C D E
F G H
I J K L M N
O P Q R
S T U V
W X Y Z
space heating - a collector (generally placed on the roof top)
is used to heat the air inside a building. A mechanical circulator
pulls cooler air from inside the building into the collector, where
it is heated by the sun. The heated air is then pushed from the
collector to a thermal storage area, which is generally composed
of a large mass of rocks or water. This stored heat can later be
pulled back into the house by the circulator when it is needed.
water heating - heat trapped in the collector box is transferred
to the cooler fluid circulating through the absorber tubing, gradually
raising the temperature of the fluid. This fluid is either the household
water itself, which goes through the tubing directly into the hot
water tank (open loop system), or an antifreeze fluid that goes
through a heat exchanger within the tank, heating the surrounding
water, but not mixing with it (closed loop system). The tank may
be located at a distance from the collector. However, heat loss
increases as the distance between the tank and collector increases.
(see also flat plate collectors,
- see ethanol, methanol
degree days - the total number of heating degree days for the
year. Higher heating degree days mean more energy is necessary to
heat a given space.
heaters - consist of one or more small fluid storage tanks placed
in an insulated, glazed collector box that is usually mounted on
the roof. A good batch heater can be built for under $1000 and is
easy to maintain, providing there is freeze protection.
- see electrochemical energy storage.
- fuels derived from oganic sources (not fossil fuels such as
oil and coal).
British Thermal Unit, the amount of heat necessary to raise one
poudn of water one degree Fahrenheit.
the amount of heat necessary to raise one gram of water one degree
collectors - have convex absorber plates to concentrate the
solar radiation and increase its efficiency. These collectors are
often used where higher water temperatures are required, as in commercial
applications. A technologically advanced type of concentrating collector
utilizes evacuated tubes connected in parallel rows. These tubes
consist of smaller inner metal tubing, which contains the heat transfer
fluid, inside larger outer glass tubes. Air is withdrawn, or evacuated,
from the space between the inner and outer tubes to create a vacuum.
This vacuum minimizes conductive and convective heat losses and
further increases the efficiency of the collector.
day, heating (base 65 degrees F) = the number of degrees Fahrenheit
that the average tempreature for the day is below 65 degrees F.
energy storage - includes batteries and fuel cells.
New, more efficient battery systems have been developed (lithium,
nickel-hydrogen, sodium-sulfur, zinc-air, etc.) and older ones using
lead acid batteries have been improved. Batteries are commonly used
to store the energy in small photovoltaic, hydroelectric or wind
energy systems. However, they remain heavy, expensive and a major
source of hazardous waste materials. An exciting and rapidly evolving
technology is that of fuel cells - electrochemical devices
that convert the energy of fuels such as methane or hydrogen into
electrical energy. Fuel cells consist of an electrolyte and two
electrodes that produce an electric current by combining hydrogen
and oxygen ions. They are efficient, create little air pollution
or solid waste, and are silent. Since they are modular they can
be used in small or large applications (e.g., automobiles, office
buildings, hotels or hospitals) as well as providing peak power
for utilities. Fuel cell systems can be designed to supply heat
and air conditioning as well as electricity.
- a means of producing hydrogen by the use of an electric current
to "split" water into hydrogen and oxygen.
- ethyl alcohol (C2H5OH),
acohol from corn and other grains
plate collectors - commonly consist of a glazed and insulated
box containing a blackened absorber plate. Mounted on this plate
is the metal tubing (also blackened) that carries the fluid to be
heated. The glazing, which acts as a cover for the collector, consists
of one or more transparent sheets of glass or plastic. This glazing
allows the sun's rays to enter the box and also traps the resulting
heat inside by means of the greenhouse effect.
- see electrochemical energy storage.
energy - geothermal means "earth" plus "heat."
This heat originates from the molten rock, or magma, deep within
the earth; this magma often comes close to the surface where it
creates volcanoes or hot springs. Geothermal energy - the second
type of renewable energy (along with tidal power) that does not
directly result from the sun's radiation - is available from the
earth's crust in hot rocks, the magma itself, and particularly in
subterranean pools of hot water.
power, or energy from falling water, is the most commonly utilized
form of renewable energy throughout the world. In most cases the
water is stored behind a dam and the overflow used for power. As
with wind power, the mechanical energy of water was primarily used
in the past to directly power various types of mills, but during
this century the powering of electrical turbines and generators
has been its main application. Including both small and large scale
facilities, hydropower generates about 10% of U.S. electricity.
A good hydro site must have a constant flow of water and a relatively
quick drop in elevation. Therefore, consistent rainfall throughout
the year is important. For average precipitation in 168 towns and
cities throughout the U.S. see to the Weather
fuels - see electrolyis, photobiological
conversion, photochemical conversion.
- kilogram, about 2.2. pounds
energy storage - there are three primary methods for storing
kinetic energy. These are:
- powering flywheels that can spin for long periods of time at very
- compressing air in places such as underground caves; and
- pumping water up to a higher elevation and then extracting energy
as it falls back down to a lower elevation.
Flywheel systems are most often used in transportation -
especially in electric vehicles - to store electrical or mechanical
energy (by regenerative braking).
Pumped hydro storage systems use falling water to generate
electricity. No energy is really saved, but this system can be useful
to complement the demand cycles of an electric utility.
