A DC surge protection device (SPD) protects your system from overvoltage due to lightning strikes or unusual high voltage spikes from the grid. In this article, I will talk about installing a surge protection device for solar panels. You size the surge protection device according to the voltage of your solar array, whether its wired in series or parallel. Let's say the combined voltage of your solar array is 500VDC; then, you need to get an SPD rated at 500VDC. There are many 1000VDC. Do solar isolators need to be double or single pole? I have written an article about it: Do solar isolators need to be single or double pole? Wiring an SPD is relatively easy. After your solar disconnect, take the positive and negative and bring it to the input of the SPD device. The output of.