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http://www.wec.ufl.edu/extension/gc/harmony/documents/EH328.pdf
June 1992
Energy Efficiency & Environmental News:
Practical Uses of Solar Energy
1
Florida Energy Extension Service and Mike West

PRACTICAL USES OF SOLAR ENERGY
You
can
put solar energy to work for you and save energy and money.
Switching
to solar helps protect Florida’s beautiful and delicate
environment, and
reduce our dependence on fossil fuels. Today, there are
three practical
uses of solar energy for the homeowner: pool heating,
hot water, and
electricity for remote locations.
Less use of
electric power
generated from fossil fuels means less greenhouse gas and
acid rain
emissions. Every kWh saved eliminates 1.5 pounds of carbon
dioxide, 0.2
pounds of sulfur dioxide, 0.25 pounds of carbon monoxide,
and 0.01
pounds of nitrogen oxide emissions.
To purchase solar
systems,
consult a local contractor. Many communities are served by an
energy
conservation or solar contractor. Check the yellow pages under
“Solar
Energy Systems.”
Follow up on each potential contractor’s list of references.
Solar Pool Heating
The
most
practical and popular use of solar energy for the homeowner is
solar
pool heating. A solar pool heater extends the swimming season from
May
through October to February through November (in Central Florida,
water
temperature at least 75 degrees). This amount of heating is
equivalent
to $1500 worth of electricity (heat pump) or natural gas for a
24’ by
20’ pool.
A solar system for a 24’ by 20’ pool costs
$3200 to $4200.
The installed cost of a solar system is about the same
as a heat pump,
or about twice the cost of a natural gas heater ($1500
to $7000,
depending on the desired pool temperature and the size of the
pool).
Solar heater maintenance costs are much less than either type
of
conventional heater. An additional advantage of solar is
quiet —
solar pool heaters are almost silent.
The
best type of pool heater
collectors are the rubber mat type, according
to FEES specialist Gary
Cook. The mats are virtually indestructible, and
if damaged, are easily
repaired. Gary has had this type of collector on
his roof for over 12
years. The mats heat his 700 gallon hot tub from
75°F to over 100°F in
less than one hour (two hours in winter). His
swimming season is
extended three months (Gary lives in Gainesville).
Solar Water Heating
Today,
there
are thousands of solar water heating systems installed in
Florida. They
put the sun to work heating water for showers, hot tubs,
and dish
washing.
Reliable solar water heating systems are
economical where
natural gas is unavailable. Modern systems can supply
at least 70% and
up to 90% of a family’s hot water needs. This can cut the
typical
Florida home electric bill by 10% to 13%. In this sense, a solar
hot water heater is a good economic investment.
The
return on
investment is the cash saved on utility bills. This
corresponds to an
annual rate of return of 7-9%, very respectable for
such a safe
investment. Quality systems last as long as the home they
are installed
in. The Florida Solar Energy Center can provide their
ratings of solar
collectors and systems (see References).
Solar
water heating systems
range in price from $1600 for a small system
serving two people,
up
to                                                                                                                                                                                                              

