My Failed Passive Solar Heater Experiment (And What I Learned From It)

Like most bloggers, I want to be able to show you cool things, tell you everything is wonderful, and especially share my successes. I was optimistically expected to be able to do just that today but it’s not the case. You see, it all went wrong when I decided to do my own thing and not follow what someone had proven already worked. Some people have the knack of improvisation, I do not.

The problem was that I neither wanted to spend the money nor the time to make something as permanent as these videos showed; in fact, while I’ve seen some very cool YouTube videos about passive solar heaters, some of these guys really put serious effort into their designs! I just wanted to prove it worked… now I’ve got myself wondering.

Anyway, here’s the build I came up with (I’ll explain some lessons learned later and even link to one of the videos I liked at the very end):

Steps (follows the pictures in order):

1. Find a nice large box that was heading for the recycle bin. In the future, find a much smaller box because this needed entirely too many cans (it’s about 3′ x 3′).
2. Fill the box full of soda cans (96 total) which doesn’t sound like much but, trust me, it was a lot of work getting that many cans together!
3. Mark the top and bottom of the box before removing the cans and the guess (better yet, measure) where to cut holes for air to enter and exit.
4. This is what one side (I think it’s the top) looks like when the holes are cut out. Be sure to cut them a little less than the diameter of the can lips (maybe an inch wide).
5. Put holes in the bottom of all cans. I started off using a large screwdriver but I wanted to the hole a bit larger so I opted for a dandelion digger instead. A few taps with a hammer and then round it out a bit. BE CAREFUL: you’ll now have exposed metal which can cut you VERY easily.
6. This is what a typical hole looks like. Not pretty but I figured it would be functional.
7. The holes in the soda cans didn’t exactly line up with the holes in the cardboard box but I figured I wasn’t sending an astronaut into space so no big deal.
8. Paint the cans black. What you don’t see is my *brilliant* idea to simply caulk the tops and bottoms of the cans together while they were laying in the box. It’s works but wasn’t the best use of caulking.
9. I decided that it needed to be held together a bit better, especially where the holes in the cans met the box so I used strategic placement of packaging tape to close the gaps (which sort of worked).
10. Cover with clear plastic and tape down. Sadly, the 3.5 mil thick plastic I used was not nearly as clear as I had remembered so it wasn’t letting much sunlight through. (Note: this step was not shown in the gallery but can be seen completed in the thumbnail picture at the start of the post.)

I was going to take some temperature readings but could neither find an appropriate thermometer for the task nor the desire because the amount of heat was minimal at best and, even worse, the amount of airflow was lackluster at best. So, I didn’t even bother.

Lessons Learned (generally follows above):

1. I should have started like everyone else with a wood frame for sturdiness. Cardboard can get wet, is flimsy, and didn’t allow for precise alignment.
2. Since I just wanted to prove the concept, I could have used half the number of cans and still got a good idea of what to do.
3. I should have taken my time to properly mark and cut the holes so that I could later seal the cans directly to the frame for less airflow lost.
4. I really need a few good metal working tools. The video below shows how the guy put three nice holes in the bottom of each can which is a lot cleaner and probably allows for quite a bit more airflow. He also cut off the tops of each can, which I did not; I really figured this would be too much removed but I guess not.
5. I should have also choose to completely seal the tops and bottoms of cans together (as well as the cans to the frame) so that no air would be lost during heating. This was a big mistake.
6. Cover the heater with something more durable and definitely 100% clear! Another huge mistake here. I really don’t think the “clear” plastic I used helped my cause whatsoever.

THE MOST IMPORTANT LESSON?

If you’re going to bother to take the time, put forth the effort, and spend the money (yes I did spend a few dollars)… then DO IT LIKE YOU MEAN IT! Or, better yet, build it like I intended to keep and use it. 🙂

Don’t make my mistakes. Follow what somebody has already proven works…

YouTube Video that was useful (there are plenty of others):