From Coke Cans to Solar Heating Panel

Upcycling is a way of life here, but that is only one reason I love our new Coke Can Solar Heating Panel. The best part is all that lovely heat in our old house. Before we installed the panel, we often saw winter temperatures warmer OUTSIDE than inside. Admittedly, the winters in Northland aren’t known for being punishing, but going outside to get warmer isn’t something I like to do.

Plus, Frugal Man calculates that using the system will cost us approximately $1.50 in electricity per year. No typo there. That is PER YEAR. You can see why I gaze upon our panel fondly.

The panel consists of Coke and beer cans, plywood and a sheet of polycarbonate. We used a whole sheet of plywood as a base, so it is HUGE 2.4m x 1.2m (7’11” x 4′). Many people build similar heaters with old window panes, so don’t think they all have to be so massive. It’s just that we weren’t messing about when we built ours. We mean business!

How we built the solar heating panel

We started out with a whole heap of cans. Over 300 of them.

Some we collected on our own over the summer, but the vast majority were donated by friends or scrounged. Frugal Man cut out the bottoms of the cans with a drill press then I washed them. There were many slugs. And snails. And the house smelled like stale beer.

Next Frugal Man cut the tops of the cans to form baffles. I tried to do this, but the tin snips were too big for my hands and we couldn’t find a smaller version that I could use comfortably. He worked on baffling these over the course of several evenings whilst watching TV.

When he was done baffling the tops, he glued the cans together in sets of three. They were eventually glued together in columns of 16, but sets of three were much more manageable to have sitting around the living room.

Once the cans were glued in threes, he spray painted them a matte black all the way around. I thought he’d just paint the front where the sun would hit, but he’d read that you got improved performance with an all around spray. We used about seven cans of spray paint.

He installed the cans in columns in the plywood box he built that we’d painted with some dark brown fence paint we had lying around. We ended up with 17 rows of 16 can high columns for a total of 272 cans. The columns fit into holes he’d drilled in the plywood that connect the cans to the top and bottom manifolds.

He then screwed a large sheet of polycarbonate on to cover the can area.

How the solar heating panel works

The air from the house enters into a round opening in the back of the bottom manifold. Once in the black cans, the air heats up and naturally rises to the top manifold. The air then re-enters the house through the round opening in the back of the top manifold.

Some people leave it at that and have a completely passive system. Frugal Man decided on a more active approach for us. On the inside of the house, he installed two small, 12V, 100,000 hour life at 40C (104F), super-quiet, low-power fans from Jaycar. One pushes air into the panel at the bottom and the other pulls heated air out of the top. He’s put the fans on a temperature controller-the same type we use for our ultra-efficient Chest Fridge– so they start running around 29C(84F). We still get warm air trickling in at lower temperatures as you would with a passive system, but it isn’t fan assisted.

He also cut a small sheet of clear plastic out of a Ziploc bag and installed it over the top inlet grill. The sheet is easily blown open when heat is entering the house, but it prevents cold air from streaming into the house by blocking the “waterfall effect”.

House modifications

Our system requires two holes in the side of the house through to our living room. Best to get THAT right the first time. No pressure.

Frugal Man, of course, managed perfectly, attracting the attention of smaller denizens of the house in the process. The calendulas got trampled in the process, but I can plant more.

The system on the inside of the house looks nice and tidy. We have the two manifold holes, covered by grids and the temperature controller box next to the upper manifold inlet.

Effect on temperatures in the house

The heat from our panel, spread across our great room, doesn’t immediately feel like a huge boost when it comes on. What DOES happen, is that the thermal mass of the whole large space is lifted by several degrees. Morning temperatures in our house this time of year, in the dead of winter, commonly range from 8C (46F) to 13C (55F). Without the solar heating panel, those numbers don’t increase much during the course of the day, as we have no sun from the north to heat the house with our house situation.

Using the panel, we are seeing temps rise into the 15C (59F) to 17C (63F) range. Not screamingly hot, by any means, but much more comfortable. In addition to the daytime lift in temperatures, we find the heat is holding in the house through to evening. It is much cheaper to heat the house to 20C (68F) from 17C(63F) than it is to do it from 13C (55F), assuming our heat pump could manage to get to that temperature before, which it couldn’t. A similar size heater warming a smaller room would, of course, produce warmer temperatures.

As the weather warms up when we head into spring, we should experience even more comfortable conditions with higher starting temperatures and longer sunshine hours giving the system a boost. As we head into summer, we will be able to block off the manifold inlets if we are getting too warm AND we have plans to turn the panel into a solar dehydrator for those sunny warm months. Two for one!

Cost and time to build the solar heating panel

With all of the materials: polycarbonate sheet (NZ$150), 1.5 sheets of plywood ($52), 7 cans of spay paint ($77), 2 tubes of silicon glue ($40), metal inlets, grills, fans, temperature controller, etc, the whole project priced out around $500. This puts it out of the “fun project” budget range and into “investment” range. So far we are happy with the performance and it should provide essentially free heat to us for a number of years, so it is an investment we are pleased to have made. Frugal Man worked on this project over several weekends, as well as the time he spent in the evenings cutting baffles, so expect to put some time in, if you decide to build your own.

If you are interested in the details of building your own Coke Can Solar Heating Panel, check out the many free plans available on Build It Solar. The site is an excellent repository for DIY solar projects of all kinds.

Do you use alternative heating? Do you want to? What kind?