Roof Garden Baking - Hot Off the Grid
- For Beth Terry, roof gardeners, & others
copy into your browser this whole string:
Hot off the grid
Solar ovens utilize nature's rays for energy-efficient, everyday
cooking -- even in foggy San Francisco
Tara Duggan, Chronicle Staff Writer
Wednesday, July 11, 2007
Global warming. Dwindling energy resources. Deforestation and
pollution, natural disasters and power outages.
These are just some of the things to worry about in today's world.
Yet a small but growing group of advocates says a simple tool exists
that can help address them: the solar oven.
Sun-heated ovens are nothing new. The idea has been around for
centuries, and people of a certain age may remember using ragtag
cardboard-and-foil contraptions to bake carrot-lentil loaf back in
their hippie days. But with today's new versions that produce results
comparable to conventional ovens, solar ovens are poised to move into
"For people who are interested in being carbon-neutral or being
green, the idea of using something like a Sun Oven is very
appealing," says Paul Munsen, president of Sun Ovens International,
based in Elburn, Ill. He expects to sell 5,700 ovens in the United
States this year, up from around 1,000 in 2004.
Lynn Langford of Ross purchased a Sun Oven a year ago and uses it to
prepare dishes such as baby beet salad with walnuts and feta. Instead
of boiling the beets on her stove and toasting walnuts in her oven,
she places the beets in a dark pot, wraps the nuts in parchment paper
and tucks both into the oven to cook in her sunny backyard.
"When you care about not heating up the whole planet, it's a fun and
easy way to do it," says Langford, who says her electricity bills
dropped by 30 percent in the first month of using her solar oven
about three times a week.
Solar ovens alone will not solve the energy crisis. A typical family
of four consumes about 500 kilowatt-hours per year using an electric
range and oven combination, which adds up to only around $65 a year
on Bay Area utility bills. Still, it's a start.
"People look into installing solar panels or a solar water heater,
and it's a sticker shock when they start to think about that initial
investment," says Munsen. "Then they look at a $260 oven and it's a
lot more immediate."
Munsen's company focuses primarily on getting solar ovens into the
developing world, as does Sacramento organization Solar Cookers
International, which promotes their use for impoverished people who
lack access to cooking fuel (see "A tool for the developing world,"
The ovens work best in sunny climates like California's Central
Valley and the American Southwest, but even those who live in cooler
parts of the Bay Area also can take advantage of them on sunny or
mostly sunny days year round, and on camping or boating trips.
Some people purchase them in the event that a major earthquake or
hurricane -- not to mention terrorist attack -- wipes out power for
days, or weeks. Solar cookers provide additional energy savings to
those who use air-conditioning, because the air conditioner doesn't
have to fight the heat produced by an indoor oven.
"We bought our house in Sonora, and it's so hot and I thought, 'I
have to have one of those sun ovens,' says Sharon South, who recently
moved from San Jose to Tuolumne County. "Because in the summer, who
wants to turn the oven on?"
This spring, South started using her solar oven about three times a
week and plans to buy a second one so she and her husband can cook
more dishes at once when they have guests.
Solar cookers like the Sun Oven can maintain temperatures of 350
degrees or higher and start around $230. Less-insulated and simpler
versions such as one called the CooKit cost about $32 and cook food
in the low to mid 200 degrees -- hot enough to boil water, which is
all you need for most cooking.
Most solar ovens rely on the greenhouse effect. The Sun Oven, for
example, consists of a well-insulated box with a glass lid and four
reflective panels that direct sunlight into the box. As the sunlight
is absorbed by the oven's black interior and any dark-colored dishes
place inside, it converts into heat, which is trapped inside by the
glass lid. (For more on how solar ovens work, see graphic, F5)
There are disadvantages. Solar ovens don't work on super-foggy or
rainy days. They also can't be used with recipes that require high
heat or lots of stirring; heat escapes each time you open the oven or
lid, adding another 15 minutes of cooking time. On the other hand,
the ovens can't burn food because there aren't any hot spots.
Solar cooking typically takes two to three times as long as
conventional cooking. But once you get used to the relaxed rhythm, it
can be easy and convenient, kind of like using a Crock-Pot. If your
backyard has sunlight all day, you can place a one-dish meal inside
the oven in the morning, position it toward where the sun is at its
height in the middle of the day, and come home from work to a fully
cooked, warm dinner.
"Someone who likes precise cooking might be frustrated with these
ovens," says Langford, a mother of twin preschool-age boys. But,
partly because she works at home as a consultant, she says, "I'm not
concerned with how long it takes. I see it as a different kind of
The Food section purchased a Sun Oven and conducted a range of tests
on the roof of our often-sunny South of Market office, with
surprisingly good results.
