My main interest in electric cars lies in their role in moving us toward
a sustainable way of life.The biggest barrier to this goal is its
perceived cost.Yet my back-of-the-envelope calculations below indicate
that a net-zero energy house and net-zero energy automobile combination
would be much cheaper over 35 years for a household than our current use
Specifically, a typical household today will spend over $150,000 in
energy over the next 35 years for house and cars, whereas a net-zero
energy house and car combination would cost less than $100,000 for the
same time period.Below are the calculations, references, and data for
such a conclusion.I would appreciate it if others would examine my
data, assumptions, and calculations to determine the extent of their
Here is the list of my estimates for various costs, as well as references
(using the "tiny URL" facility) that I use in my calculations.
o Assumed dates when this calculation should be valid:2012.This
is when a sizable number of electric vehicles should be available
(Nissan, Aptera, TH!NK, iMiev, Chevy Volt, Tesla White Star, ...)
o My (conservative) estimate for household energy costs: $2000/yr.
- Ref: $2350/yr according to: http://tiny.cc/3TxW8
o My (conservative) estimate for current MPG:25.
- Ref: 19.8 MPG according to:http://tiny.cc/h2Wbl
o My estimate for household miles driven per year: 20,000
(based on usuallymore than one car per household).
- Ref: 21,000 miles according to:http://tiny.cc/IXFvU
o The European passive house:my estimate is that building to this
standard would increase the cost of a house by an average of 8%.
Thousands of these houses have been built across Europe. They
look like ordinary houses, apartments, condominiums, etc.They
tend to be more comfortable, much quieter, have healthier indoor
air quality, require less maintenance, reduce heating/cooling costs
by a factor of 5 or 10, eliminate the need for a central
system, and use 4 times less energy overall.
Here are various other estimates:
- Ref: 5-7% in Germany : http://tiny.cc/qQEfF
- Ref: 4-5%: http://tiny.cc/fVTtw
- Ref: up to 14%: http://en.wikipedia.org/wiki/Passive_house
- Ref: 75% less energy : http://www.efcf.com/reports/E20.pdf
o My estimate for a home energy monitor: $500.
- Ref: $200 - $600:http://tiny.cc/U7wZ5
o My estimate for solar hot water heating: $10,000.
- Ref: 4000 Euro/$5600: http://tiny.cc/sw9VI
- Ref: $10,000 - $18,000:http://tiny.cc/s99BU
- Ref: $9000 - $15,100 for *cold* Northern states
as per "Solar Today", June 2009, page 40.
Solar heaters in "average" locations in the US
should be cheaper than in Northern states.
o My estimate for *current* PV solar cost is $8/watt.
- Ref: $7.6-$8.10:http://tiny.cc/vmzZ1
o My (conservative)estimate for PV solar in 2012 is $5.60/watt.
Until 4 or 5 years ago, PV costs were declining until they hit
a plateau determined by the supply of purified silicon (the
supply was set by the electronics industry, not PV).But that
has changed and the supply is growing so that the cost of
purified silicon is dropping by a factor of ten.This, as well
as many other reasons, is why the cost of PV will plunge.
My estimate assumes a reduction of 30% by 2012, but others predict
a steeper decline.
- Ref: $1/watt cell ~ $4/watt for PV:http://tiny.cc/LlTdu
o My (conservative) estimate for PV degradation is 1.00%/year.
- Ref: appears to be less at 0.75%/yr:http://tiny.cc/rIRkH
o My (conservative) estimate is that in an average location in the
US, over a 35 year lifetime, a 1 KW PV array will generate an
average of 1100 KWH/yr.This is based on the average 1st year
output of 1300 KWH/yr for a 1 KW PV array, degrading over
35 years at 1%/yr to 900 KWH/yr: (1300 + 900)/2 = 1100.
- Ref: PV watts per state:http://tiny.cc/p3c3R
So, if we put this altogether we get these results:
o Using current house, car, and energy data the average household
in the US spends $154,000 for energy over 35 years.
