Sea leavels are rising and the world lacks water so get a desalination plats up and running
- From: "robhingston@xxxxxxxxxxxxxx" <robhingston@xxxxxxxxxxxxxx>
- Date: Sun, 14 Sep 2008 18:31:10 -0700 (PDT)
Vast greenhouses that use seawater to grow crops could be combined
with solar power plants to provide food, fresh water and clean energy
in deserts, under an ambitious proposal from a team of architects and
engineers.
The Sahara Forest project would marry huge greenhouses with
concentrated solar power (CSP), which uses mirrors to focus the sun's
rays and generate heat and electricity. The installations would turn
deserts into lush patches of vegetation, according to its designers,
and without the need to dig wells for fresh water, which has depleted
acquifers in many parts of the world.
The team includes one of the lead architects behind Cornwall's Eden
project and demonstration plants are already running in Tenerife, Oman
and the United Arab Emirates.
Plants cannot grow in deserts because of the extreme temperatures and
lack of nutrients and water. Charlie Paton, one of the Sahara Forest
team and the inventor of the seawater greenhouse concept, said his
technology was a proven way to transform arid environments.
"Plants need light for growth but they don't like heat beyond a
certain point," said Paton. Above a particular temperature, the amount
of water lost through the holes in its leaves, called stomata, gets so
large that a plant will shut down photosynthesis and cannot grow.
The greenhouses work by using the solar farm to power seawater
evaporators and then pump the damp, cool air through the greenhouse.
This reduces the temperature by about 15C compared to that outside. At
the other end of the greenhouse from the evaporators, the water vapour
is condensed. Some of this fresh water is used to water the crops,
while the rest can be used for the essential task of cleaning the
solar mirrors.
"So we've got conditions in the greenhouse of high humidity and lower
temperature," said Paton. "The crops sitting in this slightly steamy,
humid condition can grow fantastically well."
The designers said that virtually any vegetables could be grown in the
greenhouses, depending on the conditions at which it is maintained.
The demonstration plants already produce lettuces, peppers, cucumbers
and tomatoes. The nutrients to grow the plants could come from local
seaweed or even be extracted from the seawater itself.
Michael Pawlyn of Exploration Architecture, who worked on the Eden
Project for seven years and is now part of the Sahara Forest team,
said the seawater greenhouse and CSP provided substantial synergies
for each other. "Both technologies work extremely well in hot, dry
desert locations – CSP produces a lot of waste heat and we'd be able
to use that to evaporate more seawater from the greenhouse," he said.
"And CSP needs a supply of clean, demineralised water in order for the
[electricity generating] turbines to function and to keep the mirrors
at peak output. It just so happens the seawater greenhouse produces
large quantities of this."
Paton said that the greenhouse produces more than five times the fresh
water needed to water the plants inside so, in addition to producing
water to clean the CSP mirrors, some of it can be released into the
local environment. Sea leavels are rising and the world lacks water,
So why not kill two
birds with one stone get a desalination plats up and running
to clean the sea water.
Then everyone gets water and you save the land from flooding using
seawater greenhouses could reverse the environmental damage done by
the greenhouses already built in places such as Almeria in southern
Spain. More than 40,000 hectares of greenhouses have been built in
this desert region during the past 20 years to grow salad vegetables.
"They take water out of the ground something like five times faster
than it comes in, so the water table drops and becomes more saline.
The whole of Spain is being sucked dry. If one were to convert them
all to the seawater greenhouse concept, it would turn an unsustainable
solution into a more sustainable one."
"In places like Oman, they've effectively sterilised large areas of
land by using groundwater that's become increasingly saline," said
Pawlyn. "The beauty of the Sahara Forest scheme is that you can
reverse that process and turn barren land into biologically-productive
land."
Neil Crumpton, an energy specialist at Friends of the Earth, said the
potential of desert technologies was huge. "Concentrated solar power
mirror arrays covering just one per cent of the Earth's deserts could
supply a fifth of all current global energy consumption. And one
million tonnes of sea water could be evaporated every day from just
20,000 hectares of greenhouses."
He added: "Governments around the world should invest serious money in
these solar energy and water technologies and not be distracted by
lobbyists promoting dangerous nuclear power or nuclear-powered
desalination schemes."
Harnessing the desert sun's rays is already at the heart of an
ambitious European scheme to build a €45bn (£35.7bn) supergrid that
could allow countries across the continent to share renewable
electricity from solar power in north Africa, wind energy in the UK
and Denmark, and geothermal energy from Iceland and Italy. The north
Africa solar plan has already gained political support in Europe from
Gordon Brown and Nicolas Sarkozy. Though expensive, it is in line with
International Energy Agency estimates that the world needs to invest
more than $45tn (£22.5tn) in new energy systems over the next 30
years.
.
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