A photovoltaic panel may be connected directly to
a pump to harvest some heat from a solar collector...
UNFORTUNATELY this crude method of solar heat collection is often counterproductive, because sunlight intensity is not always proportional to the difference in temperature between the solar collector and the heat storage chamber. As a matter of fact a PV panel connected directly to a pump may sometimes produce a net heat loss. The PV Controller improves the performance of solar heat collection by responding to a difference in temperature rather than a difference in sunlight intensity. The thing that makes the PV controller special is its ability to function without a battery back up. As you know a Charge Controller prevent PV power supplies form overcharging or undercharging batteries. A 12 volt PV system normally puts out about 18 Volts in bright light or dim light under no load conditions. BUT without a battery back up PV voltage drops like a stone when a pump initially turns on. if the voltage gets too low most controllers chatter because there is insufficient voltage available for controller regulation. This is where the PV controller comes to the rescue. My new PV differential heat controller remains stable at voltages below 4 VDC. Of course dim light low voltage conditions diminish pump speed but the PV controller still remains stable under low voltage conditions.
EXAMPLE 1. Bright sunlight with a
low collector temperature... DIRECT CONNECT
Bright sunlight is normally associated with high collector temperatures, but there are numerous occasions when a bright sun turns on a pump too fast and too soon. A bright sun on a cold morning supplies more than enough power to circulate water through a collector, but pumping water through a cold collector is not a good idea since it produces a net heat loss.
EXAMPLE 2. Dim sunlight with a
high collector temperature.....BASIC CONTROLLER WITH BATTERY BACK UP
Dim sunlight is normally associated with low collector temperature, so let's say the sun has been out for awhile and the collector is quite hot and the pump is humming along collecting plenty of solar heat... All is well until a large cloud drifts across the sky and PV power is diminished so a low speed pump will take longer to extract the remaining solar heat in the collector. A standard differential controller without a battery back up will chatter under low voltage in dim sunlight.
EXAMPLE 3. Intermittent sunlight
with PV Controller.................PV CONTROLLER WITHOUT BATTERY BACK
A Basic Differential Controller with a battery back up provides an ideal interface between PV power and pump regulation, by bridging the gap between periods of bright sunlight and periods of dim sunlight. Without a battery back up in dim sunlight the supply voltage drops as soon as the pump turns on. Diminishing the voltage to the pump reduces pump speed which is not a major problem, but it also reduces voltage to the controller and this is a problem for most differential controllers without a battery back up. When the voltage to standard differential controllers drops too low the relay chatters due to voltage fluctuations. Remember, a 12 VDC panel supplies about 18 VDC under no load conditions, but under dim light conditions the PV supply voltage may drop below 4VDC. My PV Controller was designed to operate without a battery back up under a wide range of voltage fluctuations that take place under dim light conditions and supply voltages fluctuations due to pump on/off states..
How does the PV Controller work?.... I thought you'd never ask!
The PV Differential Controller is basically the same as a Basic Differential
Controller except it uses a solid state metal–oxide–semiconductor
field-effect transistor ( a MOSFET) instead of a mechanical relay. The
advantage of the MOSFET has to do with the
high input impedance at the Gate which allows the MOSFET to turn on between 2 and
4 Volts. A tiny capacitive charge at the gate allows the MOSFET to stay on even
if when the controller voltage drops below levels that other controllers can not
tolerate. If you have a PV panel with a battery back up connected to a charge controller
a simple Basic Differential Controller is all you need to improve the heat collection of your
PV/ solar collector system. If all you want to do is improve heat collection
efficiency with the addition of a controller alone I recommend the PV
Controller. The PV controller was specially designed for small PV DHW
systems without a battery backup.
Differential Controller KIT
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