One of the challenges of building a passive home is that you want the big windows facing south for the winter to harvest all the light and heat you can, but in the summer these same windows will allow unwanted heat into your home.
I have Passive House certified windows that are very energy efficient and have a high Solar Heat Gain Coefficient (SHGC). This is great in the winter but a bummer in the summer. I did not install indoor blinds or curtains as this does not really do much to keep this heat out. This just blocks your view and I quite enjoy my view.
Outdoor blinds or shutters keep the heat out. You see these quite often in Europe and they are quite effective when closed in the morning and opened in the evening.
I opted for a seasonal solution – outdoor blinds. I put these in the big south and east facing windows. These are Coolaroo Blinds (https://www.coolaroousa.com/) and can be bought at Lowes or Home Depot. They are from Australia and I would think they know about keeping the heat out.
These blinds were chosen specifically due to their lightweight. They weigh between 11- 15 lbs. I have dense cellulose insulation under my siding so not really a great material to attach anything too. The blinds are attached to my window trim which is attached to strapping which is attached to the CLT.
As you can see the blinds allow light in but not a clear view of the outdoors. These also protect your furniture from UV damage.
In the winter, you can uninstall the blinds from the brackets and store them but I will leave mine up as they are protected by the large overhang of my roof.