of Alternate Energy Sources
There are a ton of resources on the
web describing every aspect of alternate energy technologies and it
is simply not possible to explore them all in depth here. I have
listed a few popular sites if you want to explore further.
On this page I am only providing my summary and opinions.
relation between my opinions and actual reality is pure conjecture.
Density - maximum solar energy is often given
as a bit over 1 kw per square meter, which is close to 100
watts per square foot. This only occurs with the sun directly overhead
with a very clear, dry atmosphere. As the sun approaches the horizon
the energy must travel through more and more of the atmosphere with
a corresponding lose of energy. Moisture, dust and haze also reduce
available energy (and of course clouds really reduce energy). Practical
collectors can only gather a fraction of the energy which falls
Availability - the most obvious fact of solar energy
is often overlooked in casual analysis: it is unavailable the majority
of the time. Over a year, a tracking solar collector (one that moves
to keep pointing directly at the sun) can produce most of
its rated power about 45% of the time if the sightlines are clear
to the horizon. A fixed (non-moving) collector will produce most
of its rated power only about 25% of the time (more in summer, less
in winter). This is a theoretical maximum based on geometry, before you
make any allowance for cloud cover. You might get close to this
value in the desert, but in a place like New England you will only
get near rated power 1/6 to 1/8 of the time averaged year round. The
key question is: what do you do when the sun isn't shining?
is the first form of solar energy many of us saw as the 1970's energy
crisis led to solar collectors sprouting on roof tops across the country.
This was most commonly a black flatplate collector under glass with
either air or some kind of fluid running across it so as to pick up
the heat of the suns rays. It sometimes was used to provide some space
heating but the favored use was to help provide hot water.
designed and built collectors looked crappy and broke before they
ever payed back the energy and money used to create and install them.
Take: in sunny climates, newer, properly designed systems
can effectively provide most of the energy required to produce hot
water (which is often the second highest energy use in the
the house to align with the sun, put the correct amount of windows
on the south side, add the proper amount of thermal mass and the home
can collect a fair percentage of its heating needs with no moving
Issues: excessive glazing, lack of shading and insufficent
thermal storage often led to spaces that overheated during the day,
leaked heat at night.
My Take: given a well designed, properly
insulated house, passive solar can provide much of the heating required
spring and fall. Usually you still need auxiliary heat during mid-winter
when the sun is lowest. A well integrate passive solar component
can be the best way to utilize solar energy, but it sometimes isn't
recognized as such because it doesn't make the power meter spin.
Idea: Focus the
suns rays on a boiler to produce steam to generate electricity. A
thermal plant can sometimes capture a higher percentage
of the suns power than most photo-voltaic cells, although
photo-voltaic cell may eventually catch up in that department.
to do this efficently on a large scale. Requires bright, direct sunlight.
Take: Might make some sense in the desert where land and unobstructed
sun are plentiful. Best opportunity may be in combined fuel plants
which incorporate some thermal storage to cover short interruptions
(passing clouds) and a natural gas burner (typically) to take over
at night. This lets the same turbine/generator run full time using
whichever mix of energy is available at that moment.
Idea: Build panels
that use the Photo Voltaic effect (basically photons of light knocking
electrons out of atoms in a semiconductor material) to generate electricity.
There are several common types of PV cells. Crystaline silicon cells
are currently around 15% efficient. Non crystaline cells are in the
range of 8 to 10% efficient but cheaper to produce.
cells produce DC current, require an inverter to produce house power
or tie to power grid. Storage or backup source required. Cost is an
issue although it is coming down. Contrary to common belief,
PV cell do not last forever, but degrade over time. There is
lots of exciting research into new production techniques but increasing
efficiency, reducing cost and making a long lasting cell is hard to
do all at the same time.
