Building a Parabolic Solar Hot-Water Heater using 123D

For this project I set out to create the solar equivalent of the hot-water tap on a coffee machine: a solar on-demand hot-water heater.  I was inspired by the functionality of a new software called 123D-Make that makes it easy to build large, geometrically precise forms.  My goal was to build a device using 123D-Make that illustrates the power of the sun and has many practical uses.  I decided to make my solar water heater by creating a mirrored parabolic dish that focuses sunlight to a point, then add copper tubing that runs a thin stream of water through the very hot focal point, creating near-boiling water on-demand.  By creating a way to boil water without electricity or gas, this project will hopefully lead to less Carbon Dioxide emissions and be a net-positive for the environment

Tools:  

Calculator (or spreadsheet)
123D (free CAD software by Autodesk)
123D Make (free slicing software by Autodesk)
CorelDraw or Inkscape
Laser Cutter (a shopbot or waterjet would also work)  I used a 120W Epilog Legend 36 EXT with a 36"x24" cutting bed
Utility Knife
Hot Glue Gun
Spackle Spreader
Paintbrush
Hammer
Pipe cutter
 

Materials:

Plywood
Wide Masking Tape
Spackle
Sandpaper (Coarse & Fine)
Paint (to use as a sealant) like Acrylic base or Polyurethane
Stick-On Mirrored film
Thin copper tubing
1/2 cup of table salt
High-temperature black stove paint
1/2 inch metal conduit pipe
Rubber tubing. Use high-temp stuff if you plan to use it for a long time.
 

Step 1: Is it Possible?

My first step was to do a calculation to figure out if my idea was crazy.  I started with my goal:  Make the solar equivalent of the hot-water tap on a coffee machine.  

How much power do I need?

Lets say I want to fill up my mug with hot water in about 15 seconds.  That means I'll need to do about 1 liter per minute starting at room temperature (~20°C) and ending at tea temperature (~80°C).  That's a 60°C temperature change, and water has a heat capacity of 4.18 kilojoules per kilogram °C.  So, for 1 liter (one kg.) we need 250.8 kilojoules.  To do that in 60 seconds, we need about 4.2 kilowatts of power.  That's a lot!

How big of a mirror is that?

In most places, on a clear sunny day, there's about .8 kilowatts of sunlight per square meter.  That means that we would need 5.25 square-meters of mirror, which would be a dish 2.6 meters (8.5 feet) across!

That was a lot bigger than I could make, but it gave me an idea of scale.  For example, if I could wait 1 minute instead of 15 seconds for my cup of water, I only needed a 4-foot dish.  In the end, I decided to make a 36" dish because that was the biggest I could make on my laser cutter without slicing up my support rings into smaller pieces (which is certainly an option.)

 

Comments

[nsundqvist]

Nice work!!! Whot do you think about my heater?

http://www.youtube.com/watch?v=a2b7c9WnRhA

[nzqwack]

Using Copper pipe polish it then Just heat it up with a gas flame and surface will oxidise to copper oxide on air contact in seconds which is black saves having to paint!

[M2Field]

How come you did not simply use a discarded satellite antenna for this project? Would have saved a ton of time and calculations. The receivers are already mounted at the focus point and the bracket is already made to the correct length.

[roccopeterbilt]

This was going to be my question. Be really cool to get one of the big old ones that had a diameter closer to what your data showed you needed, then swap out the copper coil for a magnifying glass and make a death ray!

[straight]

I had an experience like you bt the biggest problem was the sun movement as you know after minuts you have to change the dish location .do you have any solution for this problem? Id like to know your idea .thanks

[person%]

awesome! i want to try that!

[grt57]

Bacon is good!

[rkrayer]

Great instructable. Would love to see ideas for heating or supplementing a conventional tank-style water heater.

[Buckshott00]

The best way to do this would be to setup a thermal battery and recirculate a thermal fluid between a storage tank and the heating coils of your water tank. If you're on a budget try it with peanut oil. It has a decent heat transfer coefficient and can go to around 475F before it starts to degrade, plus it is way cheaper than a lot of other materials. You have to really insulate your tanks and lines. Again for the budget minded I would suggest Superwool and Dap or Great Stuff. There is better choices but those are pretty good and won't break the bank. The only trick is sizing your thermal battery to be large enough to meet your hot water demands given losses to inefficiency in the pumps, lines, and transfer. Although if you lived in the southwest US you could meet the US average quite easily.

[icej75]

ben for some ideas here is a professional solar cooker we make where I work. this is a write up on a customer's opinion on it.
http://www.solarcooker-at-cantinawest.com/andersen-solar-cooker-parabolic-with-optional-rotisserie-motor.html

[Kold]

hey, your video is private! i really wanted to see this thing work =D

[Linksep]

Wahoo! Video fixed (I like my bacon a little crispier than that though).

[ben.chapman]

The dark part of the bacon cooks well. The white fatty part is harder to get cooked since it reflects more of the light beaming at it.

[alcurb]

You need to be in his inner circle :-)

[windshadow]

Yeah dude what is up with the video ?

[mikeputnam]

Bump! Cannot view the video.

[Linksep]

Bump +1

[mbainrot]

Bump +2 :)

[ben.chapman]

Hi All, The video should now be public. I forgot to hit save the last time I tried to make it public (and I've been backpacking for the last 4 days). Thanks for all the great comments!

