3 Ω, 50 W
Figure 8. Half bridge network.
Data acquisition system, signal conditioning,
and PV panel heating temperature sensor
The data acquisition system consisted of a datalogger
(CR10X), two multiplexers (AM416), a storage mod-
conditioning circuitry, all housed in an enclosure. The
datalogger, multiplexer, storage module, power supply,
and enclosure are all products of Campbell Scientific of
Logan, Utah. The signal conditioning circuitry was
designed and built by CRREL engineers and technicians.
The signal conditioning circuitry is an interface
between the PV panel and the input channels of the data-
Figure 9. PV panel junction box (note panel output termi-
nals, splices, and thermistor).
logger. This circuitry consists of two half bridge net-
works (Fig. 8) for each PV panel. The half bridge net-
aspects of sampling and processing of the PV panels'
works are used to scale the PV panels' output voltage to
electrical performance. The PV panel electrical output
an acceptable range for the datalogger input channels.
is measured every 15 minutes and is averaged and stored
One half bridge is used to determine the PV panels' out-
put power by measuring current through a 3-Ω load via
a sense resistor, while the second is used to determine
the PV panels' output voltage potential.
A net radiometer (Fig. 10), manufactured by Radia-
Connected from the data acquisition system to each
tion and Energy Balance Systems Inc., model Q-7, was
PV panel is a 20-awg four-conductor wire. Two of the
used to sense the net radiation values present at the ARO
conductors (red, black) are attached to the PV panels'
building. The Q-7 is a high-output thermopile sensor.
output terminals, which are located in the junction box
The thermopile sensor measures the algebraic sum of
on the back of the panel (Fig. 9). The remaining two
incoming and outgoing all-wave radiation (i.e., short-
conductors (green, white), terminating in the same junc-
and long-wave components). Incoming radiation is made
tion box, are attached to a thermistor (107B tempera-
up of three components--direct beam and diffuse solar
ture sensor) that senses the PV panels' temperature.
radiation plus long-wave irradiance from the sky.
Reflected solar radiation plus the terrestrial long-wave
radiation make up the outgoing all-wave radiation. Net
A program (SOLARB.CSI), written for the datalogger
radiation has the units of W m2.
with Campbell Scientific PC208 software, controls all