My Take: A favored technology because
it produces power with no moving parts and no noise and can be integrated
right into the roof if a building is properly oriented. Current cost
is around $4 per peak watt. People have been waiting for the big breakthrough
on cost for decades, which hasn't exactly happened. What has happened
is a continuous incremental improvement. Cut costs 10% per year and
after 10 or 20 years it starts to add up to a big breakthrough. However,
even if the cells themselves suddenly became free, solar electricity
has issues simply because it isn't there the majority of the time.
Storage or backup generation is a major cost, unless the load is
perfectly matched to availablity.
Idea: Use windmills (wind turbines) to extract energy from
winds to pump water or generate electricity. At 15 MPH (a typical
average speed for a good windy site), a wind turbine can
generate about 6 watts per square foot (64 watts per square meter)
of swept area. Most turbines produce their rated power at around 30
MPH. The power is proportional to the cube of the wind speed. At 15
MPH a turbine only generates 1/8th as much power as at 30 MPH. So
there is usually a big difference between the rated (maximum) power
of a wind turbine and the actual average power produced. Understanding
the distribution of wind speeds at a particular site is critical.
takes a LOT of BIG wind turbines to equal one large conventional
power plant. To produce 500 MW of average power it might take: 1,000,000
turbines of 10 foot diameter or 40,000 turbines of 50 ft diameter
or 1600 turbines of 250 ft diameter. People object to impact
on birds, noise from turbines, visual impact. Wind is variable. At
many sites, most of the power is concentrated in "energy winds"
that average about 2 days out of 7.
Currently the fastest
growing AE source of electricity. In a good wind site (and with good
tax breaks) cost per kw-hr can be competitive with
conventional power plants. As with solar power, the biggest problem
is the fact it is intermittent so storage or alternate generation
is required. Click here
for the America Wind Energy Association website.
Idea: There are many ways to
use natural plants, cultivated crops or biological organisms to produce
useable energy. The use of wood for heating is probably the oldest
form of energy known to man. Many crops or agricultural by-products
can simple be burned to generate energy. Other options include using
fermentation to produce alcohol (ethanol) from plant material. Pressing
some plants can produce vegitable oils than can be used in diesel
engines. Methane from decomposition of organic material (ranging from
municiple waste to cow poop) can heat buildings or generate electricity.
There is much discussion over which processes actually
produce a net surplus of energy. Click here
for a good Wikipedia
article summarizing this. (Producing ethanol from corn seems to be
one of the less energy efficient options but farm state politics makes
it popular.) All of these forms of energy are basically solar energy
captured by the plants. While it is a big plus that energy storage
is inherent in the plant material, the percentage of solar energy
that gets captured and converted is rather low. Therefore it takes
a LOT of land area to grow an energy crop on a useful scale. I've
read estimates of 100 to 500 square miles of wood lot to support a
1000 MW wood fired electric plant. So there is a large effect
on the local environment, lots of water required, etc.
My Take: There
are really two major categories of bio-energy. The first is utilization
of waste material we already produce. Methane from land fills can
be captured and used to generate electricity. People with bio-diesel
cars often fill up at McDonalds taking the used oil from the fryer.
Did you know that Maine gets almost 30% of its electricity from wood
burning power plants that run on the left overs from the paper and
lumber plants? All forms of organic waste can be looked
at as an energy resource. This often has a big energy payback
since the energy to produce it has already been expended for other
reasons. This can be as close to the mythical "free energy" as you
The second category is crops grown specifically for
the energy they can produce. This takes more thought to get right.
Ideally an energy crop should grow fast without taking too much
water or fertilizer. It should yield a product with high energy
density (liquids are preferable for convenience) and the energy
input for processing must not be too high.
of the analysis showing corn base ethanol took more petroleum
to produce than it displaced is unsurprising. Many of the processes
used were created 80 or 100 years ago when oil was plentiful and cheap
and the energy efficiency was not a consideration. Just because one
process is inefficient doesn't mean there can never
be a useful biofuel
process. We are just starting to figure this out. One interesting
examines 29 different options and that is only scratching the