Contents

1. Extracting water from ‘dry’ desert air
2. Distillation of contaminated water
3. Freeze desalination
4. Healing brackish water aquifers
5. Greening the hot deserts and scrublands
6. Lithium extraction

1          Extracting water from ‘dry’ desert air

Desert air is not completely dry; it contains a small quantity of water vapour that can be condensed out if the air is cooled. Building a plant solely for producing water in this way would be expensive, but becomes cost effective if linked with LP Turbine power generation or air cooling.

Key facts

• (i) If “dry” air is cooled so that dew is formed, then the extraction of one kW of heat for one hour produces approximately 1.5 litres of water in the form of dew.
• (ii) Warm dry air holds more water than cool dry air. So, if water collection is important, then it is more efficient to start off with warm air.
• (iii) At night, the ground temperature in warm arid regions falls rapidly and dew is formed. But this very thin covering of water is difficult to collect.
  However, a warmer layer of air, 100 metres or so above ground level is common. This holds more water and is easier to exploit.

One option would be to gain access to this warm layer using a tall "chimney" and use the warm air to generate electricity at night.

Figure 1. The "chimney" works in reverse, drawing down relatively warm air at night.

2          Distillation of contaminated water

Reverse osmosis is the simplest and cheapest way of purifying water contaminated with dissolved solids such as salt, industrial waste or sewage.

But it is impractical to use reverse osmosis to extract all of the water, so alternative methods are required if we want to end up with dry solids for recycling or disposal.

Using solar energy to dry out the solids is an old solution to the problem. But this is a slow process and the water that evaporates off escapes to the atmosphere because cooling the vapour to condense it is not an economic proposition.

We propose a more efficient solution to the drying problem. This uses simple optics to concentrate the sun’s energy and employs LP Turbines to cool the water vapour.

But, there is another design problem to be overcome because the position of the sun in the sky varies throughout the day. Existing solutions involve complex systems of solar tracking motors.

Our preferred design dispenses with the need for moving parts. It overcomes the elevation problem by using long (say 100 metres) lengths of North to South arrays of micro prisms. We also employ broad water troughs that have different hot spots in a West – East direction throughout the day.

Figure 2. Concentrating the solar energy speeds up the evaporation process. It also sterilises any organic material.

The solar still can be integrated into a range of architectural designs. Here is a simple example:

Figure 3. This design can be used to create a cool indoor space for living and plant growing. In hot regions that have cold nights, the trough acts as a thermal buffer.

3          Freeze desalination

If brine is cooled sufficiently, pure ice is formed and the concentration of the residual brine increases. This is a useful alternative to evaporation because freezing out one kilogram of ice only requires the extraction of one eighth of the heat required to condense out one kilogram of water vapour.

Figure 4. Combined freeze desalination and Latent Power electricity generation.

There are limitations to freeze desalination because it cannot remove all of the water from the salty brine.

A niche advantage of freeze desalination compared with reverse osmosis

Reverse osmosis is still the preferred method of desalinating sea water, with Latent Power turbines being used to provide the electricity. But freeze desalination has the merit that melting the ice can provide a convenient cooling resource.

Here is an example of ice being used to cool a hot climate horticultural glass house:

Figure 5. Melting ice could provide glasshouse cooling in hot climates. The same method could be used for cooling shaded outdoor walkways and underground station platforms.

4          Healing brackish water aquifers

Brackish water contains too much salt for most agricultural, domestic and industrial purposes, but it is not as salty as sea water. Fossil brackish water aquifers have existed for many thousands of years. But others are a man-made accident.

Freshwater aquifers can degrade into brackish water aquifers if too much water is pumped out of them. This is often a 'tragedy of the commons' type of degradation with aggressive withdrawal of water on the edges of the freshwater zone drawing in salt water from the surrounding salt contaminated ground.

The strategic use of LP Turbines to pump out and desalinate the brackish water at a distance from the freshwater zone could reverse this process by providing ground space for additional fresh water to flow back into the margins. This healing process is only possible for aquifers that are regularly replenished by rainwater or melting snow.

5          Greening the hot deserts and scrublands

 Background

The UN predicts that the world population will increase by about 25% to 9 billion by 2050. Most of this expansion will occur in the developing world. In contrast the populations of the established democracies are stable or falling. [http://www.un.org/esa/population/publications/wpp2008/pressrelease.pdf]

But the inhabitants of the advanced nations should not be co placement about this. If we cannot find enough food, water, land and jobs for these extra people our present refugee and terrorist problems will only get worse.

5.1     The opportunity open to us

A partial greening of the hot deserts and scrublands would go a long way towards easing the problems caused by increased populations.

This map shows the hot deserts of the world.

Figure 6. In addition to true deserts, there are many regions of low productivity scrubland in southern Europe and elsewhere.

The primary use for LP Turbines in hot desert reasons would be to cool the interiors of glasshouses used for growing crops. The electricity generated would be a by-product of the cooling process. The following table, which is intended to be thought provoking, rather than a practical suggestion, answers the question, "What fraction of the world's deserts would need to be used for glasshouse horticulture, to meet all of our energy needs?"

If you want to check our calculations, this is the data we have used.

(i) The mean annual direct solar energy density for the Sahara desert is 2.9 x 103 kWh/m2. This is about twice the solar energy density in southern Italy. [2]

(ii) For the desert area calculations we have assumed a cautious value of 1.0 x 103 kWh/m2/year. (=109 kWh/km2/year). This is about the solar intensity in southern Europe in summer. We have also ignored any energy captured from the desert air at night.

