Visualizing Environmental Science

Winter sun

Summer sun

Overhang

blocks summer

sun.

.

South-facing double-paned

glass allows winter light to

enter directly into the room.

Double panes reduce heat loss

on cold nights. Thick adobe or stone walls and

floor store heat (in winter).

Warm air

escapes

(in summer).

Vent allows hot air

to escape (in summer).

Insulated

drapes or

window shades

prevent heat

loss at night

(in winter).

Attic and north-facing

wall are heavily

insulated.

James P. Blair/NG Image Collection

a. This home in Santa Fe, New Mexico,

requires no heating in winter.

b. Several passive design features are incorporated into this home.

Direct Solar Energy 445

household use or for swimming pools. Heat absorbed
by a solar collector is transferred to a fluid inside the
panel, which is then pumped to the heat exchanger,
where the heat is transferred to water that will be stored
in the hot water tank. Solar domestic water heating can
provide a family’s hot water needs year-round. Because
more than 8 percent of energy consumed in the United
States goes toward heating water, active solar heating
could potentially supply a significant amount of the
nation’s energy demand.
Active solar energy is not used for space heating as
commonly as it is used for heating water, but it may be-
come more important as natural gas, oil, and electricity
prices continue to rise.
In passive solar heating, solar energy heats build-
ings without the need for pumps or fans to distribute the
heat. Certain design features are
incorporated into a passive solar
heating system to warm buildings
in winter and help them remain
cool in summer (Figure 18.2).
In the Northern Hemisphere,
large south-facing windows re-
ceive more total sunlight during
the day than windows facing other directions. Sunlight
entering through the windows provides heat, which is

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passive solar

heating A system

of putting the sun’s

energy to use that

does not require

mechanical devices

to distribute the

collected heat.

then stored in floors and walls made of concrete, packed

earth, or stone, or in containers of water. This stored

heat is transmitted throughout the building naturally by

convection, the circulation that occurs because warm air

rises and cooler air sinks.

Buildings with passive solar heating systems must

be well insulated so that accumulated heat doesn’t

escape. Depending on a building’s design and location,

passive heating can save as much as 80 percent of heat-

ing costs. Currently, about 7 percent of new homes built

in the United States have passive solar heating features.

Photovoltaic Solar Cells

Photovoltaic (PV) solar cells can

convert sunlight directly into elec-

tricity (see What a Scientist Sees).

Individual PV cells can be used

to power small devices like wrist

watches. However, in order to

generate energy to power a build-

ing or supply electricity for indus-

trial or commercial uses, PV cells

are usually arranged on large pan-

els that absorb sunlight even on

cloudy or rainy days.

photovoltaic

(PV) solar cell

A wafer or thin film of

solid-state materials,

such as silicon or

gallium arsenide,

that is treated with

certain metals in such

a way that the film

generates electricity

when solar energy is

absorbed.