17 August 2008

Whilst Michelle and Adam are away I've had a chance to start playing with making a heliostat for directing sunlight into the lounge in winter.

The main windows in our lounge faces 23 degrees off west. This means in winter we get very little sun till late afternoon. So why not build a reflector to bounce some free sunlight providing extra light and a bit of heat?

What is a heliostat?


  • In order to provide substantial benefit I should have the reflector track the sun - a tracker is quite a lot of hassle
  • The sun is real powerful - looking into the reflector would/could damage your eyes
  • I need to make sure it never bothers my neighbours


  • It's coooool
  • Sunlight is free
  • Sunlight is good for your mental and physical health - especially in winter
  • I'll learn some stuff

So... yesterday I glued some sisilation (aluminium reflective insulation) onto a single 2400mm x 1200mm sheet of 3-ply plywood. The sisalation was left over from my insulation frenzy a few years back. The aluminium is reasonably shiny - it's not a mirror finish, but good enough for playing/experimenting.

And today the sun came out and I had a quick play to see if this was going to work at all.

Attach:heliostat01-500x375.jpg Δ|First experiment with the heliostat.

And yes - it does throw a noticeable patch of sunlight onto the lounge windows.

Attach:heliostat02-400x300.jpg ΔAttach:heliostat03-400x300.jpg Δ
Without heliostat.
Photo taken from behind the heliostat.
With heliostat. Notice you can see light inside the lounge through the french doors. The camera was on auto exposure mode so there's a bit of shift between the two pics too.

What next

  • Build some sort of frame so that it doesn't blow away in the wind
  • Do I want to build a tracker?
  • Would it work "good enough" if it set it on one place in the morning and let it drift across the wall over the morning?
    • need to plot the path over a morning
  • Is it better to have a flat heliostat (unfocused) or focused? Focused would be more dangerous - so probably not.

20 Sept 2008

I've had the heliostat positioned resting against the garage door at just the right angle to reflect 9am sunlight into the kitchen, and by 10am it drifts over to the lounge windows. That seems to work OK.

The main problem to resolve is when you're inside, looking out the window, you get the full glare of reflected sunlight. I'm cogitating on that problem. Hopefully a solution will occur at some point.

Last weekend we had several days of beautiful sunny weather and everything warmed up. We didn't need any room heating (day or night) and the solar water heating was giving us 54o C. Our electricity usage dropped from 25 Units to 12 Units. So - nothing beats a sunny day.

General thoughts so far:

  • install a dome skylight and reflect the sunlight into that?
  • build another heliostat for the solar PV panels on the roof? (Could just mount it flush on the roof so that it reflects some winter sun.
  • add winter reflectors under windows to reflect some sun up onto the interior ceiling?

29 December 2008

The heliostat is hidden in the garage now that it's mid summer. We don't need any extra light or heat.

Page last modified on May 03, 2011, at 05:06 am
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