Topic: Energy Geographic Area: Austin, Texas Focal Question: How can solar energy aid in moving toward a more
sustainable energy future? Source:
(1) Ewert, Micheal. Journal of Solar Energy,"A Case Study of Electric
Utility Demand Reductions With Commercial Solar Water Heaters" V 113,
May 1991. Reviewer: Peter A Luber, Colby '96 Review:
Introduction
Since the Initial oil shock of the 1970's engineers have been frantically
trying to find an alternative and sustainable energy source. Yet in the
wake of what has been thus far a frustrating search a few bright hopes have
arisen. One of the most promising discoveries has been the use of solar
energy. Although solar energy has not reached a level where it will be able
to power the globe, it has many useful aspects that make it an even better
source than fossil fuels. This case study will illustrate one of the most
effective uses of solar energy, peak load management. The study takes place
in Austin Texas where one passive and two active solar water heating systems
were installed on city-owned commercial buildings which had electric water
heaters, the system was monitored for two years.
Problem and Approach
One of the major problems with energy is the strain that is put on systems
during peak hours, the hours in which there is the greatest demand for energy.
Traditionally this is early in the morning between the hours of 7am and
9 am and then again from 3 PM to 9 PM. Satisfying an expanding peak demand
with fossil fuels means building new plants which add pollution. To provide
an alternative a solar energy system was implemented in three buildings
in Austin Texas in 1985. The data were collected beginning in 1986 for approximately
two years. The system was implemented in an attempt to reduce the strain
placed on the buildings hot water heater during the peak hours of the summer
months.
System Description
The first building to receive the system was the Rosewood Zaragosa Multi-Purpose
Center. An active drain-back solar water heating system consisting of three
4 ft by 8 ft flat-plate solar collector and two 82-gallon solar storage
tanks, was installed on the building.
The second building to receive the system was Fire Station 21. An integral
passive solar water heating system, consisting of two 37-gallon solar collector/storage
units plumbed in series with the backup tank, was installed on the fire
station.
The final building was the South Austin Recreation Center (SARC) This building
was equipped with an active drain-back solar water heating system consisting
of eight 4 ft by 8 ft flat plate solar collectors and three 120 gallon conventional
water heaters set at 140 degrees Celsius
Note: None of the three buildings fit the classical double peak hour profile
as described above. Each had its own unique peak hours.
Analysis
The amount of energy saved from the solar water heaters is divided into
two types of peak demand, noncoincident and coincident. Noncoincident peak
demand occurs when the solar water heaters peak is not coincident with the
utility's peak. Coincident peak demand is that portion which occurs during
the utility's peak.
Rosewood
The Rosewood Zaragosa Multi-Purpose Center had its largest peak in hot water
demand a little after 1 PM. This is attributed to the running of the center's
dishwasher after lunch. Without the solar water heater in place a peak of
6 kW was reached every day. With the solar system in place the peak was
decreased to a level of 2.5kW. This is due to the solar heater storing large
amounts of solar heated water which was subsequently used first during the
coincident peak. The savings during the coincident peak (5-6 PM) were only
.5kW, because not much hot water was used during this period. Coincident
and noncoincident savings totaled 5.8kW during the day.
Fire Station
The fire station had its noncoincident peak in the morning around 9 am,
mostly due to morning showers. The savings were not as impressive as Rosewood's
with a noncoincident peak saving of 1.8kW and a coincident peak savings
of .2kW. For seven of the ten highest noncoincident peak load days the reduction
reached as high as 2.2 kW
South Austin Recreation Center
Unfortunately the data on the recreation center are not totally accurate
due to a leaky pressure valve that artificially inflated the results by
increasing the daily August 1987 hot water consumption average to 346 gallons,
a normal daily average is 104 gallons. In any event the noncoincident reduction
was 2.5kW and the noncoincident reduction was 1.8kW
Results
Site
Annual SSR
Savings
Percent of System Initial Cost
Rosewood
.30
$179
2.7
Fire Station
.18
$65
2.4
SARC
.65
$274
2.9
The SSR(Solar Savings Ratio) is the percentage of electrical energy which
is saved because of the solar water heating system
Conclusion
This study supports the notion that solar water heaters can be extremely
effective during hot summer days when they are coupled with regular electrical
heating systems. Much of this can be attributed to the fact that solar heaters
deal very well with peak load hours because the energy can be stored in
the batteries of the system as opposed to conventional systems which traditionally
require expanding the system to accomodate the excess demand. Results show
that the average coincident peak demand reduction ranged from .3 to .8 kW
and the average noncoincident peak demand reduction ranged from .8 to 5.8kW.
Savings could be even higher if noncoincident peaks overlap with coincident.
This would occur if hot water usage peaked from approximately 4-6 PM, depending
on the utilities coincident peak. The money saved from the implementation
of the systems ranged from 150-350 dollars annually. This translated into
a system payback period of 1.3 to 3.3 years, more than justifying the use
of the systems. Although solar energy is practical on a large scale, these
studies show that it can aid in reducing the energy demands on current systems.
It is also a first step toward sustainability in that once the science of
solar energy reaches the level where it can operate cost effectively on
a large scale, systems will already be in place.