Engineering sciences/2. Energetics
O. Sagan, K. Chala
National
University of Food Technologies (Kiev, Ukraine)
Solar
energy
Solar technologies are broadly characterized as either
passive or active depending on the way they capture, convert and distribute
sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to
convert sunlight into useful outputs. Passive solar techniques include
selecting materials with favorable thermal properties, designing spaces that
naturally circulate air, and referencing the position of a building to the Sun.
Active solar technologies increase the supply of energy and are considered
supply side technologies, while passive solar technologies reduce the need for
alternate resources and are generally considered demand side technologies.
Sunlight has influenced building design since the
beginning of architectural history. Advanced solar architecture and urban
planning methods were first employed by the Greeks and Chinese, who oriented
their buildings toward the south to provide light and warmth.
A solar chimney (or thermal chimney, in this context)
is a passive solar ventilation system composed of a vertical shaft connecting
the interior and exterior of a building. As the chimney warms, the air inside
is heated causing an updraft that pulls air through the building. Performance
can be improved by using glazing and thermal mass materials in a way that
mimics greenhouses.
Deciduous trees and plants have been promoted as a
means of controlling solar heating and cooling. When planted on the southern
side of a building, their leaves provide shade during the summer, while the
bare limbs allow light to pass during the winter. Since bare, leafless trees
shade 1/3 to 1/2 of incident solar radiation, there is a balance between the
benefits of summer shading and the corresponding loss of winter heating. In
climates with significant heating loads, deciduous trees should not be planted
on the southern side of a building because they will interfere with winter
solar availability. They can, however, be used on the east and west sides to
provide a degree of summer shading without appreciably affecting winter solar
gain.
Solar concentrating technologies such as parabolic
dish, trough and Scheffler reflectors can provide process heat for commercial
and industrial applications. The first commercial system was the Solar Total
Energy Project in Shenandoah, Georgia, USA where a field of 114 parabolic
dishes provided 50% of the process heating, air conditioning and electrical
requirements for a clothing factory. This grid-connected cogeneration system
provided 400 kW of electricity plus thermal energy in the form of 401 kW steam
and 468 kW chilled water, and had a one hour peak load thermal storage.
Evaporation ponds are shallow pools that concentrate
dissolved solids through evaporation. The use of evaporation ponds to obtain
salt from sea water is one of the oldest applications of solar energy. Modern
uses include concentrating brine solutions used in leach mining and removing
dissolved solids from waste streams.
Solar power is the conversion of sunlight into
electricity, either directly using photovoltaics (PV), or indirectly using
concentrated solar power (CSP). CSP systems use lenses or mirrors and tracking
systems to focus a large area of sunlight into a small beam. PV converts light
into electric current using the photoelectric effect.
Commercial CSP plants were first developed in the
1980s. Since 1985 the eventually 354 MW SEGS CSP installation, in the Mojave
Desert of California, is the largest solar power plant in the world. Other
large CSP plants include the 150 MW Solnova Solar Power Station and the 100 MW
Andasol solar power station, both in Spain. The 250 MW Agua Caliente Solar
Project, in the United States, and the 221 MW Charanka Solar Park in India, are
the world’s largest photovoltaic plants. Solar projects exceeding 1 GW are
being developed, but most of the deployed photovoltaics are in small rooftop
arrays of less than 5 kW, which are grid connected using net metering and/or a
feed-in tariff.
Concentrating Solar Power (CSP) systems use lenses or
mirrors and tracking systems to focus a large area of sunlight into a small
beam. The concentrated heat is then used as a heat source for a conventional
power plant. A wide range of concentrating technologies exists; the most
developed are the parabolic trough, the concentrating linear fresnel reflector,
the stirling dish and the solar power tower. Various techniques are used to
track the Sun and focus light. In all of these systems a working fluid is
heated by the concentrated sunlight, and is then used for power generation or
energy storage.
NREL compilation of best research solar cell
efficiencies from 1976 to present
A solar cell, or photovoltaic cell (PV), is a device
that converts light into electric current using the photoelectric effect. The
first solar cell was constructed by Charles Frits in the 1880s.In 1931 a German
engineer, Dr Bruno Lange, developed a photo cell using silver selenide in place
of copper oxide. Although the prototype selenium cells converted less than 1%
of incident light into electricity, both Ernst Werner von Siemens and James
Clerk Maxwell recognized the importance of this discovery. Following the work
of Russell Ohm in the 1940s, researchers Gerald Pearson, Calvin Fuller and
Daryl Chapin created the silicon solar cell in 1954.These early solar cells
cost 286 USD/watt and reached efficiencies of 4.5–6%.By 2012 available
efficiencies exceed 20% and the maximum efficiency of research photovoltaics is
over 40%.
Literature:
1. http://rentechno.com/solutions/solar.html
3. Bolton, James (1977). Solar Power and Fuels. Academic Press, Inc.
ISBN 0-12-112350-2.