Intro: Easy to Build High Powered Solar Water Heater From C-band Dish
This build can be divided into a few easy steps or subcomponents. The Dish, The tracking system, and the heat exchanger/collector.
These are things you will need for this build
1. An old C-Band sattelite dish. These are still floating around in peoples yards and junk piles.If you ask some people will probably let you have it for removing it. You will need the pole,mount and actuator to go with it. If the actuator is bad you can get new ones from ebay for $30-$50. The dish needs to be the solid panel type not mesh, but it can be the spun aluminum (1 piece) or multiple pieces that bolts together. I think some of the 1 piece are plastic or fiberglass this would work too all you really after is the shape. One thing to remember is that size=power and size changes as the square of power so a 5 foot dish will only have 1/4 the power of a 10 foot
2. A roll of mylar mirror film. You can get this from greenhouse supply places for indoor gardens pretty cheap.
3. 1-2 cans of Spray glue available at the big box store.
4. 1/4 inch soft copper tubing. This is the stuff that you plumb to the icemaker in you freezer with. You will also need the associated compression fittings to connect to your home or pool or whatever you're going to use it for.
5. Solar tracking circuit. I got this from ebay for about $30 it has 2 wires for power in from your 12 or 24 volt source and 2 for power out to the output which is going to be the C band actuator.
Step 1: Converting the Dish to Focus Light Instead of Radio Waves
This step is you'll be attaching the mylar film to the dish. Its about as easy as it sounds. One thing to remember is that even though the film may have came on a 4 foot wide roll dont plan on covering a 10 foot dish in 2.5 passes it won't work. Cut it into manageable strips to avoid massive wrinckles. So attaching the film to the dish is as simple spraying glue onto the dish and laying the film on. A few noteworthy hints in this step: make sure you have the dish clean i even went as far as lightly sanding it before i started; after you spray the glue wait about 15 seconds before you start to apply the film so that it becomes tacky and sticks instead of sliding around initially. It should be noted at this point that before taking the dish outside after it has been mirrored to remove the LNB radio reciever from the dish to avoid it melting it or catching on fire and possibly causing damage to the dish, people or property. Also remember that there is alot of power focused into a small point in space. Great care should be given to avoid putting things you dont want destroyed including people or pets. The results will be much more serious than a mild sunburn as this video demonstrates.
Step 2: The Tracking System
This step is pretty much as simple a plug and play. Wires in from you 12 or 24 volt power source and wires out to the actuator. The only thing to think about is polarity. Wire it up if the dish goes the wrong way reverse the polarity of the wires going to actuator. Now you need to put the tracking circuit into a weather proof container. Anything like tupperware or a pickle jar would suffice. The final step for the tracking system is to mount it to the dish in a way that you can fine tune it's aiming to make the focus point the solar collector we'll build in the next step.
Step 3: Building the Heat Exchanger/collector(The "focus" of This Instructable)
As is the theme of this instructable this step is also pretty straight forward. Your going to take copper tubing and make it into a shape to recieve the focused light and put the heat into the water. To determine the size we need to build the collector we need to determine the size of the focal point of the dish. To do this i removed the LNB reciever from the dish leaving the supporting arm in place. This is pretty easily done and shouldnt really need any explanation. Now with the mirrored dish focused at the sun I nailed a piece of scap wood to the end of another peice of wood sufficiently long to keep body parts out of the danger are. At this point hold the piece of wood where the LNB was mounted. Hold it there for about 10 -15 seconds letting catch fire slightly. Now remove the wood from the focus point and lay it on the ground to cool for a few minutes. Measure the size of the blackened wood that you just burned to determine the size of the focus point and therefore the collector. In my case it measured roughly 6 inches across which with my 10 foot dish equates to roughly a 400 X concentration/magnification. Not to make the collector you will need your copper utility tubing. You can get this at the big box store for a few bucks. I used 1/4 inch to allow for sharper bends and close contact with the hot copper. The size of your focus point determines how long of a piece of tubing you need. It usually can be had in lengths of 10 ,20, or 50 feet. I opted for the 20 foot section which was more then enough. In order to allow the tubing to make tight bends you will need to use a little trick I picked up watching them make trombones on "How It's Made". Fill the tubing with water and put it in the freezer for a few hours. If you get a fitting that adapts from 1/4 compression to garden hose this task is really easy. Just remember to have the open ends of the tubing up when you put it in the freezer to keep the water from running out. The ice inside the puting will create a pressure from the inside to reduce the chances of kinking the tubing. It's still possible to kink it but makes it possible to create much tighter radius turns before it does kink. As soon as you pull the tubing out of the freezer start to wrap it around something to give you a nice smooth contour. After the first revolution on your form continue to going around building one wrap ontop of the last untill you reach a diameter slightly larger than the focus point. At this point you have the choice of cutting any excess tubing off or making another rap behind the first in the same manner as the first. after you have done this i decided to solder a peice of copper to supply a little bit of structure. I used a piece of 10 Ga copper wire and a propane torch to accomplish this. One thing to remember here is let the ice melt and drain the water before soldering to avoid being burned by hot water or steam.
Step 4: Putting It All Together and Try It Out
Now that you have the dish mirrored , the tracker wired and mounted in its weatherproof container, and the collector made all thats left to do is to attach the collector to the dish and try it out. You have several options on the on mounting The easiest is to simply wire it to where the LNB used to live. You could go slighly more elaberate but the by adding something like mini pie pan and some fiberglass insulation to the back side to increase efficiency slighly. The original C band actuator and the solar tracking circuit will be tracking from east to west (left/right) for time of day tracking. For seasonal tracking along the North South (up/down) axis dishes are equipped with a threaded rod that can be adjusted with a wrench. To determine the North south adjustment you can simply tweek the nut and look at how the sun is falling on the collector. This should be done every week or so to account for the change in the attitude of the sun for the changing seasons. If someone wanted to replace the threaded rod with another actuator and tracking circuit they could achieve nearly automatic operation. All that is left to do now is hook up the water supply to collector and let it create free hot water for whatever need you find. If you plan to use the dish to heat a hot tub or pool then the pressure from that pump can be used to provide flow through the collector. If the plan is to use the dish for domestic water a small pump will be needed to provide flow through the collector. If the plan is to use to provide heat into a domestic hot water tank you must take provisions to keep the dish from overheating the water in the tank risking burns and massive destruction from a water tank explosion. This could easily be done by with a snap disk thermostat just like the one used on an electric water heater. If the snap disk was wired in series with one of the light sensors on the tracking circuit. In this way when the water tank temperature because hot enough to open the snap disk circuit the dish would simply part itself to one side eliminating the thermal input because the sun would no longer be focused on the collector.