We found it perfect for low-and-slow cooking, such as a whole-grain
rice pilaf. It also did a lovely job baking up corn bread and peach
and blackberry cobbler, and cooked up sweet and tender baby beets and
It took us awhile to get the hang of the oven, and our results were
better after we learned more about sun patterns. Box cookers like the
Sun Oven are most effective when adjusted about once an hour so the
glass top is always perpendicular to the sun's rays.
"What it is with the solar oven is you start to develop an intuitive
sense. It's a little closer to nature," says Don Larson, assistant
manager at Common Ground, a nonprofit organic garden supply and
education center in Palo Alto, where he teaches classes on solar
cooking and building solar ovens. "You notice, for example, if it's
windy you leave it in 15 minutes longer."
Common Ground sells about eight solar ovens a month during spring and
summer. At their San Jose home, Larson, his wife, Susan, and their
two children have three homemade solar ovens. Larson first got
interested in solar energy when visiting a technology expo as a
junior high student. He went home and built a model solar heater out
of a cigar box and has been hooked ever since.
"It's a very positive form of environmentalism," says Larson. "You're
not out there protesting and marching. I'd rather be taking action,
and this is a very social form of it. Everyone congregates around
Still, Larson insists that the primary reason he uses solar ovens is
even simpler: "How it tastes when you get it all done."
History of solar cooking
Ancient Greeks, Romans and Chinese experiment with the use of curved
mirrors that could be angled toward the sun and cause objects to
burst into flames, for military purposes.
16th century. The Dutch, French and English begin widespread use of
greenhouses, which are heated when sunlight passes through glass and
becomes trapped inside, to raise tropical plants.
1767. Swiss scientist Horace de Saussure develops a solar cooker
using the greenhouse effect, in the form of several glass boxes set
inside one another and placed on a dark surface.
19th century. French mathematician Augustin Mouchot uses curved
mirrors to angle the sun's rays into an insulated box that traps
1894. A restaurant in China serves solar-cooked food.
1950s. Maria Telkes of the Massachusetts Institute of Technology
develops the present-day box solar cooker, an insulated, glass-topped
box with four reflectors to direct light into the box. The United
Nations and other agencies begin studying how to bring solar cooking
to countries where fuel is scarce; early programs do not take off.
1973. The first solar cooking convention is held in China, where
solar cooking has become widespread.
1992. China reports the use of 100,000 solar box cookers.
A tool for the developing world
Over 2 billion people, a third of the world's population, rely on
wood-fueled fires to cook food. Of these people, around 500 million
frequently encounter fuel shortages yet live in ideal climates for
solar cooking, says Kevin Porter of Solar Cookers International (SCI)
Many women, especially refugees, trek miles to obtain cooking fuel,
and the reliance on wood for fuel has led to deforestation in many
SCI and other organizations help impoverished communities gain access
to solar ovens to cook food, pasteurize water and sterilize medical
equipment. Since 1995, SCI has taught 30,000 families in eastern and
southern Africa how to use solar ovens and has helped establish solar
businesses in refugee communities.
The majority of funding comes from individual donors; to donate or
learn more, visit solarcookers.org.
-- Tara Duggan
Where to find solar ovens
The following organizations and companies sell solar ovens; some
offer lots of online resources:
ClearDome Solar Thermal. (888) 277-7547, Ext. 3427, or
Common Ground Organic Garden Supply and Education Center. 559 College
Ave., Palo Alto; (650) 493-6072 or www.commongroundinpaloalto.org.
Solar Cookers International. (916) 455-4499 or www.solarcookers.org.
Solar Living Institute/Real Goods. 13771 S. Hwy. 101, Hopland; (707)
744-2017 or www.solarliving.org.
Sun Ovens International. (800) 408-7919 or www.sunoven.com.
--- In ZeroWasteOakland@yahoogroups.com, "Beth Terry" <beth@...>
> My name is Beth Terry. I just joined this group because I am
> in ways to reduce the amount of plastic that enters the waste-stream, by
> eliminating unnecessary sources of plastic, re-using plastic items,and
> also recycling the plastic that can be recycled. I am interested toas we
> find out what Oakland is doing about plastic curb-side recycling,
> recycle way fewer types of plastic than San Francisco.reduce
> In an effort to educate myself and contribute to the dialogue in the
> online world, I have created a blog about my personal quest to
> the plastics in my life. It's at www.fakeplasticfish.comnow,
> <http://www.fakeplasticfish.com/> . I welcome all to come visit and
> leave comments/ideas.
> I also enjoy roof gardening, running, movies, and music. But right
> my main obsession is plastic ever since I read an article calledfitness/Our_oceans_are_\
> "Plastic Ocean" that just broke my heart:
> Since I am new to thinking about these kinds of issues, I welcome
> information that you wish to impart. Feel free to e-mail medirectly.