The ED uses current transformers to measure AC only current I believe. No DC.
Yes, but I think they said they also measure/monitor solar panel output which would be DC. (Unless it's after the inverter.)
http://www.theenergydetective.com/SolarI see what I will call a mistake on their web page. They call solar an investment. Solar is a horrible investment. A solar system will never increase in value. It's not an investment at all. An investment is something which should increase in value over time like real estate, bonds or stocks.
Solar panels are an asset. They are something your purchase and own like cars, furniture and appliance. Assets can be sold for cash and you don't expect them to increase in value. They are depreciated.
The reason you buy solar is to reduce expenses. Specifically the amount of money you will pay for electricity in the future. Electricity is an expense and just part of the cost of living if you want to use electricity. Buying solar is off-setting future expense of paying for electricity.