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Solar Mirror Array

A proof of concept multipurpose heliostat

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I built a cryptocurrency mining rig, early summer of 2017. My rig runs 24/7 and consumes around 15 kWh in a day. That's about $2.50/day where I live. With that kind of energy usage I started to look around at my options to mitigate the electrical cost while also looking toward the future of alternative energy.

Wind power is not exactly feasible in a city(low altitude and often times never pays itself off. Solar cells are becoming less expensive and abundant but efficiency still stuck at a maximum of 22.5%. I would need quite a large surface area to make up for the inefficiency

Enter Heliostats! They can be built from parts you may have in your own home or can be found for quite cheap online. They can be multipurpose(solar cooker/forge, solar concentrator, telescope, and a light reflector to increase the amount of light on solar cells.)
The plan is to focus the solar mirror array to a 6"X6" area to boil water and run steam through a turbine powering

     To start on this project I first needed to know how much solar radiation at the earth's surface is available in the region I live. There are many maps and charts online. (http://www.kcc.state.ks.us/images/PDFs/charts/Solar_KansasSolarRadiationMap.pdf) I found that average my region receives ~4.1 kWh/m^2/day. This kind of took me by surprise since it means I only need close to 4m^2 to power my mining rig if there were no losses.

      First I needed to figure out what kind of material I could use to construct a frame. An aluminum frame would be perfect for this project but I don't have that kind of money let alone a friend that can TIG weld. After some time thinking about it; I remembered that the student CO-OP I lived at had a pile of old steel bed frames in the attic. I looked into a design with the various lengths of the bed frames and decided 63" x 63" would allow me to have a 10x10 array of  6"x6" mirrors each spaced 1" apart.( later I found a minor flaw in my design). This design also minimized the number of bed frames needed. I don't have a lot of experience in designing structures and probably could have done better to reduce the twisting moment in the frame but I may just tact on some diagonal pieces when its finished.

      I also looked into mirrors, what frequencies of light they reflect and their efficiencies in reflecting light? I don't remember my source but I believe it said there will be about a 16% loss from 1/8" mirrors. I happen to find 3x (3'x6') mirrors on Craigslist for $20ea. I'm trying hard to keep this project as cheap as possible while also making something that will last a while.

      I also need a way to position each mirror individually. As I was surfing around online I ran across some ball head mounts for camera tripods that allow you to pick any angle in a half sphere range. They are the most expensive piece coming in at $1.50 a piece from ebay.(free shipping)  The rest of the hardware can be easily found at any hardware store(nuts, bolts, locktite, paint, etc.)

     The Steam production and power generation planning will come a little later since I need to iron out all the details of how exactly I'm going to implement the system. So far I have pulled a permanent magnet DC motor out of a Treadmill for the generator. I am looking into potential steam engine hacks. One idea is to use a GAST compressed air motor, another is a converted weedwacker engine and last a modified diesel turbo from a school bus engine. It is difficult to find a decent steam turbine that is spec'd closer to my power needs. they pretty much go from handheld hobbyist turbines directly to thousand dollar power plant generators, no middle ground. Please leave a comment if you think of something better!!

Solar Mirror Array.obj

Current Work

obj - 36.12 kB - 09/23/2017 at 01:20

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  • 12 × Steel bed frames Free from Co-op and can be found for cheap on Craigslist
  • 24 × Composite deck balusters Purchased from Lowes. One box holds 14 pieces for $40/per box. (This was originally meant to save weight on the frame but it really wasn't worth it)
  • 200 × 6"x6" mirrors (hand cut) I found 3 (3'x6') mirrors on Craigslist for $20ea. Will need to find more!
  • 120 × 2 1/2", 1/4" 20 All Thread bolt These pass through the composite deck baluster and metal frame to attach Ball head mounts
  • 200 × 1/4" 20 nuts Used to lock down Ball head mounts

View all 15 components

  • Day 5

    wkpsahl09/19/2017 at 23:47 0 comments

    I managed to find 2 rear DLP projection TVs with mirrors in the back of them. When running calculations for surface area of the mirrors needed, I came up short, these 2 extra mirrors should help out. Besides there is a bit of a learning curve for cutting glass so I've got some room to make mistakes. The mirrors were removed from their frames and cut into 6" strips that I will later cut into 6"X6" squares. The cutting process is pretty straight forward, just score the glass, support the two sides with boards, place the score line on the tables edge and press downward. The next steps will be to sand the edges of the mirror and then seal them with specifically designed outdoor mirror sealant, then cut a 1/4" hole in the center of each mirror in order to attach it to the ball mounts. 

