Sun Tracker & Heliostat Safety


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This documentation is part of the Open Sun Harvesting Project.

Here are a few safety tips that you should keep in mind when operating either a sun tracker or a heliostat. This list is certainly not meant to be exhaustive, it is just a collection of some of the more important things that you should remember when operating either a sun tracker or a heliostat.

Please note that sun trackers and heliostats are quite safe when used in a responsible manner and designed with safety in mind. If, however, you go overboard and build something that is either too large or concentrates the light to too high of a temperature, then you should really think twice before setting it up somewhere where it could either harm someone or cause property damage.

Also remember that these are autonomous machines that may or may not behave in a predictable manner. So, for example, do not build a 16 foot parabolic solar concentrator (yes I have actually heard of people building these in their backyard) and just assume that it is not going to run amok and ignite everything that happens to be within reach of its focal point.

Unexpected “Death Rays” from thin flexible mirrors

When building a heliostat it is important that you make sure the mirror doesn’t accidently focus the sun’s light. When a mirror bends it becomes parabolic and the reflected light gets focused into a line. This “line” will get very hot, enough so that it could damage something or even start a fire under the right circumstances.

The below video is from Green Power Science on YouTube. It is a good example of how mirrors can be bent to focus the sun’s light and achieve much higher temperatures.

httpv://www.youtube.com/watch?v=geh1FEpIXuQ&list=PLBEF40B354EAE928E&index=33

You can avoid these “unexpected death rays” simply by making certain that your heliostat has a rigid enough frame for the mirror. As long as the mirror doesn’t bend into a parabola, you will be fine.

Unexpected “Death Rays” from multiple mirrors

A single heliostat with a single mirror is quite safe. If you have a whole bunch setup, however, you can run the risk of property damage. It would take a lot to accidentally start a fire, but the higher temperatures can still do some unexpected things. Through some experimenting, I have noticed that vinyl siding warps at relatively low temperatures. This is why I play it on the safe side and never focus more than three mirrors onto one spot either near or on my house’s siding.

It’s no different than the sun

The reflected light from a heliostat is essentially identical to the light that comes directly from the sun. Since is well  known that the sun can cause damage to your favorite objects (i.e. picture, furniture, etc.),  it would be smart to also keep them out of the path of a heliostat’s reflected light.

My Eyes My Eyes!!!

Staring at the light reflected from a heliostat is no different than staring at the sun, don’t do it! This much you probably guessed, but something else you should consider is that walking  through the path of the reflected light will obscure your vision, probably unexpectedly. This means that someone could accidentally trip when they walk through the light beam. It would be wise not to reflect the sun’s light across walking paths and steps.

Powerful Motors and Fragile Bones

In general, I don’t use motors powerful enough to cause harm should someone put a body part somewhere inside the machine where it shouldn’t be. If you must use a powerful machine for your application though, make sure there is no way someone could accidentally hurt themselves on it.

[bad]

7 Years Bad Luck

When using a heliostat with glass mirrors, it is important to remember that the glass might accidently break into a bunch of razor sharp pieces. Try not to set these up anywhere where someone could easily cut themselves if they do break. (You will especially want to keep these away from young children. The little punks tend to enjoy throwing rocks at things that break.)

You might also look into some of the different reflective foils that are available if this is a specific concern for you.

Flying Parabolas … of DOOOM!

This particular tip is made largely in reference to those individuals who are intent on building some of the more extreme types of solar concentrators (i.e. parabolic concentrators and fresnel lenses). I call these machines “extreme” because the temperature gets “extremely” hot at their focal points. The focal point of some of the larger concentrators can get hot enough to melt steel, and will easily start a fire if you aren’t careful.

I have seen solid, professionally built solar trackers that have been snapped like a twig after freak storms with uncommonly high winds. Obviously, anything that has been blown around in a storm is going to end up in an essentially random location. Had one of these been a parabolic dish or fresnel concentrator, there would have been a decent chance that they could have started a fire.

It is of course entirely up to you whether or not you decide to build one of these machines, but I personally would never make one, except perhaps for applications where the machine  is constantly monitored.

 

This documentation is part of the Open Sun Harvesting Project.

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