Improvements to a Beer Can

Solar Air Heater increase the output temperature

When I recently considered making a Beer Can Solar Air Heater, I naturally did a preliminary scan of the internet for articles on the subject, that would give me advice from previous constructors.

Whilst most of the information I found was very useful and practical, I was a bit reluctant to follow the usual route described for the initial modification of the beer can to provide the required air path.

Beer Can Airflow diagrams

Most constructors suggested cutting a relatively small hole (approx 25mm dia) in the centre of can base, for entry of the air, allowing it to exit at the top through the existing ring-pull hole.

My reasoning was that, as the heat generated in the aluminium wall of the can was only effectively conducted to the outermost layer of air, having small inlet and outlet holes would mean that this layer would be relatively stagnant, compared to the smaller, central column of un-heated air, resulting in a lower than optimum output temperature.

To avoid this problem, I therefore considered how to remove the complete end cap of the beer can, in order to free up this outer air layer.


Tools for beer can modification

To remove the complete ring-pull end cap, I found that a 50mm dia hole saw located snuggly inside the raised rim, and that a few turns by hand were enough to cut through the thin material.

A different method was needed to remove the partially-domed bottom cap, and I found that the simplest way was to just file across the bottom (although using a belt sander would probably achieve the same result).

Here's the resulting parts:

The removed beer can parts

I was about to discard all the removed parts, when a thought struck me that the domed bottom cap could possibly be re-used to an advantage, by inverting it for use as a deflector to direct the circulating air close to the can wall.

Modifying the bottom end cap

In order to hold the inverted end cap in a position that would allow a small annular gap for air to enter the can, I needed to form a set of three legs that could be used to glue the cap to the base of the can.

I first made up a cardboard template with a hole cut out that matched the diameter of the domed end cap, then I marked around the edge of the hole where the three equispaced legs would be.

With a small pair if side cutters, I then made pairs of cuts around the lid, approx 6mm apart and 8mm deep, at each of the marked points.

Then, using a pair of long-nosed pliers, I shaped each of the legs with a double bend such that the whole set would form a good location to the base of the beer can.

Domed end cap modification

Assembling the deflector

All that then remained was to glue the inverted end cap back onto the base of the beer can (I used Araldite adhesive) and allow to cure.

The assembled end cap deflector

NOTE: For the 'wall air layer' idea to work successfully, it is vital that all the cans that make up a column of the complete solar air heater have deflectors fitted at their lower ends, otherwise the guidance effect will soon be dissipated.

This might seem like a lot of work, but my experience has shown that output temperatures of over 50°C are quite easy to obtain even when the ambient temperature is only just above freezing.

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Photo Gallery

Completed Solar Panel
The Completed Solar Panel

Here are some pics I took of a small solar panel installation I fitted to the south facing wall of my wife's craft workshop, comprising a 48-can array (8-columns of 6-cans) housed in a 1200 x 600mm enclosure.

The air intake was taken from the inside of the workshop, close to the floor, to the heater via standard 68mm rainwater downpipe, lined with aluminium kitchen foil and insulated on the outside (waterproof covering over polystyrene strips not yet in place).

Two computer fans were fitted to this pipe; one in the air intake filter box and another at the entry to the heater.

In the heater itself, the airflow was split in two by a diverter board, feeding it equally through each set of 4-cans, being similarly combined at the output end

Inlet Filter Box
Inlet Filter Box
Inlet Pipe (lower end)
Inlet Pipe (lower end)
Inlet Pipe (upper) and Fan
Inlet Pipe (upper) and Fan

I used the same pipework for the output side of the heater, needing to transport the air across the workshop to exit above my wife's sewing table

Outlet pipe (at wall)
Outlet pipe (at wall)
Outlet Pipe (at exit)
Outlet Pipe (at exit)

To automatically control the heater fans, I asked a work colleague to construct a differential thermostat circuit board, from a diagram I found on the internet.
This utilised a couple of thermister sensers; one to sense ambient room temperature and another to sense the temperature at the heater outlet.
By adjusting a trimmer potentiometer on the circuit board, I was able to set the device up to only switch on the fans when there was a sufficiently higher temperature at the heater output than inside the workshop.
I also fitted a standard timer switch before the fan power supply unit, so that operation was limited to just the 'sunlight' hours of the day.

Thermister in Outlet Pipe
Thermister in Heater Outlet Pipe
Differential Thermostat
Differential Thermostat Circuit Box
Power Supply and Thermostat
Timer, Power Supply and Thermostat
Temperature probe in pipe exit
Temperature probe at oulet pipe shoe

As you can see from the temperature gauge reading, I got a quite high output reading of 47°C at my first attempt (on a cold but bright February noontime in East England).

If you would like any further information on my method of construction, then please feel free to contact me.

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Webpage created: October 2010 - Last updated: 15 December 2020
Author and webmaster: Peter Attwood