Water is pumped up when the utility has excess generating
capacity during low demand times; it is released to fall back down
and generate excess electricity during high demand (such as in the
evenings when people come home from work and turn on their air conditioners,
electric fans, etc.)
- methyl alcohol (CH4OH), also called wood alcohol
space heating - the house or other structure to be heated is
designed to absorb the sun's energy during colder months and to
block it from entering during warmer periods. Examples of this design
include south-facing windows, sunspaces, special window glass that
reflects the heat back into the house, thermal mass such as brick
or stone that stores heat, and overhangs that block the summer sun.
Design with the sun in mind was important in traditional architectures;
it can be a cost-effective approach in most climates today.
heating - see batch heaters,
conversion - takes advantage of the fact that certain strains
of algae and bacteria produce hydrogen as a photosynthetic waste
product to convert biomass into hydrogen.
conversion - sunlight strikes a container holding a liquid electrolyte
and a catalyst. The catalysts absorb the solar energy to create
electrical fields that trigger the splitting of water into hydrogen
cells - when light strikes these cells, it causes electrons
to migrate in one direction and positive charges to migrate in the
opposite direction, creating an internal electric field within the
cell. The current in this field is collected by a grid of contacts
on the top and bottom of the cell. PV cells are joined in modules
and arrays of modules that can generate anywhere from 5 to several
hundred watts of 12 Volt DC (direct current) power. An inverter
must be used to convert the DC to AC (alternating current) in most
cases. Since the sun shines intermittently, it is important to be
able to store the electricity by a means such as batteries (see
- average annual amount of rain and melted snow and ice. More precipitation
plus a hilly terrain creates better hydropower potential.
energy sources - result directly or indirectly from the heat
energy radiated by the sun and can be replenished quickly. Direct
solar radiation can be used for heating and cooling, or it can be
converted to electricity. Indirectly this same energy drives the
heat engine that produces wind and water power. It is also stored
as plants grow, plants that later can be used for biomass fuel.
Since most forms of renewable energy are available intermittently
(i.e., when the sun shines or the wind blows), it is necessary to
develop superior methods of energy storage.
collector - see flat plate collectors;
- kw hours per meter squared; indicates potential solar electricity
or BTU's per square foot; indicates potential solar, water or space
heating (see also sun angle)
heating - see passive space heating
and active space heating.
electric power - concentrated sunlight is used to boil water,
producing steam that rotates a turbine, which in turn powers an
heating - see active water heating
systems; batch heaters; thermosiphon
Angle - at noon facing due south. It is necessary to calculate
the approximate average sun angle to determine what angle to slant
a stationary collector so that the sun's rays are as close to perpendicular
as possible on average.
energy storage - the storage of heat energy. Various substances
can be used. These include:
- water - from small domestic water
tanks to large solar ponds or underground reservoir;
- pebbles or rock;
- masonry; or
- phase-change materials.
Phase change materials - including eutectic
salts, paraffin wax, and polyethylene glycol - generally require
a much smaller storage volume than rocks, masonry or water. These
materials absorb a lot of heat when they melt (change phase from
solid to liquid). The heat to melt them can be supplied by solar
energy. After the sun sets and the temperature drops, the phase
change material cools; when it gets cool enough to freeze it releases
the stored solar heat. Phase change materials are most effective
for heating air if they melt/freeze in a temperature range of from
70 deg. F to 90 deg. F.
Water is actually a good phase change material,
but its freezing point is far too low (32 deg. F.) to be useful
for space heating. Therefore, it is generally used in greater volume
to store heat at temperatures well above 32 deg. F., particularly
for liquid heating systems.
systems - here the storage tank is attached directly to the
top of the solar collector. As water in the collector heats up,
it becomes lighter and rises naturally into the tank above; at the
same time water in the storage tank that has cooled flows down into
the collector, replacing the heated water that has risen out of
it. Thus a natural convection circulation occurs when as water is
heated by the sun. Thermosyphon systems, which may be placed on
locations other than rooftops, are reliable and relatively inexpensive,
but allowance must be made for the weight of the water and - as
usual - for freeze protection.
- or energy from the ebb and flow of tides results primarily from
the gravitational pull of the moon, and therefore is not strictly
a form of solar energy. A large tidal power plant has been generating
electricity in LaRance, France for over 30 years. In North America,
the greatest potentials exist in Maine, New Brunswick and Nova Scotia.
power - an underutilized type of renewable solar energy that
combines the energy of wind and water. Wind blowing over long stretches
of ocean transfers its mechanical energy to the seawater as it forms
waves. Different energy designs use the rising and falling of the
waves on our coastlines to generate electricity. These include buoys,
pendulums, oscillating water columns, and air turbines. The highest
concentration of wave energy is in latitudes between 40o and 60o
in each hemisphere.
- is extracted from air currents by wind turbines with blades that
rotate around a horizontal or vertical axis. Both horizontal- and
vertical-axis turbines are now commonly used to generate electricity.
To be effective, wind turbines mounted on towers high off the ground
and located in areas where the wind blows at a constant speed. Many
regions, including the Atlantic seacoast, the Great Lakes, the Great
Plains and the Rocky Mountains, have enormous wind power potential.
- areas with consistently high average wind speeds are good candidates
for wind power.