White
Gold !
Electricity generation and
water desalinisation - powered by heat collected in highly saline
lakes
How many people in rural Australia realise that
the ongoing scourge of salinity has a gold lining. White gold -
perhaps?.
Salt lakes can be used to produce ENERGY -
surely one of the most valuable commodities in our community. There
are many parts of Australia being used to produce wheat at a margin
of $150 /ha/year when they could be producing energy worth $15,000/ha
/year !
Solar
ponds - what are they ?
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Energy from
salt lakes<
Any lake absorbs heat from the sun.
Normally, heat is lost as warm water rises to the surface and
cools by evaporation. But water is a VERY poor conductor of
heat and if this circulation can be stopped, the heat can be
trapped in the bottom of the lake. A salt lake, (ideally
about 3m deep), managed so that the water on top is of
(relatively) low salinity and the water on the bottom is of very
high salinity, will not circulate to release heat because the
water on the bottom is so heavy with salt it cannot rise. The
deeper water gets very hot - to over 100 degrees in the right
circumstances - 80 degrees is common in the tropics. In Southern
Australia 60 degrees C is easily achievable - even in winter.
The main management problem is to extract heat at the right rate
so the lake does not boil or 'turn over' and lose its heat.
Run like this, such ponds are called 'Salt
Gradient Solar Ponds' or just 'Solar
Ponds'. Effectively, the pond acts as a very large, low cost,
collector of solar heat. (There are
also other types of solar ponds)
As a form of solar energy, the solar pond
collector has major advantages.
The heat
storage is massive, so energy can be extracted day and night -
hence it is a source of 'base load' solar power - no
batteries or other storage needed !
Solar ponds
can have very large heat collection area at low cost.
The major
production potential is during peak electrical power demand (and
price) in mid summer
The
technology and scientific principles for collection and
extraction of heat and its conversion to electricity are well
understood and well documented in scientific papers.
Any qualified engineer would be able to
build one of these systems (being a refrigeration specialist
would be useful if you wanted to build a Rankine engine)
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Solar ponds in
action
Solar ponds are currently used
in Europe, USA, the Middle East and Australia. The heat they
produce is used to warm swimming pools and glasshouses and for a
range of industrial processes.
(as
well as power production)
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Getting the energy out of
the pond
Energy, in the form of hot
water, is extracted by circulating fresh water in pipes laid on
the bottom of the pond.
This picture of the Solar
pond at Pyramid Hill (near Kerang in Northern Victoria) shows the
mesh of pipes running down the wall of the pond. These run across
the bottom of the pond and up the other side. Fresh water
(or radiator coolant) is circulated through them, and is heated by
the saline pond water. This hot fluid is then used to heat glass
houses, boil refrigerant in a rankine engine to make electricity,
or (in the case of Pyramid Hill) used to heat air to flash dry
gourmet salt products.
(The
plastic rings visible on the surface of the water are used to
reduce water movement caused by wind)
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Electricity from
solar ponds !
To create electricity from the solar pond hot
water is also a well understood technology. The convertor is called
an 'Organic Rankine Cycle Engine' an ORC engine for short - named
after a 19th century engineer. This is the same process
used to extract energy from deep ocean temperature gradients off
Japan. There are several more sophisticated
technologies than the Rankine engine - but this is the easiest to
describe and build.
A Rankine engine is used to convert waste heat
from a solar pond (or any other source - such as industrial waste
heat) into energy to drive a rotating shaft - which (most often) is
used to drive a conventional alternator to make electricity.
The Rankine engine works by using the hot water
to evaporate a low boiling point chemical, such as those used in
refrigerators. That vapour then becomes a high pressure gas
which can be used to drive a turbine and produce electricity. Once
used, the gas is recirculated, cooled, condensed and recycled - same
as in a refrigerator.
In fact, a low cost version of a Rankine
engine can be build using 'off the shelf' industrial
scale air conditioner parts. The units at Alice Springs and
Birdsdville were built this way.
Solar pond built at Alice
Springs in 1972 with close up of the Organic Rankine Engine power
generator.
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Pure, fresh, drinkable water
from solar ponds
In all of Southern Australia, water supplies
are overused and lack of fresh water is limiting development in many
areas. Groundwater based supplies for both town water and irrigation
are becoming salinised, and in many places there are very limited
supplies of drinking grade water..
In many places - such as the Eyre Peninsula,
most of south western and central WA, development has come to a
standstill because of limited supplies of adequate quality water.
Scientists tell us that climate change will cause rainfall to reduce
and population continues to increase. We are running out of
water, we need to look at new ways to obtain fresh water.
The popular conventional method of making fresh
water from sea water is Reverse Osmosis - it requires a lot of
electrical power and hence produces a lot of greenhouse
gas. The vast, cheap supply of solar heat from a solar
pond can be used to improve the output of old technology solar
distillation systems and to improve the output of conventional system
with less greenhouse gas emissions. More
detail
Why are these
technologies not better known?
There are four fundamental needs for this
technology to be applicable.
It requires a
lot of land area - land must be very low cost.
It requires a
VERY large supply of salt water.
It works best
if there is a high level of solar energy*
It requires an industry capable of using
the hot water - (to justify the expense)
* however, solar ponds are used in
northern countries to heat glass houses during freezing winters
These requirements usually only come together
in desert areas which are near coasts and in salinised agricultural
areas. The requirement for low cost land usually means a very low
population where there is seldom an industrial base to use the power.
