From: Essential Information <ei@igc.apc.org>
Newsgroups: sci.energy
Date: 31 Dec 92 12:38 PST
Subject: Re: Energy Ideas -- Solar Power
Nf-ID: #R:cdp:1466300121:cdp:1466300125:000:10036
Nf-From: cdp.UUCP!ei    Dec 31 12:38:00 1992



SOLAR THERMAL ENERGY SYSTEMS

Solar thermal energy uses sunlight as heat rather than converting
it directly to electricity through the use of semiconductors.  

Solar thermal energy can be used to generate electricity.  Sunlight
heats a working fluid, such as a synthetic oil.  The fluid is
circulated through a heat exchanger, where it heats water until it
boils.  The resulting steam drives steam turbines.  This produces
enough power not merely for a single appliance, but an entire
utility grid.  For example, over 400 megawatts (million watts) of
electric power is generated in California by using parabolic
mirrors to concentrate sunlight onto pipes containing a synthetic
oil; this heated oil passes through a heat exchanger which converts
water to steam.  The steam spins turbines to generate electricity.

In developing nations, solar thermal energy may provide the power
needed for basic mechanical work and appliances.  Parabolic mirrors
can collect sunlight to heat an oven or generate steam to drive a
mechanical pump.  Solar heat can also provide the input energy
necessary to drive an absorption chiller, creating a non-electric
solar refrigerator (the system works on the absorption and
evaporation of ammonia in water rather than the compression and
evaporation of a refrigerant).  The primary commercial use of solar
thermal energy is to heat water.  This heated water may then be
used directly as hot potable water for bathing, swimming, cleaning
or cooking.  The heated water may also be circulated through
radiators to provide space heating. 

Some solar thermal systems have been financed through lease
contracting.  A contractor installs and maintains a heating system.

The owner of the building pays a percentage of the cost that it
would have paid for its previous fuel supply, either natural gas,
propane, oil or another fossil fuel.  The vendor recovers its
investments through these payments, and the owner saves money by
using a less expensive system.

Most systems for municipal pool heating or commercial heating use
active solar systems.  These systems work by circulating a working
fluid (usually water, though sometimes an antifreeze in colder
climates) through solar thermal panels.  The panels used most often
for these systems consist of copper waterways attached to either
copper or aluminum fins.  Solar radiation heats the fins and the
heat conducts along them it into the copper waterways.  

SOLAR HEATING SYSTEMS: WHY WASTE ROOF SPACE ?

Solar heating systems for buildings can reduce the cost of fuel for
hot water for heat and washing.  The cost-effectiveness of these
systems largely depends upon the fuel being used for the current
heating system.  The systems can even cost-effectively replace
systems in buildings which use natural gas, currently an
inexpensive fuel source.  

Other factors make the benefits of solar power more attractive. 
Boilers in many buildings must run throughout the year just to heat
water for washing.  The operation of the boiler during summer
months adds heat inside the building where it is not needed.  This
heat must be cooled by the air conditioning system.  Solar heating,
which uses heat from the outside of the building, does not add to
the interior cooling load.  Thus, avoided Heating, Ventilation, and
Air Conditioning (HVAC) costs should be incorporated into the
life-cycle cost analysis when considering a solar heating system.

CASE STUDIES

       St. Rose Hospital in San Antonio, Texas, installed a 5,000
sq. ft. flat-plate solar water  heater on its roof, capable of
providing 9,000 gallons of water storage.  The hospital  paid
$49,000.  A Texas state grant (from the Alternative Energy
Demonstration Pro-  gram) paid the remaining $96,000 for the
project.  This solar heating system is a  "gravity drainback"
system; when operation stops, water drains back into a storage 
tank.  This prevents the presence of water in the collectors at
times when it could  freeze.  This also causes the system to run
under a vacuum, which prevents the water  from leaking.  The heated
water yields its heat to the potable water in a linear heat 
exchanger.  The pipes are made of copper.  

The system paid for itself in seven months partly due to avoided
fuel costs but mostly  due to avoided HVAC costs.  The system was
designed to provide 1 billion British  Thermal Units (Btu) of heat
annually.  Despite abnormally low levels of sunshine in  Texas in
the first year, the system provided 1.2 billion Btus of heat.  The
system has  operated for two years without any repairs. (Contact:
Rick Fossum, Sun Trapper Solar,  134 West Rhapsody, San Antonio,
TX, 78216, (512) 341-2001.)

