re-innovation was asked by EvoEnergy to provide a test unit for their solar photovoltaic installations.
During the winter months, solar PV installations may finish after the sun has set. All PV installations should be tested to check that the solar PV panels are working correctly, the cables are good and that the PV inverter (which connects to the grid) is working. It was usually possible to test the PV panels before the sun has set and it does not matter if there is sunlight to test the cables but on a number of occasions the sun had faded before the inverter was powered up and tested.
To solve this problem, re-innovation were asked to produce a unit which would power a PV inverter and act like the PV modules so that the inverter could be commissioned.
To do this we supplied a low power (100W) isolated DC power supply. This unit could be plugged in to a local AC socket and would provide a DC output which would act similarly to a string of PV panels. This can be plugged into the DC side of the inverter and used to power up and commission the inverter.
The final device is shown here:
The unit is wired up as shown here:
The basic wiring diagram is here:
Disclaimer: This unit is at a dangerous voltages. Do not build this circuit unless you are fully trained and competent with both AC and DC supplies.
The main design is a rectifier on the input AC to give around 320V DC. There is a resistor in series with the output cable which, as the inverter draws current, will cause the DC voltage to drop. The inverter will follow the maximum power point and hence pull the voltage down. The resistor will be dumping power, equivalent to the power supplied to the inverter, around 50W. This means that resistor must have a large heatsink and a fan to ensure it does not get too hot. The transformer provides galvanic isolation. The parallel resistor discharges the smoothing capacitor on the output.
These units were supplied with an instruction manual and the installers were trained in its safe use.