$5000 for a system that serves a family of eight. A quality
system
sized for a family of 4 costs $3000 to $3500. A solar water
heater could
save the average Florida family around $300 per year, and
help protect
the environment by reducing the pollution caused by
generating
electricity from fossil fuels.
Be aware of a few
important
details when selecting a solar water heating system. A system
sized for a
typical Florida family uses two 4’ by 8’ collectors. Look
for a system
that uses a solar powered pump. According to Tom Lane of
Energy
Conservation Services, most Floridians should select closed-loop
systems
that use antifreeze to protect the system from freezing.
Drain-back
systems are another option. (Open-loop systems are suitable
in South
Florida and the Keys).
The storage tank should hold at least
20
gallons of water per family member. Extra storage capacity
is
recommended, and is inexpensive.
*
Licensed solar contractor,
Gainesville FL.(904)373-3220. FEES does not endorse brands
or
contractors.
Solar Electric Power Generation
Today,
solar
photovoltaic (PV) systems are at work converting the suns
radiation
directly to electricity. PV generated power has three main
advantages
over all other types of remote power generation:
Free
Inexhaustible
Power Simplicity Low Maintenance PVs provide electricity
to rural
homeowners, ranchers, and farmers for TV, VCR, stereo,
landscape and
security lighting, pumps, electric fences, and livestock
feeders,
without connection to the power company. Some farmers use PV
powered
pumps for watering of livestock on remote grazing areas. PV
systems
power street, billboard, bus stop, and highway sign lights,
navigational
buoys, and emergency telephones throughout Florida. Small
PV systems
provide portable power for camping equipment, computers,
fans, pumps,
and test equipment. PV cells are used in calculators and
watches.
Photovoltaic power is practical where access to utility company
lines is
costly, and for low power/portable needs.
Industry
improvements have
reduced the cost of PV systems to 25-50¢ per kWh. This
is still
considerably more than the 7-10¢ per kWh of utility power. The
U.S.
Department of Energy (DOE) goal is PV power at 12¢ to 20¢ per kWh
before
2000.
To take advantage of the economies of large scale
production,
the DOE announced a new strategy to accelerate the use of PV
power. The
DOE Solar 2000 plan calls for an increase in PV use by a
factor of ten
by the year 2000. Use of PV power is increasing by over
25% each year,
and has been for the past few years.
PV power
systems range in price
from $75 to $40,000 depending on how much
electricity the user needs.
The box below shows how system cost varies.
PV systems are a poor economic investment if power is readily available: the annual rate of return is around 1%.
However,
in outlying or isolated locations, connecting to faraway power lines
can cost more than a complete PV power station!
Table 1.
Cost
Comparison. High Capacity Solar
PV Systems Cost Considerably More Than
Low
Capacity Systems.
Appliances Powered By Solar
PV
System
Cost
Outdoor/Path lighting
$75
DC power for computer or TV
only
$800
TV, VCR, stereo, lights, computer
$7000
– above plus
refrigerator
$12,000
– above plus well pump (home)
$15,000
– above plus
ventilation fans
$17,000
– above plus central A/C
$31,000

As Table 1 shows, even modest increases in electrical capacity increases the price considerably.

When
using PV power, it is especially cost effective to replace
inefficient appliances with modern energy efficient ones —
allowing selection of a less costly PV system. Since PV cells
produce DC voltage, the use of DC (instead of conventional
AC) pumps, fans, refrigerators, lights, etc. makes sense.
Use of DC appliances reduces the cost of the PV system since they
are typically more efficient and require no invertor capacity. (
The invertor is the part of the PV system that changes the PV cells DC
voltage to AC.) In most cases, it is not yet economical to power
cooling and heating equipment with PV power since these are seasonal
loads.

Heating and cooling accounts for over half the residential energy use of a typical Florida family.

PV
power systems are modular, so they easily grow with the users budget
and electricity needs. PV system size is measured in watt-hours per
day (WH/D). Typical system cost is around $3 per WH/D of system
capacity.

The
smallest systems (around 200 WH/D) can cost up to $5 per WH/D, while
very large systems (10,000 WH/D) cost less than $3 per WH/D.

Storage
batteries
are required for power at night and on overcast days. The
required size
and cost of a PV system can be estimated using the
Sizing Worksheet given in Table 2.

Utility
bills can be used to determine the WH/D of electricity currently
consumed. Most bills give “average kWh used per day,” simply
multiply this number by 1000 to obtain WH/D. Or, (1) take the total
kWh on the bill, (2) divide by the number of days in the
billing period, and (3) multiply by 1000 to obtain WH/D. Using
this method, one can see that a conventional small home, with a $65
monthly electric bill, would require 25,000 WH/D of PV capacity
to go completely solar using the same appliances and lighting. The
great cost of such a system emphasizes the importance of using
efficient lighting and appliances, natural gas for cookingand heating,
and fans for cooling.

