Today energy-efficient and energy-harvesting buildings experience an ever-increasing interest and demand. Building integrated photovoltaics (BIPV) may in this respect represent a powerful and versatile tool for reaching the goal of zero energy and zero emission buildings. The BIPV systems replace the outer building envelope skin, thus serving simultanously as both a climate screen and a power source generating electricity. However, snow and ice formation on the exterior solar cell surfaces reduce their performance and may also lead to faster deterioration. Hence, if one could find a way to develop solar cells which were able to avoid snow and ice formation on their surfaces, one would have moved a large step ahead. This work presents a review exploring miscellaneous pathways for avoiding snow and ice formation on solar cell surfaces including superhydrophobic and icephobic surfaces.
The effect of elevated temperature during storage and curing of ultra-high performance concrete (UHPC) formulated aerogel-incorporated mortar (AIM) samples was investigated. It was found that an effective aerogel loading of 60 vol% of total bulk volume was possible for producing AIM samples with suitable thermal and mechanical properties under optimized storing and curing conditions. AIM samples with compressive strengths of up to ≈19 MPa was achieved and the corresponding thermal conductivity was ≈0.4 W/(mK). For more insulating concrete, 70 vol% aerogel was needed and AIM samples with thermal conductivity as low as ≈0.1 W/(mK) were cast. In general, AIM samples with strengths of up to 5 MPa can be achieved when thermal conductivities of between 0.1 and 0.2 W/(mK) is desired. The obtained results here estimates that there is potential in improving the AIM samples to produce structural and insulating concrete through modification of storing and curing conditions to achieve the desired requirements of a thermal conductivity value of <0.1 W/(mK) with a corresponding compressive strength of >20 MPa.
Calcined marl was identified as an insulating binder substituent mate-rial for aerogel based mortars. Further synthesis of insulating organo-nanoclays through the incorporation of polyethylene glycol (PEG) or in situ polymerisation of polystyrene (PS) in clays displayed greater promises for further reduction of thermal conductivity independent of the compressive strength, unlike more con-ventional aerogel-incorporated concrete. The organo-nanoclays were characterized by Hot Disk thermal analyzer measurements. The results so far indicated the for-mation of organoclay particles from both ideal systems of bentonite and calcined marl with lowered thermal conductivities. The calcined clay appeared to maintain its binding properties, suitable for gelling excess aerogel together in the concrete matrix. Ultimately, the final hydration mix of aerogel, calcined clay-polymer binder, organo nanoclays and cements is targeted to form novel concretes with re-duced thermal conductivity comparable to existing insulating materials, while maintaining strengths of 20 MPa after 28 days of curing.
The application of superinsulation materials (SIM) reaching thermal conductivities far below 20 mW/(mK) allows the construction of relatively thin building envelopes while still maintaining a high thermal resistance, which also increases the architectural design possibilities for both new buildings and refurbishment of existing ones. To accomplish such a task without applying vacuum solutions and their inherit weaknesses may be possible from theoretical principles by utilizing the Knudsen effect for reduced thermal gas conductance in nanopores.
This study presents the attempts to develop nano insulation materials (NIM) through the synthesis of hollow silica nanospheres (HSNS), indicating that HSNS may represent a promising candidate or stepping-stone for achieving SIM. Furthermore, initial experiments with aerogel-incorporated concrete and the conceptual work concerning NanoCon are presented.
Improvements to concrete will have a large impact in the construction and building sector. As the attention is drawn towards energy-efficient and zero emission buildings, the thermal properties of concrete will be important. Attempts are being made to decrease the thermal conductivity of concrete composites while retaining as much as possible of the mechanical strength. In this study experimental investigations of aerogel-incorporated mortar (AIM) with up to 80 vol% aerogel are prepared utilizing a reduced ultra-high performance concrete (UHPC) recipe. It was found that at 50 vol% aerogel content, the AIM sample possessed a compressive strength of 20 MPa and a thermal conductivity of ≈0.55 W/(mK). This strength decreased by almost a factor of 4–5.8 MPa, while gaining only a 20% improvement in thermal conductivity when aerogel content increased to 70 vol%. No preferred gain in properties was observed as compared to a normal mortar system. This can be attributed to the imbalance of the particle–matrix ratio in the mortar system, causing a decrease in adhesion of the binder-aggregates. The AIM samples have been characterized by thermal conductivity and mechanical strength measurements, alongside scanning electron microscope (SEM) analyses.