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1B. Principles and Practices


In winter there is no sun in our garden. Once in a while the sun is reflected into the garden by a neighbors window. This lasts just for a couple of minutes but I always enjoy this moments of sun. This made me think - what if I put a mirror on my neighbors roof which adjusts to the sun’s position so that it reflects sun into my garden all day long?

Once I searched the internet I discovered that I’m not the first one to come up with this idea and that such a mirror that adjusts to the sun is called a heliostat.

Heliostat definition from

An instrument consisting of a mirror mounted on an axis moved by clockwork by which a sunbeam is steadily reflected in one direction

As a final project I want to build a heliostat to reflect sun from the neighbors roof into our garden.

Control mirror angle

How do I know how the mirror should be positioned to reflect the sun to the right place? These are some options I can think of:

  • Calculate sun’s position, know target position, calculate mirror angles
  • Sensor at destination (where sun should be reflected)
  • Sensor between heliostat and target

Mirror movement mechanics

The horizontal and vertical angle of the mirror have to be adjustable. There are many possible mechanical designs to have this freedom of movement. I took a look at some existing designs for inspiration.

Open questions

  • Necessary range of movement?
  • When the mirror reflects the sun to a place which is far away (e.g. 100m) a small change in mirror angle leads to a big movement of the spot of reflected sun. How accurate does the mirror positioning have to be to provide an acceptable positioning of the reflected spot?
  • How fast does the mirror’s reflective property degrade when it gets dirty?
  • Can I make it solar powered? That would make it easier to put on a roof
  • It would be really handy to be able to adjust the target location remotely (without having to go on the roof). How can this be achieved?



Focus, transmit, spread

Sunlight can be moved by focusing it with a parabolic mirror, redirect the focused beam to the desired place via mirrors and then spread out the light beam. Video about Lowline - A project building an underground park by bringing sunlight down there

Fiber optic sunlight system

While reading about heliostats I found out that there is another way to “transport” sunlight: “Feed” it into an optical fiber, transmit it, and emit it wherever wanted.

Last update: June 18, 2022