Conversion Factors
Natural Gas (70-85%)1 Therm10 Therms
Electricity (70-95%)1 kWh293.3 kWh
#2 Fuel Oil (60-85%)1 Gallon7.2 Gallons
LPG (70%)1 Gallon10.5 Gallons
= 100,000 BTU= 1,000,000 BTU
= 3,413 BTU= 1,000,000 BTU
= 138,690 BTU= 1,000,000 BTU
= 95,475 BTU= 1,000,000 BTU
Comparative cost and value
$10^6BTU=(Cost of Energy Unit) x (Energy Units Per Million Btu’s) / (Efficiency of Energy Conversion)For electricity costing 10 cents per kWh: $.10* (293.3 kWh) / (95%) = $30.85/MMBTU KWh 106 BTUNatural gas costing $1.40 per Therm: $1.40* (10 Therms) / (70%) = $20.00/MMBTU
106 BtuPropane (LPG) costing $2.00 per Gallon: $2.00/gal* (10.5 gal) / (70%) = $30.00/MMBTU
106 Btu
Solar Applications
Sounds Great!
What’s it Cost?
What’s it worth?
Where do we start?
Economics of Solar
How can we compare the costs of Solar to Conventional Energy?
The problem is that the solar energy is free, typically the cost of solar is the initial cost of the installation and the operation & Maintenance costs to operate it (which is minimal)
Compare the cost of solar and conventional energy directly on a Life Cycle cost basis.
Comparing the cost of solar to Other energy Sources
What is the cost of energy for: Water or space Heating or Cooling? Pool or Process Heating? Electric Power Generation?
How much do you pay for:
Electricity? Natural Gas? Oil? Propane?
Which is the better value?
Comparing Operating Costs & Energy Efficiency of Water Heaters
Efficiency (output/input)In same units i.e. (BTU in)/(BTU out)
Natural Gas fired water heater: 75% Oil Fired Water Heater: 70% Electric water Heater: 95% Boilers:
NG Fired: 83% Oil Fired: 80-85%
Compare Apples to Apples
Requires looking at different energy sources on a delivered energy bases:
Heat-BTUsElectricity - kWh
Solar Costs for Energy
Determine the effective cost per energy unit when using solar
How? We purchase solar energy in advance We purchase it with “First Cost” and
add a small O&M cost Solar requires an initial investment but
provides free energy over an extended period-determine the amount of energy produced and its value!
Solar System Value ($/Energy Unit)
Solar Water heating MMBtu per Year
Photovoltaic kWh per year
Basis Average climatic data System parameters (energy ratings)
Solar Equipment Energy Ratings
Solar water heating SRCC Rating of Solar Collectors
Based on climatic data for location & Collector performance
Photovoltaic Manufacturers STC Rating
Based on Standard test conditions 1,000W/m2 , 25°C Cell temperature
Must be adjusted for site parameters
Solar System Comparative Value Determination
Total life cycle cost ($) Installed cost O&M (1%/yr)
Energy Delivered (MMBTU – kWh) Annual/monthly energy production Life of system
Levelized cost $/MMBtu or $/kWh
System Sizing
Available Options for Solar Water Heating System Sizing – and Evaluation
Solar Water Heating
Rule of thumb FSEC simplified sizing procedure FSEC simplified residential solar hot
water system calculator F-Chart RETScreen TRNSYS
Rule of thumb
Residential homes 20-gallons per day for first two people Then 15-gallons for each additional person Family of one or two= 50 gallon system Family of four = 80 gallon system Family of six or more = 120 gallon
system 1 to 2 gallons per square foot of collector Typical residential systems are 80 or 120
gallon solar tanks with electric or gas back up.
Rule of thumb
4 person family 20 + 20 + 15 + 15 = 70 gallons Thus use 80 gallon solar tank
1 to 2 gallons per square foot of collector Choose 2 gallons 80 / 2 = 40ft2
Thus use a 40 ft2 collector 80 gallon solar tank with 40ft2 collector Very rudimentary method – not much
taken into consideration
Rule of thumb
Gathering information – Site survey Determine the volume of storage Determine the temperature differential Calculate the energy demand Determine the solar resource Putting it all together
Rule of thumb
Determining the Volume of Storage Collect the number of persons or number of
bedrooms in the home Allow 20 gals/person for the first two persons
and 15 gals/person for each additional person(s) Calculate the required volume of storage
Example: (Family of 4)2 x 20 gal = 40 gallons2 x 15 gal = 30 gallons40 + 30 = 70 gallonsAn 80 gallon model would be selected for this
application.
Rule of thumb
Determining the Temperature Differential
Subtract the Avg Cold water inlet Temperature listed from a desired Tank Temperature of 140° F (▲T)
Calculate the temperature differential 76° = Avg cold water inlet temp for
Florida140° - 76° = 64° ▲T
Rule of thumb
Calculate the Energy Demand (Btu’s) A BTU (British Thermal Unit) equals the amount of
energy required to raise 1 pound of water, 1 degree Fahrenheit
Water weighs approx. 8.34 pounds/gallon Calculate the energy demand
Example: (80 gals – Florida)
80 Gallons x 8.34 lbs/gal x 64° F = 42,701 BTU’s
NOTE: Use standard storage tank sizes for calculation purposes. Using the calculate volume may result in an undersized system.
Rule of thumb
Determine the solar Resource Determine the solar
collector performance using the certification at right.
Calculate the number of collectors required by dividing the energy demand by the intermediate Temperature rating listed.Example:42,701 / 21,700 = 2 (AE-26)
collectorsThus, this system is 2 AE-26
collectors and one 80 gallon storage tank.
