to about $40 per square foot. Utilizing the avoided reroofing cost to fund the installation of a BIPV roof and sizing the PV system to the solar resource can result in a short payback period and provide immediate environmental benefits. Department of Defense (DoD)-wide implementation of this technology has the potential to increase energy security, generate renewable energy certificates to meet DoD renewable energy goals, decrease energy consumption by reducing building interior cooling loads, reduce greenhouse gas emissions, improve air quality, and lower building life-cycle costs. To maximize benefits associated with this technology, the project will provide guidance on system implementation. (Anticipated Project Completion - 2011)