I happened to stumble across this today and thought it was worth a mention.
This is not a recommendation, i just thought it was noteworthy as there have been various discussions about monitoring DC on the forum and I have had some good results using the PZEM-014 and PZEM-016 AC energy monitors.
It seems the PZEM-017 DC monitor is also modbus over rs485 and works using an external shunt, it is available with a range of shunts (50A,100A,200A,300A) and appears to be the same unit otherwise, there is a modbus register to set the current range (ie shunt used).