Two PMBLDC motor/fans of different ratings (9.5 W and 20.3 W) were tested with a 10 Wp PB Solarex polycrystalline PV module at Napier University in Edinburgh. Initial tests were performed on the PV module and each of the fans separately for performance evaluation and determination of the motor/fan constants given in Eqs. 2, 3, 6 and 8. Each of the PV module-fan combinations were then installed in a slate roof section and performance was monitored

1.3 The PV module

The method used for predicting the PV module I-V characteristic as a function of irradiance and module temperature requires the measurement of the PV module reference I-V curve. Voltage and current were recorded for different selected resistive loads using two multimeters and a variable resistor. The reference data and derived constants for the 10 Wp module are shown in Table 1. Figure 2 shows a comparison between measured I-V curves and those generated by the newly developed method.

1.4 The motor/ fan

Due to the absence of motor parameters from existing manufacturer’s data, stall conditions, no-load conditions and Eq. (7) are used to evaluate motor parameters. Table 1 shows Ra, Km and Kf for both motors.

Manufacturer’s H-Q curves for the two fans are shown in Fig. 1. These curves are generated from the affinity fan laws at ю = 2000 r / min.

The fans were also tested to determine their I-V curves as shown in Fig. 2. Furthermore, measurements of speed and voltage were carried out in the roof section where the fans were installed. These measurements serve as a means to calculate the measured speed from voltage measurements across the fan. The reason such a relationship is needed is because it is possible to log voltage data into a data logger while this is not possible for speed measurements.

1.5 Roof section

The fans were fixed into a plenum centred between the rafters in a roof section which was prepared for solar preheating and ventilation testing. Irradiance, module temperature and the voltage across the fan (V) were measured for several days at 5-minute intervals. Irradiance measurements were obtained using a Kipp and Zonen pyranometer directly connected to a data logger. A k-type thermocouple placed in the middle at the back of the PV module [14] was used for temperature measurements. The voltage of the motor/fan was also logged into the data logger.