Linear Fresnel Lens Research Articles

Comparison of Fresnel concentrators for building integrated photovoltaics

To develop concentrating photovoltaic systems for building integration applications, two optical devices are proposed. The concentrators are based in stationary linear Fresnel lenses and secondary CPC. The moving focal area is ten times smaller than the Fresnel lens aperture. Concentrator characteristics are studied in detail: shadowing effect, placement of the focal area and optical concentration efficiency. The main contribution of this paper is the three-dimensional optical analysis of the non-imaging concentrating systems. In terms of solar radiation, photovoltaic moving modules placed in the focal area of stationary concentrators are compared with simply fixed photovoltaic modules. In favourable weather locations, the beam radiation incident on the concentrating modules would be a large percentage, more than 50%, of the global radiation received by the fixed photovoltaic devices.

A two-stage solar photobioreactor for cultivation of microalgae based on solar concentrators

A novel two-stage experimental photobioreactor (PBR) with a total volume of 450 L and based uniquely on solar concentrators—linear Fresnel lenses—has been constructed and tested. Daily courses of irradiance, and also its distribution inside cultivation tubes, were studied in two unit types. The supra-high irradiance units in the ‘roof’ achieved a maximum summer value above 6 mmol photon m−2 s−1, while irradiance in the vertical-facade units was lower than ‘ambient’. In model cultivations, cultures of the cyanobacterium Arthrospira platensis were cultivated at much higher solar irradiances than those usually recorded outdoors in summer, indicating that this organism is resilient to high-irradiance (photoinhibition). Starting from a biomass density of 0.5 g L−1 at optimum temperature, the cultures grew exponentially. A two-stage cultivation process of the green microalga Haematococcus pluvialis was investigated with respect to correlations between photochemical activities and astaxanthin production. The culture was first grown in low-irradiance units, and then exposed to supra-high irradiance when the rate of astaxanthin production was 30–50% higher than in the culture exposed to ‘ambient’ irradiance. Within 4 days, the astaxanthin content reached 3% of dry weight, whereas under ambient irradiance the astaxanthin content was 25% lower.

Design Process of an Area-Efficient Photobioreactor

This article describes the design process of the Green Solar Collector (GSC), an area-efficient photobioreactor for the outdoor cultivation of microalgae. The overall goal has been to design a system in which all incident sunlight on the area covered by the reactor is delivered to the algae at such intensities that the light energy can be efficiently used for biomass formation. A statement of goals is formulated and constraints are specified to which the GSC needs to comply. Specifications are generated for a prototype which form and function achieve the stated goals and satisfy the specified constraints. This results in a design in which sunlight is captured into vertical plastic light guides. Sunlight reflects internally in the guide and eventually scatters out of the light guide into flat-panel photobioreactor compartments. Sunlight is focused on top of the light guides by dual-axis positioning of linear Fresnel lenses. The shape and material of the light guide is such that light is maintained in the guides when surrounded by air. The bottom part of a light guide is sandblasted to obtain a more uniform distribution of light inside the bioreactor compartment and is triangular shaped to ensure the efflux of all light out of the guide. Dimensions of the guide are such that light enters the flat-panel photobioreactor compartment at intensities that can be efficiently used by the biomass present. The integration of light capturing, transportation, distribution and usage is such that high biomass productivities per area can be achieved.

Ka-band Fresnel lens antenna fed with an active linear microstrip patch array

The design of a linear microstrip array and Fresnel lens combination as a potential candidate for Ka-band satellite communications is presented. Medium-power amplifiers are distributed within the array to achieve a high EIRP required for satellite communications. This architecture may be used as an alternative to the conventional horn-fed reflector antenna with a single high-power amplifier.

Six-degrees-of-freedom alignment technique that provides diagnostic misalignment information.

We introduce a new six-degrees-of-freedom alignment technique that enables the precise alignment of two optical device planes. The method combines linear diffraction gratings and cylindrical Fresnel lenses that allow the diagnosis of misalignment in each degree of freedom independently. The technique was used to align two 20 mm x 20 mm fused-silica substrates separated by 17 mm. The worst-case alignment precision was found to be better than +/- 5 microm laterally, +/- 20 microm longitudinally, +/- 0.036 degrees rotationally, and +/- 0.007degrees in tilt.

