Water Desalination

[matthewtrigg]

Are there any ways to justify the energy demands of water desalination?

[Johnny Electriglide]

Originally Posted by matthewtrigg

Are there any ways to justify the energy demands of water desalination?

There are quite a few and all are to satisfy the human basic need for water to live. Without water, a person will die in less than a week, without food twp weeks to over a month. Of course, without air, it is only several minutes.
Climate change from CO2 takes much longer. Overpopulation's short term needs trump the species long term needs in most human's psychology. The basic animal instinct to survive without the ability to think long term.
In Florida, salt water influx into ground water supplies that were overdrawn, pushed the need to the front. Many other coastal areas had the same thing happen. Desalination aboard nuclear ships is done to reduce space needed for long mission water requirements and weight.
Small scale solar evaporative/ natural condensation desalinators use no outside energy. However, these are rare.
The short answer is overpopulation is not justified with an intelligent species, and thus the energy demands of desalination without overpopulation would be much, much less.

[H2-PV]

Originally Posted by Johnny Electriglide

The short answer is overpopulation is not justified with an intelligent species, and thus the energy demands of desalination without overpopulation would be much, much less.

Unless you are advocating population reduction (Euthanasia), there is no point in making your point. The population is what it is and is not going to change appreciably by attrition in your lifespan.

With 70% (some say 71%, some 72%) of the planet covered with liquid water, to a depth of seven miles at it's deepest, water is not a limiting factor.

Energy for desalination is provided abundantly free of charge by a very dirty fusion reactor at the closest safe distance you ever want to be near one: 93,000,000 miles.

Hurricane Rita in 2005 gave an example of solar desalination and concentrated solar power.

In the amount of time that it took Rita to transit one whole diameter (15.5 hours) the calculated evaporation energy required to lift the sea water to fall back as rain (8" average) was 9,422,085,000,000 kilowatt-hours.

The CIA fact book reports USA electric consumption at 3.717 trillion kWh (2004).

9,422,085,000,000 kilowatt-hours RITA in 15.5 hours.
3,717,000,000,000 kWh USA consumption in a year.

Hurricane Rita could have supplied the entire USA for 2.5 years from the energy represented as rainfall evaporated from sea surface in the time it took to cross one point.

Since neither energy nor water are factors of significance whatsoever in the survivability of an "intelligent" species, your use of "intelligent species" is wrongly applied to the human species.

Until and unless you can master the most abundant elements on the face of the planet you have not yet earned the right to be called "intelligent".

The fact that you cannot describe the physical steps required to take raw silicon ores and convert it to photovoltaics means that your educational process is stunted and prematurely aborted.

You do not graduate into being a 21st century human until you can make photovoltaics by using common off-the-shelf parts and public domain process.

It is one of the keystone questions in any "intelligence test".

[robertp]

Concentrating Solar Power (NOT photovoltaics) can provide both electricity and desalination.

Every year, each square kilometre of hot desert receives solar energy equivalent to 1.5 million barrels of oil. Multiplying by the area of deserts world-wide, this is nearly a thousand times the entire current energy consumption of the world.

The cost of collecting solar thermal energy equivalent to one barrel of oil is about US$50 right now (already less than the current world price) and is likely to come down to around US$20 in future.

An area of the Sahara of 254 km × 254 km would generate the equivalent of the entire current world demand for electricity.

Waste heat from electricity generation in a CSP plant can be used to create fresh water by desalination of sea water: a very useful by-product in arid regions.

A CSP plant in California has been supplying electricity to around 500,000 people since 1985.

A recent report from the American Solar Energy Society says that CSP plants in the south western states of the US "could provide nearly 7,000 GW of capacity, or about seven times the current total US electric capacity".

The technology is relatively simple and robust, and apart from the energy used in construction, is totally carbon-free. The fuel never runs out (unlike uranium, coal, gas)

see www.trec-uk.org.uk for much more detail.

