World of Solar Thermal.com | Solar Thermal News and Information: MEDIUM TEMPERATUR COLLECTORS

MEDIUM TEMPERATUR COLLECTORS
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Pangea on 10/12/2009 17:00:00
 
Medium-temperature collectors
These collectors could be used to produce approximately 50% of the hot water
needed for residential and commercial use in the United States.
In the United States, a typical system costs $5000-$6000 and 50% of the system
qualifies for a tax credit. With this incentive, the payback time for a typical
household is nine years. A crew of one plumber and two assistants with minimal
training can install two systems per week. The typical installation has
negligible maintenance costs and reduces a households' operating costs by $6 per
person per month. Solar water heating can reduce CO2 emissions by 1 ton/year (if
replacing natural gas for hot water heating) or 3 ton/year (if replacing
electric hot water heating).
Medium-temperature installations can use any of several designs: common designs
are pressurized glycol, drain back, and batch systems.
COOKING
Solar cookers use sunlight for cooking, drying and pasteurization. Solar cooking
offsets fuel costs, reduces demand for fuel or firewood, and improves air
quality by reducing or removing a source of smoke.
The simplest type of solar cooker is the box cooker first built by Horace de
Saussure in 1767. A basic box cooker consists of an insulated container with a
transparent lid. These cookers can be used effectively with partially overcast
skies and will typically reach temperatures of 50-100 °C.
Concentrating solar cookers use reflectors to concentrate light on a cooking
container. The most common reflector geometries are flat plate, disc and
parabolic trough type. These designs cook faster and at higher temperatures (up
to 350 °C) but require direct light to function properly.
The Solar Kitchen in Auroville, India uses a unique concentrating technology
known as the solar bowl. Contrary to conventional tracking reflector/fixed
receiver systems, the solar bowl uses a fixed spherical reflector with a
receiver which tracks the focus of light as the Sun moves across the sky. The
solar bowl's receiver reaches temperature of 150 °C that are used to produce
steam that helps cook 2,000 daily meals.
Many other solar kitchen in India use another unique concentrating technology
known as the Scheffler reflector. This technology was first developed by
Wolfgang Scheffler in 1986. A Scheffler reflector is a parabolic dish that uses
single axis tracking to follow the Sun's daily course. These reflectors have a
flexible reflective surface that is able to change its curvature to adjust to
seasonal variations in the incident angle of sunlight. Scheffler reflectors have
the advantage of having a fixed focal point which improves the ease of cooking
and are able to reach temperatures of 450-650 °C. Built in 1999, the world's
largest Scheffler reflector system in Abu Road, Rajasthan India is capable of
cooking up to 35,000 meals a day. By early 2008, over 2000 large cookers of the
Scheffler design had been built worldwide.
DISINFECTION AND DESALINATION
SOLAR WATER DISINFECTION, ALSO KNOWN AS SODIS, IS A SIMPLE METHOD OF
DISINFECTING WATER USING ONLY SUNLIGHT AND PLASTIC PET BOTTLES.
SODIS IS A CHEAP AND EFFECTIVE METHOD FOR DECENTRALIZED WATER TREATMENT, USUALLY
APPLIED AT THE HOUSEHOLD LEVEL AND IS RECOMMENDED BY THE WORLD HEALTH
ORGANIZATION AS A VIABLE METHOD FOR HOUSEHOLD WATER TREATMENT AND SAFE STORAGE.
SODIS HAS OVER TWO MILLION USERS IN DEVELOPING COUNTRIES SUCH AS BRAZIL,
CAMEROON AND UZBEKISTAN.
A solar still uses solar energy to distill water. The main types are cone
shaped, boxlike, and pit. The box shaped types are most sophisticated of these
and the pit types the least sophisticated. In cone solar stills, impure water is
inserted into the container, where it is evaporated by sunlight coming through
clear plastic. Free of solids in suspension or solution, the water vapor
condenses on top and drips down to the side, where it is collected and removed.
The application of solar thermal power for desalination at large scale,
especially in sunny regions such as the Middle East and North Africa, is the
subject of a definitive 2007 report by the German research institute DLR.  The
report includes an excellent overview of high-temperature solar thermal
technologies as well as desalination technology options.