conversion factors natural gas (70-85%) 1 therm 10 therms electricity (70-95%) 1 kwh 293.3 kwh #2...

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)