[Chriswaterguy]

Originally Posted by robertp

Waste heat from electricity generation in a CSP plant can be used to create fresh water by desalination of sea water: a very useful by-product in arid regions.

(snip)

see www.trec-uk.org.uk for much more detail.

Very interesting. But it looks like this hasn't been done yet - are you aware of pilot projects or anything like that?

See the Appropedia page Desalination for some of the problems with desal. Until such time as a cost-effective, environmentally friendly method is proven to work, and we know how to safely dispose of a very large volume of deoxygenated brine waste, we're better off sticking to other sources, where possible.

Existing dams (not new ones - they're an ecological disaster), groundwater, rainwater and water recycling should be considered. And most importantly - Water conservation.

[Johnny Electriglide]

The problem with desalination plants is initial cost and maintenance. Paid for by increased water bills and taxes, in a society headed toward economic breakdown from overpopulation, greed, and stupidity. My solar powered house uses about 1/3 the electric for water pumping from my well and our family of three uses only 100 gallons per day versus the average of 800 gallons per day or more in the USA. There is no recycling except for septic treatment and return to the groundwater at depth after seeping down. I have designed water recycling systems like in "Earthship 3" that would support a family of three (population goes down, demand goes down) in a situation of 12-15"annual rainfall collected from 1500 sq. ft. of roof space, and two plumbing systems. The black water would be from grease of dishwashing, small compost toilet outflow, and a "Y" valve from the clothes washer(and greywater overflow/cleanout). The rest of the water would be collected in a low tank with sand filter, for grey water gravity planter output and toilet tank valve pump to upper water tank (each 2500 gallons). The upper tank water is drawn by pressure pump through several filters(and UV) to a pressure tank, for theoretically using the same water over and over when you take a shower.
It is unfortunate that most of humanity breeds until the water pollution, depletion of soil and good water, and pollution of the air to the point of unstoppable climate change beyond adaptation and livability. Along with mercury pollution, persistent insecticides, and other pollutants along with fished out oceans---they take those that could live sustainably with them.
Even Earthship villages where they grow their own food, recycle everything, and have a small manufacturing capability for PV panel and battery maintenance/re-manufacture, and enough breeding intelligent couples to prevent genetic erosion---will get wiped out by the climate change, and global; mercury pollution, or attacks of cannibal gangs that out-gun them. The rich can live in supplied bunkers for a hundred years, but it will take the planet many thousands of years to support human life. Economic breakdown is happening and has been happening as a result of overpopulation. If you can't see it now or what is to come, you better do some more research.
Even the mentioned "euthanasia" is beyond logistical reality to lower population in time to prevent a mass cascading die-off 2040-60 (preceded by 20 years of economic depression 4 times worse than the 1930s from US extreme debt and trade imbalance along with lowering to third world status by immigration), and with the climate catastrophe, a truly ELE event(89% species loss), off the 26 million year cycle of probability(Nemesis), by 2100. Even a massive effort will run out of money fast, and I don't think the momentum can be stopped for running out of water, food, energy, and a benevolent climate. Overpopulation trumps them all, and running out of water, oil, and climate change to malevolent are just coup de graces. Too little, too late. The horror.....

[Chriswaterguy]

I see no sign of economic breakdown in sight. More likely is that the economy will keep growing strongly for the rich, or at least protect them from the worst of the damage they've inflicted on the earth, while some of the poor will escape poverty, while others of the poor will be hit hard by climate change.

That's not to play down the seriousness of what's happening to the climate. It's too late to stop it, but I believe we need a massive effort to prevent the worst of it - not the token efforts they're talking about, like 20% cuts by 2020. More like 20% right now, massive investment in R&D and 50% cuts by 2015. (I've more or less pulled those numbers out of the air, but the point is that it's not adequate to define our response in terms of what doesn't impact our current way of life.)

[H2-PV]

Originally Posted by robertp

Concentrating Solar Power (NOT photovoltaics) can provide both electricity and desalination.

