Hot off the grid
Solar ovens utilize nature's rays for energy-efficient,
everyday cooking —
even in foggy San Francisco
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 the mainstream.
"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," this page).
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
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 cooking."
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
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 skewered shrimp.
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 food."
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 heat.
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) in Sacramento.
Many women, especially refugees, trek miles to obtain cooking fuel, and
the reliance on wood for fuel has led to deforestation in many areas.
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
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 www.cleardomesolar.com.
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.
Baby Beet Salad with Feta, Walnuts & Arugula
This recipe comes from Lynn Langford of Ross, who grows baby beets, herbs and
nasturtiums in her garden. Baby beets, which are about 2 inches across, are
sweeter and more tender than mature ones and take less time to cook.
24 baby beets, or about 14 ounces loose beets
(without greens), scrubbed and trimmed
Salt to taste
3/4 cup walnut pieces
2 tablespoons minced mint
2 tablespoons minced chives
3 tablespoons champagne or white wine vinegar
1 1/2 tablespoons extra virgin olive oil plus more to drizzle
Freshly ground pepper to taste
6 cups baby arugula, lightly packed
3/4 cup crumbled feta cheese
Nasturtium flower petals (optional)
Instructions: If using large beets, cut into
halves or quarters.
Solar cooking directions: Preheat solar oven for 30 minutes.
Place enough salted water to just cover the beets, about 2 quarts, in a
black, lightweight covered pot and place in the solar oven. When the water
comes to a simmer, about 30 minutes, add the beets. Cook until fork-tender, 1
to 2 1/2 hours, depending on oven temperature.
Wrap walnuts loosely in parchment paper. Tuck into the oven at some point
when you open the door. Toast 30 minutes to 1 hour.
Conventional cooking directions: Bring a pot of salted water to the boil
and cook beets until fork-tender, 30 minutes.
Preheat the oven to 375° and place the walnuts on a pan. Toast until
fragrant, 8 minutes. Let cool.
To finish the salad: Drain and let the beets cool. Peel skins with your
fingers or a cloth (use gloves to avoid staining from red beets). Cut the beets
in half lengthwise. Toss in the mint, chives and vinegar. Set aside until most
of the moisture is absorbed, 5 minutes or as long as you like. Toss in the
olive oil and season with plenty of salt and pepper to taste.
Place the arugula in a round on a large plate. Mound the beets in the
center, and drizzle any extra oil and vinegar from the beets on the arugula.
Season the arugula with salt and drizzle with a little olive oil. Scatter the
top with the nuts, feta and nasturtium flowers.
Per serving: 215 calories, 7 g protein, 11 g carbohydrate, 17 g fat (4 g
saturated), 17 mg cholesterol, 287 mg sodium, 3 g fiber.
Makes 9 pieces
Adapted from "Cooking with Sunshine" (Marlowe & Co., 2006), by Lorraine
Anderson and Rick Palkovic. Those who like sweet cornbread may want to double
the amount of syrup or honey.
1 cup cornmeal
1 cup unbleached white flour
2 1/2 teaspoons baking powder
1/2 teaspoon salt
2 tablespoons maple syrup or honey
2/3 cup buttermilk
1/3 cup milk (for conventional cooking only)
1/3 cup melted butter
1 cup corn kernels, frozen and thawed or fresh and cooked
Solar cooking directions: Preheat a solar oven for
20 minutes. Grease a 9-inch round baking pan; it should be a dark one for a
In a large bowl, stir together the cornmeal, flour, baking powder and
salt. In a separate bowl, combine the maple syrup, buttermilk, butter, egg and
corn. Gently stir the liquid mixture into the flour mixture.
Pour batter into prepared baking pan. Cover pan with a clear or dark lid,
and place in the solar oven until a toothpick inserted into the center comes
out clean, 1 to 2 hours. Cool and cut into 3-inch squares.
Conventional cooking directions: Preheat oven to 400°. Grease a 9-inch
round baking pan. Prepare the batter as directed above, adding the milk to the
liquid ingredients. Pour into prepared pan. Bake for 20 minutes or until a
toothpick inserted into the center comes out clean.
Per piece: 200 calories, 5 g protein, 28 g carbohydrate, 8 g fat (5 g
saturated), 43 mg cholesterol, 291 mg sodium, 2 g fiber.
Peach & Blackberry Cobbler
Adapted from a recipe
by Susan and Don Larson of San Jose. Don Larson teaches solar cooking at Common
Ground in Palo Alto.
For top crust:
1 cup flour
1/4 teaspoon nutmeg
1 1/2 tablespoons sugar
6 tablespoons chilled butter, cut into small pieces
2 ounces chilled cream cheese, cut into small pieces
For fruit filling:
2 pounds peaches, or about 4 cups peeled, pitted and sliced peaches
3 cups blackberries, washed
1/4 cup quick tapioca
1/2 cup sugar
1/2 teaspoon cinnamon
Ice cream or whipped cream, to serve
Instructions: To prepare the top crust (can be
done by hand or food processor): Combine flour, salt, nutmeg and sugar and stir
or process until blended.
Add small chunks of butter and cream cheese, and stir or process until
moist clumps form.
Form into ball, flatten slightly, wrap loosely and chill for 1-2 hours.
Solar cooking directions: Preheat the solar oven for 30 minutes. Butter a
dark 8- or 9-inch round casserole with a lid. You can also use an 8-by-8-inch
pan and cover it loosely with a dark or black pan, even a round one, as long as
it covers most of the pan.
