[Greenbuilding] cost of electric versus natural gas and gasoline

[Ted Inoue]

Ben,
For a comparison like this, one must also consider the efficiencies of the
energy conversions involved as that makes a substantial difference in the
outcome of the comparisons.

For example, if you use electric baseboard heaters to heat a house, that
delivers "electric heat" at essentially 100% efficiency. Every kilowatt hour
of electricity pumped into the baseboards delivers the full 3413 BTUs of
heat.
On the other hand, a natural gas furnace will have a combustion efficiency
that diminishes the actual BTUs delivered to heat the home. If you buy one
therm and that is combusted at 85% efficiency then you've lost 15% of the
energy right off the bat, and have to figure that in.

Next, you typically wouldn't run straight electric resistance heat, but
instead would use a heat pump. A good heat pump delivers 8-9 BTUs of heat
for every one watt put in (see the HSPF rating). This effectively improves
the comparison in favor of electric heat by a factor of 2+.

A lot of people have been asking me this question recently. Download the
following document:
http://www.etccreations.com/ComparisonofEnergyCosts.pdf

In my area, electricity for heating costs 7.1 cents/kwh while natural gas
costs $1.29 per hundred cubic feet. Running the calculations shows that
natural gas supplied heat costs about twice what electric heat pump heat
costs for the same heat delivered to the house.

The automotive calculations are more complicated, but those can be found on
the web. Here is one such analysis:
http://www.ecoworld.com/blog/2006/08/04/electric-car-cost-per-mile/

As for costs, I think people in general see fossil fuel prices increasing
faster than electric prices because electricity is generated from a variety
of different sources and so is somewhat less sensitive to the vagaries of
the fossil fuel supply/demand cycle.

-ted




On Sat, Mar 8, 2008 at 11:58 PM, Mike O'Brien <obrien at hevanet.com> wrote:

> Hi, Ben--
>
> A therm of natural gas is equal to 100,000 Btu.
>
> A kiloWatt hour is equal to 3413 Btu. So it will take 100,00 / 3413
> or 29.3 kWh to equal one therm of gas.
>
> At your rate, that's 29.3 x .086 or $2.52.
>
> I reckon all energy is going to go through the roof within your
> lifetime. Best to cut down your need as much as possible.
>
> Mike O'Brien
>
>
>
>
> On Mar 7, 2008, at 2:48 PM, Benjamin Pratt wrote:
>
> > I'm paying about .086 per kWh for electric and 1.02 per therm for
> > natural gas (in US dollars). Would anyone be willing to do the math
> > and tell me which is the less costly energy source?
> > I'd be curious as to the cost of electric versus gasoline (at 3.20 a
> > gallon) for the purposes of powering a car. I know in California,
> > people are hacking their Hybrids to make them plug-in, but i have no
> > idea if that would make sense here.
> >    Also, anyone have any views on which energy source will increase in
> > cost more quickly in the future? I'm in Saint Paul, MN
> > -Ben
> >
> > --
> > Ben Pratt
> > Professor, Design
> >
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