DC power meter suitable for a data logger?

I'm installing a multi-part solar PV system to do a head-to-head test of three different panels. I'll gang the panels into an AC inverter that I already have, and drive a test load of four 100 watt light bulbs. My installer wants to grid-tie and pay for the data collection at least, but I haven't made my way through the maze of local regs yet.

Since the power is being ganged parallel into the inverter I'm going to need to log upstream on the DC side. I'll likely end up with the 4- channel HOBO (U12) as the basic collection system, but they don't sell a DC power meter.

Can anyone suggest a DC power metering solution with a suitable output? The U12 supports "any third-party sensor with 4-20mA or 0 to

Thanks!

Maury