Concentrator modules

PV systems with concentrators may provide economical advantages, if high-efficiency multi-junction III-V cells are combined with cheap optical concentrators providing high concentration ratio (500-1000x and above). A promising way for concentrator system development is a concept of small-aperture area submodules in PV module design. In this case the advantages of a concentrator system (rise in efficiency, saving the semiconductor and structural materials) may be realized at retention (in the whole) of a distributed character of sunlight conversion and heat dissipation-similar to the case of systems without concentration. 

  Different types of concentrator modules have been designed and manufactured for space and terrestrial applications in PV Lab at Ioffe Institute. In the modules, refractive-type concentrators (Fresnel lenses) have a composite structure: microprisms are formed from transparent silicone rubber contacting with front glass sheet as a protective superstrate. The lenses are arranged on a common superstrate in a view of lens panel. The cells as small as 2 or 1.2 mm in designated area diameter operating at concentration ratios 500-1000x are intended for used in the PV modules. Developed formation process allows fabricating the lens panels of total area 0.5 x 0.5 m2

Solar cell           50x50 cm concentraror modules
Solar cell, mounted to the copper heatsink.   Terrestrial concentrator PV modules with composite 12x12 lens panel (50x50 cm).

  The panel of primary Fresnel lenses is arranged as a number of identical strings of six lenses in each string. In regard to the panel of cells, it is arranged as a corresponding number of identical units, where six cells and one by-pass diode are mounted in parallel circuit on a common heat sink. 

Lens string and cell unit
Individual lens string and cell unit, intended for work with one of the lens strings.

Tracker Development

High accuracy of tracking to the sun is a specific feature of the high-concentration PV method. During last year an improved version of the 1 kWp tracker was designed and built in the Ioffe Institute. In construction of the tracker the cheapest structural materials have been used, such as perforated steel channels and angles. The possibilities for transportation have been considered in the tracker design. For this, all members and parts are no longer than 2 meters and no wider than half of meter . At the same time, necessary rigidity is completely ensured owing to structural features of the tracker frames. 

Indoor overall conversion efficiency measurement by means of a specially developed flash solar simulator with large aperture area Fresnel-type collimator

Sun tracker   Sun tracker parts ready for transportation
Sun tracker with concentrator PV modules installed on the roof of the Ioffe Institute.             Sun tracker parts ready for transportation.

The tracker is equipped with main (accurate) sensor and additional one, both equipped with tandem-type III-V cells and operating as a part of a close-loop system. Main sensor can align the tracker with the sun to within 0.05 degree of arc accuracy with acceptance angles of 70 . Additional sensor makes wider the "East/West" turning angle (up to 270 ). Both sensors are mounted on the suspended frame together with PV modules. An advantage of the developed sensors is protection from influences caused by illumination level changes due to light reflections from various objects during a day and presence of clouds. For this, main sensor includes two sub-channels in both horizontal and vertical channels. Differential signals are generated in correspondence with misalignments of the tracker to the sun in azimuth and elevation. The shadowing tube limits acceptance angles of the cells in accurate sub-channels to 1-2. Photocurrents generated in accurate sub-channels give rise to switching all the other cells off. Electronic board includes solid-state relays, motor microdrives and voltage-current measuring units. Simplicity and consumption of current as low as 45 microamperes from a rechargeable 12V-battery in stand-by regime are the positive features of the developed electronic board. 

Main sun sensor
Main sun sensor installed together with concentrator PV array powering the tracker.

Compact sealed 12V battery with capacity of 5 A hours serves as a buffer power source for automatic operation of the tracker. Charging the battery is carried out from a small-size concentrator PV array installed on the suspended frame of the tracker together with main sun sensor. Overall power consumption for tracking including West-East returns was estimated to be no more than 0.2% of installed power.