The impact of mirror shape on energy production in Skyline Solar's reflective trough medium concentration photovoltaic system is reviewed using a combination of commercial and proprietary modeling tools. For linear concentrators, an important parameter for efficiency optimization is the uniformity of the flux line on the photovoltaic cells. A significant source of nonuniformity is the discontinuity of reflected light due to the gap between mirrors along the length of the trough. Standard concentrating solar power trough mirrors have a typical length of 1.5 m with a gap between mirrors of 10 to 20 mm. To reduce nonuniformity of the flux line due to this mirror to mirror gap, Skyline Solar developed a dual curvature mirror that stretches the flux line along the trough axis. Extensive modeling and experiments have been conducted to analyze the impact of this design. The methodology of optimization is presented for the X14 Skyline system architecture, and benefits of up to 3% of energy can be realized at locations with latitude below 30 deg.
The high work to volume ratio and the stress recovery of Shape Memory Alloy (SMA) thin films with temperature
makes them an ideal choice for microactuators. However, these materials have not gained widespread acceptance due to
issues associated with phase transformation. Primary concerns are rapid change in stress at the transformation
temperature giving the actuator a step function like response and a significant shift in transformation temperatures due to
a wide hysteresis. In the present research, TiNiCu (53.59at%Ti, 39.05at%Ni), TiNi (50.32at%Ti) and TiNiHf
(39.56at%Ti, 48.63at%Ni) composite SMA thin films that display close to linear stress temperature behavior (slope: 2-7
MPa/°C) with high stress recovery (300-550MPa), wide transformation range (60-130°C) and low hysteresis (10-30°C)
were fabricated. Properties were achieved through the deposition of SMA thin films with varying composition in a
layered (composite) format on Si wafers. The TiNi+TiNiCu composite exhibited a two-step transformation (slopes of 2.5
and 3.9 MPa/°C) without a significant impact on stress recovery. Displaying identical recovery stresses, the TiNiHf film
possessed a 65°C transformation range and the TiNiHf+TiNi composite exhibited a wider range of 120°C. A strong
correlation between deposition conditions, annealing parameters and transformation characteristics was observed for all
the SMA films.
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