The main purpose of this project is to build an affordable proof of concept of a small sized solar generator using parabolic mirror and thermal storage instead of solar cells. However I've built this project with the intention of teaching some concepts such as magnetic and planetary gearboxes, steam turbine, parabolic mirrors, heat transfers and so on.
Since a small generator like that isn't very efficient, the parabolic mirror with the water circulation system can be use to heat domestic wwater or directly water in radiators. This solution is almost as cheap as classic black solar heater but a lilte bit more complex but also more efficient.
I wanted this part to be as affordable as possible so I've used a lot of scrap wood, if you want to built something like that, I recommand you to use apropriate wood with varnish to resists the environnement conditions.
Since the miror's curvature need to be verry precise I have cut the wood with a CNC machine. You can also print the shape on paper and cut with a jig saw, the result will be less precise but sufficient.
All the parts are design to fit in my 260x220mm homemade CNC but if you have acces to a fablab with a bigger one I'll recommand you to design your own parabolic support.
First things first, you need to find the necessary supplies:
- For the miror I had some 1x1m .5mm aluminium sheets laying around (from a printing house). There is two mains other options, you can buy aluminium sheets in a hardware store it can cost between 10 to 50€ depending of the thikness (the thinest is good as long as it isn't aluminium foil). The last option is to use very thin plywood and shape it with water or alcohol. The plywood need to be cover with a reflective surface, an emergency blanket is a good option but the best option is to use miror foil.
In function of what you have in hand, the next step is to define the miror size! I've choose to make a 0.5m² miror so 0.75m long 0.65m so the aluminium sheet is about 0.75m by 0.80m.
| Part | Quantity | Cost |
|---|---|---|
| L shape aluminuim extrusion | 3-4 | 25€ |
| Wood | 1 | 15€ |
| Screws | 50 | 10€ |
| M4 Bolts and nuts | 10 | 5€ |
| Nails | 100 | 3€ |
| Steel wire | 1 roll | 5€ |
| Bearings 606zz | 8 | 4€ |
| Arduino nano | 1 | 5€ |
| Photoresistors | 10 | 1€ |
| GT2 belt | 1 | 3€ |
| GT2 pulley | 1 | 1€ |
| 1Kg/cm or more servomotor | 1 | 3€ |
Drawing a parabol is quite easy on most cad softwares, on solidworks just use the parabol tool and then you need to lock horizontally the two up point and the midle vertically. There is two distances to define, the width 60 on the image bellow, and the distance between focal point and the middle of the parabol, a short distance will be easier for the the solar tracking part but you need to have enougth clearance between the pipe and the miror.
The support is quite straigth forward, the only specific part is the ring in the middle which will be used to support the copper pipe with steel wire. I have split the parabolic ring in 3 part to match with the size of my CNC but if you have acces to a bigger one this step is not requiered.
The middle ring is also use for the roation of the miror.