- $2000/yr * 35 years for house energy = $70,000.
- 20,000 miles/yr, at 25 mpg = 800 Gallons.At $3/gallon
that comes to $2400/yr, or $84,000 over 35 years.
Total energy costs over 35 years: $70,000 + $84,000 = $154,000
o For the net-zero energy house and net-zero energy car scenario we use
- The house is built according to the European passive
house standard.The average cost of a house now is about
$250,000, so an 8% increase is $20,000.
- To this we add a solar hot water heater and an energy
- This should reduce the total energy needs of the house
to about 5000 KWH/yr, so a 5 KW PV array would easily
make this a net-zero energy house.But instead we will
use an 8 KW PV array, at a cost of $5.60/watt * 8000 watts
= $44,800. The extra 3 KW will be used to power the cars.
So the total cost increase is:
$20,000 + $10,500 + $44,800 = $75,300.
- We will give this family 3 electric cars: one full size
full function 5-6 passenger, high performance electric
car, and two tiny 8x5 foot 800 lbs. electric micro cars
limited to 35 MPH.
- The high performance family electric car is superior
to a gas equivalent car in almost every way, except
for range and recharging time, due to the qualities of
electric motors and the architectural design freedom
of electric drive trains.If designed from scratch
it should get 5 miles/KWH.
Ref: the 2850 lb. EV1 got 5.5 miles/KWH
Ref: the 3000+ lb Chevy Volt gets 40 miles on 1/2
of its 16 KWH battery, and so gets 5 miles/KWH.
- There are a number of cultural, safety and other reasons
why Americans do not like micro cars, such as the SMART
car.However, some of these reasons are due to the fact
that downsizing a gas engine car makes it uglier,
noisier, dirtier, less efficient, and much more cramped.
This is because gas engines are such obnoxious devices
that they must be surrounded by all sorts of other
things to make them acceptable, such as mufflers,
catalytic converters, variable speed transmissions,
fuel, cooling, and oil distribution systems, pumps,
belts, hoses, filters, etc.And it is these very things
that get heavily compromised when the car is greatly
But electric motors are always quiet, clean, smooth, and
efficient regardless of their size; and limited
performance (say, 35 MPH) lightweight cars can be
designed where the drive train takes up zero space: the
battery, charger, and inverter can be a long, wide, but
thin pack that makes up the floor of the vehicle (taking
up no space), and the 4 motors are inside the wheels.
Thus a tiny 8x5 foot car that is 10 inches shorter than
a SMART car and 1 inch narrower should still be able to
hold 4 adults.So there is reason to believe that a
tiny electric car may be more acceptable to the American
Each of the two micro cars is assumed to get 15
miles/KWH (this compares with the Aptera which is
twice as heavy and far more powerful and which gets 10
- If the micro cars drive a combined total of
12,000 miles/year, and the full size car drives 8000
miles/year, then the theoretical annual KWH/year is
8000/5 + 12,000/15 = 2400 KWH/year.
However, there are various losses of efficiency, such
as wall plug-to-battery and other losses.So we build in
another 25% loss in efficiency, to get to 3000 KWH/year.
Thus we end up with a net zero energy house and cars
combination from the 8 KW PV array.So, the current
energy scenario costs $154,000 over 35 years, versus
only $75,300 for the net-zero energy approach.
In order for this NOT to save a lot of money, the
electric cars would have to cost $78,000 more
than gas engine cars.
- Note: all of these calculations are for an average house in
an average location in the US.However, there is about a
35% variation, plus or minus, in solar intensity in the
contiguous states.For example, in Tucson, a 1 KW PV array
produces 1663 KWH/year, whereas in Seattle (where I live)
it produces 970 KWH/year.So, looking at the cost of solar
hot water and PV, the figure of $10,000 + $44,800 = $54,800
should be modified by up to +/- 35%.So in Seattle,
the cost would be about $20,000 + 73,000 = $93,000, whereas in
Phoenix it would be about $20,000 + $43,000 = $63,000.