We built our house with a full daylight basement that includes a mother-in-law apartment. This means that all rooms, except the bath and laundry room, have large egress windows. They allow enough light into all rooms, so the basement is nearly as bright as the main floor. There is a large window well around the outside of each of these windows.
In years past, my husband made frames for the south-facing windows. These frames were covered with builder’s plastic and functioned as mini-greenhouses when we started our garden plants. On sunny days, we could open them to warm the living room and bedroom. If the temperatures were going to plummet, we could easily pull the plants back into the house, so they would not freeze. There are two drawbacks to this method. It is not possible to see outside through the plastic. The plastic only lasts a couple of years.
My recent Internet search for more permanent window well covers was rewarded. Window well covers made of Plexiglas can be custom-made for any window well. Some of these covers come with the well surround attached. I suppose they do not come cheap but neither does a greenhouse and these are multipurpose. Having the wells covered will keep the house warmer in winter. I will no longer have use a step stool to get down into the well to rescue the small animals that sometimes fall in. I do not know if they will make the house hotter in the summer, and that is something to consider.