Hydraulic and Geothermic Energies
No-limits energy production for the future?
Hydraulic and Geothermic Energies are some of today main
objectives for an eco-compatible energy development.
Hydraulic Energy
Energy is created by the water-cycle induced by solar radiation.
Hydroelectric power plants make use of the potential energy of:
a)
water stored in large basins (natural or dam-contained)
b) water flowing downstream between two different levels.
Hydraulic Plants are classified according to:
1. Elevation difference (water jump, H in m)
2. Water Flow amount (Q in m³/s)
3. System type (Usually installation using large flows and lower
jumps are ‘running water’ type; those using limited water flows
and medium or high jumps are ‘reservoir’ and ‘pumping’ types)
4. Turbines type (Pelton, Francis, Kaplan: chosen according to H
and Q)
Hydraulic Power Plants in general can be promptly put in
service or shut-down, as well adapted to load variations within
short times.
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There are operation differences according to the installation type.
1. Running water installation: suitable for continuous
operation at constant load (in case of reduced load excess
water must overflow and its energy is wasted).
2. Reservoir installations: filled during some periods (seasons,
rivers), are gradually emptied according to load demands: can
adapt to peak demands or highly variable loads.
3. Pumping installation: basically with two basins at different
levels and connected by pumps: water flowing to down-level
basin supply energy during the day while at night (when energy
demand is less) it is pumped back to up-level basin.
Future major developments for new Hydroelectric Plants are
not expected, apart from ways to improve efficiency.
Because large installations have cost and environmental
limitations, now days it is foreseeable the construction of a
number of mini-installation in carefully selected areas.
Energy from Ocean’s waves and heat
1. Due to winds and streams, waves hold kinetic energy, causing
water level increase and air compression: this energy may be
used to rotate a turbine.
2. Due to solar radiations, there is a significant temperature
difference in the sea between the surface and a depth of say
500m that could be used to generate steam.
A study to use the energy from sea-waves foresees two joint
reservoirs positioned at different levels: the incoming weave is
collected in the upper reservoir that then is immediately closed;
water flows to the lower reservoir and causes a turbine to rotate;
the lower basin is emptied by the flowing away wave (like Venturi
suction), and the system is ready for the next cycle.
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Large scale projects based on these systems have not yet been
realized; due to water heat capacity energy production by these
means is expected to be rather limited.
However they may be considered of possible usage in some
suitable coastal regions.
Sea tides energy
Due to the Moon attraction and the Earth rotation sea is subject to
tides twice a day.
The elevation difference between high and low tides depends
essential from the shape and characteristics of the cost line.
To use such energy tide amplitude has to be of several meters and
take place in a large bay that has to be closed by a dam.
There are few places around the world with such characteristics.
One such tides-powered plant, of 240MW with 24 bi-directional
turbines, is in operation on the Atlantic coast of France (St.Malo),
where tides amplitudes are between 8-13 m.
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Because of:
1. high construction costs,
2. 50’ daily change of tides timing during the whole year,
3. Down-time gap between each tide,
this type of installation is not flexible with the load demand,
and future projects are on hold.
Geothermic Energy
• Below ground surface temperature increases of 1°C/30
m; the liquid magma is at 4000°C due to the radioactive
decay process.
• At places the magma heat is closer to the surface and
high temperature can be measured and used to produce
steam produced.
• Such Power plants (more than 150) are operating in New
Zealand, USA, Mexico, Italy, and Indonesia.
• This type of installation requires the presence in the same
area of high surface temperature as well as large quantities
of water to produce steam.
• When above condition is not satisfied, some trials are being
performed by digging two deep wells to reach the rock bed
at 200-300°C. Cold water, injected in the first deepest well,
warms up in contact with the hot rocks, pressure increases
and warmed water is then recovered from the second well.
• Large scale projects of this type are not yet implemented.
• Geo-heat can be more easily utilized for general heating
(household heating, hot water supply): warm water flowing
underground at small or medium depths is often available; at
60°C or more it can be used directly, at lower temperature a
heat-pump may be used to increase the temperature of the
water (and air conditioning at the same time).
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Forward ahead
• Geothermic power plant even with their limited range of
applications, do have the advantage of extended operation
at maximum capacity and low operation costs.
• Go-not-to-go criteria for future power generating projects
are the environment impact and the economic evaluation,
which in turn depends on amount of energy available, well
digging costs, availability of water of suitable chemical
quality.
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