FSEC Simplified Sizing Procedure
Developed for residential solar water heating systems in Florida
Step up from back of the envelope calculation
Requires information input Based on mathematical calculations Provides final solar fraction
Amount of hot water heated by the sun
FSEC Simplified Sizing Procedure
http://www.fsec.ucf.edu/en/publications/pdf/FSEC-GP-10-R01.pdf
FSEC Simplified Sizing Procedure
Step 1 estimation of daily hot water use and selecting tank size
FSEC Simplified Sizing Procedure
Step 2 Selecting cold water temperature for geographic location
FSEC Simplified Sizing Procedure
Step 3 Calculate how much energy is needed (BTU Needed) to heat the water to 122° F
BTU Need = 8.34 x Gallons x (122 – COLDTEMP) x Standby loss factor*
BTU Need = 8.34 x 55 Gallons x (122-72) x 1.12
BTU Need = 8.34 x 55 x 50 x 1.12 Btu Need = 25,687 (Round off to 25,700)
FSEC Simplified Sizing Procedure
Step 4 Determine penalty factors that affect system sizing
Table 3 system Factors Table 4 Tilt Factors Table 5 Orientation Factors
FSEC Simplified Sizing Procedure
Step 4 Determine penalty factors that affect system sizing
Table 3 system Factors Table 4 Tilt Factors Table 5 Orientation Factors
FSEC Simplified Sizing Procedure
Step 4 Determine penalty factors that affect system sizing
Table 3 system Factors Table 4 Tilt Factors Table 5 Orientation Factors
FSEC Simplified Sizing Procedure
Step 6 for collector selected, record the thermal performance rating at the intermediate temperature (BTURATING) in Btu/day and gross collector area (GROSSAREA) in Ft2 from the FSEC ratings Use alternative energy technologies
collector Model: AE-40 Gross area: 40 ft2
Intermediate Temperature Rating: 34,400 Btu/day
FSEC Simplified Sizing Procedure
Step 6 for collector selected, record the thermal performance rating at the intermediate temperature (BTURATING) in Btu/day and gross collector area (GROSSAREA) in Ft2 from the FSEC ratings
Estimate number of collectors needed: Number = RATREQD / BTURATING Number = 30,840 / 34,400 Number = 0.90 = 1 collector
FSEC Simplified Sizing Procedure
Step 7 select the actual number of collectors to be used. This is to the nearest whole number. Select 1 collector The total area of the collector array is
Total area = number of collectors x Gross area
Total area = 1 x 40ft2
Total area = 40ft2
FSEC Simplified Sizing Procedure
Based on the actual number of collectors to be used, compute the Solar Fraction Solar fraction = 0.70 x Number of
collectors = (0.70 x Step 7 [# of collectors]) / Step 6c [# of collectors before round off]
Solar Fraction = (0.70 x 1) / 90 = 78 Solar Fraction = 78
FSEC Simplified Residential Solar Hot Water system Calculator
Provides consumer information on the energy, cost and environmental savings potential of residential solar hot water systems in Florida
To use this calculator Answer the two questions under the heading
“Basics Solar System Information” Using the pull-down menus provided
For the input “Florida Climate Zone,” If your home is north of Volusia county, select “North” and if your home is south of St. Lucie County, select “South.” Otherwise select “Central.”
FSEC Simplified Residential Solar Hot Water system Calculator
The calculator depends on a number of pre-selected assumptions. To view and change these assumptions,
select the checkbox below and the additional input fields will appear
If you choose to not change these assumptions, simply uncheck the box below anytime.
FSEC Simplified Residential Solar Hot Water system Calculator
http://www.fsec.ucf.edu/en/consumer/solar_hot_water/homes/calculator/index.htm
F-Chart
http://www.fchart.com/fchart/fchart.shtml
F-Chart
Computer program useful for the analysis and design of active and passive solar heating systems
Developed at the University of Wisconsin Solar Energy Laboratory to estimate the long-term average performance of: Domestic water heat (DWH)Systems Pebble bed storage space and DWH Systems Water storage space and DWH Systems Active collection with building storage space heating
systems Direct-gain passive systems Collector-storage wall passive systems Pool heating systems General solar heating systems (Process heating
systems) Integral collector-storage DWH systems
F-Chart
Weather data for hundreds of north American locations, the 16 California climate zones and numerous other locations are included with the program User can add new weather data.
Florida City Habitat for HumanityEnergy Consumption Study
Water Heater: 19 (19%)
Range: 4 (4%)Dryer: 9 (9%)
Refrigerator: 8 (8%)
HVAC: 40 (40%) All Other: 20 (20%)
Average annual consumption for ten Habitat homes =43 kWh/dayAugust 31, 1994 - September 1, 1995
Homes built by Florida City Habitat for Humanity
Similar Annual Energy Use Profile in All Climates
• Heating and/or Cooling (~40%)
• Water Heating (~20%)
• Appliances (~20%)
• Lighting & plug in devices (~20%)
Annual Cooling Load ComponentsTampa FL, 2000 sqft Residence
Duct Gain: 12 (12%)
Duct Leaks: 10 (10%)
Infiltration: 6 (6%)
Windows: 30 (30%)
Walls: 6 (6%)
Roof: 20 (20%)
Appliances: 16 (16%)
Monthly Electric Cost
Monthly electric cost
Dollars0 100 200 300
Mon
th
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
212
190
172
146
128
179
181
207
187
172
121
126
Average Daily Electric use 57 kWh ($2021)