Solar Thermal Cogeneration
By drawing our energy directly from the sun we minimize geological,
social disturbance. The Solar-Thermal
Cogeneration (STC) System
is a complete energy
system, providing both electrical and thermal energy for a detached
residental or commerical structure. Solar
describes converting the
radiation into usable heat energy and cogeneration
describes generating electricity while using excess heat for
needs such as space heating/cooling. Cogeneration is sometimes
combined-heat/power. High efficiencies can be
achieved with cogeneration,
making the STC competitive
when full costs and benefits are considered. A drawback of
flexibility in independently
specifying the electric and thermal capacities.
The STC system
residential energy in a flat-roof-mount
configuration. The system can supply all electric and
thermal needs for a
conservation-oriented residence. On a clear winter day in a sunny
climate in mid-latitude an STC system occupying 1000 sq. ft.
area can provide 25 kilowatt-hours of
electric energy and another 56 kilowatt-hours of thermal energy for
space heating, water
heating and refrigeration. This provides 16 to 19
kilowatt-hours of residential electric energy plus 15 to 30 miles of
range per day for an electric vehicle. In summer these outputs
by 2.5, providing an extra 125 miles of range per day for electric
vehicles, and plenty of thermal energy for space cooling.
According to the J.T. Lyle Center *
, for a
given latitude, the least sunny climates yield at least 2/3 of the
capacity of the sunniest climates, indicating widespread feasibility
for solar-based systems.
The STC system employs a Rankine cycle heat engine with a closed-loop
water-steam boiler. Components include a solar
turbine/generator, and electrical and thermal output subsystems.
collector consists of a concentrator (optical
reflector) and a receiver (heat pipe). The reflector geometry is
parabolic trough, a practical geometry for low-profile roof
tracking mechanism maintains concentrator focus as the sun traverses
the sky. The turbine is of the boundary-layer type and
drives a permanent
magnet generator. The electrical output subsystem includes
lead-acid batteries, high-efficiency charge
controller and AC /DC distribution controllers. The thermal
subsystem includes ammonia/water absorption space
cooling/refrigeration, and space heating/water heating. The steam
circuit is operated with water at night to radiate the system's waste
the sky and to supplement space cooling.
provides extensive design
information, fabrication procedures, and supplemental resources,
enabling widespread production of STC systems in small workshops with
simple tools, limited skills, and available materials.
Roof Mount for
Economy and Aesthetics
The STC is intended
for mounting on a flat
roof. A roof
completely or partially hide the
concentrator. The concentrator might partly show above
parapet during the winter to reach more sun in the low sky but hide
the parapet during the summer. The equator-facing wall might
have a lower parapet for better exposure. Besides aesthetics,
roof mounting preserves wildlife habitats, economizes space, economizes
transfer, and keeps sunlight off much of the roof.
Comparison With Alternative
wind systems are two alternative approaches to generating electric
Photovoltaic has no moving parts and requires
less maintenance than solar-thermal systems. Photovoltaic panels
less expensive but their manufacture is enormously
resource-intensive (electricity, water) and capital-intensive, with
associated environmental and social costs. Schott has calculated
that photovoltaics take five years to produce the energy embodied in
while solar-thermal and wind systems
take five months.
In 2005, high labor costs kept photovoltaic costs high and material
Photovoltaic panels lose as
much as 90% of energy absorbed to heat. This heat
collected and utilized but it is not as versatile (i.e. hot) as that
produced by concentrated solar-thermal. Photovoltaic panels are
Wind systems may be more economical
than solar-thermal systems, having fewer mechanical/thermal components,
but they can be lethal
to wildlife and an aural and visual blight for some people.
In a six-week period, FPL's
44-turbine wind facility in West Virginia
killed an estimated 1,364 to 1,980 bats .
fairly frequent and zoning restrictions
and permit fees are likely in suburban/urban communities .
Wind energy is more erratic and off-peak than solar, often requiring a
larger battery reserve.
Photovoltaic and wind systems may generate electricity
in tandem with a low-temperature solar thermal system for hot water
space heat. Refrigeration and space cooling require doubling to
tripling the electrical capacity, including batteries, or fuel
systems economize by utilizing the
waste heat from electric generation to supply all thermal loads.