References

Solar Photovoltaics: Out of the Lab and onto the Production Line. Mechanical Engineering
, January
1992 by Steven Ashley.
Solar Equipment Standards: some Questions and
Answers. Florida Solar Energy Center #GP-9.
Energy
Rescource
Directory #421. Contact the
Center at 407-783-0300.
Simplified Sizing Procedure for Solar Domestic Hot
Water Systems. Florida Solar Energy Center #GP-
10. ERD #417.
Thermal Performance Ratings of Solar Collectors.
Florida Solar Energy Center #’s GP-14 and GP-16.
FSEC Approved Solar Energy Systems: Domestic Hot
Water and Pool Heating. Florida Solar Energy
Center #GP-15.
Measurement of Solar Radiation. IFAS publication
#CIR-827, ERD# 214.
Solar Water Heating: A Question and Answer Primer.
Florida Solar Energy Center #EN-5. ERD #426.
Solar Heating of Swimming Pools: A Question and
Answer Primer. Florida Solar Energy Center #EN-6.
ERD #422.
Solar Swimming Pool Heating in Florida: Collector
Sizing and Economics. Florida Solar Energy Center
#GP-13. ERD #423.
Solar Water Heating Options in Florida. FSEC #EN-9.
ERD #425.
Sources of Solar Consumer Protection. Florida Solar
Energy Center #FS-29. ERD #428.
Global Climatic Change Primer. Florida Energy
Extension Service # EES 72.
The Greenhouse Effect. FSEC #EN-16. ERD #431.
The worksheet in Table 2 will aid in estimating the
required size of a solar photovoltaic electric power
system. In the first block, list all the appliances which
are to be powered by the PV system. Check the
appliance label or nameplate for its rated wattage. Next,
estimate the number of hours per day each appliance is
“on”. Then, follow the calculation instructions in lines
A
through
G
to arrive at the estimated cost of a
complete PV power system.

Table 2.
PV Sizing Worksheet. Check Appliance Labels For Wattage. For Ratings in AMPS, Multiply AMPS x
VOLTS (120 or 240) to Obtain WATTS. HOURS/DAY is Hours Used Per Day.
List All Appliances to be PV Powered
WATTS
HOURS/DAY
WH/
D
A. Load: Sum of all WH/D above LOAD WH/D =
B. Battery and Invertor Losses: 25% of line A. LOSSES WH/D =
C. Net energy needed per day: Add lines A and B. NET WH/D =
D. Desired number of days of storage capacity. STORAGE DAYS =
E. Total required system size: Multiply line C by line D. TOTAL WH/D =
F. System unit cost. (typically $3 to $5) $ per WH/D =
G. Total system cost. Multiply line E by line F. TOTAL COST =
$
When using PV power, it is especially cost effective to
replace inefficient appliances with modern energy
efficient ones.

SIMPLY SAVING

Energy Efficient
Economical
Environmentally Sound

Practical Uses of Solar Energy

You
can put solar energy to work for you and save energy and money.
Switching to solar helps protect Florida’s beautiful and delicate
environment, and reduceour dependence on fossil fuels. Less use
of electric power generated using fossil fuels means less greenhouse
gas and acid rain emissions.

Solar Pool Heating

The
most practical and popular use of solar energy for the homeowner is
solar pool heating. A solar pool heater extends the usable
swimming season from May through October to February through
November (in Central Florida, water temperature at least 75 degrees).

This amount of heating is equivalent to $1500 worth of electricity (heat pump) or natural gas for a 24’ by 20’pool.

Solar Water Heating

Today,
there are thousands of solar water heating systems installed in
Florida. They put the sun to work heating water for showers, hot
tubs, laundry, and dish washing. Reliable solar water
heating systems are practical where natural gas is unavailable.
Modern systems can supply at least 70% and up to 90% of a
family’s hot water needs. This can cut the typical Floridians home electric bill by 10% to 13%.

Solar
water heating systems range in price from $1600 for a small
system serving two people up to $5000 for a system that will serve a
family of eight. A quality system sized for a family of 4 will cost
$3000 to $3500. A solar water heater will save the average
Florida family around $300 per year, and help protect our
environment by reducing greenhouse gas and acid rain emissions
from electric power generating plants.