Those large areas of the planet covered by salt ponds may be yet be of some use after all. Work today is being carried on in Israel where they have the best location for work of this kind, that being the Dead Sea where they have built a power station using heat stored in this sea .There are also other areas in the United States of America and even in Australia. Areas In rural Australia which are being destroyed by a salt may yet be made useful for energy production. These Ponds to be useful must have three differing zones of salt concentration not easy to obtain which work together to trap and store heat originating from the sun.
The surface zone the lightest in salinity allows the heat to travel down but not upwards and also acts as buffer to the second zone. The second zone prevents heat from returning to the surface. The third zone with the greater concentration of salinity acts as thermal storage and readily absorbing the solar heat rays`.
The weather pattern in the area has a great bearing on the effect of this heat storage pond where evaporation and wind patterns can completely destroy any heat storage capability
The wind can cause the three zones to mix therefore destroying the heat thermal storage properties of the pond. Floating wind barriers have been introduced to reduce the ripple effect of the wind across many lake surfaces. Some solar ponds can have a temperature of 100 degree c in the lower zone, whilst having a considerable lower one on the top zone..
Brine is pumped from the pond at the correct level and passed through a heat exchanger and maybe a temperature phase changer and is put towards a number uses from power generation to desalination plants. Water from the top of lake could be used in the process for cooling as there is a temperature difference between the zones. Although a large surface is required for the collection of the solar energy ,I have noticed an effect when I was storing gherkins in large wooden barrels containing salt water.
When the gherkins were removed and the brine was left to stand after a period of time in the sun there was always a cold top layer and a warmer bottom layer whenever I inserted my hand to drain them. I am sure this idea using a large wooden barrel or insulated container bottom and sides and connected to solar panel with water flowing to bottom layer could be used as a heat storage unit. This could also be improved by having a glass top to direct sunlight into bottom layer .
NB: The following article first appeared in The Renew Technology for a sustainable future. check out their website at Renew Website Under title of Kids stuff Noel's treasures from trash issue 78 page 68 January March 2002
To make your own solarpond
you will need:
( A large cardboard box
( A sheet of black plastic a 200 litre plastic garage bag could also be used instead
( a soft drink bottle
( a plastic funnel
( 3kg of cooking salt
( a piece of 19mm black polypipe
A recent Landline program on Australian ABC TV circu late 2001 featured a factory at Pyramid Hill in northern Victoria which uses heat from a solar pond to produce premium dried salt and, hopefully electricity to run the factory.
A solar pond is usually two to three metres deep and lined with black plastic. It is filled with water which has a salt gradient, -starting from very salty at the bottom of the pond through to fresh water at the top.
Even when the sun heats the water at the bottom, because it is so heavy, it can't rise to the top. Because water is also a good insulator of heat, the water at the bottom of the pond can reach 80 degrees Celsius. By putting a system of pipes in this layer, heat can be extracted from it by pumping fresh water through them.
The easiest way to make a solar pond is to dig a hole in a sunny spot about 800mm x 800mm with sloping sides, about 300 or 400mm deep. Line it with black plastic and 3/4 fill it with fresh water. Alternatively, you could build one out of a large cardboard box and tape, like we did.
Because sunny spots are often in the open, they can be windy, so you need to stop the wind from stirring up the water and mixing the layers. This can be done by making a 'surface calmer' from an old soft drink bottle.
Cut the bottle across its middle to form a lot of plastic rings about 10mm wide, and glue them to each other side by side to form a mesh.
Then attach a few small styrofoam blocks to the mesh so that it floats on the water.
This is how you make the surface calmerOnce you have made the surface calmer, place it on the surface of the pond and leave the pond for two hours, until it is completely still.
Now you need to make the salty layer. Mix 3kg of cooking salt into 12 litres of water and stir until dissolved.
Take a 40mm long piece of 19mm black polypipe and warm one end until it is soft. Put the blade of a knife into the warm end and place a block of wood on the end and squash it by standing on it.
While still warm, bend the pipe at 90 degrees next to the block of wood. Once the knife is removed, you will have a thin, flat nozzle. Now fit a funnel into the other end, and pour water through it and make sure that it comes out the nozzle in an even stream.
Gently lower the filler into the pond, so that the nozzle touches the bottom, and fasten it in place. Be careful not to stir up the water. If you do, leave it for a while to settle.
Now slowly pour all of the water into the funnel. It should form a layer of water at the bottom of the pond. Leave it to settle for a while, and carefully lower the end of the thermometer into the pond. After a while in the sun you should see that the temperature at the bottom is going up.
If you want to remove some heat from the pond, you will need to put a two or three coils of thin plastic tubing at the bottom of the pond, with both ends hanging out of the pond. You may need to weigh it down to make it stay there. When you put cold water into one end of the tube, you should get warm water out of the other.