Improvements will continue to be made to both photovoltaic and wind
technologies but solar-thermal is a complete energy system
with low full costs
especially good for a
structure in a sunny climate.
Availability of either wind or solar energy at
location should be researched
early. Wind and/or solar measurements should be collected over a
of one year, or preferably more, in the immediate vicinity of the
installation. Buildings and trees may interfere with
both wind and solar systems, probably more with wind.
light for a 'green' energy source | csmonitor.com
 A War Over Wind Turbines - Los Angeles Times -
December 7, 2005
Residential energy has been conventionally supplied by
grid electricity and piped natural gas and fuel oil. The STC may
supplement these sources for flexibility, or entirely replace
them, which may be simpler and in some cases more feasible.
When replacing them, it is
important to size the STC carefully.
energy needs is an art, not a science. Energy needs can change,
for example, with the number of residents. A strategy to address
this dynamic, and reduce investment risk, is to start with a minimum
system and expand as needed. The STC's solar collector, thermal
are expandable. The rest of the system must be sized initially to
accommodate the later expansion.
the the energy from the sun is free, energy systems still have embedded
costs. To minimize the needed system capacity for active
heating/cooling, ideally, new
construction would employ passive solar/passive
techniques. Passive design can completely satisfy
space heating/cooling requirements in many climates. If an
electric vehicle is planned that would likely become the primary energy
consumer resulting in a surplus of thermal energy.
The table below shows the US DOE's data of average residential
energy consumption in four large US
states. Space heating and cooling
represents a minority percent of total energy usage in warmer
climates. The remaining applications include water heaters,
lights, clothes and dish washers, televisions and
In a conservation-oriented household powered by the STC, water heating
and refrigeration are handled as thermal loads.
Clothes and dish washing and drying can be handled the same (the STC
program will later expand to include appliance designs).
Cooking duty might be shared between a biofuel stove and a solar
appliances utilize efficient motors and avoid large transformers and
illuminated displays. Low-power televisions and computers are
LED-backlit LCD displays. Generally, laptop computers are lower
Distributed Energy Systems
systems enable the efficiency of cogeneration but
have additional advantages over large-scale systems.
Small-scale distributed systems have reduced
development, security, environmental, and transmission costs.
systems can preserve the landscape if held to certain constrains, e.g.
solar-thermal systems mounted in low-profile configurations on the
roofs of building
structures. The materials cost of small-scale energy systems
beyond that of large-scale production/transmission is very small.
In particular, small scale solar concentrators require less structural
strength against wind forces than larger scale concentrators.
Small-scale systems protect consumers from
market turmoil that may arise from speculation, geopolitics, and
In turbine/generators, the
material's molecular bonding
strength is the same in small and large scale equipment, so the
large scale equipment has considerably more mechanical stress/fatigue
problems. Large-scale turbine/generators must be taken
offline and rebuilt as often as every six months. A small-scale
turbine/generator may last a decade before it needs rebuilding.
The engineering cost of small scale systems is much lower.
One of the environmental costs of centralized
energy production is the condensing stage of the
Rankine cycle, which is used in the vast majority of electric
generating plants. This process alters
ecosystems, by evaporating and/or warming the water that is the habitat
of many species. In industrialized nations the volume of water
affected is nearly equal to the total amount otherwise consumed by the
human population. In 2006 it was reported that Global warming is
inducing water shortage, forcing centralized electric plants to scale
back production (see Global Warming
In 2007, the US EPA was seeking to classify water vapor expelled into
the atmosphere by human activities as a pollutant *
Environmental effects of the waste heat from the distributed
heating/cooling of residential and commercial structures are not well
known at this point but one of the STC design goals is to emit as much
of the waste heat as possible to the sky.
Industrial and Commercial
- US Office of Technology Assessment - 1983 (archive
expressed considerable interest in decentralized energy systems and in
cogeneration. Cogeneration is a major issue in the National Energy Act
of 1978, parts of which were designed to remove existing regulatory and
institutional obstacles to cogeneration and to provide economic
incentives for its implementation. In addition, the House Energy and
Commerce Committee, the House Science and Technology Committee, and the
Senate Energy and Natural Resources Committee have held hearings on
cogeneration, and several committees in both Houses of Congress have
held hearings on the general concept of decentralized energy systems.
new power with old system proves costly
Technology: Shaping Energy Markets
The STC is designed to be built in local workshops from as raw
materials as possible. Things that
can be built and maintained locally bring economic opportunity to the
local level. The knowledge, skills and tools acquired to build
can be used to build other things.
