# How to design a static heliostat?

An heliostat is a device capable of reflecting the sun in a fixed point while the sun itself moves into the sky, thanks to a moving mirror.

But this company astonished me with its invention: a static heliostat! Rather than mounting a mirror on a pan&tilt mechanism, they designed a curved mirror which, at any time in the day, reflects sun in a same point (actually same strip).

http://cleardomesolar.com/solareflexpanels.html

How can I design a static mirror which reflects a sun-strip over a wall all along a day? Let's suppose I have these data:

• Wall exposed to North.
• Mirror 5 meters away.
• Apprximate location: 42N, 12E.

I am trying experimenting with Geogebra and OptGeo but with no luck so far.

I can reorient the mirror by hand every week or month, but I don't want to have to reorient it hour by hour!

Geogebra example:

https://www.geogebra.org/m/ukkrcv3c

Optgeo example:

Maybe Sunpath3d page can help:

http://andrewmarsh.com/apps/staging/sunpath3d.html

https://www.sunearthtools.com/dp/tools/pos_sun.php

• The exit is fantastic, thanks! I'll delete my old answer and if there's not already a great answer in the morning or if there is and I have something to add, I'll post something new. Thanks!
– uhoh
Mar 26, 2021 at 14:15
• it is less easy than it seems :-( Mar 27, 2021 at 8:10
• It would be trivial in Blender, but I'm not good at it yet. See answer(s) to How to simulate reflection of people in a 4 meter parabolic mirror to show that they won't appear upside down? I'll add a simple calculation for a conic section mirror in 1D soon but using normal math/python, not Blender.
– uhoh
Mar 27, 2021 at 9:11
• This is still in draft, but the simulator allows viewing how sun is reflected along a wall during the day (sunAngle parameter) and during the year (seasonAngle parameter). It's weird to notice how on some specific positions of mirror, the line representing how it moves along the wall rotates along the year, but it always pass in one some point. If it's true and it's not a geometry error, it could be very important for an heliostat. Geogebra project: geogebra.org/classic/xg9uqpqn Mar 29, 2021 at 19:09
• This new project shows how a circular mirror (seen from above) could produce a sunstrip covering a wide angle, depending on circle radius and target distance: geogebra.org/m/w6sfffwk Apr 12, 2021 at 11:02