  • Day 4

    wkpsahl09/19/2017 at 17:47 0 comments

    Each frame requires 64X 1/4inch holes to be drilled into the steel. I spent half the day drawing out the positions onto the frame, part of that time I spent fixing the problem I mentioned earlier about not taking the material width into account (rookie mistake). The enemy of high speed steel drill bits is heat!! and I can tell you now that it's not easy to slowly drive a corded power drill while also spraying lubricant on the bit. After getting frustrated a couple times and just letting the drill bit spin in the steel and ruining a couple bits, I decided it was prolly worth buying a couple of cobalt bits designed for cutting hardened steel. 

  • Day 3

    wkpsahl09/19/2017 at 17:32 0 comments

    We are finally ready for welding up the frames!! After cutting all the steel I decided it was probably going to be too heavy and so I looked at options to reduce weight. I believe I could replace 3 cross beams per frame quadrant for total of 12 per frame with Composite Deck Balusters. They certainly weren't cheap at $40 per box of 14 at Lowe's. It wasn't exactly a drastic reduction in weight but it will work. My step-dad attempted to weld the corners with oxy/acetylene torch but the joints would crack as the angle iron cooled so we switched over to an arc welder that worked perfectly and we didn't even need to brush the paint off the bed frames before starting the weld. In the image above you can see the completed frames with the balusters setting in place. 

  • Day 2

    wkpsahl09/19/2017 at 17:16 0 comments

    After having the dimensions planned I started cutting the bed frames into 63" long pieces. With that length it will allow 1" of space between the mirrors (I forgot to take into account the thickness of the angle iron itself and therefore lost 3/4" of space between the outermost mirrors and the second outermost. I later fixed this by giving a 1/2" of space to the outermost and 3/4" to the next outermost. If anything it will just give it an interesting look in the end.) I chose to make a notch and cope joint on the corners and lap joints for all the cross beams of the frames. All of the cutting was done with an angle grinder by hand. 

  • Day 1

    wkpsahl09/19/2017 at 17:00 0 comments

    Today I spent cutting apart the bed frames and removing all the rivets with an angle grinder. I would grind off one side of the rivet and then use a punch and hammer to drive it out the opposite side. Later after getting length measurements from the bed frames I sat down and drew up a plan for the frames. I found that having a 10x10 mirror arrangement allowed minimal use of steel while also keeping it structurally strong. You can see this in the image with the red,orange, and green highlighter.

View all 5 project logs

  • 1
    Cut Your Mirrors

    Find or buy a good quality glass cutting pliers. This tool has a glass cutting wheel on one side and a pliers/breaker on the other.

    When dealing with large mirrors make sure your cutting surface is always FLAT and CLEAN. Put some double stick carpet tape on the bottom of your straight edge. The first step is to cut the large sheet into 6" stripes. Measure out 6", lay the straightedge along the line on the glass and use the glass cutting wheel to etch the line all the way across. Do not retrace the line, press hard the first time and keep the cutting tool pressed slightly toward the straight edge or IT WILL WANDER. Place the score line on the edge of your table and put a piece of wood on top of the piece you are going to break off. Gently applied force until the glass fractures. If you did everything correctly it should break perfectly along the score line.

    Repeat until all the strips are cut and then start on cutting the 6"x6" pieces. Instead of using the table method to break the 6"x6" pieces off the strip, use the pliers on the tool to apply pressure on the score line and you will get a really nice yield from your mirrors! Make sure to keep your work area clean and also clean the mirrors off before you stack them or the small piece of glass will scratch your mirrors when you move around the stacks.

  • 2
    Your Regions Solar Radiation

    Go out and search online to find a couple reliable sources for intensity of solar radiation for your region and use that data to determine if this project is going to be feasible or useful to you.

  • 3
    Start Cutting/Grinding

    If you chose bed frames like I did you need to cut/grind away the rivets holding the pieces together. I used an angle grinder with metal cutting wheels(NOT GRINDING). Use a punch and hammer to knock-out the rivets once the heads are gone or just hit the piece on the cement. Cut all the pieces down to their predetermined length. I chose to use coped joints on the corners because it provides more surface area for stronger joints.  I used lap joints on cross beams by simply cutting out a section on the end of the angle iron.

