Welcome to the Shoulder Season

It's a beautiful 14C day in Halifax and we've been enjoying a steady stream of sunny days over the last two weeks. March has been unseasonably nice and today students are wandering campus in short sleeves and bare shoulders.

This is one of the two shoulder seasons for the heating year, a term I'm appropriating from the tourism business. Due to cloudy and deep cold, there isn't much opportunity for my pop can solar furnace to work during December to February. But in March and April, and again in October and November, there is the perfect combination of sunshine and mild temperatures. The last few evenings have been cold, sometimes dipping below zero. I haven't had to use electric heat or even start a fire because the solarium has been hot enough to warm the house to 22C or higher. The pic above is the temperature in the solarium (32C!) just after opening the door around 5pm. The heat drifts into the rest of the house, which, now insulated, holds the heat quite nicely for the entire evening. By bed time, I slide the door to the solarium closed to minimize any drafts and the process is ready for the next day. I expect to see some serious savings on my next power bill.

Of course, I will have to remove a few of the pop can solar furnace panels by the end of April. The room will simply too hot by then to be enjoyable and the heat won't be needed in the house at all. If only I could store it for the winter...

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Solar Powered Fans (continued)

I've done some research and found that my current panel will put out about 5.5W of power. That's pretty small, but luckily, so are the fans with which I'm working.

My memories of my old electronics courses in junior high are pretty sketchy, but after playing around a little bit, I found that I could easily wire the fans in a circuit. The trick now is to gather a few more and incorporate them into the design of the next pop can solar furnace panel. I have a few fans that also have LED lights in them, so they will be a nice touch, indicating when the panel is operational. I don't expect I'll need anything else in terms of wiring. If there's enough sun to run the fans, there should be enough to heat up the solar furnace as well.

The idea now is to build a third panel with the fans built in. Each column of cans will have their tops and bottoms removed and a fan will be put at either the top or bottom of the column. I may need some sealant to get good airflow through the column. We'll see.

[A little while later...]

Having played with an additional fan, I'm less thrilled with the airflow from the case fan that I tried out. Looks like some decent processor fans will be the way to go.

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Solar Powered Fans

I've been planning for a while to incorporate some solar powered fans into my pop can solar furnace. They should help to draw air through the panel and thus circulate the air better. Today, I was able to get started on this part of the process.

I found a few old computer fans kicking around the house. Each is surprisingly quiet and draws a little less than a Watt of power. I also happen to have a small PV solar panel that puts out a couple of watts, but I will test that further as the design goes on.

Today, I simply trimmed the wires on the fans and connected them to the solar panel. Sure enough, they worked! I'm going to gather a few more and test how much air flow I can get before building a new panel with the fans built in. Ideally, I'd also use a PV collector that is just big enough to run the fans, but I will play with that next.

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How to Build a Pop Can Solar Furnace - Recap

Welcome to Lower Footprint! For those of you who may be listening to CBC's Mainstreet today, I thought I'd post a quick list of the links for the articles about the "Pop Can Solar Furnace" so you could find them easily!

In the interest of full disclosure, this was not an original idea or project! These things have been around for a while, both as commercial products and D-I-Y. I based my design on the best one I could find online in 2008 (here's the link). Each one I build is better than the last and I'm willing to bet you could build one too! All you need is a South-facing window and less than $20.

The first solar furnace was very crude, but worked very well. It cost about $7 to build. It was installed in one of the 'sky lights' or ceiling windows of my solarium. It was installed in February of 2008 and the hottest reading recorded was in April of 2008... 82C (185F) on the surface of the panel and over 52C air temperature in the room.

The orginal Pop Can Solar Furnace Post. There is a link to pictures on Facebook, or another link in the comments if you can't see them there.

The first temperature readings from the solar furnace.

Neat pictures from the hottest readings in the solarium.

Some Q & A about the installation from a blog reader.

The second pop can solar furnace was built for one of the normal windows that face South. This one cost under $20, but could be made cheaper if you have some recycled fence boards or other light wood around your garage.

This design does block most of the available light coming into the room, so it may not be the best option if it's the only window in a room.

Step by step instructions (with pictures) on building a pop can solar furnace window insert.

Part 1

Part 2

Part 3

Results and thermometer readings at the end of October, 2009.

Thanks for checking out the pop can solar furnace! Look for a new design and other projects in the near future!

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Pop Can Solar Furnace 2.0 - Part 2

Yesterday, I showed you how to assemble the frame for the Pop Can Solar Furnace 2.0. Today, I'll show you how to place and paint the cans.

The reason this solar furnace works as well as it does has to do with the particular properties of the aluminium cans. When coated with high-heat black paint, it heats up very quickly and it transfers that heat into the surrounding air quite easily. I'm sure other materials would work well, and some would work even better, but aluminium is cheap and easy!

Placing the cans

I don't use any special adhesive or anything, so you simply place the cans end to end in your frame. The ridges of the cans fit nicely together and I was lucky in that my frame had 13 cans fit nicely in.

This time, I didn't punch the bottoms out of the cans, but I may have to if the panel doesn't perform well enough.

Once all of the vertical cans are placed, I squeezed a few more into the top to fill that space. In my next design, I may use another piece of wood to create an air gap at the top and bottom, but this time, I maxed out on cans that could be fit in. I even crushed a few of the mini cans so they'd fit in even better. (Incidentally, Coke Zero is not yet a sponsor of this project, but they are welcome to contribute! I figure 25k would go a long way in other solar equipment!)

Once in, there was still a touch of room, so I used a little cardboard to shim the bottom of the cans so they wouldn't all fall out the minute I moved the panel.

Finally, using the left overs from last year's panel, I started to paint the cans a very flat black.Of course, any painting like this should be done outside or in a well ventilated location. I ended up running out of paint about halfway through, so I needed a quick trip to Canadian Tire to get another one. It should do for another panel after this one.

Half of the cans painted.

All of the cans painted.

Now, just allow the cans to dry, and you're ready to place it in your window!

Next, placement and ventilation! (Go to Step 3.)

Pop Can Solar Furnace 2.0 - Part 1

I finally found time to assemble my second Pop Can Solar Furnace! I'll be posting step by step instructions this week, as well as reporting on it's output as the week goes by. Here's hoping for sunshine!

What makes this pop can solar furnace different from the last one is pretty simple: it's stronger, more stable, and has a custom fit in a vertical window.

Materials

1 piece 1/4" thick pressboard, cut to fit your window

4 pieces pf 1x3 or 1x4 cut to fit the dimensions of your window

approximately 100 pop or soda cans made from aluminium

1 can high-heat black bbq paint

a handful of finishing nails

Assembling the box

First, cut all the wood to build a frame that will snugly fit into your South-facing window. In this case, I used a mitre saw to create nice 45 degree corners, but you could use a simple butt-joint if you didn't have a fancy saw. Using the finishing nails, tack it together and test your fit before moving on to the next step.

The goal here is to create a light weight frame for your furnace that will look attractive from the inside of the house.

Of course, I recommend you use recycled materials whenever possible for a project like this.

Next up, place and painting the cans. (Go to step 2.)