A closed solar photobioreactor for cultivation of microalgae under supra-high irradiance: basic design and performance

An account is given of the setting up and use of a novel type of closed tubular photobioreactor at the Academic and University Centre in Nove Hrady, Czech Republic. This "penthouse-roof" photobioreactor was based on solar concentrators (linear Fresnel lenses) mounted in a climate-controlled greenhouse on top of the laboratory complex combining features of indoor and outdoor cultivation units. The dual-purpose system was designed for algal biomass production in temperate climate zone under well-controlled cultivation conditions and with surplus solar energy being used for heating service water. The system was used to study the strategy of microalgal acclimation to supra-high solar irradiance, with values as much as 3.5 times the ambient value, making the approach unique. The cultivation system proved to be fully functional with sufficient mixing and cooling, efficient oxygen stripping and light tracking. Experimental results (measurement of the maximum photochemical yield of PSII and non-photochemical quenching) showed that the cyanobacterium Spirulina (= Arthrospira) platensis cultivated under sufficient turbulence and biomass density was able to acclimate to irradiance values as high as 7 mmol photon m−2 s−1. The optimal biomass concentration of Spirulina cultures in September ranged between 1.2 to 2.2 g L−1, which resulted in a net productivity of about 0.5 g L−1 d−1 corresponding to a biomass yield of 32.5 g m−2 d−1 (based on the minimum illuminated surface area of the photobioreactor).

Space solar arrays and concentrators

This paper presents some research activities conducted at the Centre Spatial de Liege (CSL) in the field of space solar arrays and concentration. With the new generation of high efficiency solar cells, solar concentration brings new insights for future high power spacecrafts. A trade-off study is presented in this paper. Two different trough concentrators, and a linear Fresnel lens concentrator are compared to rigid arrays. Thermal and optical behaviors are included in the analysis. Several technical aspects are discussed: • Off-pointing with concentrators induces collection loss and illumination non uniformity, reducing the PV efficiency. • Concentrator deployment increases the mission risk. • Reflective trough concentrators are attractive and already proven. Coating is made of VDA (Aluminum). A comprehensive analysis of PV conversion increase with protected silver is presented. • Solar concentration increases the heat load on solar cells, while the conversion efficiency is significantly decreasing at warm temperatures. To conclude, this paper will point out the new trends and the key factors to be addressed for the next generation of solar generators.

Energy flow in a greenhouse equipped with glass raster lenses

A specially-equipped greenhouse has been evaluated by measuring the distribution of incident solar energy into heat, and vegetable and fish biomass production. The south-facing half of the roof of the solar greenhouse is equipped with a glass raster of linear Fresnel lenses (LFLs; see Jirka et al., same volume) which concentrate the heat energy from direct solar radiation in collectors while allowing diffuse light to pass through unhindered.

The study of the performance and efficiency of flat linear Fresnel lens collector with sun tracking system in Iraq

Two flat linear Fresnel lenses and two absorbers connected in series. Tracking system is constructed so that it tracks the sun in two directions. Thermal and optical losses are introduced. The thermal efficiency of the first lens is higher than the second lens and reaches 0.65. The FLFL all-day collector efficiency reaches 0.58 and it varies depending on weather condition.

Linear Fresnel lenses, their design and use

A linear Fresnel lens (LFL) designed according to Fermat's principle is slightly modified with respect to used technology for mass production from glass. Manufactured Fresnel lenses are used in a fully tracking concentrating collector with aperture about 36 m 2 and in a collector with stationary concentrator and movable absorber, which may serve as solar collector with temperature and illumination control. A combination of linear Fresnel lenses with PV cells may reduce cost of autonomous solar installations.

Response of Monocot and Dicot Weed Species to Fresnel Lens Concentrated Solar Radiation

Fresnel lenses are used to concentrate solar radiation to a line or point. A linear Fresnel lens (0.91 by 1.52 m, 0.74-m focal length, 0.01- by 1.52-m line focus) was investigated as a method for weed control. Field experiments were conducted to assess the effect of Fresnel lens concentrated solar radiation at various exposure times, stages of plant growth, and soil surface moisture conditions. On a dry soil surface exposure times of 1 to 10 s at 290 C resulted in control of redroot pigweed from 100% for a 1-s exposure at the cotyledon stage to 89% for a 10-s exposure at the 10-leaf stage. Redroot pigweed and kochia control was similar at exposures of 3 to 10 s, but less for kochia at 1 and 2 s. Green foxtail control was less than that of kochia and redroot pigweed. Control was reduced on a moist compared to a dry soil surface. Concentrated solar radiation holds the greatest potential for control of small dicot weeds on a dry soil surface.

