For now, let's content ourselves with just a parabolic solar concentrator.
Before we begin, it is important to know that concentrated solar energy is very dangerous. Reasonable precautions should be taken. I cannot take responsibility for individual choices you make in the design, construction, modification, or use of this project. Have fun and be safe.
Step 1: Obtain parts
1) About 17 aluminum angle stock rods 5/8 inches (or thereabouts). An aluminum siding store will probably have this much cheaper than your corner hardware store. They're friendly folks, usually.
3) Some chrome-plated aluminum sheeting. Again, an aluminum siding store will usually provide this. You may have to special-order it. I ordered it under the name "light sheet". I am not sure if it was a brand name or a description. You will need approximately 40 square feet of it and ask them to cut it into 6 inch square mirrors. They will try to talk you out of it and think you're crazy for asking them to. They will also charge you for the cutting service. Let them. They deserve to make an honest living, but ask them to be careful in cutting it into _exactly_ 6 inch squares.
4) About 300 machine screws, 500 machine nuts and about 500 large washers. I used 3 inch screws in a 10-32 pitch. 10-24 is sometimes cheaper. It doesn't really matter, but be consistent. 10-32 and 10-24 look just alike and with so many of them, you won't want to waste time sorting them.
5) A screwdriver, drill, wrench, and ruler that will measure inches and millimeters.
6) Various other common household tools.
7) Some creativity and basic high-school level geometry.
For the heat-exchanger (if you choose to build it)
8) A length of 1/2 inch copper pipe and about 20 "T" junctions, some end caps, solder, propane torch, gloves, a little soldering know-how.
Step 2: Measure, cut, measure cut
Next, measure accurately an interval of 6 and 3/8 inches. This is VERY important. I took a small piece of medium density fiber board and drilled two holes VERY CAREFULLY to be exactly that distance apart. Then, I took a hole punch and a hammer and pounded small dimples into the soft aluminum at this interval all across the length of the angle stock. Do this for each of 13 of the angle stock pieces. This means more than 160 dimples exactly the same distance apart.
The reason they must be so carefully measured is that the mirrors are all 6 inches square. The machine screws are 3/8 inches wide. This means you will have space for one mirror, one bolt, one mirror, one bolt, etc.
Step 3: Drill, drill, drill
Measure halfway in between the 6 3/8 inch intervals on the first, last, middle, and 1/4, 3/4 up each bar.
These will be the holes for the cross-beams.
Now, each of the dimples that was made will be drilled out with a 3/8 inch drill bit. This is a lot of drilling and I highly recommend an electric drill and some understanding neighbors. It will be loud because the aluminum will ring as you drill. That's ok. Also, because you're using power tools, don't forget to keep your fingers clear and your eyes protected. I got a piece of aluminum in my eye once. I do not consider eye injury to be an important step for completing the project, so wear eye protection.
Once drilled, you will want to file the holes flush because aluminum is soft and as such creates lots of sharp edges when you drill it out. An ordinary file will help you remove those edges so you don't slice your fingers.
Step 4: Assemble the frame
Take another couple of scraps of aluminum and do a pythagorean theorem problem (you know, x2+y2=d2) to figure out how long the triangle brace should be. A 3-4-5 right triangle is a pretty good one to apply. In the picture, you will see 2 of these triangle pieces.
Now that the assembly is fairly stable, start inserting the 3 inch machine screws. You may want to use 4 inch screws around the outer edges. You'll see why later. Hold them in place using a machine nut. This is perhaps the most time consuming part of the project.
Step 5: Mirror alignment.
What happens is that when you get past the 3rd row out from the center is that your distance up each screw starts to get bigger than the screw is long. This is not really a problem. The trick is to offset all sides of a given mirror so that the lowest edge is as low as you can make it. What you get is rows of mirrors at the same angle, but not in the same plane. This is similar to a fresnel lens for those who understand optics.
If all of this is lost on you, I have attached a screenshot of the spreadsheet. This is a list of the mirror offsets for each of the mirrors as measured in millimeters. This will give you a focal distance of 72 inches. It works fairly well.
Step 6: Focal Assembly
NOTE! When you're not around the concentrator make VERY SURE that it is pointed in a direction that the sun will NEVER be. It WILL catch things on fire. Think very carefully about how the sun moves and remember that it traces out an arc in the southern hemisphere (northern if you're an Aussie).
The broom below took only 30 seconds to burst into flame. I cannot stress enough that concentrated sunlight is VERY dangerous. Also much fun if you're careful.
Step 7: Completed concentrator
Step 8: Heat exahgner.
The structure will look much like this. Note that there are gaps between the rows. You can take yet more copper and just solder them in between as shown on the right-most end of this example.
The gap filling ones don't need to be watertight. They're only there so that the light hits them and conducts the heat instead of passing through the gaps.
Step 9: Measure performance
I finally abandoned this design and disassembled it mainly because I was not able to track the sun accurately enough for it to be practical. It sure was a lot of fun though.