Introduction: Solar Oven With Tracking...

By

Whilst surfing the net one day I came across a site that showed you how to make simple solar cookers. The next day I made one out of cardboard and tin foil. I was amazed at how well it worked. After a lot more surfing and learning I came up with this design that any handyman with basic electrical skills could make.
What makes it really easy is there are no elaborate electronics with lots of components and circuit boards. You just need a small battery, couple of small solar panels, a motor and a switching device. Your comments are most welcome so please feel free to praise or criticize. Suggestions most welcome...



Step 1: Constructing and Insulating the Box...

I am lucky enough to have a nail gun so that made building a lot easier. So most of it is built with nails and wood glue. I built the two sides separate and filled them with corrugated cardboard which I already had. I made the walls about 80mm (3") thick for good insulation.

(Unfortunately the image notes are not working so please ask if anything is not clear)

Step 2: Joining Sides...

The two sides are joined to each other. The other two sides have to be left open at this stage because one will be all glass and the other removable doors for getting the food in and out.. What a difference a good sanding and a coat of paint makes...

Step 3: Working Out the Mechanics...

I needed some way of mounting the oven to tilt and rotate. So I made a frame out of slotted angle and screwed it to a base. I could put a steel bar through the oven near its balance point and then rest it on top of the frame. Using bearings I would make this the swivel point for tilting the oven up and down to maximize direct sunlight. I could then mount it all on a Lazy Susan so it could track the sun...

After assembly I discovered it was a bit front heavy once the mirrors and glass were added. The balance point needs to be towards the front more. This does not effect the operation of the oven, just makes it a little easier tilting..

Step 4: Mounting the Motor...

Now I needed a motor to make the oven rotate. I got a really high torque one that only does two RPM. The oven was quite heavy already and there is still a lot more to go on so I had to make sure the motor could handle it. The motor has an off centre shaft so by turning it you can adjust its ground clearance. So I made this box that the motor could be twisted in to adjust its height. The motor sits slightly proud so when the top is screwed down it locks the motor in place. 

Step 5: Motor and Base Plate Installed...

I got a small rubber wheel that I fitted to the shaft of the motor. This was attached to the underside of the frame. The Lazy Susan bearing was fitted to the base and the frame and oven would rotate on it. This was why it was critical that the motor could be twisted to get the optimum pressure on the rubber wheel. I fitted wheels to the base so it can be moved easily..

Step 6: Making and Fitting the Rear Doors...

I built a frame in the back of the oven that the doors would slide in and out of. I made the doors the same way I made the oven sides with plenty of cardboard insulation. The doors can be slid out independently depending on what is going into the oven.

Step 7: The Electronics...

Now we come to what I believe is the most exciting part of the project. Even though most will agree it is a very simple system it took weeks to get it just right. I built several solar panels of differing sizes to find the one that would operate the electrics most economically. I tried several switches and switching devices until I found one that worked each and everytime without fail. There is probably still room for improvement, but this has performed better than my expectations...

I made up two small solar panels each producing about 3.3 volts in good sunlight. I joined them together with hinges.I then cross wired them to each other. That is I took the positive(red) from one and the negative(black) from the other and joined them. I did the same with the other two wires. I then got a servo and modified it by taking out most of the electronics leaving me with the DC motor and gearing. I connected the two motor wires to the two wires now coming from the solar panels....
I'll explain how it will work. The solar panels are set up so they face away from each other. That means where ever you place them one will be getting more sunlight than the other. Providing they are not pointing directly at the sun when both will be getting the same amount of sunlight. So the panel facing the sunlight will be producing more power (volts). That means that panel is controlling which way the servo will rotate because of the cross wirering. The servo reacts to the signal and either pushes or pulls the rod connected to a toggle switch. The toggle switch via a small 12 volt battery sends power to the motor which turns the oven towards the sun.
The switch is a DPDT (double pole double throw) with six connectors and three positions. On, off and on. It is wired up in such a way that the two on positions are reversed to each other. So when you connect a motor  it will turn clockwise or anti clockwise depending which way the switch is moved. The centre position is off....
So the oven is rotating towards the sun. When the oven reaches a position directly facing the sun both panels receive the same amount of power which causes the servo to centralize and move the switch to the off position stopping the motor. If the oven goes past the sun the servo will turn the other way making the motor reverse until the oven directly faces the sun.I installed an on off switch that kills the power from the 12 volt battery to the motor when the oven is not being used. Most other systems I have seen need a reset function to turn the oven back to the east for the next day. My system will automatically find the sun wherever it is in the sky. I mounted it all on a triangular piece of plywood that can be moved from side to side for fine adjustments.
I can see this system being utilized in other applications that need a simple and reliable way of tracking the sun...

Step 8: Fitting the Panels That Will Hold the Mirrors...

I used two piano hinges to attach the panels that will hold the mirrors to the oven. The optimum angle for the mirrors to reflect the maximum sunlight into the oven is sixty degrees. I cut out a template that I used to measure the angle. I made up some wire retaining hooks to hold the panels in position. I may improve this later but it works for now. I installed the self leveling shelves and fitted a temperature gauge...

Step 9: Adding the Mirrors and Glass...

I used double sided tape to attach the mirrors to the panels. To ensure I got them straight I fitted two pieces scrap angle for the mirrors to sit on. You do not get a second chance if you line them up wrong.  After the mirrors were firmly pressed on I fitted the glass front. I used two sheets of 6mm toughened glass. There is a 25mm space between them giving it double glazing. This helps to retain the heat.
I wheeled it into the sunlight and within 30 minutes the internal heat had passed boiling point with the ambient temperature being twenty eight degrees Celsius. I am expecting temperatures around 300f on good days.
Thats the oven more or less finished. There are a few more little things I want to do. At the moment when the oven is tilted backwards it rest on the frame. I want to make a spring loaded locking system to hold it at any angle to the sun. I want to improve how the mirrors are held in position. I will also fit angled aluminum on the edges to improve water proofing and for a more professional look.


VIDEO  A short video would not embed its self but you can watch it here.....  http://www.youtube.com/watch?v=92xBhfcUX0A.

3rd Epilog Challenge

Participated in the
3rd Epilog Challenge