To make informed decisions about your future energy commitments, you should make an “apples-to-apples” comparison of the various energy systems available to you.
The basis of determining energy usage for various heating applications starts with an understanding of the production of energy referenced in British Thermal Units, or BTUs.
A BTU is defined as . . .
. . .one unit of energy necessary to raise the temperature
of one pound of water by one degree Fahrenheit (F).
As an example, if a homeowner on a well with water temperature of 50 degrees (F) sets his water heater to maintain a constant temperature of 120 degrees (F), when he takes a 10 minute shower which consumes 30 gallons of hot water, then his water heater would need to produce 16,800 BTUs of energy to replenish the heat consumed during the shower.
The calculations in arriving at this figure are as follows:
30 gallons of water consumed with each gallon of water weighing 8 pounds results in 240 pounds of water to be heated
The difference between the incoming well water temperature of 50 degrees(F) and the desired water storage temperature of 120 degrees(F) is 70 degrees(F).
240 pounds of water multiplied by the desired 70d degree(F) temperature rise results in 16,800 BTUs of energy necessary to provide a 10 minute shower consuming 30 gallons of hot water.
The next question an energy consumer must ask is “What is the cost of my energy?” For this information, contact your utility company or propane supplier. If you’re heating with electricity, the cost will be in Kilowatt Hours (KWH). If your energy consumption is in the form of natural gas, you most likely will be billed in “therms.” Propane is usually delivered and billed by the gallon.
To make an apples-to-apples comparison between the three energy forms, convert to BTU equivalents as follows:
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- One Kilowatt (KW) = 3,413 BTUs
100,000 BTUs divided by 3,413 = 29.3
29.3 KW = 100,000 BTUs
- 1.1 gallons of Propane = 100,000 BTUs
(or, stated differently, one gallon of propane = 91,500 BTUs)
- One therm of Natural Gas = 100,000 BTUs
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So, for purposes of illustration, let’s assume the residential cost for
electricity is 11 cents/KWH, Propane runs $1.97/gallon and natural gas
costs $1.50/therm. |
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Then for 100,000 BTUs . . .
- Electricity costs $3.22 (29.3 X .11/KWH)
- Propane costs $2.16 (1.1 X $1.97)
- Natural Gas costs $1.50
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. . . and the cost for the feedstock of a Solar Thermal
System . . . ?
---------------------------- $ 000.00* --------------------------------
. . . Sunshine is free . . .
* If the Solar Thermal System is utilizes a circulation pump or fan powered by an AC electrical current, a nominal cost for electricity should be factored in.
Solar v. Conventional Heating
So, how does Solar Thermal stack-up against Conventional Heating?
A high-efficiency furnace (90% +) may produce 100,000 BTUs/hour.
A good Solar Thermal Liquid Collector (40 sq.ft.) will produce approximately 40,000 BTUs/day*
The above data begs the question . . .
“Why would I purchase a Solar Thermal System that generates only a portion of the output of a conventional, hydrocarbon fuel system?”
The answer to this question is two-fold. First, your conventional heating system will cycle on and off at various intervals to maintain a preset temperature. It doesn’t run constantly, only when the thermostat calls for heat. Your conventional heating system isn’t running 24 hours a day, only a fraction of the day and producing only a fraction of its maximum output capabilities. A solar Thermal System supplies heat uninterrupted as long as the sun is shining.
The second point which supports the benefits of a Solar Thermal System is that once the equipment is installed, the owner never pays for the fuel to heat the given application.** A portion of future energy costs are locked in against the upfront cost of the Solar Thermal System. The amount of BTUs the Solar Thermal System replaces are never subjected to the cost and availability of the conventional heating fuel. An energy consumer who buys a conventional heating system pays for the equipment upfront and the fuel ad infinitum.
For a definitive analysis on the feasibility of a Solar Thermal System, we offer professional consultation services. Our consultation services include determination of the available solar window, software analysis of system inputs, outputs and the resulting financial benefits of Solar Thermal Systems as well as determining the appropriate type and size of various Solar Thermal Systems.
* Per SRCC ratings
** If a system is powered by an alternating current (AC) pump or fan, the nominal cost of electricity necessary to power the device should be taken into consideration. If the system utilizes a direct current (DC) pump or fan powered by electricity from a photovoltaic panel, the upfront cost of the photovoltaic system eliminates future costs of electricity purchased from the utility company.
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