EMHEATER Solar Drives allow for simultaneous connection to an AC and DC Power Supply, referred to as Solar Assist Mode. In such a scenario it is important to also install Diodes (Photovoltaic Anti-Reverse Diodes with Diode Voltage = 1600V and Amp Rating = 5 x Solar Drive Amp Rating) on the two DC Cables connecting to the Solar Drive to protect the PV Array from the AC Power Supply. Please also note that some of the smaller kW range Solar Drives only allow for a single power supply (only have one set of terminals) and therefore do not support Solar Assist mode (please confirm beforehand).
Solar Assist Mode Working Principle:
When using Solar Assist Mode (both AC and DC Supply connected at the same time), the Solar Drive will always run the motor at the max speed (and not slow the motor down if the DC Supply is inadequate – as it would do when using a DC Supply only). In Solar Assist Mode, if the DC Supply (PV Array) power is not enough to run the motor at the max speed, the Solar Drive will draw the required additional Amps from the AC Supply. It’s very important to note that the drive will prioritise the DC Supply (PV Array) as long as the PV Array Voc at the time is more than the Rectified AC Supply Voltage (Vac x 1.414), otherwise it will immediately switch over to the AC Supply only. For this reason it is thus important to rather design the PV Array with a Voc value as high as possibly allowed to ensure longer/better DC Supply (PV Array) utilisation (please see the PV Array Design FAQ page Entry for more details regarding PV Array Design requirements).
Switching Examples (switching to AC Power alone due to DC Power Supply Voc being lower than the Rectified AC Power Supply Voltage):
- For SP1/S Series Solar Drives the switching to AC Power alone (no DC Supply utilisation) will occur when the DC Supply Voltage (Voc) is less than 220V*1.414 = 311V (if the AC Supply is 240V it will be at 339 Voc).
- For SP3 Series Solar Drives the switching to AC Power alone (no DC Supply utilisation) will occur when the DC Supply Voltage (Voc) is less than 380V*1.414 = 537V (if the AC Supply is 415V it will be at 586 Voc).
Wiring Diagram:
