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I thought the bubble chart on the annual energy bill for
a typical home (“Home Energy Upgrades That Pay,” March
issue) was a great graphic that I could use in teaching. But then
I got to thinking about the graphic and what was portrayed, and
it did not make sense to me. Knowing what I do about electric
usage, I was stumped that the heating and cooling category
was represented as such a huge part of the load. So I went to
the source cited in the graphic, energystar.gov. Their graphic
is a pie chart and shows that heating and cooling account for
49 percent of a typical home’s annual energy bill. Looking at
SOLAR TODAY’s bubble chart, it certainly appears as though
the heating and cooling bubble is at least three, maybe four,
times greater than all the rest of the usages combined.
Revised graphic represents usage differences.
When I showed the documents to my daughter, a master
teacher in math who specializes in graphics, she discovered
the problem. While the diameters of each bubble are proportional, the areas are not. Increasing the diameter four times will
increase the area 16 times.
So, the bubble chart should have represented the differences
by area, not diameter. This would have made all the smaller
bubbles, representing 51 percent of the typical home energy
bill, about equal to the large bubble for heating and cooling,
which represents 49 percent of the bill. This would have been
a more accurate representation.
10 June 2009 SOLAR TODAY
SOLAR TODAY, Kutscher Win Gold
SOLAR TODAY was recognized in April with a Gold
EXCEL Award in the Society of National Association
Publications annual EXCEL Awards program. The
award, for the January/February editorial, “Tackling
Climate Change: The Debate Is Over! (Or Is It?)?”
by Chuck Kutscher, is SOLAR TODAY’s second Gold
EXCEL in three years. The award will be presented in
Washington, D.C., in June.
In “Firefighters Learn To Work Around Rooftop PV” (April issue, page 12), we sought
to clarify some issues regarding rooftop access and the potential for electric shock near
photovoltaic modules. Our short article was illustrated by an out-of-date diagram from the
Los Angeles Fire Department, indicating a 4-foot setback between the roof edge and the PV
panel. In fact, this is a recommendation, not a code requirement, and the margin at the roof
peak is 3 feet. Matt Paiss, whom we quoted in the article, writes, “It is our recommendation
that all DC conduit be considered energized in daytime hours, instead of making a possibly
fatal error assuming the conductors are de-energized when the disconnect is opened.”
The article “Integrated Module/Inverter Systems Produce Rooftop AC” (April issue,
page 14) concluded with a reference to “a big red emergency cut-off switch for use by
firefighters and utility company emergency crews.” John C. Wiles, program manager of
the Southwest Technology Development Institute, writes that many utilities no longer
require any such disconnect. He also points out that charge controllers, also mentioned
in the article, are used only in off-grid, battery-backed systems and are rarely used where
grid-tied systems have battery back-up.
In the “New Products” section of the March issue (page 48), our headline on the Electra Therm Waste Heat Generator implied that the machine is a cogeneration unit, which it
is not. The generator produces electricity from waste heat.
Copyright © 2009 by the American Solar Energy Society Inc. All rights reserved.