Hot off the grid

Solar ovens utilize nature's rays for energy-efficient, everyday cooking -- even in foggy San Francisco

San Francisco Chronicle
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 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, IL. He expects to sell 5,700 ovens in the United States this year, up from around 1,000 in 2004.

Solar flair: Lynn Langford positions her solar oven for baking chocolate zucchini cake in the backyard of her home in Ross. Chronicle photo by Liz Hafalia

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 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 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 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 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."

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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.

Source: solarcooking.org

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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 communities.

The majority of funding comes from individual donors; to donate or learn more, visit solarcookers.org.

-- Tara Duggan

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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.

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Baby Beet Salad with Feta, Walnuts & Arugula
Serves 4-6

Baby Beet Salad with Feta, Walnuts & Arugula. Styled by Tara Duggan. Photo by John Lee, special to the Chronicle

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.

INGREDIENTS:
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:
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.

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Buttermilk Cornbread
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.

Cornbread comes hot out of the solar oven during recipe test on a SoMa rooftop. Chronicle photo by Chris Stewart

INGREDIENTS:
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 egg

1 cup corn kernels, frozen and thawed or fresh and cooked

INSTRUCTIONS:
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 solar oven.

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.

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Peach & Blackberry Cobbler
Serves 6

Adapted from a recipe by Susan and Don Larson of San Jose. Don Larson teaches solar cooking at Common Ground in Palo Alto.

Peach & Blackberry Cobbler. Styled by Tara Duggan. Photo by John Lee, special to the Chronicle

INGREDIENTS:
For top crust:

1 cup flour

1/4 teaspoon salt

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:
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.

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Rice Pilaf
Serves 8-10

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.

INGREDIENTS:
1/4 cup olive oil

2 cups finely diced onions

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

INSTRUCTIONS:
Solar cooking directions: Preheat a solar oven for 30 minutes.

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 minutes.

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 markets.

Per serving: 355 calories, 11 g protein, 61 g carbohydrate, 8 g fat (1 g saturated), 0 cholesterol, 80 mg sodium, 6 g fiber.

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Wheatless Apricot Cake
Serves 8

Wheatless Apricot Cake can be baked in a solar or conventional oven. Chronicle photo by Craig Lee

INGREDIENTS:
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)

INSTRUCTIONS:
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, if desired.

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.

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Shrimp & Lemon Skewers
Makes 12

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.

A solar feast: Lynn Langford's beet salad with feta and walnuts (right) and shrimp skewers. Chronicle photo by Liz Hafalia

INGREDIENTS:
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

INSTRUCTIONS:
Solar cooking directions: Preheat solar oven for 30 minutes.

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 lemon wedge.

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 minutes.

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. Serve immediately.

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.