|
Using Solar in
Your Home
The four main
applications of solar energy in homes are daylighting, passive solar heating,
solar hot water systems, and photovoltaic systems. Daylighting and passive solar
heating are the most cost-effective uses of solar energy in homes. Although it
is best to incorporate these features into new home designs, they should also be
considered when remodeling or adding to your home.
Solar hot water and photovoltaic
systems may have high initial costs, but many homeowners choose to install them
because they are reliable, have low environmental impact, and can provide
independence from utilities and other energy providers. Some utilities are also
offering rebates or subsidies to homeowners who install these systems on their
roofs.
Using Passive Solar Heating in
Your Home
Although passive solar heating
is best incorporated into a house during the initial design, the concepts of
passive solar heating can also be used when remodeling or adding to your home.
Window design, and glazing choices in particular, are critical factors for
determining the effectiveness of passive solar heating in a home. In heating
climates, large south-facing windows are used, as these have the most exposure
to the sun in all seasons.
Windows can also be located to
provide solar heating in cold climates or avoid solar heating in hot climates.
In cold climates, large south-facing windows allow significant solar energy
into the house and also provide daylighting; properly sized overhangs can
prevent overheating in the summer. In hot climates, north-facing windows can
provide daylighting without heating the house.
East- and west-facing windows
generally cause excessive heat gains in the summer and heat losses in the
winter, and are usually sized small. Although overhangs are impractical for
east- and west-facing windows, vertical shading can be used, or trees and
shrubs can be strategically located to shade the windows. Landscaping has
other benefits, including natural cooling and protection from the wind. See
the fact sheet, "Landscaping for Energy Efficiency."
Windows can now be designed for
a number of purposes. Some windows are designed to let the sun's heat in while
insulating against the cold, and are ideal for south-facing windows in cold
climates. Others are designed to reject the sun's heat while providing
insulation, and are ideal for all windows in hot climates and east- and
west-facing windows in moderate climates. See the "Buying for Energy
Efficiency: Windows" factsheet for information about which windows you
should buy for your location.
Thermal mass—such as tiles,
masonry, or even water-filled walls—provides a means of storing the solar
energy that enters through the windows. Built into the floors and walls near
the south-facing windows, thermal mass will absorb solar energy during the day
and keep the house from overheating. At night, the thermal mass will release
the heat, keeping the house warm.
An alternate approach is to
locate a thermal mass wall on the south-facing side of the house, with glazing
on the exterior, separated from the wall by only a few inches. The wall
absorbs heat on the sun-facing side and releases it slowly into the living
space over the course of the day. Although the wall will block the sunlight,
daylighting can still be achieved through narrow windows located above the
thermal wall.
For thermal mass to be
effective, air must circulate freely through the house to carry the heat from
the thermal mass to the places where it is needed. Fans are sometimes used,
but natural convection will often circulate the air sufficiently. For
instance, a central staircase provides an effective means for allowing hot air
to rise, and to complete the circuit, vents between the upper and lower floors
along the exterior walls will allow cooler air to flow back to the thermal
mass. Doors must be left open for this approach to work.
Solar Water Heating
Solar water heaters use a solar
energy collector, usually mounted on the roof of the house, to heat a fluid
such as water, which is pumped through it. The hot fluid is stored in a tank,
usually located in a basement or utility room, and the cool household water is
piped through a heat exchanger in the tank to heat it. The hot household water
can then be stored in another tank, or it may be piped into a standard water
heater, which can serve as both a storage tank and a backup water heating
system.
The basic concept described
above can be accomplished using a wide variety of solar collectors and a
number of plumbing configurations. For systems in regions where the
temperature can go below freezing, an automatic drainback system is also
employed to drain the solar collector when freezing conditions become a
threat. For more information about solar water heaters, see the fact sheet,
"Solar Water Heating."
To make the most of solar water
heating, minimize hot water use through low-flow showerheads and faucets and
through dishwashers and clothes washers that use low amounts of hot water. See
the factsheets on Saving Water and Heating It Efficiently and Buying for
Energy Efficiency: Appliances.
Photovoltaic Systems
Photovoltaic cells, or solar
cells, convert sunlight directly into electricity. Photovoltaic systems use
large panels comprised of many solar cells connected together to work in
unison. The photovoltaic panels are usually mounted on the roof of the house,
preferably on a south-facing slope.
Because photovoltaic cells
produce dc (direct current) power, systems usually include a device called an
inverter, which converts the dc power to ac (alternating current) power to
match it to the electric utility's power supply. Although homes can be
completely "off the electric grid" and disconnected from the
electric utility, this requires large battery systems to store the electricity
produced during the day.
Most homeowners prefer systems
without battery storage that are connected to the power grid. In some states,
electric utilities will allow the photovoltaic system to add electricity back
into the power grid when the system is producing more electricity than is
being used in the home. In this arrangement, called "net metering,"
the electric meter will literally run backwards, reducing the homeowner's
electric bill.
To extend the economics of
photovoltaic systems, and to make their use in buildings more appealing, new
products that integrate photovoltaic cells into building materials are now
coming on the market. Colored skylights, awnings, and even roof shingles are
now incorporating photovoltaics, allowing them to generate electricity while
serving a purpose in the home's exterior. The roof shingles, for instance,
look nearly identical to asphalt roof shingles and will serve the same
purpose, while also generating electricity.
Photovoltaic shingles look
similar to asphalt shingles and provide the same protection for your roof
while they generate electricity.
For more information about
photovoltaic systems, see the fact sheet, "Photovoltaics: Basic Design
Principles and Components."
U.S. Department of Energy
Path:
Home>Education>Energy
Information>Using
Solar in Your Home
|
