Heating...? Front is all window!

[ApS]

Upthesaukee brought up the topic at the "visitor at our front yard" thread, and suggested that it needed to be a new thread.

Here it is!

To extend my place's usefulness into the colder seasons -- maybe all year -- I'm thinking of adding a poured concrete 1st floor to be used independently of the raised cottage above. (Some would call it a basement, but it's on a steep hill).

If I get my way, it would have tall windows all across the front for light-gathering and view-gathering -- but for the heating concern.

How does one start off today with heat?

(The windows would face NE, and may include a small bay-window extension).