A greenhouse with Fresnel lenses in the south facing roof and a receiver for concentrated Photovoltaic with water cooling (CPVT system) will result in electrical and thermal energy output from the solar energy excess entering a greenhouse. The PV system converts about half of the direct radiation into heat and electricity. During periods with direct radiation this will significantly reduce the heat load on the greenhouse For an optimal performance the roof elements must be asymmetric with a steep inclination at the north side (the exact angle of course depends on the latitude of the building site). The Fresnel lens structure is best oriented in upwards direction. In the current design, two lenses are placed in the inner space of a double glass. This prevents pollution and condensation on the lenses. By the upward facing of the lens structure, the focus quality is preserved over a much broader range of angles of incidence compared to a lens with downward facing structures. Each PMMA lens with a size of 1.20m x 1.52m is composed of 12 ‘tiles’ for easy production. The focal distance of the lens is 1,875m and the geometrical concentration factor is 50×. This means that in most cases the focus line is thinner than 3 cm. The performance of the lens with respect to the shape of the focal area and the position of the focal line has been analyzed with ray tracing techniques. From this analyses and by the development of a smart tracking system only two motors can bring the receivers in the required positions. One motor controls the distance between lens and receiver and the other controls the translocation of the receivers parallel to the lens. The second conclusion was that the positions of the focal line are within the bounds of the greenhouse construction for almost the whole year. Only in winter, in the early morning and at the end of the day, the focal line will be unreachable. The light sum is very stable in the greenhouse compared with the light sum outside. The 480 m2 greenhouse, with the LCPVT system based on Static Fresnel lenses and a 12 m CPVT-module and a 200 m CT-module, is designed by Bode Project Engineering and constructed by Technokas in Bleiswijk the Netherlands. An electrical power of 37W/(m2 greenhouse) is measured at an incoming global radiation of 870 W/m² (on a horizontal plane). The fraction collected thermal yield is about 20% of the total incident direct radiation

Janssen, H.J.J.

Sonneveld, P.J.

Swinkels, G.L.A.M.

Tuijl, B.A.J., van

Zwart, H.F., de

English

Name not available

A concentrator system for BI-CPVT with static linear Fresnel lenses

Wageningen Yield 

A CONCENTRATOR SYSTEM FOR BI-CPVT WITH STATIC LINEAR FRESNEL LENSES 
 
 
G.L.A.M. Swinkels, P. J. Sonneveld, B.A.J. van Tuijl, H.J.J. Janssen, H.F. de Zwart  
Wageningen UR Greenhouse Horticulture, P.O. Box 16, 6700 AA Wageningen, 
The Netherlands, email: gert-jan.swinkels@wur.nl 
 
 
ABSTRACT: A greenhouse with Fresnel lenses in the south facing roof and a receiver for concentrated Photovoltaic  
with water cooling (CPVT system) will result in electrical and thermal energy output from the solar energy excess 
entering a greenhouse. The PV system converts about half of the direct radiation into heat and electricity. During periods 
with direct radiation this will significantly reduce the heat load on the greenhouse  For an optimal performance the roof 
elements must be asymmetric with a steep inclination at the north side (the exact angle of course depends on the latitude 
of the building site). The Fresnel lens structure is best oriented in upwards direction. In the current design, two lenses are 
placed in the inner space of a double glass. This  prevents pollution and condensation on the lenses. By the upward facing 
of the lens structure, the focus quality is preserved over a much broader range of angles of incidence compared to a lens 
with downward facing structures. Each PMMA lens with a size of 1.20m x 1.52m is composed of 12 ‘tiles’ for easy 
production. The focal distance of the lens is 1,875m and the geometrical concentration factor is 50×. This means that in 
most cases the focus line is thinner than 3 cm. The performance of the lens with respect to the shape of the focal area and 
the position of the focal line has been analyzed with ray tracing techniques. From this analyses and by the development of 
a smart tracking system only two motors can bring the receivers in the required positions. One motor controls the distance 
between lens and receiver and the other controls the translocation of the receivers parallel to the lens. The second 
conclusion was that the positions of the focal line are within the bounds of the greenhouse construction for almost the 
whole year. Only in winter, in the early morning and at the end of the day, the focal line will be unreachable. The light 
sum is very stable in the greenhouse compared with the light sum outside. The 480 m2 greenhouse, with the LCPVT system 
based on Static Fresnel lenses and a 12 m CPVT-module and a 200 m CT-module, is designed by Bode Project 
Engineering and constructed by Technokas in Bleiswijk the Netherlands. An electrical power of 37W/(m2 greenhouse) is 
measured at an incoming global radiation of 870 W/m² (on a horizontal plane). The fraction collected thermal yield is 
about 20% of the total incident direct radiation. 
 
