Ask A Scientist© Engineering Archive

Index Key:   ENG027
Author:      kartraice d hooper
Subject:     Cost of energy.
What is the average cost of energy in dollars per kW of all sources of heat,
such as fireplaces, electric heating, and gas heating.  Please include heat
pumps as well.

Response #:  1 of 1
Author:      david r munoz
Wow, this is quite a difficult question, but also a very good one.  My first
answer is that I do not know and let me tell you why it is complicated and
perhaps I can help you answer the question (at least in part) on your own.

Part of the problem is that there are so many things that enter in when you
talk about cost.  Time for instance is one factor.  If you were interested
in putting in a solar heating system, you would quickly find that the
initial cost of the system is quite high when compared to a gas forced air
furnace.  If you were just comparing the initial cost, then you would have
only part of the story because the energy cost for the gas would be higher
than say the electricity needed to run the pumps on your solar collection
and storage system.  So then you would have to look at the cost over say a
10 year period.  This in turn gets into the question of the value of money
over time.


Another thing that enters into the  equation, but is many times left out is
the ecological impact of using the energy.  For instance, if we are using
nuclear energy to generate electricity should we consider the cost associat-
ed with storing the waste over a period of time.  From the examples that I
have given it may sound as though I am pro-solar, anti-nuclear (I am not). 
These are meant as only examples of things that can complicate the calcula-
tion.  The other aspect that should be considered is the second law of
thermodynamics.  In simple terms, this law would help us determine which
form of energy is best for a particular application.  In other words, some
energy is more valuable to us than other forms of energy.  Electricity is
very valuable to us because it can be used directly to make motion (for
instance turning a motor), whereas to use solar energy to turn a motor, we
either have to design a rather intricate heat engine or convert it to
electricity in a photocell.  Temperature of the application can be used to
determine the appropriate form of energy to use in satisfying the applica-
tion.
I suggest that you spend some time thinking about smaller questions that
will eventually help answer the big question you have asked.

I ran across some data from the United States Energy Information Administra-
tion, a document entitled "Monthly Energy Review"  November 1994.  If you
want a copy you could contact the US Department of Energy and ask for
document #DOE/EIA-0035(94/11).  The energy costs listed there for the US
are:
Finished Motor Gasoline (pre tax):  $0.80/gallon
No.@ Diesel Fuel (pre tax):         $0.60/gallon
Kerosene/Type Jet Fuel:             $0.60/gallon
Propane :                           $0.45/gallon
No.2 Fuel Oil:                      $0.55/gallon
Residual Fuel Oil:                  $0.40/gallon
Electricity:                        $0.08/kW-hr (residential)
Electricity:                        $0.07/kW-hr (commercial)
Electricity:                        $0.05/kW-hr (industrial)
Natural Gas:                        $6.00/thousand cubic feet (residential)
Natural Gas                         $4.50/thousand cubic feet (commercial)
Natural Gas                         $3.00/thousand cubic feet (industrial)

I hope that this is what you were looking for.  Remember the other things
that I mentioned before.  Even though these are the dollar prices for the
fuel or energy that we as a society have paid, I do not think that these
represent the true costs.  The true costs are more difficult to really
measure.