56
Solar array
Photovoltaic (PV) cells produce
electricity directly from sunlight (not from
heat). Light causes electrons to jump from the
top layer of the cell, into “holes” in the layer
underneath. When a circuit is made between
top and bottom layers, electric current flows.
Each cell produces about 1/2 volt. As sunlight
varies, the current (amps) varies while the
voltage stays nearly constant.
PV cells are connected in series for the
desired voltage, and sealed under glass to
make a “PV module”.The assembly of
modules is called a “PV array”. There are no
moving or wearing parts in PV modules. The
glass used in high quality PV modules is
tempered, and is extremely strong. It is
tested to federal standards that include
resistance to a 1" ice ball traveling at 100
mile per hour.
Some
PS-Pump
systems use a “passive” or
active solar tracker, which tilts the array to
follow the sun through the day. Daily output
can be increased by that feature up to 50%.
Our ETATRACK systems reduce system cost
Brushless motor system
PS-Pumps
use a
“brushless DC motor system”. This consists of
a special 3-phase AC motor (synchronous,
permanent magnet), and a controller that
changes the solar DC power to 3-phase AC.
AC creates a rotating magnetic field that
causes the shaft to spin. The motor’s speed is
determined by the frequency of the AC power.
The controller varies the frequency (and the
voltage) to bring the motor up to speed slowly.
It then adjusts the motor speed according to
the power available from the sun.
Older-technology solar pumps have a tradi-
tional DC motor that uses “brushes” (small
blocks of carbon-graphite) to conduct current
to the spinning part of the motor. Not only do
the brushes wear out in a few years, but it is
necessary to have air in the motor and a
perfect seal to keep water out. The brushless
motor is filled with, and lubricated by water. It
is similar mechanically to conventional AC
submersible motors.
Controller
The PS-controller starts the pump
slowly and adjusts its speed according to the
pumping load and the power available from
the solar array. Power output from the array is
optimally matched to the load by
maximum
power point tracker
(MPPT) and
linear current
booster
(LCB) functions, to produce maxi-
mum power transfer throughout all condi-
tions. The LCB function is analogous to an
automatic transmission in an automobile. It
starts the pump in “low gear” (it lowers the
13 REFERENCE SECTION
13.1 Principles of Operation
array voltage and boosts the current). Under
low sun conditions, it stays in “low gear” to
resist stalling. As sunlight increases, it
advances continuously toward “high gear”
(higher voltage). The MPPT system refines
the LCB function by tracking changes in the
array voltage. Array voltage varies primarily
with temperature (it is higher at low tempera-
tures). When the pump stalls in low sunlight,
the controller switches the pump off.
The controller converts the DC power from the
solar array to 3-phase AC power to run the
motor. Due to the special natuerl of this AC
voltage which is made with PWM technology
it cannot be measured with a multimeter.
Motor speed (RPM) is proportional to the AC
frequency. The frequency starts low (about 20
Hz), and increases gradually to a maximum
of 3400 RPM (70 Hz).
The float switch circuit operates at 12VDC,
carrying maximum current of 4.7mA. The
controller has terminals for either normally
open (N.O.) or normally closed (N.C.) switch-
ing.
The low-water probe circuit applies 5VDC to a
probe. The water conducts a small amount of
current between the two electrodes of the
probe. If the probe is out of the water, the
controller stops the pump. When the water
level recovers, there is a 20 minute delay
before restart.
Pump end – centrifugal models
Pumps
with a MODEL NUMBER CONTAINING “C”
use a multi-stage centrifugal pump end,
similar to that of conventional well pumps –
this is for high volume at 75 feet (23m) or
less.
Pump end – helical rotor models
Pumps
with a MODEL NUMBER THAT DOES NOT
CONTAIN “C” have a helical rotor pump end
(also called “progressive cavity” pump). The
rotor fits closely into a rubber stator that has a
helical groove of a different pitch. The mis-
match between the rotor and stator forms
sealed cavities that trap water. As the rotor
turns, the cavities progress toward the outlet.