 
Keywords: Ray Tracing, Concentrators, Energy systems, PV cells, PV module, Solar energy, Greenhouse. 
 
 
1 INTRODUCTION 
 
 An important issue in greenhouses is the different 
needs of solar energy to the system through the year. In 
summer the excess of solar energy is often  too large and 
greenhouses has to be cooled (mainly by ventilation), 
while in winter all energy and light can be usefully 
applied. A variable solar energy collector which absorbs 
0 to 50%  of the direct solar radiation is possible with the 
 combination of a linear Fresnel lens and a thermal or 
photovoltaic module (CPVT module). A linear Fresnel  
 
Figure 1: Impression of the 480 m² Fresnel greenhouse 
with 4 roof spans with Fresnel lenses mounted at the 
south facing roof segments. 
 
lens focuses direct light onto a narrow strip. In this focal 
line, a photovoltaic module can convert this radiative 
energy into electricity. Of course this PV-module, which 
has to be suitable for the high radiation densities in the 
focal line, will become very hot so cooling is necessary. 
This cooling water, running from e.g. 20 °C to 40 °C, can 
be considered as another means to harvest solar energy, 
although at a relatively low temperature. The Fresnel 
lenses focus the direct radiation only, so the diffuse 
radiation, and some scattered direct radiation, passes the 
obstructions from the relatively tiny collectors and can be  
 
Figure 2: Details of the modular constructed Fresnellens.  
Each lens is assembled from 12 parts and two lenses are 
mounted in one double glass pane. 
used for plant growth. In fact,  the possibility of 
separating direct and diffuse light with the Fresnel lens, 
as mentioned by Jirka et al. [1] and Tripanagnostopoulos 
et al. [2], can be used as a special type of shading 
screen.In case of low light intensities (early morning, end 
of the day , cloudy weather and during winter), the CPVT 
modules can be parked aside. This means that the 
greenhouse has its maximal transparency. During bright 
 
Figure 3: Details of the motor for the tracking  
mechanism for linear movements. 
sunshine, the receiver is placed in the focus and direct 
light will be blocked. The thermal and electric energy 
from the receiver enables a large step in the construction 
of more energy efficient greenhouses. This investigations 
following  more basic research performed at this field by 
the Greenhouse technology group of Wageningen UR [3-
6]. 
 
2 MATERIALS AND METHODS 
 
2.1 Integration in the greenhouse 
 Due to large efforts of Bode Project Engineering in 
the design stage and the accurate building of the 
greenhouse builder Technokas (both companies from de 
Lier, the Netherlands), a greenhouse was erected that 
supports Fresnel lenses, receivers and a sun tracking 
system in the roof structure.  The main structure of this 
prototype greenhouse with a size of 480m2 (length is 30m 
and the width is 16m) consists of four asymmetric roof 
elements (see Fig. 1 left side). Each roof element  has a 
span of 4 m and an inclination of the south side of 30o 
and on the north side of 54o. This asymmetric roof is a 
result of maximizing the potential energy yield, while 
preventing direct light entering the greenhouse through 
the north facing roof (which does not have lenses), giving 
the ecliptics at the 52nd latitude. The spans, trellis 
girders, and stability bracings are made of steel. The 
walls of the greenhouse are covered with a 16 mm double 
wall polycarbonate sheet material. The span of the trellis 
girders is 8.00 m with two roof segments of 4.00 m. The 
trellis girders are 5.00 m interspaced. The ventilation 
windows are mounted in the north facing roofs and are 
implemented as windows sliding along the roof. This 
prevents unwanted shadows on the on the other, south 
oriented, roof panes with the Fresnel lenses during 
ventilation. In total, 25 meter of linear Fresnel lenses are 
mounted in every roof (the first 2.5 meter on each side of 
the roof are cladded with diffuse glass). The lenses have a 
focal distance of 1.875 m, and a geometric concentration 
factor of 50x. The lenses are divided in pieces of 1.20 × 
1.54 m. and each such a lens is composed of 12 tiles (see 
Fig. 2).  Two of these lenses are fitted between a double 
AR coated glass cladding panel. A tracking motor for the 
receiver movements is depicted in Fig.3. This motors are 
connected to gearboxes with a cogwheel rack (see Fig. 4). 
At each 5 m this gearbox is mounted on the trellis girders 
and connected with the axis of the motor. This linear 
movement is transferred to steel cables, which bring the 
 
 
Figure 4: Details of the tracking motor (right) and the 
gearbox (left) of the tracking mechanism for linear 
movements. 
 
 
receiver to the right tracking position. Each receiver is 
connected with two steel cables: one for the distance to 
the Fresnel lens and one for movements parallel to the 
lens.  
 
