I have begun to warm the shady side of my house with reflected sunlight in winter.
This winter’s set-up (2017).
The first photo shows the present temporary set-up, done on the 10th of March 2017. That is, soon after I had changed the house from its summer regimen (to keep cool) to its winter regimen (to keep warm).
As shown, I attached aluminium foil to the courtyard wall on the south boundary of my block. The foil forms mirrors that reflect winter sun onto the south wall of the house, the edge of the floor slab, the footings and some nearby concrete paths.
The mirrors are sheets of aluminium cooking foil (“Alfoil”) 300 mm wide, cut to 900 mm lengths. I attached the foil to the wall in vertical strips with double-sided tape. As the wall is 12.6 metres long, the total mirror area is 11.3 square metres.
The mirrors that were set up in March 2017 were taken down on 1 November 2017. On 5 May 2018, the same “temporary” set-up (as pictured above) was done again. The mirrors were removed on 3 November 2018. I continue to monitor temperatures and plot correlations.]
[Note added October 2019.
During 2019, I arranged to have new mirrors installed, made of aluminium-faced “Foil Board” insulating panels 20 mm thick. Mounted in frames, these would be more robust, and would have the advantage of providing shade in summer.
These new mirrors are not yet installed. Consequently, temperature data for winter 2019 is all in the category “without mirrors”.]
The first trial set-up: winter 2016.
Last year, during April and May (2016), I attached only 17 strips of foil 700 mm long in the same way. The total area then was 3.6 square metres. In that winter, the wind did a little damage, which I taped over. Much worse damage was caused by a magpie-lark attacking his reflection. By October, they were torn as shown in the third photo.
I repaired some of that damage, too, using builders’ foil, which is stronger. On 6 November 2016, I removed all the foil. By then I wanted shade. not sunlight.
Effect of the mirrors
The white-painted courtyard wall reflects nearly all the sunlight it receives. However, this is diffuse reflection, going equally in every direction. Only a small part of it goes to points likely to warm the house.
The aluminium foil reflects in a specular (mirror-like) way, sending nearly all of the solar energy downward at the same angle that it arrived. Because the foil is wrinkled, these mirrors spread the beam of sunlight out to about twice the width of the mirror surface. It is still quite concentrated as can be seen in the last photo, which is lit mainly by reflection from the foil.
Light reflected from these aluminium mirrors is not aimed precisely at points where it would best warm the house. The mirrors are not mobile, and their location owes a lot to chance. Furthermore, the house shades the mirrors for parts of each day; different parts as the season changes.
However, I think the warming effect will be useful, and I hope to be able to measure it.
The mirrors are part of the Courtyard that I have described in posts and pages listed in “My House Page”.
I raised the question of mirrors to reflect sunlight in a thread titled “Reflective Film” on a forum of the Alternative Technology Association in Melbourne, now re-named “Renew”. (I posted as “Catopsilia”, my first post being the 15th from the top.)