Agriculture Reference
In-Depth Information
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
Angle of incidence
New three-layer film
Used three-layer film
New thermal PE film
Used thermal PE film
0.2 mm thickness
6
1100
900
700
500
300
100
0
6
12
18
24
Solar time (h)
7
700
600
500
400
300
200
100
0
0
6
12
18
24
Solar time (h)
Plate 5.
The transmissivity to direct radiation, expressed as a percentage of the incident radiation, decreases as
the angle of incidence increases (see Fig. 3.3). The transmissivity varies depending on the characteristics of the
material. The ageing of plastic films, influenced by their use, decreases transmissivity (Montero
et al
., 2001).
Plate 6.
Evolution of solar radiation intensities in the open air and in the greenhouse around the winter
(21 December) and summer (21 June) solstices, on sunny days (coast of Granada, Spain). The daily total
radiation in each case is the area of the surface delimited by each curve and the abscissa axis. Black line, open
air, summer; pink line, greenhouse, summer; green line, open air, winter; blue line, greenhouse, winter.
Plate 7.
Evolution of solar radiation intensities in the open air and in the greenhouse on a not completely cloudy
day in spring and another one in winter (coast of Granada). Black line: open air, spring; pink line: greenhouse,
spring; green line: open air, winter; blue line: greenhouse, winter.