 
Figure 5: Details inside the greenhouse with an overview 
of the cultivation area 
 
 
 The structure and orientation of the Fresnel lenses 
was optimized with ZEMAX software, as reported 
previously (Sonneveld, 2010). The ray tracing computer 
program RAYPRO, developed by Wageningen UR, was 
used to determine  the position of the focus line for every 
day of the year at any time of the day. It appeared that 
tracking the focal line with the receiver could be 
performed by two motors. One motor controls the 
distance between lens and receiver and the other  motor 
controls the movement parallel to the lens (and 
perpendicular on the groove direction).  
 
 
2.2 The CPVT and CT module and tracking 
 Two types of receivers are applied in this greenhouse. 
There is 200 m of concentrated thermal collector (CT-
modules. And there is 12 m of receiver with concentrated 
photovoltaic-cells with thermal output (CPVT -modules, 
see Fig. 6). The photovoltaic cells are silicon solar cells, 
suitable for concentration ratios up to 50×. The heat 
excess is removed with water cooled tubes  which are 
laminated under the CPVT-module [7.  Each CPVT 
receiver starts and ends with a 5 meter CT module 
because the first and last parts of the receiver are in the 
cover area without lenses. This module is the same as the 
other 200m of CT-receiver. The CT-receiver consists of a 
black painted rectangular steel profile covered with AR-
coated glass with an air gap of about 7 mm. The 
development and testing of the new type of greenhouse 
with an integrated linear Fresnel lens, receiver CPVT-
module and  
. 
 
Figure 6: Details of the receivers inside the greenhouse 
with two receivers per roof 
 
 
  
  
  
 
Figure 7: Intensities at the focal area for different angles 
groves of the lens) made with Raypro ray trace 
simulations. 
 
 
an innovative tracking system makes it possible to exploit 
the direct radiation in a solar energy system. Moreover, 
for shade tolerant plants (like ornamentals), removal of 
the direct radiation will drastically reduce the need for 
cooling and the need for screens or white wash, in 
summer conditions. 
 
 
Figure 8: Trajectories of the Focal line at different times 
during a year. The loops each span one day course. (——
01-03; ——01-05; ——01-07; ——01-09 and ——01-
11) 
 
 
Figure 9: The intensity and width of the focal line as a 
function of time 
 
 
3 RESULTS AND DISCUSSION 
 
3.1 Measurement of the yield of the system 
 A selection of the  results of the ray tracing program 
which determines the position of the focus line as a 
function of the angle of incidence, are presented in Fig. 7. 
The angle of incidence (φ) is defined from a line 
perpendicular to the lens surface,  and the azimuthal 
angle (is defined from the direction of the focal line 
(which is the same as the grove direction) In the graphs, 
the shortening of the distance between the focal line to 
the Fresnel lens can be noticed at increasing angles of 
incidence at an azimuth angle zero (radiation from the 
direction of the grooves). In the situation of azimuth 
angle 90° (so perpendicular to the grooves), the focal line 
moves with the angle of incident according to the Figs. 
7d, e, f. At higher angles of incidence the focal area 
spreads out to larger areas. In these situations there is a 
large area instead of a small spot where the collector 
could be placed to receive a line of light. This means that 
 
 
  
= 0°,            φ = 0° 
= 0°,                φ = 30° 
= 0°,            φ = 60° 
= 90°,  φ = 30° 
= 90°,  φ = 15° 
= 90°,  φ = 45° 
the ray tracing software was used to find the optimal 
place, based on a selection from possible locations. This 
exercise resulted in pathways for the receiver as 
presented in Fig. 8.  The knowledge on the course of the 
(optimal) focal line during the day is used for an 
automated positioning of the receiver for each moment of 
the day. In addition to this, a fine tuning of the receiver 
position is performed by a feedback signal from a light 
responsive diode array which measures the light intensity 
in a 0.75 cm linear grid, perpendicular to the receiver. 
Fig. 9 shows the result from this diode array. A dark, 
narrow line in the center of the graph indicates a sharp 
intensity in the focal line. Between 10:00 and 12:30 and 
between 16:00 and 18:00, the dark region in the graph 
gets more blurry. This is the consequence of less a sharp 
focus line as could be seen in Fig. 8 at the less favorable 
angles of incidence (the three graphs at the right side).   
 