Most of the first world does not have these land characteristics and
the third world does not have the technology.
The "Catch 22' is that scientists
don't bother with this technology, don't research it, and don't apply
for research grants, because it is well understood, routine, and 'low
tech'. So it does not get
publicity !
There seems to be no technical or economic
reason why solar pond produced power and water is not done more
often. The reasons seem to be geographical and political.
While Israel uses the Dead Sea as a solar pond
to make electricity, the Dead Sea is so saline that reverse osmosis
is not an option. Many Middle Eastern countries use reverse osmosis
to get fresh water from the sea, but have ready supplies of
electricity powered by cheap oil - so they have no incentive to
develop solar ponds. While there have been many small scale solar
ponds built in the Southern USA for industrial and community heat
supplies (eg town swimming pools), there seems to be a problem in
those areas in getting an adequate salt supply and cost of salt is
major running expense. The USA also has very cheap oil
A local
history of solar ponds
This technology was used at several remote
sites in Australia in the 1970's. Australian Solar Ponds P/L (now
disbanded) built an experimental 0.5ha solar pond system at Alice
Springs which produced electricity (net 15kW) on and off for several
years. Enreco P/L built conversion units in the 1970s (Powered by hot
water from the Great Artesian Basin) of up to 150kW - one of these is
still functional at Birdsville. For more detail on solar pond
development see 'History of solar ponds'
What will it
cost?
For a detailed cost analysis see 'Economics
of solar ponds for power and fresh water supplies'
In brief, the cost of power produced by a solar
pond is about $180/MWh - about twice that of wind ($20-60 /Mwh- in a
windy area) and three times that of coal fired power ($40/MWh).
Photovoltaic (solar cells) combined with batteries to provide 24hour
supply cost around $1000/MWh. Solar ponds come in at
about three times the cost of wind power per watt but they are much
more reliable - delivering power 24 hours a day and 365 days a
year. ( For comparison , retail consumers in
Adelaide pay around $200/MWh)
Like most solar energy systems, the running
cost of solar pond power systems is negligable but the capital
investment is considerable - most of the cost derives from the 'cost
of capital'
Rises in power prices - particuarly recent peak
power price in summer (when these systems are most effective) could
make mains connected solar pond power systems financially viable in
their own right.
Improving
industrial efficiency
The energy conversion units will work on any
form of waste heat. There are many sources of waste heat in industry,
and the potential exists to convert this waste to readily saleable
electrical power with a consequent increase in the efficiency of
industrial processes.
Development
partners required
We are seeking partners with an interest in
dealing with the hydrological, biological and engineering problems of
maintaining solar ponds. Some of the skills required relate to the
behavior of larger bodies of water, others to dam construction and
refrigeration engineering.
Where
are the Opportunities ?
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I see this as an opportunity to develop a new
technology (or to be more precise, a new application of established
technologies). There are many places in the world which have all the
requirements for solar pond generated electricity and the need of new
supplies of fresh water. While many of these places are in the third
world (where much of our aid money is already targeted at providing
potable water), there is also great opportunity in Australia.
RIGHT NOW, Streaky Bay and other towns on Eyre
Peninsula cannot develop because they need both a power supply and a
water supply. All the requirements are there:- salt water, sun, and
low cost land.
RIGHT NOW, many towns in South Western
Australia and many of the towns just west of the Great Divide in NSW
have rising saline water which is wrecking buildings and roads and
contaminating groundwater supplies. Solar ponds have the potential to
provide decentralised town power as well as to provide power to run
pumps to lower saline water levels - the same saline water which
would be used to generate the power.
RIGHT NOW, the Murray-Darling basin authorities
are spending millions of dollars to pump salt water from the ground
into saline evaporation lakes to lower saline water tables and
protect the river. 200GigaLitre /year in 2006 and rising -
enough to maintain a 200ha lake and produce 10Mw of power.
Converting them to lined solar ponds would stop the huge
environmental damage they cause now.
Add on
industries Return to index
While solar ponds are a novelty, they would
represent a minor tourism opportunity.
There is obvious potential to add a salt
extraction operation, although at $30/ton raw salt is generally not
worth harvesting if it needs to be transported any distance.
Depending on the source of the saline water, impurities in the salt
may be worth harvesting - magnesium and potassium salts are valuable
On a large scale, there are many tourism
industries - A hypersaline lake resort coupled with hot spa
(powered by solar pond hot water) is just one possibility. In Isreal
the Dead Sea has a huge tourist industry based on hypersaline
swimming - some hotels there have over 400 beds+. But
that's just one idea - we came up with many, from the sort of things
a school could set up, to multimillion dollar tourist ventures. See
(Making money from saline water)
The most likely add-on industry is the
production of brine shrimp - a valuable fish food for fingerlings in
the aquaculture industry.
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Who
are we ?
The partners in this group are
Cliff Hignett -
agricultural consultant , cliff.hignett@enersalt.com.au 61 8
8276 7706
Ray White -
retired manufacturing refrigeration specialist (manufacturer of the
ORC units pictured)
Heinz Rechten - Crest Energy
Solutions, North Adelaide SA
Primary contact Cliff
Hignett 61 08 8276 7706 , cliff.hignett@enersalt.com.au
Our aim is to revive the technology of solar
ponds and make it a serious player in the alternative energy stakes.
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