Solar thermal applications
SEA Groups Ltd.
We harness the power of the sun for our future
Solar . Energy . Application
SEA Groups Ltd.
We harness the power of the sun for our future
Solar . Energy . Application
Solar thermal technologies can be used for water heating, space heating, space cooling and electrical
power generation
.
Water heating
Solar hot water systems use sunlight to heat water.  In low geographical latitudes (below 40 degrees)
from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar
heating systems.  The most common types of solar water heaters are vacuum tube collectors (44%) and
glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors
(21%) used mainly to heat swimming pools.

As of 2007, the total installed capacity of solar hot water systems is approximately 154 GW.  China is the
world leader in their deployment with 70 GW installed as of 2006 and a long term goal of 210 GW by
2020.  Israel and Cypress are the per capita leaders in the use of solar hot water systems with over 90%
of homes using them.  In the United States, Canada and Australia heating swimming pools is the
dominant application of solar hot water with an installed capacity of 18 GW as of 2005.
Space heating and cooling
In the United States, heating,  air conditioning (HVAC) and ventilation systems account for 30% (4.65 EJ)
of the energy used in commercial buildings and nearly 50% (10.1 EJ) of the energy used in residential
buildings.  Solar heating, cooling and ventilation technologies can be used to offset a portion of this
energy.

Solar heating is the usage of solar energy to provide process, space or water heating.  The heating of
water is covered in solar hot water.  Solar heating design is divided into two groups:
Active solar heating uses pumps which move air or a liquid from the solar collector into the building or
storage area.
Passive solar heating does not require electrical or mechanical equipment, and may rely on the design
and structure of the house to collect, store and distribute heat throughout the building.

A typical household solar heating system consists of a solar panel (or solar collector) with a heat transfer
fluid flowing through it to transport the heat energy collected to somewhere useful, usually a hot water
tank or household radiators.  The solar panel is located somewhere with good light levels throughout the
day, often on the roof of the building.  A pump pushes the heat transfer liquid (often just treated water)
through the panel.  The heat is thus taken from the panel and transferred to a storage container.

Solar cooling.   Active solar cooling wherein solar thermal collectors provide thermal energy to drive
thermally-driven chillers (usually ADsorption or ABsorption chillers.)

There are multiple alternatives to compressor-based chillers that can reduce energy consumption by
80%, with less noise and vibration.  Solar thermal energy can be used to efficiently cool in the summer,
and also heat domestic hot water, and the building in the winter.  Single, double or triple iterative
absorption cooling cycles are used in different solar-thermal-cooling system designs.  The more cycles,
the more efficient they are.

In the late 1800s, the most common phase change refrigerant material for absorption cooling was a
solution of ammonia and water.  Today, the combination of lithium and bromide is still in common use.  
While using water as the refrigerant, is today’s best choice in air conditioning for protecting the
environment and reducing the cost of energy.  Double-effect cycles and advanced technology ensure
high performance and long term reliability.  One end of the system of expansion / condensation pipes is
heated, and the other end gets cold enough to make ice.  Originally, natural gas was used as a heat
source in the late 1800s.  Today, propane is used in recreational vehicle absorption chiller refrigerators.  
Innovative hot water solar thermal energy collectors can also be used as the modern "free energy" heat
source.

Efficient absorption chillers require water of at least 190 degrees F (88 degrees C).  Common,  flat-plate
solar thermal collectors only produce about 160 degree F (71 degree C) water, but several successful
commercial projects in the US, Asia and Europe have shown that vacuum tube solar collectors specially
developed for temperatures over 200 degrees F (featuring all glass double glazing, vacuum insulated,
etc.) can be effective and cost efficient.  Heat pipe vacuum tube solar panels will be the best used for
generating high temperature hot water.  Concentrating solar collectors required for absorption chillers
are less effective in hot humid, cloudy environments, especially where the overnight low temperature and
relative humidity are uncomfortably high.  Where water can be heated well above 190 degrees F (88+
degrees C), it can be stored and used when the sun is not shining.

For 150 years, absorption chillers have been used to make ice (before the electric light bulb was
invented).  This ice can be stored and used as an "ice battery" for cooling when the sun is not shining, as
it was in the 1995 Hotel New Otani in Tokyo Japan.  
House heating with both
thermodynamic and
photovoltaic panels
Water heating with heat
pipe vacuum tube
collectors
Concentrated Solar Power.    Where temperatures below about 95°C are sufficient, as for water heating
and space heating, flat-plate / vacuum tube collectors of the non-concentrating type are generally used.
The fluid-filled heat pipes can reach temperatures of 150 to 220 degrees Celsius when the fluid is not
circulating.  While this temperature is too low for efficient conversion to electricity.

The efficiency of heat engines increases with the temperature of the heat source.  To achieve this in
solar thermal energy power plants, solar radiation is concentrated by mirrors or lenses to obtain higher
temperatures — a technique called Concentrated Solar Power (CSP).  The practical effect of high
efficiencies is to reduce the power plant's collector size and total land use per unit power generated,
reducing the environmental impacts of a power plant as well as its expense.

As the temperature increases, different forms of conversion become practical.  Up to 600°C, steam
turbines, standard technology, have an efficiency up to 41%.   Higher temperatures are problematic
because different materials and techniques are needed.  One proposal for very high temperatures is to
use liquid fluoride salts operating above 1100°C, using multi-stage turbine systems to achieve 60%
thermal efficiencies.  The higher operating temperatures permit the power plant to use higher-
temperature dry heat exchangers for its thermal exhaust, reducing the plant's water use — critical in the
deserts where large solar plants are practical.  High temperatures also make heat storage more
efficient, because more watt-hours are stored per kilo of fluid.

Since the CSP power plant generates heat first of all, it can store the heat before conversion to electricity.
With current technology, storage of heat is much cheaper and more efficient than storage of electricity.  In
this way, the CSP plant can produce electricity day and night.  If the CSP site has predictable solar
radiation, then the CSP plant becomes a reliable power plant.  Reliability can further be improved by
installing a back-up system that uses fossil energy.  The back-up system can reuse most of the CSP
plant, which decreases the cost of the back-up system.

With reliability, unused desert, no pollution and no fuel costs, the only obstacle for large deployment for
CSP is cost.  Although only a small percentage of the desert is necessary to meet global electricity
demand, still a large area must be covered with mirrors or lenses to obtain a significant amount of
energy.  An important way to decrease cost is the use of an innovation and simple design.

Central tower Power.  The power plants or 'heliostat' power plants use an array of flat, moveable
mirrors (called heliostats) to focus the sun's rays upon a collector tower (the receiver).

The advantage of this design above the parabolic trough design is the higher temperature.  Thermal
energy at higher temperatures can be converted to electricity more efficiently and can be more cheaply
stored for later use.  The concentrated energy is then used to heat a boiler atop the tower to 550 degrees
Celsius, generating steam that is piped into a turbine, where electricity can be produced.  Furthermore,
there is less need to flatten the ground area.  In principle a power tower can be built on a hillside.  
Mirrors can be flat and plumbing is concentrated in the tower.  The disadvantage is that each mirror
must have its own dual-axis control, while in the parabolic trough design one axis can be shared for a
large array of mirrors.
Thermal-electrical power generation
Concentrated solar power
plant using parabolic
trough design.
Central tower power
receive heat energy from
the helicostats.
Solar cooling by using
heated hot water to
reduce cost of energy
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