An assessment of linear Fresnel lens concentrators for thermal applications

This paper describes an assessment of linear Fresnel lens concentrator technology for use in thermal applications. System performance and cost data for a Fresnel lens concentrator were developed and compared with data for a parabolic trough system. Two thermal applications of these technologies were chosen for the comparison. The first is a water preheat application where energy is transferred from an antifreeze, collector field working fluid to preheat 60 °C water through a heat exchanger. The other application is the generation of saturated steam at 177 °C. Annual performance predictions were generated using a simulation code that includes the effects of both thermal capacitance and heat losses from all piping and system components. Performance was simulated at three different geographic locations. Costs for the collectors were based on documented estimates. Overall costs included all major equipment, site development, and installation. The performance and cost data were combined to arrive at a levelized cost of energy. Based on the performance predictions developed here and on the current documented costs, results indicate that the Fresnel lens systems have a levelized energy cost about one-third less than the parabolic trough systems. This is primarily due to less expensive concentrators.

Design of one-axis tracked linear Fresnel lenses

The most frequently used criterion in the design of linear Fresnel lenses consists of minimizing the radiation spread at the collector when the lens is illuminated by rays that are contained in the full lens acceptance angle and are incident on the lens in the plane perpendicular to the lens axis. This paper analyzes this topic and concludes that when the lenses are one-axis-tracked this criterion can be improved by replacing the perpendicular plane with another forming a certain angle to it. When calculated for a specific lens, at the location of Madrid, the new criterion was found to yield an increase of more than 7% in the total annual energy collected.

Concentrating collectors with flat linear fresnel lenses

Abstract Optical properties of flat linear Fresnel lenses manufactured from glass are presented. Behaviour of Fresnel lenses in perpendicular and inclined beams of rays is discussed. Considerations related to the concentrating collectors design with some results from particular installations are briefly surveyed.

Two stage linear Fresnel lenses

A new design of a second stage reflective element, which is closely related to the earlier trumpet configuration, is presented. The implementation for linear Fresnel lenses is derived, leading to high solar concentration with both convex and flat lenses.

Linear Fresnel lens with polar tracking

The performance of coma and color corrected linear Fresnel lenses for solar concentration is evaluated for use in polar tracking systems. Effective concentrations of up to 90 at 75% efficiency were obtained.

Direct Conversion of Solar Radiation to Mechanical Power Using Bimetals and Linear Fresnel Lenses

ABSTRACT CONCENTRATION of direct solar radiation on bi-metallic helical coils caused a simple sun-powered motor to produce rotational shaft power on an intermit-tent basis. Solar radiation was concentrated onto the bimetallic coils with linear Fresnel lenses. Data ac-cumulated during actual and simulated operations allowed performance of a detailed heat balance which in-dicated that continuous rotational motion of the motor might be attained in one of two ways: reduction of bimetal mass; and/or use of a bimetal with greater deflection at lower operating temperatures.

Convex fresnel lens with large grooves

The concentration capability of linear Fresnel lenses is limited mainly by coma and chromatic aberrations and by the width of the individual grooves of the lenses. We consider new designs for these lenses in which the concentration is almost independent of the groove's size, and which are free of coma at the edge of the acceptance field. Specifically, a concentration factor as high as 34 is achieved for monochromatic radiation coming from an acceptance angle of ± 1°.

Linear fresnel lens with grooves of finite size

Linear convex Fresnel lenses of a finite thickness and size of grooves are analyzed with emphasis on production constraints, and evaluated by using a ray tracing technique. It is shown that these lenses may efficiently concentrate the solar radiation. A simple fabrication-process for such a lens is suggested.

Color-corrected Fresnel lens for solar concentration

A new linear convex Fresnel lens with its groove side down is described. The design philosophy is similar to that of the highly concentrating two-focal Fresnel lens but includes a correction for chromatic aberration. A solar-concentration ratio as high as 80 is achieved. For wide-acceptance angles, the concentration nears the theoretical maximum.