Hygrothermal impact of adhesive-applied rooftop photovoltaic system

Adhesive mounting of photovoltaic (PV) modules on residential roofs can significantly reduce the installed cost. The potential for undesirable moisture buildup under the module, however, may reduce shingle life and degrade the underlying roof elements. High moisture levels in roof elements may also adversely affect the energy performance of the building. This study investigates whether an adhesively mounted PV system causes a preferential moisture buildup under the module on an asphalt shingle roof. Lightweight PV modules were adhesively mounted on half of the roof of an instrumented test hut located in Boston, MA. Moisture pin sensors, installed in various locations of the roof deck, determined the moisture content (MC) of the wood in the roof assembly. The MC is found to follow a seasonal pattern: lower values (7-11 %) during the summer and higher values (11-15 %) during the winter. MC measurements during the winter and summer seasons showed no adverse impact of the adhesive-mounted rooftop PVs on the hygrothermal behavior of the underlying roof deck element over the 1-year measurement period

Thermal impact of adhesive-mounted rooftop PV on underlying roof shingles

Adhesive mounting of residential rooftop photovoltaics (PV) is an alternative to traditional rack mounting that reduces installation costs. Adhesive mounting is fast, simple and reduces the need for skilled labor. In our novel design that further reduces the installation costs, a lightweight (glassless and frameless) PV module is directly adhered to a shingled roof using an adhesive tape, creating a <5 mm air gap between the PV back-panel and the roof shingle surface. Although the gap is sufficient for moisture and rainwater transport under the PV panel, potential heat buildup under the module may adversely impact the long-term durability of the shingles. Heat buildup may also increase the heat flux through the roof, resulting in an overall increase in building cooling loads. This study investigates the thermal behavior of the roof under an adhered PV system. Two identical test huts with dark shingle-covered roofs were located in the hot, desert climate of Albuquerque, NM. Adhesively-mounted lightweight PV modules were installed on the south-facing roof of one of the test huts (PV hut), with the other one serving as a reference hut. During the summer season, the asphalt roof shingles under the PV modules experienced a 13 °C reduction in daytime peak temperature compared with the exposed shingles. No evidence of heat buildup under the PV module was observed. It was also found that the temperature of shingles underneath the adhesive was up to 6 °C higher than for shingles underneath the gap space at the daily peak time. Thin but ventilated air gap between the PV back-panel and the roof shingles helped remove the heat, while the adhesive pads (patches) served as thermal bridges between the PV module and the roof. Daily peak heat flow through the attic ceiling was almost 49% lower in the PV hut compared to the reference hut. These results show no evidence of an adverse thermal impact of the adhesive-mounted PV system on the roofing materials, while demonstrating a potential for a notable reduction in space conditioning energy requirements

Residential solar systems as an appliance - Plug and Play PV

The DOE SunShot-funded Plug and Play PV project seeks to dramatically reduce the soft costs of US residential solar by simplying the installation and commissioning processes. Adhesive mounting of lightweight (frame-less, glass-less) modules is one technology being studied. Temperature concerns due to the small gap between the shingled roof and the adhered module are examined in field testing in Albuquerque, NM. Compared to a conventional module, a 3% yield loss was measured after one year of data collection. The temperature of shingles underneath the adhered modules are lower than those for exposed shingles indicating that the modules cool the roof during sunlight hours. Modeling of the attic thermal profile demonstrates an average drop in the attic air temperature of 1°C in hot climates

Mechanical load testing of solar panels - beyond certification testing

Mechanical load tests are a commonly-performed stress test where pressure is applied to the front and back sides of solar panels. In this paper we review the motivation for load tests and the different ways of performing them. We then discuss emerging durability concerns and ways in which the load tests can be modified and/or enhanced by combining them with other characterization methods. In particular, we present data from a new tool where the loads are applied by using vacuum and air pressure from the rear side of the panels, thus leaving the front side available for EL and IV characterization with the panels in the bent state. Tightly closed cracks in the cells can be temporarily opened by such a test, thus enabling a prediction of panel degradation in the field were these cracks to open up over time. Based on this predictive crack opening test, we introduce the concept of using a quick load test on each panel in the factory as a quality control tool and potentially as a type of burn-in test to initiate cracks that would certainly form early on during a panel's field life. We examine the stresses seen by the cells under panel load through Finite Element Modeling and demonstrate the importance of constraining the panel motion during testing as it will be constrained when mounted in the field

Effect of Stretching on the Structure of Cylinder- and Sphere-Forming Styrene-Isoprene-Styrene Block Copolymers

Two styrene-isoprene-styrene block copolymers Vector 4111 and 4113, exhibiting cylindrical (18 wt % PS) and spherical (16 wt % PS) morphology, respectively, have been examined under uniaxial elongation up to 200% strain. On the basis of stress-strain data, mechanical properties are compared for isotropic and oriented polystyrene domains. The structure at various stages of deformation has been determined from SAXS patterns in three planes and two principal deformation directions with respect to orientation. Samples showed a very high degree of hexagonal packing, resulting in an X-ray pattern taken parallel to the cylinder alignment approaching single crystal ordering. Cylinders were aligned with the closest packed planes parallel to film surface. Particular attention has been paid to a lattice deformation process occurring during the first stretching and relaxation cycle. For a copolymer with oriented cylindrical morphology the deformation was affine up to 120% strain. The microdomain spacing was calculated parallel and perpendicular to the stretching direction. The cylindrical microstructure orientation, quantified by Hermans' orientation factor reduced during elongation of oriented polymer, while the elongation of isotropic sample caused an increase of orientation. Deformation of all studied morphologies was reversible