Monitoring power consumption without a multimeter

Projects General Guidance
1

Hello,

I am working on a project to measure a power consumption of a controller that is linked to a BIG source of energy(more than 40V!)

I would like to use a current and/or voltage sensors and here's the problem. Also, I wish to waste as little voltage as possible.

Any idea will be appreciated! I am new to electrical stuff.

2

use a CT to monitor current, and use a solar panel to power everything. voltage is the easy part.