       The Adams County Detention Facility in Brighton, Colorado,
had a solar thermal  heating system installed on the grounds of
their facility.  The project initially was  intended to be a
cogeneration facility, selling electricity to the local utility;
however,  certification costs assessed by the utility for the
cogeneration equipment made that  aspect of the project too
expensive.  Nonetheless, the solar system provides up to 85 
percent of the facility's heating needs.

 The project cost $290,000.  Half of that sum was for the
cogeneration equipment.   Half of the total cost was paid with oil
overcharge monies provided by the Colorado  Office of Energy
Conservation.  Private investors paid the other half.  The
detention  facility pays the contractor 70 percent of what it would
have cost to provide the heat  using natural gas.  Thus, the
facility saves 30 percent on its heating costs.  The  contractor
installed and now operates the system.  The system has worked
flawlessly.   The only maintenance has been mowing the lawn around
the system.  (Contact: Andy  Walker, Colorado Office of Energy
Conservation, 1675 Broadway #1300, Denver, CO   80202, (303)
620-4292.)      

SOLAR HEATING SYSTEMS FOR SWIMMING POOLS

Solar power can effectively provide the heat necessary for swimming
pools.  Many solar projects in the 1970s were pool heating
projects.  Many of these projects failed.  In the Village of Grady,
New Mexico, the staff at the community pool stopped trying to keep
a pool cover, designed to trap the heat from sunlight, from blowing
off.  Two pool heating systems in San Jose, California, needed to
be replaced after three years when the water had corroded the pipes
and caused leaks.  The solar industry has vastly improved the
design of these systems.  Recently, many private institutions have
installed solar heating systems for their pools and have been
extremely pleased with their results.

CASE STUDY

       The community of Columbia, Missouri, built their own
swimming pool.  The funding  for the pool was provided by
individuals and local businesses, and the community  volunteered
their time for the labor.  Seeking to create an
environmentally-friendly  pool, the volunteers researched solar
heating systems for the pool and applied for a  grant from the
Missouri Department of Natural Resources' Division of Energy and
the  U.S. Department of Energy.  Though the estimated cost for the
system was $16,000,  the final cost of the active solar system for
heating the 30' x 80' pool was only  $8,900.   The choice of pool
systems ultimately depended upon the ease of installation for the 
volunteers. They selected a manufacturer who provided a 10-

year warranty and also provided the most detailed instructions. 
The installation of the  heating system extended pool hours and the
pool season by a few months.  The  operation of the heating system
raised the pool temperature from 78o F to 83o F while  pumping
95,000 gallons daily.  In order to offset the energy cost
associated with the  pump for the pool's active solar system, $40
per month, the volunteers installed a  passive solar heating system
for the locker room showers which saved $60-$80 per  month in
natural gas costs.  A bubble-pack pool cover helps keep the pool
warm at  night, reducing temperature loss to only one degree, and
also prevents the escape of  the chlorine gas, saving on the amount
spent on chlorination. (Contact: David Mars,  Columbia Power &
Light, P.O. Box N, Columbia, MO, 65205, (314) 874-7307.)     

WATER DISTILLATION AND PURIFICATION ACHIEVED WITH SOLAR POWER

Solar stills create a continuous gentle steaming of water which is
then trapped and allowed to condense. The conventional method,
boiling water and condensing it, requires eight gallons of water to
provide one gallon of purified water, while solar stills provide
one gallon of purified water from just over one gallon of water. 
Solar stills provide a higher quality of water than conventional
purification Pollutant concentration can be reduced to 1 ppm while
store-bought spring water only goes below 100 ppm. 

CASE STUDIES

       San Diego State University installed three solar stills in
1965 to provide water for their  water quality and soils
laboratories.  The price of these stills is now only $400-$600.  
While reverse osmosis systems cost only half of that, the
difference in the water lost  and energy used makes the stills less
expensive.  It addition, the stills have required no  maintenance
or replacements in the 27 years that they have operated.  The
stills  provide two gallons of distilled water each day.  (Contact:
Professor Bayard Rehkopf,  Department of Civil Engineering, San
Diego State University, 5300 Campanile Drive,  San Diego, CA,
92182-0189, (619) 594-606.)

According to  McCracken  Solar Co.,  solar stills can  produce 3 
million  gallons of  pure drinking  water per  square mile  per
day.  One  solar still, 40  miles south of  San Jose,  California, 
produces 100 gallons per week of pure drinking water.  At a cost of
$8,000, the  system will pay for itself in two years by eliminating
the purchase of bottled water.   Mexico's government ordered
$50,000 worth of stills to provide 800 gal/day of fresh  drinking
water for a small village.  (Contact: Horace McCracken, 329 West
Carlos,  Alturas, CA, 96101, (916) 233-3175.)