by Vera Delahy
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The solar oven and tracking turntable.
Click here for an enlarged view. |
Dyeing wool in a solar oven with natural dyestuffs has interested
me greatly since I first learned about the technique in
Spin-Off
Summer '93 edition. I have been spinning wool, and, to some extent,
other fibres, for at least sixteen years.
I am fortunate to have a son-in-law who is very handy and
he built me a beautiful upright treadle wheel. It is made from
turned timber, is a delight to use and is much admired by all
who see it. It will probably become a family heirloom.
But back to solar dyeing. I have successfully dyed wool on
the cooktop for some time now using natural ingredients, but
the novelty of using solar energy really appealed to me. I live
in a country town some 33 miles west of Melbourne, Victoria,
and with the exception of winter, we have extensive periods of
clear sunny weather. With a latitude of 38 degrees south, the
sun is reasonably high in the sky during this period - ideal
of solar dyeing. So I had to have a solar oven!
The solar oven
My son-in-law, the handy one, and my daughter, live in Sydney,
New South Wales, some 600 miles north and so I expected to wait
for their next visit before my wish could come true. Having reached
the "autumn years" of my life I did not feel that I
could build it myself! As it happens I have a nephew-in-law who
is also a handy man, and hearing of my interest, he built me
a very fancy oven. It is constructed with inner and outer boxes
of sheet metal with polystyrene foam in between for insulation.
All inner surfaces are lined with foil as is the lid, which has
an adjustable prop for setting the angle. The glass is hinged
at the rear for easy access to the dyepot for checking the contents.
The dyepot is aluminium painted matt black. Of course the oven
must be realigned with the sun every hour or so as the sun moves
across the sky. A number of successful dyeings have been achieved
and while I do not have a thermometer capable of reading such
high temperatures, we estimate that the liquid in the dyepot
stabilises at about 180°F - quite hot enough to set the dye.
The oven is about 16" square by 13" deep. The maximum
pot which would fit in the oven holds about three gallons but
my pot is considerably smaller.
Solar powered tracking turntable
Click here for schematic diagram
During a visit, my son-in-law observed that the need for frequent
realignment of the oven was rather a nuisance and felt that it
would be novel to apply some modern day "hi-tech" solutions
to the problem.
Being inventive by nature, he designed and constructed a solar
powered tracking turntable for the oven to sit on. It now automatically
turns the oven all day long to face the sun. My son-in-law provides
the following description of the solar tracker:
In brief the solar tracker consists of a turntable mounted
on a large ball race. This provides low friction motion so that
a quite small electric motor can turn the table after the speed
of the motor is reduced enormously through a set of reduction
gears. Power to the motor is provided by a pair of small solar
panels which convert the sun's light into electricity. As the
oven turns towards the sun a shadow is cast across the panels
by a shield. This cuts off the sunlight and reduces the electricity
generation. The motor slows down and finally stops when the oven
is exactly aligned. As the sun moves, the shadow moves off the
panels and the motor starts again.
Dyeing experiments
I only use natural dyestuffs in all my dyeing work. The following
materials have been successfully used on both washed spun wool
and unspun fleece.
Most ingredients were used in equal or greater amounts to the
quantity of wool by weight. Mordants were not used with any of
these materials.
Technical details of the solar tracker
For those people interested in the technical details of the
solar tracker, my son-in-law provides these additional details:
Apart from the solar panels ($5.00), all other bits and pieces
were recycled from the workshop scrap box. The two solar panels
are connected in series and produce nearly 1 volt at 0.45 amps
in full sunshine. Each is 2.75" x 1.75" in size. The
DC motor is about 1" in diameter and was salvaged from a
discarded battery-operated toy. It was probably designed to run
on 3 volts, but on 1 volt it runs well and starts reliably. Speed
is approximately 2000 rpm. The gear reduction unit is key to
the whole design since a very large reduction is required. The
unit was salvaged from a precision scientific chart recorder
and, along with the final reduction stage, provides a reduction
of about 300,00:1. Ratchet safety clutches are provided so that
the oven may be turned manually for initial alignment to the
sun. The turntable is mounted on a single large double row ball
bearing of about 3" outside diameter, which also came from
the scrap box. The unit turns through about 15° in 7 minutes.
The solar panels are slanted at 45° which is a compromise
for the spring-summer-autumn angle of the sun.
A very light cloud haze does not stop the solar drive, but
any substantial cloud stops it dead. As soon as the cloud passes
the motor starts again. It is quite uncanny. In winter the sun
angle is too low and actually passes behind some trees in a neighbour's
garden so solar dyeing is not possible anyway.
The whole project has created considerable interest and all the
members of our local spinning group at "the Laurels"
have visited to see the solar tracker and oven in action. Husbands
have been welcomed also and hopefully will be inspired to build
an oven even if they draw the line at a solar tracker.