 
 
 
 
 
Figure 10: The generated electric power (Power) and 
direct and diffuse radiation (Radiation) as a function of 
time on top: cloudy day August 6th, and bottom: bright 
day August 7th, 2011 
 
3.2 Performance of the CPVT system 
 The performance of the CPVT system with linear 
PMMA Fresnel lens was determined with practical 
measurements. In Fig. 9 the light intensity and width of the 
focal line is given for  a clear day: 3th May 2011. An 
overview of the solar radiation and the electrical energy 
yield on a cloudy day (August the 6th) and a bright day 
(august the 7th) is given in Fig. 10 respectively top and 
bottom. For Dutch climate conditions, a peak power of 
approximately 30 W/(m² greenhouse) electrical output can 
be expected at a maximal global radiation of 870 W/m2. 
The yearly electricity production is expected to be almost 
20 kWh/(m² greenhouse) and the thermal yield on 110 
kWh/(m2 greenhouse). The average collected thermal yield 
and direct global radiation as function of time is given in 
Fig. 11.  The fraction collected thermal yield is about 20% 
of the total incident direct radiation. Measuring daily the 
light sum (Fig. 12) result in a very stable light sum in the 
greenhouse compared with the light sum outside. 
 
 
 
 
Figure 11: Incident direct radiation and amount of 
collected thermal energy in 2011. 
 
 light [mol PAR/day] 
 Figure 12: Light sum in- and outside the greenhouse   
  2011. 
 
4 CONCLUSIONS 
 
 A 480m2 greenhouse with a CPVT system based on 
Static Fresnel lenses and both 40 m CPVT-module and a 
200 m CT-module is constructed in Bleiswijk, the 
Netherlands. The greenhouse construction is 
characterized by a asymmetric roof with a south facing 
roof with a slope of 30o and a smaller north facing roof 
with a slope of 54o. The south facing  panes contain two 
lenses, made from PMMA. The focal distance of the lens 
is 1,875m and the geometric concentration factor 50×. In 
most cases, the focus line is thinner than 3 cm.  
The performance of these lenses has been analyzed with 
ray tracing techniques with respect of the shape of the 
focal area and the position of the focal line. From this 
analyses it was concluded that tracking of the receiver 
module is possible with two motors. One motor controls 
the distance between lens and receiver and the other 
motor controls the movement parallel to the lens (and 
perpendicular to the groove direction). The second 
conclusion was that the positions of the focal line will be 
within the bounds of the greenhouse for most of the year. 
Only in winter, in the early morning and at the end of the 
day, the receiver will not be able to reach the focal line, 
which is considered to be no problem because of the low 
intensities in those periods. The light sum is very stable in 
the greenhouse compared with the light sum outside. An 
electrical power of 30W/(m2 greenhouse) is measured at 
outside 
inside 
an incoming global radiation of 870 W/m² (on a 
horizontal plane). The fraction collected thermal yield is 
about 20% of the total incident direct radiation. 
 
 
5 REFERENCES 
 
[1] V. Jirka, Kučeravý, K. Malý, M. Pech, F.and 
Pokorný, J. Energy flow in a greenhouse equipped 
with glass raster lenses. Renewable Energy, 16 
(1999) 660 
[2] Y . Tripanagnostopoulos, Ch. Siabekou, J.K.Tonui, 
The Fresnel lens concept for solar control of 
buildings, Solar Energy 81 (2007) 661 
[3] P. J. Sonneveld, G.L.A.M. Swinkels, B.A.J. van Tuijl,  
H.J.J. Janssen,  J. Campen, G.P.A. Bot,  Energy 
performance of a concentrated photovoltaic energy 
system with static linear Fresnel lenses integrated in a 
greenhouse, Solar Energy, 85 (2011) 432 
[4] P. J. Sonneveld, G.L.A.M. Swinkels, G.P.A. Bot,  
G. Flamand, Feasibility study for combining cooling 
and high grade energy production in a solar 
greenhouse. Biosystems Engineering 105 (2010) 51 
[6]  P. J. Sonneveld,  G.L.A.M. Swinkels, J. B.  
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van Zolingen, A.A. van Steenbergen, The thermal 
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Energy flow in a greenhouse equipped with glass raster lenses. Renewable Energy,

Energy performance of a concentrated photovoltaic energy system with static linear Fresnel lenses integrated in a greenhouse,

Feasibility study for combining cooling and high grade energy production in a solar greenhouse.

Performance results of a solar greenhouse combining electrical and thermal energy production Biosystems Engineering 106

The Fresnel lens concept for solar control of buildings,

The thermal and electrical yield of a PV-Thermal collector.

A concentrator system for BI-CPVT with static linear Fresnel lenses

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