41
instructions for each of these devices. A broad overview, however, is important because of the significance
solar tracking plays in the measurement of direct and diffuse radiation.
The following general characteristics are common to all solar pointing devices.
(1) The tracker location must be known. The more precisely the location can be determined,
the easier the setup of the tracker. With modern GPS receiver systems the position of the
tracker can be determined (latitude and longitude) to within ±3 m . From a 1:50,000 topographic
map the location can be determined to within better than 50 m. Depending upon the size
of the installation care should be taken so that the actual location of the tracker is determined
and not simply the central location of the BSRN observatory.
(2) In all cases a reliable power supply is necessary. Synchronous trackers not only require a
constant power supply, as do other trackers, but also a constant and accurate electrical frequency
if the tracker is to maintain accurate alignment on the solar disk at all times. Changes in power
line frequency will alter the speed at which the solar disk is tracked. Most utility companies
are required by law to maintain the power line frequency to some stated accuracy within a
24-hour period with a maximum excursion from that stated frequency at any given moment.
Stepper-motor-controlled trackers are less susceptible to such changes because of their internal
conversion from AC to DC power. The use of UPS systems on synchronous motor trackers
is also of limited utility because many inverter systems output frequency as square waves
rather than the sinusoidal wave required by the tracker.
Figure 4.7. The contribution of the solar disk to the
irradiance of pyrheliometric sensors depending on the
pointing error. (A) Case of mountain aerosol and 60°
solar elevation. (B) Case of continental aerosol and a 20°
solar elevation. (Calculations and graph courtesy of G.
Major)
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Komentarze do niniejszej Instrukcji