The STC design is
fully documented online. High quality
documentation helps enable better construction and
maintenance of the
systems, extending system life and reducing costs.
Undocumented designs can result in poor
maintenance and shortened system life. The
STC documentation helps reasonably skilled craftsmen successfully
maintain the systems and make successful
material substitutions and design alterations.
components may be purchased and connected
together to make a solar-thermal cogeneration system. These
components should be high-quality, well-documented and serviceable to
life. The STC design may include some commercial components which
Still in Short Supply - June
21, 2005 - The Energy
shortage on Solar Grade Silicon was evident at the 20th European
Photovoltaic Solar Energy Conference, Barcelona, Spain and Exhibition last
week. With the resulting shortages in wafers, solar cells and modules,
it was a major topic and it seems it will remain high on the agenda for
at least the coming 2 years.
Stifle a Boom Time for the Solar Industry - August 6, 2005 - New York Times
suppliers for the solar energy industry say that burgeoning demand both
domestically and overseas, a weak dollar and shortages of raw material
have created back orders of several months on electricity-generating
photovoltaic, or PV, panels.
Due to a
world-wide shortage of Photovoltaic
Panels we are unable to offer specific models for purchase here at this
time, however, with our connections to suppliers and manufacturers, we
are able to find panels to meet your needs.
Global warming is a trend of increased atmospheric and terrestrial
temperature due mainly to the greenhouse effect from carbon dioxide
from combustion of fossil fuels and livestock, and increasing feedback
effects such as the albedo change in the arctic with ice melt, methane
release from thawing Siberian peat bogs, etc. The increased
temperature leads to erratic weather patterns, rising sea levels
causing coastal flooding, and adverse pressures on societies,
ecosystems and biodiversity, i.e. species extinctions. Additional
pollutants from combustion of fossil fuels include sulfur oxides,
nitrous oxides, carbon monoxide, ozone, particulates and mercury.
*millions of metric tons of carbon equivalent
kidnappers demand $1.5bn and
control of oil, Times
burned alive in Lagos pipeline
blaze - The Guardian UK,
260 people were killed yesterday - burned alive when a ruptured oil
pipeline burst into flames in Lagos. Crowds
of local residents had gone to scoop up petrol using plastic containers
after an armed gang punctured an underground pipeline to illegally
siphon off fuel. The Christmas shortage has caused all the more
hardship as petrol is
not only essential for transport, but for the generators on which most
homes and businesses rely in the absence of reliable mains electricity.
Warming, Not Just Heat Wave,
Inter Press Service, 7-21-06
said that over the last
century temperatures in Germany
rose 0.8 degrees. "Over the next 75 years, we expect a warming of
between 1.8 to 3..6 degrees for our region."
The heat is also taking its toll on
agriculture, and affecting
the generation of electricity, especially in nuclear power
The lack of fresh water for the nuclear
systems has led German private electricity suppliers to slow down their
In France, the state-owned
Electricité de France (EdF) was
allowed to continue to drain hot water from the cooling system into
rivers, although the water temperatures exceeded the limits imposed by
environmental authorities. But output has had to be lowered.
EdF has been importing electricity to
compensate the nuclear
power plants' lower performance. In Italy, hydroelectric plants have
slow down due to a shortage of water in rivers.
Future Bright for Solar Thermal - Green Inc. Blog
Oil Figures Were Distorted by US Pressure
- IEA projections shown
to be unreliable
& Toolkit for consumers
as peer-to-peer energy
IPCC - Intergovernmental Panel on Climate
Air/ Dirty Power (pdf) : Coal adds $167 billion to annual US healthcare bill
Copyright (c) 2005-2009 Robert Drury
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Disclaimer: This information may contain inaccuracies and is
without warranty. Safety first when working with high
pressures, potentials, speeds, energies, various
tools and materials.