Concentrator

A NEW LOW COST TRACKING RIDGE CONCENTRATOR

A new tracking soft (C=1.5 -1.7) concentrator (front page photograph) which can double PV energy harvest (in comparison with fixed panels) and substantially reduce price of PV energy is presented.

The new system combines simple low-cost tracker [1] with flat booster mirrors but unlike V-trough concentrator [2,3] by the new ridge concentrator the “outer“ mirror has been eliminated (Fig.1). On single axis trackers, both horizontal and polar, the mirror have to be extended beyond PV panels to ensure uniform illumination of panels at seasonaly variable elevation of the sun. Triangular extension of the mirror shows Fig.2. On polar axis trackers with seasonaly adjustable slope [1] of the axle the extended mirror (Fig.2) is not needed.

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It is advantageous that soft concentrators for photovoltaics does not need highly specular expensive mirrors. Weather resistant (at least 10 years) mirrors with high total reflectance are needed.

The mirror can be made:
a) of rolled stainless steel sheet with special surface finish [4].
b) of rolled aluminium alloy sheet (plated with pure aluminium) protected by a weather resistant polymer (PVF) film [4,5].
c) of silver coated polymer (acrylic) film [6] or sheet.
d) of aluminium coated polymer (acrylic) film [4] or sheet
e) of silver coated hardened glass

Choice b) could be the best trade off between reflectance and price. Instead PVF lacquer [4] the aluminium mirror of the ridge concentrator is protected by adhesive laminated transparent PVF film. Manufacturing of one self-supporting “bended“ sheet mirror is very simple.

The new tracking soft concentrator is very compact and simple (reliability). Proven existing tracker hardware is used. Unlike V-trough concentrators no additional mirror supporting structures are needed and wind induced torque is strongly reduced.

The ridge concentrator is easily scalable. Standard version of the tracking ridge concentrator can accomodate from 2 small PV panels (50Wp) up to 20 PV panels with 120 Wp output power (in arid climate eqvivalent to 40 x120Wp PV panel fixed system). Application of the ridge concentrator on different tracking systems is also very easy. It can be used on polar or horizontal single axis trackers [8], two axis trackers as well as on 360o trackers for space and terrestrial applications [7].

Concentration ratio (1.5-1.7) reduces temperature of PV panels (higher efficiency) and avoids degradation of the encapsulant. The new design also improves (against V-through) air flow around PV panels (improved cooling). Concentration ratio (2-2.4) of standard V-trough concentrators frequently causes browning of the EVA encapsulant while elevated temperature reduces efficiency of PV panels.

The new tracking ridge concentrator can double annual energy harvest (100% energy surplus in arid climates like e.g. northern Africa, Arabia, Arizona or western Australia, 75% in central Europe) in comparison with fixed panels and pumping capacity surplus can be as high as 150% [2].

One year comparison of energy production between fixed tilt PV panels and PV panels mounted on tracking ridge concentrator was started in May 1999 (Prague region, 50o N). Very first results show that e.g. on clear (6,8kWh/m2) day in June 99 the energy surplus of 107% was observed.

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References:
[1] V. Poulek, M. Libra, New Solar Tracker, Solar Energy Materials & Solar Cells 51 (1998), 113-120.
[2] F.H.Klotz, PV systems with V-trough concentration and passive tracking concept and economic potential in Europe, Proc.13th European PV Solar Energy Conference, Nice 23-27 October 1995, pp.1060-1063.
[3] S. Nann, Potentials for tracking photovoltaic systems and V-troughs in moderate climates, Solar Energy 45, (1991) 385-393.
[4] P. Nostell, A. Roos, B. Karlsson, Ageing of solar booster reflector materials, Solar Energy Materials & Solar Cells 54 (1998), 235-246.
[5] B. Perers, B. Karlsson, M. Bergkvist, Intensity Distribution in the Plane From Structured Booster Reflectors With Rolling Grooves and Corrugations, Solar Energy 53, (1994) 215-226.
[6] P. Schissel, G. Jorgensen, C.Kennedy, R. Goggin, Silvered PMMA reflectors, Solar Energy Materials & Solar Cells 33 (1994), 183-197.
[7] V. Poulek, M. Libra, A Very Simple Solar Tracker for Space and Terrestrial Applications, Solar Energy Materials & Solar Cells, 60, (2000), 99-103.
[8] V. Poulek, M. Libra, A New Low Cost Tracking Ridge Concentrator, Solar Energy Materials and Solar Cells, 61, 2, (2000), 199-202.