Place dough on a lightly floured cool surface and roll out into a pie
crust that will fit over your chosen pan or use large cookie cutters to cut
into decorative shapes. Alternatively, cut into strips to make a lattice top.
In a large bowl, gently combine the peaches, blackberries, tapioca, sugar
and cinnamon. Place the fruit in the prepared pan and top with the crust or cut
shapes. If using a large crust, poke holes in it to allow steam to release.
Cover the dish. Bake in solar oven until crust is cooked through and
lightly browned, about 1 1/2-2 hours. Uncover during the last 1/2 hour of
cooking if using a tight-fitting lid. Cool at least 20 minutes before serving.
Serve warm with ice cream or whipped cream.
Conventional cooking directions: Preheat oven to 400°. Butter an
8-by-8-inch glass or metal baking pan. Prepare the dough and fruit as directed
above. Bake 30 to 35 minutes.
Per cake serving: 330 calories, 4 g protein, 47 g carbohydrate, 15 g fat
(9 g saturated), 41 mg cholesterol, 119 mg sodium, 7 g fiber.
From Susan and Don Larson of San
Jose. Short-grain brown rice, available at health food stores, makes the pilaf
satisfyingly sticky, but long-grain rice works, too.
1/4 cup olive oil
2 cups finely diced
5 to 6 cloves garlic, minced
2 leaves greens, stalks removed and torn into small pieces, such as
mustard greens, collard greens, Swiss chard or kale
2 stalks celery, finely minced
2 carrots, peeled and finely chopped
2 cups short-grain brown rice
1/2 cup barley
1/2 cup millet
6 cups low-sodium chicken stock or a combination of stock and water
2 to 3 umeboshi plums (optional; see note)
Salt to taste
2 teaspoons whole coriander seed, toasted
Solar cooking directions: Preheat a solar oven for
In a dark-colored (for solar cooking) Dutch oven or large skillet on the
stove, heat olive oil, then saute onions and garlic until crisp-tender, about 8
minutes. Add greens, celery and carrots and continue cooking until tender,
about 8 minutes.
Stir in rice, barley, millet and stock. Bring to a full boil. Add umeboshi
plums, if using, and salt. If using a skillet, transfer immediately to a
shallow, dark-colored (for solar cooking), covered baking pan and bake in a
solar oven for 1 1/2-2 hours. Stir in the coriander then bake an additional 30
Remove pits from umeboshi plums, if using, and cut into smaller pieces,
then stir into the rice. Taste and adjust seasoning with salt.
Conventional cooking directions: Preheat oven to 350°. Prepare pilaf as
directed above and transfer to a covered casserole dish. Cook for 1 hour, stir
in the coriander then bake an additional 15 minutes. Remove pits from umeboshi
plums, if using, and cut into smaller pieces, then stir into the rice. Adjust
seasoning with salt.
Note: Umeboshi or pickled plums are available in Japanese and health food
Per serving: 355 calories, 11 g protein, 61 g carbohydrate, 8 g fat (1 g
saturated), 0 cholesterol, 80 mg sodium, 6 g fiber.
Wheatless Apricot Cake
3/4 cup soft butter
1/3 cup sugar
1/3 cup honey
1/3 cup maple syrup
1 1/2 teaspoon baking powder
4 large eggs
1 cup rye flour
1/2 cup rice flour
8 to 10 apricots (washed and halved)
Vanilla ice cream (optional)
Solar cooking directions: Preheat solar oven.
Butter an 8-by-8 inch glass pan or other solar oven pan.
In a medium bowl, add ingredients in order listed, mixing well after each
ingredient. Spread batter evenly in the pan and top with fresh apricot
halves. Bake for 2 1/2 to 3 hours in solar oven. Serve with vanilla ice cream,
Conventional cooking directions: Follow directions above and bake in a
preheated 350° oven for 1 hour.
Per serving: 385 calories, 5 g protein, 50 g carbohydrate, 20 g fat
(11 g saturated), 126 mg cholesterol, 72 mg sodium, 3 g fiber.
Shrimp & Lemon Skewers
Lynn Langford maximizes
space in her solar oven by cooking beets for the salad in her favorite black
metal pot and flipping over the lid to use as a shelf for several skewers.
12 wooden skewers
1 1/2 pounds or about 36
large shell-on shrimp
1/4 cup extra virgin olive oil
1/2 teaspoon red chile flakes
1/2 teaspoon fresh minced oregano (about 1/4 teaspoon dried)
1/2 teaspoon sea salt or kosher salt, or to taste
3 Meyer lemons, cut into eighths lengthwise
Solar cooking directions: Preheat solar oven for
Place shrimp in a bowl and toss with olive oil, red chile flakes, oregano
and salt. Marinate briefly. Thread three on each skewer, alternating with a
Place shrimp skewers in one layer on a dark baking pan that will fit in
your solar oven. Cook until shrimp is pink on top or curled up, about 10
minutes. Flip and cook until pink on top and opaque in the center, another 5-10
Conventional cooking directions: Soak skewers in water 30 minutes before
cooking. Marinate the shrimp as directed above. Preheat a grill to medium or
turn on the broiler. Thread the marinated shrimp onto the skewers. If grilling,
oil the grill and cook skewers for 3-4 minutes per side. To broil, place
skewers on a baking sheet in one layer and place pan a few inches from the
cooking element. Cook for 3-4 minutes, then flip and finish on the other side.
The calories and other nutrients absorbed from marinades vary and are
difficult to estimate. Variables include the type of food, marinating time and
amount of surface area. Therefore, this recipe contains no analysis.
E-mail Tara Duggan at email@example.com.
This article appeared on page F - 1 of the San Francisco Chronicle
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