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Discussions

wrogerwroger wrote 10/12/2017 at 02:39 point

I have done the same thing, but for killing the neighbours trees..

The shit head next door with the drug habit and his over growing jungle....

Australian trees need a 25:1 concentration ratio too cook off the leaves, branches and stems - 16:1 is not enough.

But with a fixed focal point of say 15 meters, and using 5cm2 mirrors, you can cook off the tops of the trees...

Really though - your best off making a defined focal point and a dish to mount the mirrors in...

An offset parabola is the best shape

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wkpsahl wrote 10/12/2017 at 15:02 point

Yeah!! That's almost exactly the same as my project! It will have a constant focal distance but the dish shape is not necessary because each individual mirror acts as an approximation of the parabolic shape. Sort of like a Fresnel

  Are you sure? yes | no

wrogerwroger wrote 10/12/2017 at 19:00 point

Na I mean rather than having many elements that need to be INDIVIDUALLY focused on to a specific target at a specific distance, it's better to get a whole heap of mirrors and to bond them to a surface, that has a preset focal point. Like in this photo half way down the page - http://www.scmp.com/news/asia/australasia/article/2072320/australias-victoria-get-its-first-large-scale-solar-plants

Or Google: solar cooker satellite dish

http://www.sevengraylands.com/brain/projects/disco-satellite-dish/

You will find that having "many, many, many" fiddly bits IS only OK for a VARIABLE focal length set up..... And the more rigid the whole HUGE assembly needs to become, and the difficult it becomes to work them, over longer or different distances.

That is why genuine power only systems, have every thing locked into a single configuration. You know ONE (multi piece) reflector, rather than many separate reflectors.

With the picture of the solar power station on your page - here, each of the mirrors has it's own computer connection and 2 axis drive system -

It also has the advantage that by properly bonding the mirrors to a satellite dish with beads of silicon sealant, etc., you have keep the water away from the films on the back....

And for fucks sake, get some shade 3 or shade 5 oxy welding goggles or welding prefilters, on when pissing around with these things.

Your eyes were NEVER meant to look at concentrated sunlight shining on and reflecting off anything.

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mathieubrazeau wrote 10/12/2017 at 00:14 point

You could also add thermoelectric plates to convert heat into

electricity...

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wkpsahl wrote 10/12/2017 at 01:08 point

Are you talking about something like a Peltier effect plates? From the wiki page "Its(Peltier) main disadvantages are high cost and poor power efficiency."

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Joe Sestrich wrote 10/11/2017 at 19:41 point

Are you planning a mechanism to track the sun across the sky?

  Are you sure? yes | no

wkpsahl wrote 10/12/2017 at 01:11 point

Yes I am working on a design to move both frames jointly to track the sun. I've been discussing alternatives with a friend that may move the "Pot of water" instead of the array. When the frames are fully assembled they are about 120lbs as just a guess. I didn't really care too much about weight in the end.

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Robert Poor wrote 10/11/2017 at 18:46 point

I wonder if a Stirling cycle engine might better serve your needs.  They're relatively efficient, they work at atmospheric pressures and don't have all the headaches of boiling steam (water supply, scaling from minerals, etc...)

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wkpsahl wrote 10/12/2017 at 01:14 point

I looked in to them as well but found that they aren't the best at higher torque loads, do not scale well, but also it would require a heat differential on the cold side which is harder to achieve in the summer when it will be bringing in the most energy. The reason they work so well as desktop display pieces is because of the greater volume to surface area ratio at smaller scale.

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Tom wrote 10/11/2017 at 18:22 point

Love this idea,  I have been thinking about something similar for a long time.   I played around with the Tesla turbine,  its build-able and there are several youtube tutorials on them.

  Are you sure? yes | no

wkpsahl wrote 10/12/2017 at 01:16 point

What kind of efficiency are you getting out of it? For me it has been hard to find anything decent on youtube.com because the tesla turbine seems to be tied in with a lot of the fanatics that are with "Free Energy"

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Tom wrote 10/12/2017 at 12:24 point

Mostly just dreaming and a quick and dirty model made from plastic and ran with compressed air,  it spun:-)  other than that I didn't do any real tests.

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