Information sources:

[1] Desert areas, The Guinness World Data Book, ISBN 0-85112960.9

[2] Italian National Agency for New Technologies, Energy and the Environment, 2005, "Harnessing solar energy as high temperature heat".

[3] IEA Key energy statistics 2010

5.2     Greening strategies linked to LP Turbines

LP Turbines can be used for desalinating water, then using the fresh water to irrigate the deserts. But this is a very crude approach, with LP Turbines offering several more water efficient alternatives.

Our own suggestions will be described below, but there is plenty of scope for improvement by others.

Some deserts will be easier to green than others.

If there is a genuine absence of rainwater, the most efficient option is to import water and trap it inside glass horticultural houses, so that it can be recycled instead of evaporating into the open air.

Fortunately, many hot deserts receive sufficient rainfall to support plant growth, but the high temperatures cause evaporation before the ground can absorb the water. For example some North American deserts receive about 280 mm of rainfall per year. This is 40% of the rainfall in Britain’s fertile East Anglia.

Such deserts could maximise their productivity using a combination of glasshouses and reforestation.

The glasshouse solution
This is similar to the glasshouse design shown above, but uses LP Turbines instead of ice to cool the glass house.

(If the diagram looks familiar, yes we have used it before on this linked webpage.)

Figure 7. The LP Turbines are used primarily as a cooling mechanism. Surplus electricity would be generated.

A rolling desert greening strategy: The surplus electricity could be used to drive coastal desalination plants and to pump the fresh water inland. This would enable a second generation of glasshouses to be built further inland. This in turn would provide the power to expand the scheme further inland.

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Local production of glass for horticultural use

Silica is the main ingredient (72%) in glass. So, if suitable silica sand is available in the region, energy from LP Turbines could be used to make the horticultural glass locally. [The manufacturing of small, prefabricated glass making plants is an example of the type of new business that an LP Turbine economy will create.]

Reforestation

The strategic planting of trees can reverse the creeping advance of deserts.

 Pure deserts can only become fertile by importing water or climate change. But in cases where human agencies such as overgrazing and burning of wood for fuel have triggered erosion, the process can be reversed.

Planting trees is an important tool for desert reversal. The imaginative deployment of LP Turbines could speed up the reforesting process and create additional benefits.

Here is an example relating to fog deserts:

 Fog deserts can access a modest amount of water in the form of fog coming in from the sea. [https://en.wikipedia.org/wiki/Fog_desert]

Specialist plants and insects have evolved to survive by capturing this precious moisture. Human have also captured fog water by trapping it using hydrophobic meshes made from materials such as polypropylene.

The diagram below illustrates how a portable hydrophobic cover could be used to give fog desert saplings a start in life. Once the saplings have developed sufficient leaf area to be able to trap their own fog, and have grown roots deep enough to tap into ground water, the cover can be removed and used for the next batch of saplings.

Figure 8. This method of reforesting will require investment, but is attractive because trees can fight climate change by capturing CO2 from the atmosphere. In some regions where it creates jobs, it will also offer an alternative to militant Islam as a career option.

Ideally, LEDs would be used to illuminate the plants at night, to accelerate growth.

An example of a fog desert

The Sonoran Desert receives up to 380 mm of rain per year. [That is, 54% of the railfall of Britain’s fertile East Anglia.]

So, with the aid of LP Turbines and good land management, part of the desert could be converted into a food producing job creation zone. This desert straddles the USA Mexican border along a length where a border fence already exists.

Cooperating to green the desert on both sides of the border would improve relations between the two countries. In the long term it could also provide the key to solving the migration crisis.

Converting a migration threat into a business opportunity

Figure 9. Greening the desert and scrublands on both sides of the Mexican-USA border would create new prosperity and jobs.

Politicians could use this change in borderland value to help them think outside the box about solving the migration crisis. For example,

(i) Refugees could be offered a five year work permit, provided that they worked on the greened desert farms.

 (ii) ‘Business Scholarships’ could be offered to enterprising refugees from El Salvador working on the new border farmlands. These would give them the skills they need to return home when gang peace comes, to set up job creation schemes of their own. The climate in the Sonoran Desert is entirely different to that of El Salvador. But in both regions, LP Turbines could be used to transform food production and industry.]

(iii) This enterprise building culture could be extended south of the border to retrain drug gang members as honest business managers.

 Important note

This proposal will need to be computer modelled and then, if the results are encouraging, implemented slowly over several decades. Otherwise, we risk adversely affecting the climate in other parts of the globe.

6 Lithium extraction

Lithium batteries are credited with delivering clean vehicle power but mining the lithium is not so green.

The bulk of battery lithium comes from the Atacama Desert in South America where it is extracted from under salt flats in the form of lithium carbonate brine. Before it can be chemically processed the brine needs to be concentrated by evaporating off most of the water in large open ponds. In this water scarce region, the process is squandering water instead of desalinating it. We waste approximately 500,000 gallons per tonne of lithium for our clean car engines.

In addition, fresh water ground supplies can become polluted by altering the brine/freshwater balance in local aquifers. Further pollution can be caused by the leakage of the reagents used in lithium purification processes.

LP Turbines could solve the biggest pollution problems by using solar energy to partially evaporate the brine in a closed chamber and then using the latent heat stored in the water vapour to power a bank of LP Turbines. The electricity generated would allow electrolysis to be used instead of reagent based purification.

An alternative source of lithium

Tiny amounts of lithium [less than one part per million] are also present in sea water. At some future date LP Turbines may be used for combined water desalination and lithium extraction.