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Cheaper Easier Desalination and Solar Thermal

It’s strange how MIT (The Massachusetts Institute of Technology) sometimes comes up with stupid ideas (Nocera with his Artificial Leaf), sometimes clearly steals ideas, and sometimes demo’s something anyone can apply. Today it did the latter as it demonstrated high temperatures, 100 Celsius can be reached with unfocused sunlight (so called 1 sun). This is about solar thermal heaters that now reach temperatures up to 70 deg Celsius or 100 if you don’t let the water flow.

SRB Ultra High Vacuum Collector

Of course there have been improvements on the solar thermal panel front, we had RSB and another company make high vacuum solar thermal panes, that can reach up to 500 Celsius. Those products are not storming the markets, they are in our opinion held back by the dominant gas lobby who can work in mysterious ways. 500 Celsius is a lot of heat, it is highly usefull and can drive regular power plant steam turbine. We need to take care of this type of products, or they will go the way of the early solar panels.

These simple component produce higher temperatures than was possible with 40 years of DOE research

The device MIT demonstrates makes only 100 degree steam, but that’s an important product because it separates the water from its impurities. But most amazingly to me it demonstrates a principle in heat collection I never realized was true, that you can multiply heat by collecting it and then giving it only a small space to exit. What happens in the collector is that heat is absorbed by some kind of metal, copper or aluminium, which is coated with a layer that does not reflect away the heat or emit it (mat black is the best heat emittier, silvered is the least). This captures the heat in the metal, which then tries to leave by radiation (photons) or convection (heating up the environment). The trick used is to have only a tiny amount of water available to transfer (drawn up through a wick like in an oil lamp) all this energy to, which if it is a hole in the hot metal collector plate, is ‘pushed’ from all sides to get hotter. Thus a multiplication of temperature happens, and this can be optimized by spacing holes in the collector plate.

Its not clear to us why the collector has to float on water, it doesn’t seem necessary, as is mentioned the water can also be supplied at pressure, the essential part is the concentration of heat (molecular kinetic energy) onto a small amount of water.

The main difference is that the amount of water per surface of collector is much smaller..

We have written here about ionic membranes, and solar ionic membranes that will make desalination about 80% less energy intensive. With that in mind it is unclear how this solar still type and ionic desalination methods compare. The materials are cheap for both. In any case this is great news for deserts near salt water bodies, where we hope to see massive tree planting and agriculture for CO2 capture, restoration of ecosystems in a roboeconomic or extraeconomical sense.

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