Solar Power Towers
- How it works
- Heat storage and transfer
- Scheme
- Technical, Facts and Tests
- Location
How it works
Solar power towers consist of a large field of sun-tracking
mirrors, called heliostats, which focus solar
energy on a receiver atop a centrally located tower. The enormous amount
of energy, coming out of the sun rays, concentrated at one point (the
tower in the middle), produces temperatures of approx. 550°C to 1500°C.
The gained thermal energy can be used for heating water or molten salt,
which saves the energy for later use.
Heatened water gets to steam, which is used to move the turbine-generator.
This way thermal energy is converted into electricity.
Heat storage and transfer
As already mentioned there are two main fluids which are used for the
heat transfer, water and molten salt. Water for example is the oldest and
simplest way for heat transfer. But the difference is that the method in which
molten salt is used, allows to store the heat for the terms when the sun is
behind clouds or even at night. Molten salt - better: the heat of it - can
be used until the next dawn when the sun will be back to heat the cooled down
salt again.
The molten salt consists of 60% sodium nitrate an 40% potassium nitrate
(salpeter). The salt melts at about 700°C and is liquid at approx. 1000°C,
it will be kept in an insulated storage tank until the time, when it will be
needed for heating up the water in the steam generator.
This way of energy storage has an efficiency of approx. 99%, i.e.
due to the imperfect insulation 1% of the stored energy gets lost .
Scheme
Technical, Facts and Tests
E.g.: The Power Tower Project "Solar II" (California):
- 1,926 sun-tracking heliostats (mirrors)
- molten salt thermal storage system
- tower (300 ft) with central receiver
- conventional steam driven turbine and generator
- produces about 10 MWe, enough power to serve 10,000 homes with electricity
- costs about 40 million US$
- will be used in an experiment until 1998
Location
Until now, there are only few solar power towers because they're rentable only
in regions with a high amount of sunshine and the costs are at a fairly high level.
Questions, comments, t-shirts, cookies, pizza, milk and honey to:
Mustafa Mesanovic <mm@rhlx01.rz.fht-esslingen.de>
Nils Philippsen <nils@rhlx01.rz.fht-esslingen.de>
Fri Dec 20 10:44:48 MET 1996
