As the winter gradually moves in, and overnight temperatures begin to fall, we have been very busy trying to “winter-proof” the aquaponic system at Bustan Qaraaqa. This system is located on an exposed terrace close to the house, and gets the full brunt of the prevailing wind. For most of the year this is not too problematic – air movement helps keep plants strong, healthy and pollinated. However, now the wind simply blows away the warmth that the system managed to accumulate during the day.
We are growing carp and tilapia in this system. Although the carp will tolerate pretty much any temperature we throw at them, we managed to demonstrate last year that the tilapia will all die off if temperatures dip much below 15°C for an extended period. Maybe we could solve this problem by simply moving the tilapia to a warmer location over winter (such as in our bellies!), but where would be the fun in that? Moreover, if we can maintain the water temperature high enough to keep the tilapia alive, then it’s also warm enough for the carp to keep growing. Letting the system cool down too much would mean that the carp won’t put on any weight for the next four months, thus delaying that long awaited fish supper!
We are taking a two-pronged approach to winter-proof the system, involving:
1) constructing a simple greenhouse from transparent plastic sheeting to envelop the whole terrace for the winter months
2) constructing a solar water heater to try to warm up the water during the daytime
We have upgraded the shade support structure to a much more permanent affair constructed from re-bar rather than wobbly lengths of old irrigation pipe. This will hopefully last for a long time, enabling us to put the greenhouse sheeting on in the winter, and shade cloth in the summer. The framework is all in place now, we are just waiting to get hold of the plastic sheeting to cover it.
To make the solar water heater we have borrowed the ingenious idea of José Alano, the Brazilian inventor of this and finally found a use for all those Tetra-Paks that were cluttering up the recycling area at the farm. The original design suggests spray-painting the Tetra-paks black for better heat absorption, but that didn’t seem so eco-friendly to us. Instead, we are experimenting with two other methods to blacken them: wrapping them up tightly inblack plastic bags (thus finding a use for another ubiquitous waste stream) and painting them with a home-made paint, recipe as follows:
Take a few lumps of dried, sticky tree sap (we found some oozing from a wounded almond tree) and put it in a pan of water. Dissolve over a medium heat – keep stirring or it will stick! We found that it didn’t all dissolve, but the resultant liquid acquired a gloopy texture fairly quickly. Strain the liquid, this is the base to which you can add the pigment of your choice. We used crushed charcoal dust to make a nice black paint. It turns out that a food processor is not a very efficient method for making charcoal dust. A hammer was much better. There is no need to completely pulverize the charcoal – it would take too long to get it all fine enough. However, once you have a lot of very fine dust mixed in with bigger pieces, stir it all in with the tree sap base. Strain the resulting mixture through a cloth such as an old t-shirt to remove all but the finest particles of charcoal. There you have it! Silky smooth, jet black eco-paint.
Unfortunately, Tetra-paks have a glossy coating that renders them almost impossible to paint. However, we found that placing a couple of squares of toilet paper on top, and painting the toilet paper, worked very well. The paint sticks the toilet paper to the Ttra-pack, and the toilet paper absorbs the paint very well. Another option would be to use old newspaper, but we didn’t have any to hand…
We have so far built half a panel – 10 heating columns long – and plumbed it in. The water temperature at sunset today was up 2°C from yesterday… Did it work, or was it just warmer today? Time will tell…
