Читать книгу Solar Water Heating--Revised & Expanded Edition - Bob Ramlow - Страница 43

Many solar water heating systems are installed with a DC pump so that it can be powered directly by a solar electric or photovoltaic (PV) module. DC pumps come in three configurations: brush, brushless and electronically driven. This designation relates to the type of motor that drives the pump.

Brush-type motors use brushes made of carbon that contact the commutator, which is a cylinder in the motor. These brushes wear away over time and need to be replaced periodically. Brushless motors are electronically commutated and, obviously, have no brushes. Brushless motors work better in photovoltaic direct applications, but brush-type motors can work fine. Brush-type motors have a harder time starting up when powered directly from a PV panel. They will start, but not as quickly as brushless ones.

A linear current booster (LCB) can be installed between the PV collector and the brush-type motor to help the brush-type motor start more easily. LCBs need to be properly sized to match the PV collector and the pump, so do your homework if using an LCB.

Electronically driven DC pumps fall into the category of brushless pump, but they don’t have a conventional motor. These pumps use electronics to spin the impeller. Several brands of this type of pump have been developed specifically for the solar water heating industry, where low to moderate flows are required. One model even has built-in circuitry with maximum power point tracking (MPPT), which adjusts the voltage and current coming from the PV module to maximize the amount of power it is producing. Neat stuff.