[rhino]

Very worthwhile project. Can I accomplish the heater by gluing mirror tiles to a satellite dish?

[ben.chapman]

Yes. I've seen a bunch of successful projects that do that. You can probably find the mirrors that they use for Disco Balls quite cheaply.

[RAYLOGAN5]

I have gone thru all of the steps and now I am stuck. How about showing where the motor and tracking PHOTO LED'S STRUCTURE is made and where it is placed in order to make it work?

Regards,



Ray E. Walters

[maewert]

The author didn't show where to place the motor because his instructible didn't include a tracking motor. As is you have to manually point it. Shouldn't be too hard to add one though.

[Wazzupdoc]

Sweet!. If you reversed the "mold" shape, you could do a gelcoat male mold and pop out fiberglass parabolas by the blimp-load!

[godbacon]

covering the coil with glass would help it retain heat,block wind.
Adding some thermal mass around the coil would allow it to store a bit of heat, for passing clouds and the like. If you were to put the coil into a block of concrete say inside a mason jar,using a black pigment to color the concrete I think you would get a more even heating of your water. Good luck with the application,it was a nice instructable.

[devonfletch]

You can make a very simple parabolic reflector by taking a flat sheet of Stainless Steel, and bend it in one plane, to conform with a couple of ply (or other) parabolic frames.
Then, a straight piece of pipe across the focus, will harvest the heat and Bob's-your-uncle.
This configuration also has the advantage that it does not need a tracking system, just maybe a weekly adjustment up or down, to follow the sun as it 'travels' around the ecliptic.
Good shiny SS can be found in old clothes-dryer drums (the outer surface, the inner being shot-peened by the metal zippers and buttons), and SS appliances (the inner surface, the outer normally being brushed).
This system will not deliver boiling water, unless you live in Mexico, but it's a very good heater for general hot water applications.

[tabi]

Could you post some pics? this sounds great (and I do live en Mexico hehehe)

[maewert]

I meant a 3" concave mirror shiny side to the coils :-)

[maewert]

Nice instructable.

Maybe you'll want to add a convex mirror on the end of the boiler tube to focus any stray light back onto the boiler coils as it appears some light is missing the coils.
See the image for a really bad attempt to show you where to add the convex mirror.

Maybe you will want to add a solar array to generate electricity to run a small pump that would pump water from an insulated tank into the coils and back again. That way you'll be able to quickly fill your tea cup a few times a day so long as you let the system recharge (and you'll still have a cup of hot water after the sun goes down).

Adding a tracking system should not be too difficult. You'll want even more solar PV cells to drive the electronics :-)

[guruji1]

Great work my friend although if you had a satellite dish you would have half the job ready. Anyway thanks for sharing this.
Regards

[AllenInks]

re tracking: I remember an article fom Mother Earth News from back in the 70's tsome one had a dish he wanted to track the sun.. they had two ram actuators, plumbed to two flat black reservoirs. the reservoirs were mounted to rotate with the dish. the one on right had baffle shading it from sun rays from left, but could be warmerd by sun rays from right. similarly, the one on left was baffled to be shaded from right and warmed by sun rays from left. the reservoir on right was plumbed to actautor that extended to turn dish and reservoirs to right, and reservoir on left plumbed to actuator to extend to turn dish to left. thus when sun is to tp right of dish, iit warms reservoir on right and not the left, causing dish to rotate toward sun .dish stops when both reservoirs are warmed equally, and dish is pointing at sun. as sun moves, heating is unbalanced again, anf reultant difference in reservoir temps changes volume of fluids in each system, to cause actuators to work to rotate dish back into alifhnment with sun.... no electricity required.

[Bill WW]

Great, Ben; I will be back to study in detail!

Re: good comment from Rimar on Juy 2, he recommends 1 m^2 minimum area.

Incoming solar energy is max 1000 W at surface of Earth. So we have about 1 kW to work with, our challenge is to convert as much of this resource as p
ossible to useable heat and electrical or mechanical energy.

[Bill WW]

Oops! Sorry Ben, should have read your Step 1 more carefully.
You said : "In most places, on a clear sunny day, there's about .8 kilowatts of sunlight per square meter. " That is more realistic than my 1 kW per square meter.

[profpat]

nice one, very nice for the environment!

now if could just recycle those old satellite disk in the dumpster!

[breeeez]

Why would you heat hot water?

[spencer2710]

to make it hotter! duh...

[JAMEJO]

Exactly right !!!! People always tell me they want a new hot water heater, and I make the same comment: It's "water heater". It could be called a hot water tank, but it's definitely NOT a "hot water heater". Pet peeve.

[AllenInks]

actually, most water heaters ( tank water heaters) here in US are hot water heaters. even at rhe moment that heaters turn on, the water is hot, heaters just turn on to make it hotter. otherwise, if the water were cold before thermostat would turne on heters, then sometimes when you open hot water faucet, you'd get cold water, and sometimes you'd get hot water. Of course, a tankless water heater is another matter...

sorry to rain on your pet peeve....

[rdavis184]

Good job.
BTW, it's a water heater, not a hot water heater. Hot water doesn't need to be heated ;-)

[spencer2710]

It does if you want it hotter!