The solar-optimised units come with a CT Meter that allows you to activate the solar-only charging option when you have enough surplus to power your charger. On the other hand, the non-solar optimised unit is a smart charger that works with standard household electrical systems, allowing it to utilise any solar power that is generated (if you have any solar system in place) just like any other household appliance. It will make use of whatever solar energy is available and draw the remaining power required from the grid.