Welcone, Denzil, to the OEM forum.
I think, depending on how much solid house is between the utility room and garage, which will determine whether the 433 MHz ISM band radio will reach, you need an emonPi in the utility room measuring the house consumption and the PV infeed, and an emonTx in the garage measuring the nett grid power and garage consumption, both with 2 c.t’s and an a.c adapter, and the emonPi also needs a 5 V d.c power supply. (So a single socket for the emonTx, a double for the emonPi.)
If you’ve got decent Wi-Fi coverage in the garage, you could swap those around and have the emonTx in the house, giving you the availability of two spare channels in the house should you want to measure a couple of circuits independently.
If the integral ISM Band radio won’t reach, then if you have WiFi coverage in both places, you can add the ESP8266 module and a 5 V d.c. power supply to the emonTx (so a double socket now), to use WiFi instead of the 433 MHz ISM radio.
(Please can you add the country you’re in to your profile. From the way you write, you’re in the UK, but it’s helpful for us to know because different countries and jurisdictions do things differently.)