The LCB controller or Linear Current booster is used in solar direct pumping applications. It is claimed to achieve 30 - 90 % increase in the water pumped than connecting the motor directly to the solar panels. At times when the sun is not optimum, a Linear Current Booster boosts the current in the pump motor to produce the torque to turn the pump motor. It does this by sacrificing voltage on motor, hence the motor runs slower. This results in a motor that may be pumping slower (there is after all less solar power), but this is better than having a stalled pump pumping nothing which would happen if solar direct.
The LCB that we are using is from the company "Solar Converters Inc".
So, what are the things which have been observed so far?
Observations from the absence of the LCB:
In the last week of September (when LCB was not still connected), the sky was heavily clouded (leading to a (global) irradiation of <200 W/m2 for most time of the day for 4 days) and system operation was difficult. The motor was abruptly stalling, leading to significant vibrations and the motor starting and stopping almost every 10 minutes. However, that practice is not safe for the motor over extended time scales, and neither does it producing good results from which conclusions can be drawn. The situation is aggravated by the absence of a speed controller for the Pearson pump, the need for which is felt especially in times when there are wide fluctuations in the irradiation levels.
Observations with the use of the LCB:
On 3/10/2010, 5 days of system operation with LCB were completed.
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The LCB controller mounted on the wall |
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| Open without the cover |
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| The PCB of the controller with the LEDs flashing indicating the voltage levels |
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| Opening at the cover case in order to observe the LEDs with the cover on |
Experimentation trials:
29/09/2010: First trial with LCB at 13:00
30/09/2010: Full day of experimentation (2nd trial)
01/10/2010: Half day of experimentation. Campus-wide power failure of 3 hours resulted in stoppage of operation and destruction of data from the data logger.
2/10/2010: operation during first half of the day. Heavy clouds were observed after 14:00 until sunset.
3/10/2010: operation during second half of the day due to dark sky.
After connection and operation with the LCB, the following were observed:
- Motor doesn’t stall and noise is smoothened.
- Solar fluctuations smoothened by the LCB. The controller avoids deep and steep changes of motor speed.
- By observing the LCB LEDs which measure the Voltage level supplied every moment, it is easy to predict when the motor speed has to be adjusted (in clear sky conditions).
- Significant Exchange of Voltage with Current occurs most of the time, in order to supply with the maximum instant current possible. However, the limitation of the LCB is 40 A and it cannot give more than that. Luckily, the flow rate corresponding to this limitation coincides with the recommended limit of the membranes for feed flow set by manufacturer at a maximum of 6gpm (gallons per minute). After 5 days experimentation, it was observed that the 40 A were corresponding to feed flow of 6 gpm or higher. As a result, the limitation of the 40A doesn’t effectively limit the system’s capacity.
- The system operates with higher power than before the LCB during low irradiation in the morning and especially in the afternoon.
- Voltage Exchange for one specific irradiance value depends on the type of the irradiation (if it is direct or diffused). In direct irradiation the LCB manages to give more current than when the same amount if irradiation is diffused. For example, in the afternoon the LCB can give more current (corresponding to higher permeate flow) than in the morning, for the same irradiation. It is important to note here that this is attributed to the characteristics of the PV panels.
- LCB works better when there are no rapid fluctuations. When irradiation reduces smoothly, then the voltage levels also reduce smoothly (due to LCB), and current increases considerably.