Any solar system can provide both desalination and electricity. It's an engineering decision, not a physics problem. Neither one automatically provides both, and you are underestimating the challenges in maximizing productivity of either by trying to make one system do two jobs both well.

Originally Posted by robertp

Every year, each square kilometre of hot desert receives solar energy equivalent to 1.5 million barrels of oil. Multiplying by the area of deserts world-wide, this is nearly a thousand times the entire current energy consumption of the world.

The cost of collecting solar thermal energy equivalent to one barrel of oil is about US$50 right now (already less than the current world price) and is likely to come down to around US$20 in future.

So? Each square kilometer of the sun does even better -- in both cases there are engineering challenges and delivery challenges. The cost of transporting electricity is $1.5 megabuck per miles of high-tension transmission lines. The further you transport, the higher the costs.

Water, being infinitely heavier than electricity, costs extravagantly more to transport long distances. Flippant statements about "teleporting" power costlessly from where it may be abundant to where the people are is just throwing sand in peoples eyes to blind them and delay deciding on choices that make sense in the immediate future.

Why don't you suggest unicorns could transport the electricity and purified water to the world's billions?

Originally Posted by robertp

An area of the Sahara of 254 km × 254 km would generate the equivalent of the entire current world demand for electricity.

Waste heat from electricity generation in a CSP plant can be used to create fresh water by desalination of sea water: a very useful by-product in arid regions.

It takes a 40 degree C difference in temperature to operate Stirling Engines to produce AC electricity, and PV systems with coolant can do that in temperate climates where the people actually live. CHAPS is combined heating and power solar, and has produced real-world total efficiencies of near 60%.

The "Sahara Red Herring" is unicorns again. There's no water to desalinate in the Sahara, and no way to get the mythical desalinated water to say, NYC.

Originally Posted by robertp

A CSP plant in California has been supplying electricity to around 500,000 people since 1985.

A recent report from the American Solar Energy Society says that CSP plants in the south western states of the US "could provide nearly 7,000 GW of capacity, or about seven times the current total US electric capacity".

The technology is relatively simple and robust, and apart from the energy used in construction, is totally carbon-free. The fuel never runs out (unlike uranium, coal, gas)

see www.trec-uk.org.uk for much more detail.

So What? At a megabuck per mile it doesn't pay back to string wires to some of the best locations for solar or wind. Las Vegas is where it is because organized crime could manipulate a sparse population to vote for legalized gambling, not because a lot of people thought that living in deserts was the best idea. If it wasn't for the Hoover Dam nearby there wouldn't be any Las Vegas despite the high solar potential.

You are throwing around random facts casually without thinking it all the way through.

In some distant stranded places the highest use of renewable energy is to convert it straight into purified silicon PV and move it by truck to where the people are. It takes 1.2 kilograms of purified silicon to make one meter square of 13% net efficiency PV. A standard 18-wheeler big rig can move 40 tons a trip, 30240 meters square, 3,931 kilowatts per trip. With two drivers that one truck can make 200 trips of 1,000 miles each way round trip. The truck costs less than one quarter of mile of high-power electric transmission lines, and delivers 786,240 kilowatts of new PV waferstock per year. For the cost of one mile of wiring you can run five trucks from the stranded windfields of the Dakotas to Phoenix, Arizona, or Las Vegas. Once the PV is where the transmission lines already exist and are paid for, then you can plug in all that PV to the national grid.

Hydrogen Gas transmission pipelines is $600K to $900K per mile, compared to $1500K per mile of wiring. H2 gas in co-gen fuel-cells is nearly 100% efficient in providing both lights and heat/cooling/hot-water, given the best engineering known today. Co-gen is not just for CSP, but can be used with many power options, so all your arguments FOR CSP are also arguments FOR H2-PV equally.

A Molten-Carbonate (MCFC) or Solid-Oxide (SOFC) Power Plant-Sized Fuel Cell in the Megawatt range is also 1000 degrees C desalinator if you engineer it to do that.